How I assemble Diamond Hot Ends

A few people have asked me how I stop leaks around heat sinks and I’ve also read quite a few posts on various forums by people who have had problems, either with leaks or blockages. I’ve never had any problem with leaks and only on rare occasions, partial blockages. The latter were in my early days of using the Diamond and were mostly caused by my turning off the printer and hence the cooling fan, before the hot end had cooled sufficiently, resulting in “heat creep”.

I’m not sure if I’ve just been lucky but I thought it might be useful if I shared my method of assembling the Diamond hot end, as it is a little different from the official “RepRap.me” method. This is a hot end that I had to re-build as it had been fitted with the original woven thermal blankets, which had basically fallen apart and needed replacing.

Having disassembled the hot end, the first thing I needed to do was clean out the bore of the heat sinks. If you are starting with new heat sinks, it shouldn’t be necessary but it might be worth just running a 4mm diameter drill bit down the holes to be sure that the ptfe Bowden tube will slide in nicely.

reamingTheHole

RepRap.me say to assemble the heat sinks into the brass cone first, then fit the Bowden tubes. The trouble with that is that you can never be quite sure that the tube has gone all the way into the heat sink and/or it requires some very careful measuring. So I like to fit the tubes first like this, leaving them just protruding.

tubeInserted

Then, using a craft knife, I trim the end flush like this. Keeping the side of the knife against the end of the heat sink ensures a clean straight cut. Make sure you use a very sharp knife as you don’t want ragged bits of ptfe inside the tube. tubeEndTrimmed

Then I pull back the tab on the Tube holder and fit Bowden clips (plenty of designs on thingiverse). This part is as per RepRap.me instructions.

tubeClip

If you know how long your Bowden tubes need to be, you can cut them to length now. If not, leave them over long. Once they are cut to the right length, I like to form a funnel inside the extruder end. To do this, I use 2.5mm drill bit and drill down a few mm while working the bit from side to side and up and down. I use Titan extruders which have filament guides built in but even so, I’ve had problems when loading filament with it getting stuck against the very end of the tube, instead of sliding straight in. Forming a “funnel shape” in the end of the tube alleviates this problem.

formingTheBowdenTube

It’s easier to do this now if you can, because you can now take an off cut of filament and feed it right through the Bowden tube from the heat sink end back towards the extruder end. This will clear out any small bits of ptfe swarf.

The next thing I do is wrap ptfe tape, (also known as thread tape) around the thread. applyingPTFE

Note how I hold the reel of tape so that it is always kept taught. Note also that it is important to wind the tape onto the thread the same way that you would screw on a nut. Then when you screw the heat sink into the threaded hole, it will have a tendency to wind the tape onto the thread and keep it in place. If you wind the tape in the other direction, the tendency is for it to unwind as you screw it into the hole.

Do the same for the other heat sinks.

heatSinksPrepared

Now I like to prepare the thermal blankets. Thankfully, RepRap.me have gone away from the awful woven stuff that simply fell apart. This is how they look now.

thermalBlanket

I’m not sure what they are made of but it’s more fibrous than woven and doesn’t seem like it’ll fray. However, it might so I like to wrap it in Kapton tape like this.

blanketWithKapton

I use 50m wide tape and start with a length of about 100mm or so, laid sticky side up. Then I place the thermal blankets on top (ensuring that all the holes line up) and fold the Kapton tape over. Then press it down around the edges so that it sticks to itself and trim around with a pair of scissors. Lastly, I pierce the tape on both sides by cutting a cross over each of the holes with a very sharp knife.

Then I fit the 3 heat sinks and the cartridge heater to the prepared thermal blanket. I use a standard 20 mm heater which actually stand proud of the hole by 5mm. That’s not ideal I know but it has never caused me any problem.

 

heatSinksAndCartridge

 

Double check to make sure there are no bits of tape or other no debris anywhere near the ends of the tubes. I don’t fit the temperature sensor at this stage. If you use thermal paste, now is the time to apply it. Personally I use this stuff but only on the heater.

copperSlip

When I was in the automotive industry many years ago, we used to call it “copper slip” and used it on spark pug threads and the like. Some little while ago, I did some back to back testing with this stuff and there was a marked improvement in heat up time due to the high copper content which improved thermal transfer. The carrier grease does burn off at high temperatures (somewhere around 350 degC IIRC) but the copper gets left behind and improves the thermal transfer. I’m a bit dubious about using the thermal paste that RepRap.me supply as I’m not sure if it is designed to withstand hot end temperatures. Maybe it’s OK – just not sure.

The next thing to do is fit the heat sinks and tighten them up. RepRap.me say not to do them too tight and allude to the fact that they will be fully tightened later. However, that later tightening doesn’t get mentioned (or it didn’t that last time I read those instructions) and in any case, once the hot end is fitted to the fan shroud, it’s almost impossible to tighten the heat sinks further. So I tighten them fully at this stage. I use a pair of pipe grips which prevent me from doing them up so tight that they would likely snap the heat sinks. All I can say is do them up tight but take care.

tightenHeatSinks

The next thing to do (which I always forget) is to fit the screws into the mount that will retain the 40mm fan. These need to have small heads to clear the top of the heat sinks, so cap head screws are a no no. There is no way to fit two of the screws once the hot end is clipped into the fan shroud. I’ve found that making the holes in the mount slightly undersized helps to keep the screws in place.

fitFanScrews

So the last ting to do is to fit it all together. I start by partly fitting the heat sinks to the mount but not fully.  This is when I fit the temperature sensor (a 4 wire pt100 in my case). Note that the RepRap.me instructions seem to indicate that the temperature sensor wires should go inside the fan shroud, along with the heater cartridge wire. I find that part of the shroud gets in the way and presses on the wire, so I prefer to run the temperature sensor wire outside the shroud but still hold it in place with the same cable that holds the heater wires to the inside of the shroud.

fitThermistor

Then, clip it all together and fit the cable ties and finally, mount the fan.fitCableTies

Do please excuse the state of the plastic mount. I printed that with the awful eSun PETG that I wrote about in an earlier post.

I like to use nylok nuts on the fan screws. If a nut fell off and went into the fan, it could fly out and do some damage to an eye or something.

Hope some of the above may be of use. As I said in my opening remarks, I’ve never really suffered with any of the problems that some people have so maybe, this assembly method may help.

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eSun PETG and E3D Edge

I need to make some parts for my printer upgrade which will need to be strong so I thought it was about time that I tried some of the newer PETG filaments. As ever, these are just my personal experiences and I have no links with either eSun or E3D other than being a paying customer. Neither do I have any “axe to grind” or grudge against any company. What follows are just my own findings, on my machine and should not ne taken as any recommendation or otherwise.

I have for a long time wanted to try E3D’s Edge filament but the price has always put me off so I bought a couple of reels of eSun PETG from eBay. It cost me £51.48 for two 1kG reels, including postage and packing. This is quite a bit more than I normally pay for PLA but considerable less that E3Ds Edge. I was hopeful that the extra cost would be justified by the parts being stronger.

The reels arrived very well packed and each reel was inside a strong vacuum bag.

Before I go any further, I should remind readers that I use a Diamond hot end which has 3 inputs but a single nozzle. It is very important that all 3 inputs are loaded with filament at all times, otherwise the extruder pressure will simply force filament out of any unused inputs. However, buying 3 rolls of filament gets expensive when I only want to print a single colour, so what I do is pull off  a couple of 5 or 10 metre lengths of filament. Then I load the main reel into one input (tool 0) and load the short lengths into each of the other inputs. For single colour printing, I still use the hot end as a mixing hot end but I define the tool (in this case tool 0) to use 98% of extruder 0 and 1% of extruders 1 and 2. This ensures there is always filament loaded into all the inputs, even though only one is mainly used. The 1% mixing ensures that the filament in the other two inputs is always kept moving (albeit very slowly) so that the extruder doesn’t keep grinding away at the same pat every time it retracts, and also the filament doesn’t get cooked by being heated for a long time without moving.

So, I loaded the filament as detailed above, (having first removed the previous PLA) then I selected tool 3 which uses all three inputs in the proportions 33:33:34 and extruded a further 300mm to ensure that it was completely purged through.

The first thing I like to do with any filament is print a simple tower about 20mm square by 100mm or so high. Then I vary the temperature every 10mm or so and observe the finish and how well it prints, looking out for any signs of under extrusion at lower temperatures.

eSun recommend using a temperature of between 230 and 250 degC so I started at 235 and went up from there. The first thing I noticed was that the filament started to ooze out of the nozzle at around 170 degrees C. Anyway, this is the result starting at 235 deg C on the left and increasing to 250 just before the break on the right.

230to250

It was pretty awful as the picture shows. So I dropped the temperature down to 210 and carried on lowering the temperature down to 190 which significantly improved the finish. The next picture is the second half of the tower from 210 on the left to 190 on the right.

210to190

As well as the very poor finish, inter layer adhesion was appalling. That’s why the tower broke when I gently tried to remove it from the bed. In fact it broke in two places, the first was about 5mm up from the bed and not shown in the pictures.

So, I tried again this time starting at 180 and increasing to 210, then back to 190. This is the result.

190to210pic2

I was very surprised to find that it printed at all at 180, but I think I could hear the odd skipped step from the extruder and there were signs of under extrusion. At 200 and above, the finish deteriorated remarkably and the inter layer adhesion was still appallingly bad at all temperatures.

So it seemed that for whatever reason, the optimum temperature to print this stuff, on my machine was around 190deg C. This is nothing like the 230 to 250 that I was expecting and in fact is the same temperature that I print PLA. So I started to wonder if I had a batch that had been wrongly labelled and contacted the seller.

Meanwhile, having settle on a temperature of 190deg C, I decided to try and print something useful. This is the result

eSunPart

Sadly, although the surface finish was reasonable, there was just no strength to the part. It simply snapped very easily, far easier than I have ever experienced with cheap PLA.

At this point, the seller came back to me and asked that I supply a photograph of the labels so that he could contact the factory. Here is one of them.

Reel2

The seller later came back to say that the factories’ response was that “it is the right product” but also that it must be kept dry. I pointed out that I had removed it from it’s packaging, loaded it into my printer and started to use it within minutes so there had been no time for it to absorb moisture.

This is such a shame as I really hoped it would be a viable alternative to the more expensive “Edge” filament. The reality is that I can’t use it for anything due to the very poor inter layer adhesion and I’ll simply throw it all the bin.

In fairness to the seller, he did offer to refund my money which I accepted. I was however, a bit disappointed in the response he said that he has received from eSun. I was (and still am) willing to return it for analysis.

So, after that little episode, I still needed to find a strong filament so I “bit the bullet” and purchased some “Edge” filament from E3D online.  I opted for the 2.3 kg which worked out a bit cheaper at £70. That doesn’t sound too bad but then there was £4.26 deliver and then VAT at 20% on top of everything at £14.85 making the total £89.11 (for 2.3kg). Which works out at about £38.74 per kg. Not cheap……

When it arrived, I was a little disappointed to find that it wasn’t in the strong vacuum bags that I have become used to. It was OK and there was some silica gel in the packaging but just a tad disappointing. What was lot disappoint was the reel that it was on. Look at it……

spool

That’s it on the left, next to a “standard” 1kg reel. The inner hole is about 50mm diameter, then there are those huge webs taking it to 210mm before any filament gets wound onto it!  The outer diameter is about 300mm. A “standard” 1kg reel would fit inside the wasted space so the whole thing could have been half the size. It’s not the waste of packaging that irks me, it’s how the hell do I fit that monster on my machine? In the end, I had to wind it from the monstrous great spool onto an empty “normal” size spool. Now 1kg of 1.75mm filament is about 300 metres and believe me, winding that from one spool onto another is a real PITA. The moral of the story? Don’t buy the 2.3 kg option – pay the extra and buy 3 normal (0,75kg) size reels instead (that’s assuming they come on sensible size spools).

OK, winge over. So I loaded up as before and again, I started with tower 20mm x 20mm x 100mm varying the temperature every 10mm. I started at 235 deg C, increased it to 250 then went down to 190. Observing the print quality all the time. Here result.

235to245to195

The camera doesn’t show the differences which are very subtle. Basically, I found this stuff printed well at just about any temperature. I did notice skipped steps and signs of under extrusion from 200 and below but anything above that, it was hard to see any visible difference in this test cube piece. What I did notice is that it started to ooze at about 180 as the nozzle was heating up.

The part is really strong too. It’s only 20% infill but I can’t break it with my hands – I’d need a vice and hammer.

As this stuff is expensive (to me anyway), I decided not to bother doing any more test pieces to refine retraction or any other parameters but went straight on to print some parts using the (every day) settings I use for PLA. My rationale being that I might end up with something that would be functional but not necessarily pretty and I can refine the parameters “on the fly”. So here is the first printed part

firstPrint

Two things I noticed. The first was that it was a bit stringy and I’d need more retraction. The second was that the filament has quite an affinity for sticking to the nozzle. What tended to happen was that I’d get a  bit of a build up around the nozzle, especially when doing small detailed moves, which would later fall off and leave a stringy blob. I believe a silicone sock might help but as no one sells one to suit a Diamond hot end, I’ll have to look at making my own.

What was impressive was the hollow fan ducts (the two raised parts in the picture). I printed these without any support just for the hell of it. Here is a close up.

31mmBridge

That’s an unsupported span of 31mm from left to right. That kind of bridging capability opens up a whole new world of possibilities for me.

During the first print, I did play around with temperature and retraction settings. I found that I need about 50% more retraction than I’m used to with PLA. I have shortish Bowden tubes (about 250mm) and use firmware retraction because I need to retract all three filaments simultaneously and was using 2mm but with Edge I need about 3mm. Also, a faster retraction speed seemed to help too. An added benefit of using firmware retraction is that one can change the parameters “on the fly”. Also, I found that lowering the temperature seemed to help with the build up around the nozzle and blobs as did lowering the extrusion multiplier to 0.95 from 1.00

Anyway, this was the second print with a bit more retraction and the temperature lowered to 210 deg C. I know this is 10 degrees less that E3D recommend but it seems to work well for me on my machine.

thirdPrint

Close inspection shows it’s a bit “hairy” here and there and the top layer surface finish could be improved but the results are very promising. The holes, both horizontal and vertical are nice and circular.  The parts are also very strong, which was the original criteria that I hoped PETG would meet. I’ll keep playing around with settings to get this “dialled in” properly but so far, the results are very encouraging.

So, I’ll happily use E3D edge but only for parts that need to be robust due to the high cost. Sadly, I’ll not be using eSun PETG for anything due to the very poor inter layer adhesion that I encountered.

 

 

 

 

When all else fails, check your nozzle

All of sudden, I started having all sorts of problems with first layer adhesion. Since I’ve been using 3DLac on my glass build plate, this has never before been an issue. Try as I might, I just couldn’t get beyond the first layer which was a horrible stringy mess and refused to stick to the build plate. I won’t go into details of what I checked as it would be a long and boring read, but finally I decided to take a look at the nozzle itself. This is Diamond hot end, so it’s one great lump of brass. This is what I found.

nozzle1

That used to be a nice, round 0.4mm diameter hole. Here is another picture

nozzle2

That is a 0.8mm diameter drill bit inserted into what was once a 0.4mm diameter hole.

The nozzle has done many hundred of hours of printing but never with any abrasive filaments. Mostly just PLA. Of course, not every print has gone perfectly and there have been occasions when the nozzle has scraped across the previous layer.

I don’t really know what caused it, just general wear and tear I guess but the issues I had with printing were not a gradual process. One day all was well and the next day all was far from well.

I had a spare which I have fitted and now everything is back to normal. So I guess, if things go awry and you’ve checked all the obvious, take a look at your nozzle……….

Stepper motor and electronics cooling

I recently encountered a problem with my printed XY stepper mounts so thought I’d share my solution and also some other things I do to cool certain parts of my printer.

We all know that stepper motors run hot but they are mostly rated to run at around 80 degrees C so normally, cooling isn’t necessary. However, if you use a printed mount such as I do, then you may experience this.

distortedMount

I had read that this could happen but didn’t really give it any thought. What has happened is that repeated periods of 20 plus hours printing, the plastic has been softened by the heat of the motor, then the lateral force of the belt tension acting on the motor shaft has distorted the mount.

Of course, a metal mount would cure the problem but I use a sliding motor mount as a belt tensioner and not having access to metal working machinery, it has to be a printed part. It’s possible that a different type of plastic to PLA might have been more thermally stable but I decided to use a “belt and braces” approach.

The first thing I did was to buy a plumbers’ soldering mat which is made from Gold Silica and cut a couple of gaskets to go between the motor and the mount. I don’t know how effective this will be but it didn’t cost much so why not?

gasket

The next thing was to fit a heat sink and fan to the top of the motor. I used these heat sinks http://www.ebay.co.uk/itm/Nema17-Size-Stepextruder-Heatsink-Heat-Sink-Nema-17-Cooling-/151826112373?hash=item23598a9f75:g:z-wAAOSwnbZYHUUi and used some thermal paste between the motor and the heat sink.

These were the quietest 40mm 24v fans I could find http://uk.rs-online.com/web/p/axial-fans/2058310/?sra=pstk.

To fit it all together, I had to remove two of the stepper motor screws and replace them with lengths of studding (it needs very long screws which I couldn’t find). Nyloc nuts and washers keep it all together. I would have preferred it if the heat sinks had been drilled in apposite corners, rather than two holes on one side.

Lastly, the Duet electronics mean that the printer is very quiet in normal use. So much so that fan noise start to become intrusive to me. I had already changed the power supply to a fan less design (my heated bed is mains powered so I don’t need a high current power supply). The hot end fan is set to run in thermostatic mode so that it only runs when the hot end is above 45 degrees C. Likewise the fans I use to cool the electronics. So when the printer is idle, no fans run at all and it is virtually silent apart from a faint buzz from the stepper motors once they have been energised. I have the Duex5 expansion board as well which gives me extra fan and heater connections so, I decided to do the same with these stepper cooling fans.

To monitor the temperature I stuck a bead thermistor to each stepper, close to the mount, with a small amount of epoxy adhesive. Here is how the installation looks.

heatSinkandFan

Here is how it looks at the Duex5 end. The thermistors are the orange and green wires at the bottom and the fans are the red and blue coming out of each loom.

IMG_6297

Just out of shot is the thermistor that I stuck to the topmost stepper driver chip but you can see the two white wires leading into a spare heater channel. I did the same on the main board  with one of the XY driver chips. These thermistors control fans which blow air on to the back of the boards.

Next I had to configure the new fans and heaters. A note of explanation is required here. With Duet electronics, temperature channels are called “heaters” regardless of whether they are actually used to switch physical heaters or, in this case cooling fans.

So here are the relevant lines from my config.g file for the “heaters” (actually thermistors).

M305 P2 T100000 B3950 R4700; Set thermistor + ADC parameters for heater 2 – this is used to measure stepper chip temperature on Duet
M305 P3 T100000 B3950 R4700; Set thermistor + ADC parameters for heater 3 – this is used to measure stepper chip temperature on Duex5
M305 P4 T100000 B3950 R4700; Set thermistor + ADC parameters for heater 4 – this is used to measure left XY stepper temperature
M305 P5 T100000 B3950 R4700; Set thermistor + ADC parameters for heater 5 – this is used to measure right XY stepper temperature

This is the fan section of my config.g

; Fans
M106 P0 S0.0 I0 F10 H-1 ; Set print cooling fan (3) value, PWM signal inversion (off)and frequency (10 hz). Thermostatic control is turned off
M106 P1 S255 I0 F500 H1 T45; Set hot end fan (1) value, PWM signal inversion(off) and frequency. Thermostatic control is turned on
M106 P2 S255 I0 F500 H2 T45; Set fan 2 value (Duet board fan), PWM signal inversion and frequency. Thermostatic control is turned on
M106 P3 S255 I0 F500 H3 T45; Set fan 3 (Duex5 board fan) to work thermostatically on H3 temp
M106 P4 S255 I0 F500 H4 T45; Set fan 4 (Left XY stepper fan) to work thermostatically on H4 temp
M106 P5 S255 I0 F500 H5 T45; Set fan 5 (Right XY stpper fan) to work thermostatically on H5 temp

Finally, I wanted to be able to actually display these temperatures on the web interface. The way I found to do this was to create “dummy” tools without any extruders associated with them. I started with defining tool numbers 99 then worked backwards.

Here is the ending part of my tool definition section.

M563 P99 H2; define this dummy tool just so dwc shows the temperature value for the thermistor that’s stuck to the stepper driver
M563 P98 H3; define this dummy tool as above for duex thermistor
M563 P97 H4; define this dummy tool as above for left xy stepper thermistor
M563 P96 H5; define this dummy tool as above for right xy stepper thermistor

This is how it looks on the Duet Web Interface.

Screenshot-2017-4-18 TallCoreXY

I just have to remember that Heater1 is the hot end thermistor (as normal), Heater 2 is actually the XY driver chip on the Duet main board, Heater 3 is the same for the Duex5 board, Heater 4 is the left XY motor body and Heater 5 is the right XY motor. I have posted a request on the Duet forums for a better way to display these temperature channels.

I understand that future versions of firmware will have the ability to control fans based on a temperature warning signal from the driver chip itself. This would negate the need for the thermistors that I have used but as I understand it, the temperature threshold at which the fan comes on will be quite a lot higher and not user configurable.

Finally, it was time to test my new cooling arrangement and I can report that it works like a charm. I started printing a simple 200mm square object. It takes quite a while (about 45 minutes or so) for the steppers to reach 45 deg C. This may be due to the heat sinks on their own – I have no data to compare with though. When the temperature reaches 45 deg C, the fan switches on, the temperature drops, the fan switches off and there is a bit more of a drop before the temperature come back up. The cycle time for the fans is about 1 minute on, 3 minutes off and after about 4 hours, the temperature was still being controlled at 45 deg C with the same hysteresis. What is interesting is that when doing diagonal infill on a coreXY one motor is stationary and I can observe one fan switching on and off while the other hardly runs until the next layer where the situation is reversed. So I’m glad that I decided to add control to each individual motor. Maybe I need to do the same with the driver chips…………

 

 

Setting up a Metrol positioning switch

This is a very quick post on how I installed a Metrol positioning switch for Z homing with my sliding hot end mount using the Duet Wifi electronics.

Metrol are a Japanese company who make high precision switches for industrial applications. Here is a link to their web site http://www.metrol.co.jp/en/. They seem to have a direct sales site called Toolsensor.com which is here http://toolsensor.com/. It looks like you can buy from ToolSensor via their Amazon.com outlet too.

I couldn’t find a UK source so ended up going to Misumi  UK and buying one of their contact switches. It wasn’t until it was delivered that I discovered that it was in fact a Metrol switch. Misumi only sell to businesses but they don’t seem to care if the business is VAT registered (mine isn’t) and there are no  minimum order quantities. So how and where you source these Metrol switches will depend on what part of the world you live in.

These switches come in numerous configurations. The one I chose has a smooth body but there are threaded versions available too. If you can, buy one without the LED as then it can be connected to the E0 end stop connector in the normal way – i.e. just like any other micro switch. The instructions for connecting end stop switches are here  https://duet3d.com/wiki/Connecting_endstop_switches.

Unfortunately, the non-LED version was not available from Misumi so I had to buy the LED version. The Misumi part number of the one I chose was N-MSTK-ASD. The non LED version is the same part number but without the “D” on the end. There is a sleeve on the switch with the word “Metrol” (that’s how I know it is a Metrol switch) and then “CS06A -L” which I assume is the Metrol part number and I would hazard a guess that the hyphenated “L” denotes LED version.

The data sheet for this switch shows a stroke of 2.0mm, the switching point as being 0.3mm from tip and the repeatability to be 0.005 mm. Metrol do make switches with claimed repeatability of 0.001mm but IMO that would be overkill even for our Z axes.One down side is that the switch is normally open rather than normally closed so if a wire falls off, it won’t fail “safe”. As I mentioned in my other post, I installed a backup micro switch to trigger 1mm higher than the Metrol switch and initiate an emergency stop should the primary switch fail.

If you’ve managed to find a non-LED version of this switch, then you can stop reading now as the rest of this post is on how to install the LED version.

Because this switch has a series LED and the Duet electronics also has an LED with a pull up resistor, it has to be treated as an analogue switch rather than a digital switch (this was what confused me at first). So following David Crocker’s advice (DC42) I connected the switch between the In and Gnd pins of the Z probe connector, with a pull up resistor (about 220 ohm to 1 K) between in and +3.3V. The resistor value isn’t critical as long as it is within that range – lower makes the series LED shine brighter when the switch is triggered.

Here is a link to the Duet Wiring diagram. https://duet3d.com/wiki/Duet_WiFi_wiring_diagrams. NOTE. Unless you have a very early prototype board, the diagram to use is the one at the top entitled “………v1.0, v1.01,v1,02” The lower diagram is for PROTOTYPE – don’t let the “V2” fool you into thinking that its is later than the production V1.0 versions. This is important because the Z probe pins are different.

Having got the switch connected, we now need to “tell” the Duet board what type of switch it is. In this case, it is probe type 1. The relevant gcode command is M558 and the settings can be found here https://duet3d.com/wiki/G-code#M558:_Set_Z_probe_type. So my M558 line looks like this. M558 P1 X0 Y0 Z1 F180 T6000 I1. I don’t use and form of bed probing other than for homing so the “T” parameter is irrelevant in my case.

Note that unlike the mini height sensor, the “analogue” voltage from the Metrol switch does not change gradually as the sensor gets close to the bed. Instead it simply switches from one value(zero) to another. So you cannot use the facility whereby the probing speed will slow down as the sensor gets closer to the bed so you may need to drop the Z homing speed (180 mm/min works well for me).

The last thing to do is check that the switch is working and set the trigger value and trigger height.Again, it should be noted that I don’t use any form of bed compensation so I’ve only ever used G31 for homing. If you do detailed probing, you may be using G30 or G32 but the principle will be the same.

I currently have a problem with my printer and am unable to connect using the web interface so I’ll have to do the rest of this post from memory. Apologies in advance if what you see is not what I say you will see.

This is where I discovered another command that I wasn’t previously aware of. One can use M119 to report the end stop status. With the switch open as normal, send M119 via the web control and observe the switch status in the console. Then manually close the switch and send M119 again to check that it is closed. The console on the web interface may indicate that the probe is close to the bed but not actually at the bed. This is because the trigger value may not be correct, especially if you have previously been using the IR probe. So, with the switch open, observe the probe value (top right hand corner of DWC) and should read zero. Then with the switch closed, observe the probe value again. With a 500 Ohm resistor, I had a reading of 474 and my G31 was still set for the mini IR probe with a trigger value set to 500 which is why the web interface console showed that the probe was close to the bed. The actual value will depend on the resistor you used, so set the trigger value to be about half way between zero (when the switch is open)  and the reported value when the switch is closed. In my case I used 250 so my G31 ended up as “G31 P250 X0 Y0 Z-0.8”. The “Z” value is the trigger height and is set in the usual way by using a thin piece of paper between the probe and the bed or whichever method works best for you.

HTH

Ian

 

 

 

Z axis lead screws.

I just wanted to share my thoughts about lead screws and the like for Z axis motion. I have read numerous posts on various forums by people claiming that threaded rod isn’t accurate or that it is only suitable for holding things together and never for linear motion. They will then go on to say that one should use “proper” lead screws.

So my first observation is that, by definition a lead screw is a threaded rod. However, I don’t really want to enter into this endless debate, except to say that I am comfortable with my own decision to use threaded rods which were not specifically branded as being “lead screws”.

What I do have a bit of a problem with is multi-start lead screws for use on Z axes. It seems that people buy them because they are labelled “lead screw” and therefore must be superior. Many machines are built using them too – probably because the manufacturer thinks they will sell more if they can say they use “lead screws”.

One very important thing to think about is “lead” (pronounced leed not led). This not the same as pitch although often people think that it is the same thing. It happens to be the same thing for single start screws but for multi start screws, it is completely different.

To illustrate the point I have been playing around with OpenScad, wrapping a helix around a cylinder to simulate what a screw thread might look like.

Here are two images of a rod 8mm tall.

1start2mmside

4start8mmside

The pitch of a screw thread is the distance between two “peaks”. As you can see, there are 4 of these peaks over the length of the 8mm rod in each picture so the pitch is 2mm in both images.

This next image is the same as the top one but looking more from the top.

1start2mmtop

If you trace a line from the top of the rod and follow it around anticlockwise for 1 full turn, you’ll see that you end up exactly 1 pitch distance (2mm) below where you started. This is the lead and it means if a nut was held on the rod so that it couldn’t rotate, in revolution the nut would move 2mm. This is a 2mm pitch single start screw so also happens to have 2mm lead.

Now let’s look  at the top of the second image.

4start8mmtop

Here we can see that it is completely different and that is because it is a 4 start screw, with each helix offset by 90 degrees. Now what happens if you trace the line as before? To make it easier, I’ve taken away 3 of the threads and left just one……….

1start8mmtop

 

………and from the side it looks like this

1start8mmside

As you can see, an 8mm single start screw wouldn’t have much contact area between  the screw and a nut which is why they are made with 2 or 4 threads offset by either 180 or 90 degrees to each other.

So now we can see that tracing a line for 360 degrees as before moves us the full length of the rod (8mm) so the lead is 8mm. This is a 2mm pitch 4 start lead screw and people buy them because they think that 1 revolution will mean a linear movement of 2mm when in fact 1 revolution will give 8mm of linear movement.

Why is this not a good idea for our Z axis? Firstly look again at the angle of the helix and compare it with the top picture which is a single start screw. You’ll see that it is much steeper. Therefore, a heavy Z axis bearing directly down on the rod could exert enough force such that the bed would fall under it’s own weight as soon as power to the motor is lost. Also, it will require more torque to drive the rod because it has to move the load a greater distance for a given angular movement (in the case 4 times greater). So we’ll most likely need a bigger motor.

But most importantly it will have an adverse effect on accuracy, which is ironic when people buy lead screws because accuracy is their main criteria.

To elaborate on this, I need to do a little maths. An average stepper motor moves 1.8 degrees between steps (I am aware that one can buy 0.9 degree stepper motors but they are more expensive). So, I revolution will be 200 steps assuming we have 1:1 gearing and are not using asymmetric pulley sizes. For our 2mm single start screw which has a lead of 2mm we can say that 200 steps = 1 revolution = 2mm. Or it’s 100 steps per mm which means that for a resolution of 0.1mm layer height, it will be 10 steps, 0.2mm will be 20 step, 0.3will be 30 steps etc.

Now for the 4 start, 2 mm pitch lead screw which has a lead of 8mm, 200 steps = 1 revolution = 8mm. So instead of 100 steps per mm we now have 25 steps per mm and for our 0.1mm resolution we have 2.5 steps, for 0.2mm it’s 5 steps and for 3mm it’s 7.5 steps. Which means we will be relying on micro stepping for positional accuracy for anything other than our 0.2mm layer height. And micro stepping does not improve accuracy. In general, stepper motors are quoted as having a non accumulative positional error of +-5% which for a 2mm lead screw, equates to about 0.01 mm but for an 8mm lead it becomes 0.04mm which may start to become significant with 0.1mm resolution layer height.

So, multi start lead screws are designed to give a large linear movement for a given angular movement. They require more torque to drive them and provide less holding power than a single start screw of the same pitch. Basically designed for speed which would be fine for our X and Y axes but not what we want for our Z axis.

In my opinion 2 start, 2mm pitch screws are just about acceptable or 4 start but with 1:2 gearing. Finally, this is an image representing what I use.

1start1mmside

It’s 8mm diameter, 1mm pitch single start trapezoidal threaded rod. It gives me 20 full steps per 0.1mm and requires very little torque enabling me to use 3 of them to lift my 7.3 kg bed with a single Nema 17 stepper motor. If you look at my other posts, you’ll see that I can print 300mm x 300mm with no bed compensation (despite the fact that these screws didn’t have the “lead screw” label) so I’m happy with the accuracy. Maybe they will only last 30 years instead of 50 but who cares – they are cheap enough to replace (much cheaper then “lead screws”).

That was just my twopence worth……….

 

 

 

 

 

Using the Diamond Hotend with DuetWifi

Julia vase #11 Heatwave by Virtox
http://www.thingiverse.com/thing:126567
Printed Ian Pegg

This is a copy of a post I did as guest on Think3dPrint3d ‘s blog back in December 2016. Now that I have my own blog up and running, I thought I’d post it here as well, just to keep all my posts together in one place.

I have been using a Diamond hotend (3 inputs and one output) on my custom built CoreXY printer, controlled by the DuetWifi for some time now. This blog post is documentation on how to setup the DuetWifi with a Diamond hotend however it can be generalized to other multiple input – single output hotends. They might use different configurations but the principles will be the same. I have taken the definition of a mixing hot end as one which has multiple filament inputs and a single output (nozzle), although see the “issues with mixing” section at the end.

Hardware requirements.

Assuming you have the necessary number of extruders for your particular hot end, you will need to be able to drive them all. The new Duet WiFi and the older Duet v0.8.5 both have support for 2 extruders. If you have 3 or more extruders, then you will need to procure an expansion board or use another method to connect additional stepper drivers to the Duet expansion connector.
Important note. A mixing hot end must have filament loaded into all inputs at all times. Failure to do this will mean that extruded filament will find it’s way up into any unused inputs where it will cool and solidify causing a blockage which will be very difficult to clear.

Software and Firmware requirements.

 
You should have a slicer that is capable of supporting multi part objects. Although some things can be done by post processing the gcode file, objects which share the same Z position, would be very difficult to deal with using this method. Also, the slicer and the printer firmware should ideally be capable of supporting firmware retraction (G10) – more on this later. At the time of writing, Slic3r (version 1.2.9) is known to support these features. David’s (DC42) branch of RepRapFirmware supports firmware retraction as of version 1.10.

Some slicers support multiple extruders but not necessarily multicoloured objects (although there may be workarounds). It is often possible to use different extruders (tools) for perimeters or infill or support materials.

Connections.

 
Refer to the Duet wiring diagrams and connect the first extruder motor to E0, the second to E1 and any others to the relevant connectors on the expansion board. I highly recommend that you put a label on each extruder at this time to act as a reminder of which is which when you come to load filament. Remember that by default, the first extruder drive is referred to extruder 0(zero) not 1. This may initially confuse you when you start using slic3r which refers to the first extruder as “1” not rather than “0”. I believe that the latest version of Duet firmware does allow you to “remap” extruders (tools) so that the numbering system start with 1. (See reference to M563 S1 later in this post). New users might want to adopt that approach but i have become accustomed to using the 2 different numbering systems so personally, I’ll stick with it.
wiring-1
Extruders 1 and 2 connected to the main Duet WiFi board
wiring-2
Extruder 2 connected to the Duex5 expansion board
A mixing hot end will only have one heater so connect this to the first heater (marked E0). Similarly, connect the thermistor to the first thermistor connector (also E0). It’s not strictly necessary to use these exact connections but if you decide to use some other terminals on the Duet board, make a note of what you have connected to where. Finally connect the hot end cooling fan to wherever you prefer. The most common configuration is to connect the fan to one of the “always on” terminals but my fan is very high air flow and so quite noisy. Therefore I prefer to have it connected to one of the PWM fan terminals and run it in thermostatic mode so that it only comes on when the hot end is above 45deg C.

Configuration settings – tool definitions.

 
The first thing to do is define the tools. To do this, it is necessary to edit the confg.g file. The way I prefer to this is to keep a copy of all the sd card files on my PC where I can maintain back up copies. So I would edit the config.g file on my PC then upload it to the Duet through the web interface. One could also physically remove the sd  card, pop it into a card reader and copy the file across. Another way to do it is to edit the file directly, either through having the card in a card reader or via the system editor in the web interface. This is the quickest way to do it but of course this means that you have no backup copy.

There are a few different ways that you can define the tools. You will probably need a tool for each of the “solid” colours. That is to say, tools which will only use 100% of one filament. Then you will need a tool or tools that combine different filaments in various proportions.

So to define a tool which uses only one colour, it is only necessary to set which extruder and which heater it will use. The gcode to define a tool is M563. So for the first 3 tools you could use something like this;
M563 P0 D0 H1
M563 P1 D1 H1
M563 P2 D2 H1
This would define the first 3 tools (P0 to P2) to each use one of the extruders (D0 to D2) but the same heater (H1).
IMPORTANT. Be aware that Slic3r and perhaps other slicers, may use a different numbering system and the first tool is defined as 1 not 0. This can be easily rectified by either defining tools starting with tool 1 and up, or by using the M563 S1 command in config.g to tell the firmware to add a 1 to every tools number
If we want to mix filaments, we’d need create more tools and turn on mixing. So, we might have another tool defined like so;
M563 P3 D0:1:2 H1 ; Define tool 3 (P3) to use all three extruders (D0:1:2) and heater 1
M568 P3 S1 ; Enable mixing for tool 3
M567 P3 E0.34:0.33:0.33 ; Set mixing ratio for tool 3.
What this does is to define the tool T3 to use all 3 extruders (D0:1:2) then it uses M568 to enable mixing for that tool. Finally, it sets the mixing ratio using M567. In this case roughly the same quantity of each of the 3 filaments. However, this mixing ratio should always add up to 1. So, I’ve used 0.34 of extruder 0, and 0.33 of extruders 1 and 2 (0.34+0.33+0.33 = 1.00).
We could also have other tools. Say for example we had Red filament in extruder 0 and Yellow in extruder 1, we could define another tool which would blend equal amounts of the tool to create Orange. It would look like this:
M563 P4 D0:1:2 H1 ; Define tool 4 (P4) to use all three extruders (D0:1:2) and heater 1
M568 P4 S1 ; Enable mixing for tool 4

M567 P4 E0.5:0.50:0.00 ; Set mixing ratio for tool 4.

Of course, we can define as many tools as we like. The upper limit of tool numbers is constrained only by the Duet’s free memory so over 400 tools are possible on the DuetWifi.

Managing a large number of tools would become cumbersome though and there is another way. Once a tool has been defined to use all the extruders and mixing has been enabled, we can simply change the mixing ratio before or during the print. It can be done before the print commences by putting the mixing ratio into the start gcode file. It can also be done during a print by entering the required M567 command in the web interface or by post processing the gcode file that the slicer generates. In theory the tool mix ratio can be set differently for each gcode move.

So we can simply have one tool which is defined as a mixing tool. In practice, this won’t work with slicers which expect different tools for different (coloured) parts of an object. So, I have found the best compromise is to just define 4 tools (or one more than the number of extruders), one for each of the primary filaments and one which is a combination of all three. Coincidentally, in slic3r, if you set your printer to have 3 extruders, it will give you 4 tools to choose from for any object.
Taking this a step further, it is still useful to be able to use any combination of filaments for any tool. For example I could have red green and blue filaments loaded but want to print with Cyan, Magenta and Yellow. So all of my tools are defined as mixing tools but the first three use 100% of only one filament (actually this is not strictly true but we need to consider retraction before I elaborate more). Then if I subsequently want to change a tool to use a different filament or combination of filaments, I can do so but simply changing the mixing ratio at the start of the gcode file, without having to bother with all the other configuration settings. It can also be done “on the fly” from the web interface. This can also be used if one wanted to print a number of copies of the same object but in different colours. Simply slice the object once, then edit the start of the gcode file to change the mixing ratio and/or tool number.
Here is what the tool configuration part of a config.G file might look like.
; Tools
M563 P0 D0:1:2 H1 ; Define tool 0
G10 P0 X0 Y0 ; Set tool 0 axis offsets
G10 P0 R0 S0 ; Set initial tool 0 active and standby temperatures to 0C
M568 P0 S1 ; Enable mixing for tool 0
M567 P0 E1:0:0 ; Set mixing ratios for tool 0
M563 P1 D0:1:2 H1 ; Define tool 1
G10 P1 X0 Y0 ; Set tool 1 axis offsets
G10 P1 R0 S0 ; Set initial tool 1 active and standby temperatures to 0C
M568 P1 S1 ; Enable mixing for tool 1
M567 P1 E0:1:0 ; Set mixing ratios for tool 1
M563 P2 D0:1:2 H1 ; Define tool 2
G10 P2 X0 Y0 ; Set tool 2 axis offsets
G10 P2 R0 S0 ; Set initial tool 2 active and standby temperatures to 0C
M568 P2 S1 ; Enable mixing for tool 2
M567 P2 E0:0:1 ; Set mixing ratios for tool 2
M563 P3 D0:1:2 H1 ; Define tool 3
G10 P3 X0 Y0 ; Set tool 3 axis offsets
G10 P3 R0 S0 ; Set initial tool 3 active and standby temperatures to 0C
M568 P3 S1 ; Enable mixing for tool 3

M567 P3 E0.34:0.33:0.33 ; Set mixing ratios for tool 3

This is not quite how I have my tools defined but to understand the reason for that, we need to look at extruder retraction which is discussed later in this document.
extruders.JPG
The 3 E3D Titan extruders suspended centrally above the bed in a sort of counter balance “flying” arrangement

Tool offsets

 
You will notice that in the above tool definitions, there is no X or Y offset, or more precisely the X and Y offsets are set to zero (G10 Pn X0 Y0). That is because there is only one nozzle. X and Y offsets are only necessary where there are more than one nozzle and where they are physically offset from each other. Theoretically these offsets should default to zero but I always like to set them to zero, just in case something should get changed in firmware which might affect the default settings. 

Heating and standby temperatures.

You will also notice that in the tool definitions above, the initial active and standby temperatures are set to zero (G10 Pn R0 S0). That is because I don’t want the hot end to start heating whenever a tool is selected. Instead, I have the heating and standby temperatures set in my start gcode where I can also put the specific temperature as needed for a specific filament.
With a mixing hot end, we only have one heater and one nozzle so if we are using the same type of filament in all 3 inputs, we can instantly switch between tools without having for the next one to warm up, or the previous one to cool down. Therefore, we can (should) set the tool active and standby temperatures to the same values.
This is what I have in my start gcode for PLA in all 3 inputs.
G10 P0 S195 R195     ; Set tool 0 operating and standby temperatures
G10 P1 S195 R195     ; Set tool 1 operating and standby temperatures
G10 P2 S195 R195     ; Set tool 2 operating and standby temperatures
G10 P3 S195 R195     ; Set tool 3 operating and standby temperatures

Then when the print runs and a tool change is needed it can be instantly switched with no warm up or cool down delay.
Obviously, if we had different types of filament in one or more of the extruders, we would need to change these values for those extruders (tools).

Extruder retraction.

 
With “normal” retraction, only the “active” extruder will retract. That is to say that if we are only pushing one filament into a mixing nozzle, normal retraction will only pull that single filament back. In effect, all that happens is that filament is drawn from the unused inputs rather than from the nozzle tip. In practice, this is just like having no retraction at all.
What is needed is for all filaments to be retracted, regardless of whether they are actively in use or not. Fortunately Duet hardware and firmware give us the ability to accomplish this. It is done by using firmware retraction using the codes G10 (retract) and G11 (unretract). This might be slightly confusing because G10 is also used for tool offsets but without a tool number, it is used for firmware retraction.
G10 is used in conjunction with M207 to define the retraction amount and speed.
Here is what I have in my config.g file.
M207 S1.5 F3000       ;set firmware retraction

S is the amount in mm. F is the Feed rate mm/min (divide by /60 to get mm/sec).
Optionally one could also have R (additional length on unretract) and Z (additional Z lift in mm)
It is vitally important to use this firmware retraction with a mixing hot end so, the slicer software must also be configured to use this. In Slic3r this is simply a matter of ticking a check box which is in the Printer Settings tab under “General”. Whenever retraction is needed, Slic3r will insert a G10 command (and a G11 command to unretract). For other slicers, there is sometimes a facility to post process the gcode output and one could use this to replace whatever retraction codes was output with G10. Another option would be to use some sort of text editor to do a “search and replace”.

Tool Definitions revisited. 

 
Now that we have set our firmware retraction to retract all 3 filaments simultaneously there is another little issue that will become apparent but can be avoided. With a mixing hot end we must have all the inputs loaded with filament at all times otherwise extruded filament will simply find it’s way up into unused inputs where it will cool and solidify. We must also retract all filaments simultaneously for reasons discussed above. Therefore, when we print using just a single filament and extruder for a prolonged period of time, what happens is that on the unused inputs, the same piece of filament is constantly being retracted and unretracted. Eventually it will just get worn away and will cease to move and retraction stops working and our prints get stringy.
There is also another possibly even more important issue, which is that most filaments will degrade if reheated and cooled a number of times which is what will happen if we primarily use just a single filament for an extended period of time. I’ve seen with PLA that if it is left in the mixing chamber too long without being extruded, it gets completely cooked and when it comes time to extrude the first few millimetres come out as a mixture of liquid and vapour.
There are a couple of things which can help. The first one is, before starting a print heat the nozzle and extrude some filament from each of the extruders. This will ensure that there is a fresh piece of filament in each of the extruders which may well last for enough retract and unretract cycles without getting so worn that it fails to move.
The way that I prefer to do it is to define the tools so that every tool always uses the main filament plus a small proportion of all of the other filaments. In theory, one might think that this would result in muddy and muddled colours. In practice, it is hardly noticeable and it uses the main filament but just enough of the other inputs to keep them moving so that retraction isn’t always moving the same piece of filament back and forth and the same piece of filament isn’t being constantly reheated and cooled.

Here is what my final tool definition section looks like.

; Tools
M563 P0 D0:1:2 H1 ; Define tool 0
G10 P0 X0 Y0 ; Set tool 0 axis offsets
G10 P0 R0 S0 ; Set initial tool 0 active and standby temperatures to 0C
M568 P0 S1 ; Enable mixing for tool 0
M567 P0 E0.90:0.05:0.05 ; Set mixing ratios for tool 0 (90%,5%,5%)
M563 P1 D0:1:2 H1 ; Define tool 1
G10 P1 X0 Y0 ; Set tool 1 axis offsets
G10 P1 R0 S0 ; Set initial tool 1 active and standby temperatures to 0C
M568 P1 S1 ; Enable mixing for tool 1
M567 P1 E0.05:0.90:0.05 ; Set mixing ratios for tool 1 (5%,90%,5%)
M563 P2 D0:1:2 H1 ; Define tool 2
G10 P2 X0 Y0 ; Set tool 2 axis offsets
G10 P2 R0 S0 ; Set initial tool 2 active and standby temperatures to 0C
M568 P2 S1 ; Enable mixing for tool 2
M567 P2 E0.05:0.05:0.90 ; Set mixing ratios for tool 2 (5%,5%,90%)
M563 P3 D0:1:2 H1 ; Define tool 3
G10 P3 X0 Y0 ; Set tool 3 axis offsets
G10 P3 R0 S0 ; Set initial tool 3 active and standby temperatures to 0C
M568 P3 S1 ; Enable mixing for tool 3

M567 P3 E0.34:0.33:0.33 ; Set mixing ratios for tool 3 (34%,33%,33%)

If it is critical that the finished print has to be a single colour and cannot be mixed with any other colours, and it is going to be a longish print time, I cut a couple of lengths of filament off of the main roll (say about 1 metre). Then I load the main roll into the first extruder and each of the 1 metre lengths into the other two extruders. So, the machine will use 90% of the filament from the main roll and 5% from each of the offcuts, which means that all the filaments in all the inputs will be kept moving enough to prevent any of the problems mentioned above.
These are what my mixing ratios will always default to. If I want to print a 2 or 3 coloured object using “solid” colours with no mixing for each part, then what I tend to do is simply add M567 commands to the start gcode which will override the default values that I set in my config.g file.
i.e. M567 P0 E1.00:0.00:0.00, M567 P1 E0.00:1.00:0.00, M567 P2 E0.00:0.00:1.00.
For example the snowflakes were printed with White on Gold. In this case, I had two tools. Tool 1 was 100% Gold, Tool 2″ was 100% White. The base and the flake are separate stls. I added the base (gold part) to Slic3R platter, then in settings set it to use Tool 1. Then I used “Add part” to add the flake and set it to use Tool 2. So, when it printed, the first part of the flake started out Gold until the White filament purged through but that was only about an eighth of the first layer and there are 3 layers of white. Of course, this was all before I had developed the technique for moving tool changes forward in the file detailed here. Multi colour printing without using wipe or prime towers
snowfalke2
Two colour print using the Diamond hot end

Tuning and tweaking

 
With the exception of getting the mixing ratios right for whatever printed outcome is desired, there is very little tuning and tweaking necessary for a mixing hot end compared to a non-mixing hot end. The only thing that springs to mind is that, because we retract all filaments together, the retraction distance can be less.
On my particular machine, with Bowden tubes around 250mm long for PLA at 195 deg C and print speed of around 60mm/sec, retraction of 1.5 mm at 3000mm/min works well.
Of course, using firmware retraction makes setting it up a breeze. Simply print two small cubes spaced about 50 mm or more apart then during the print use Duet Web Control to change the retraction on the fly and observe the difference. Use M207 Sn.n Fnnn where S is the amount in mm and F is the speed (feed rate) in mm/min. Start with a small number and increase it slightly until signs of stringing disappear. Repeat for other materials, print speeds and temperature if necessary but you’ll likely find one value that works well for most situations.

Scripting mixing ratios

Another way to use a mixing hot end is to post process the gcode file to enter mixing commands at various places. I have a little python script which an M567 command after “n” layer changes. Tony from Think3dPrint3d kindly put it on github for me. It runs through loops, each one progressively decreasing the mixing ratio for one filament and increasing another. So the colour changes throughout the height of the printed object from colour A to colour B, then colour B to colour C. This can be extended to go from C back to A and then the entire sequence repeated. This is how I produced the following objects:

iansvase
One of my own designs
big-julie-vase
Big Julia vase design by Virtox on Thingiverse

 

The big Julia vase is printed with Red, Yellow and Clear translucent filaments. Starting at 100% red, reducing the Red by 1% and increased the yellow until 100% Yellow, then repeat going from Yellow to Clear. The mixing is changed at every 5th layer to get one complete iteration over the height of the object. The smaller rainbow Julia vase shown at the beginning of this post used Red, Blue and Yellow and changed the mixing at every layer change so ended up with Red,Purple (Red and Blue), Blue, Green(Blue and Yellow),Yellow, Orange (Yellow and Red) then back to Red and repeat the sequence.

Thoughts and ideas.

 
Most people think of multi coloured objects but even if your slicer doesn’t support multi part objects it may well support multiple extruders. This means that one could choose to use one extruder for the infill but a different extruder for the perimeters. One could then use an exotic or expensive material on the outside but cheaper “everyday” filament for the inside. Or possibly use a clear filament for the perimeters to give the object a clear coating.
Printing support material using a different extruder is another possibility that springs to mind.
Then there are other exotic materials such as electrically conductive filament. It could be possible to print an electrical circuit within an object.

Issues with mixing.

There is a fundamental restriction with the Diamond hot end. This is that there is no mixing chamber as such. The disadvantage is that when filaments are “mixed” they come out of the nozzle like stripy toothpaste. So the colour is biased towards each input. This effect can be partly negated by using translucent filament. Or it can be exploited for decorative purposes. I have printed a 3 sided pyramid with each face a different colour by using a single tool with a mixing ration of 0.34:0.33:0.33 and orientating the pyramid on the build plate such that each face is directly opposite a filament input.
300angle1-tile
The same pot viewed from3 different angles showing the effect of incomplete mixing

Video

Finally, this is a video of my custom CoreXY printing the large Julia Vase by virtox shown in the picture above: