This is a follow up to this post The Diamond 5 colour (“Fullcolor”) hot end (and other related stuff).
One of the issues I mentioned in the earlier post was that I suspected that the 5 colour version of the Diamond hot end suffered from “heat creep”. Or at least I was experiencing problems with PETG swelling in the area of the heat break which caused partial jamming of the filament inside PTFE liner. So I decided to investigate.
While I write this, I’m still convalescing so what comes out may seem a bit garbled. I hope not but feel free to point out any errors or typos (in a nice way please).
My theory for why the 5 colour version had problems which the 3 colour did not, was that it may be because the lower heat sink fins of the 5 colour were very much smaller in diameter than the 3 colour version. A possible cure might be to use a higher flow rate fan. Rather than just fitting a bigger fan and trying to print with it, I decide to try and actually measure the temperature in the area of the heat break. I’m glad I took this approach as will become apparent.
So starting with the 3 colour version, here is the test set up that I used.
Basically, I removed the hot end from the X carriage and fitted thermocouples touching the inner part of the heat sinks (the smallest diameter) on the side away from the air flow. One was fitted above the lowermost fin. Any lower and it would have been affected by radiant heat from the hot end. The other was fitted close to the top but also touching the inner part of the heat sink and opposite the air flow. The thermocouples were held in place with cocktail sticks, one wrapped in Kapton tape to make it thicker. Maybe not the best method but needs must and all that……
Here is a close up
By the way, in case you are wondering the brass nozzle is fitted with my home made silicone sock. The 5 colour doesn’t have a sock but I doubt if it would affect the temperature of the heat sinks. If anything, I’d guess it might make the readings higher with a sock so the 5 colour might be better off without? Dunno.
The tests were all run without any filament loaded and of course, the temperature inside the tubes will be different to that on the outside, so it’s not a scientific measure of actual temperature under printing conditions, merely a method of comparing one thing with another.
With the setup as shown, I then heated the hot end to 200 deg C and took readings at 1 minute intervals up to 10 minutes, then at 15, 20, 25,30, 45 and 60 minutes. Here are the results. T1 is the lower thermocouple and T2 the upper one. Note that the “Time” axis on the graph isn’t a linear scale.
Next up was the 5 colour with the same spec fan. Here is the setup
And here are the results
Note that in both cases the hot end gets up to temperature within 3 minutes so comparing T1 should be valid. Also, of note is the fact that I’m using a 40 Watt heater cartridge on both hot ends, rather than the 80Watt heater on the 5 colour that for some unknown reason is thought to be necessary.
T1 for the 3 colour version reaches about 58 deg C after 4 minutes or so and stays at that temperature for the rest of the time. Actually it drops about a degree at the end of the hour. Not sure why that should be – maybe just a drop in ambient air temperature? What is also of note is the T2, the temperature close to the top of the heat sink is only slightly above ambient so the lower fins dissipate most of the heat and the upper fins do very little.
T1 for the 5 colour version reached around 66 deg C after 4 minutes which is 8 degrees higher than the 3 colour but it continued to drift upwards, reaching a peak of 70.8 after 30 minutes which is 12.9 deg C higher than the 3 colour version. Also, the temperature near the top of the heat sinks (T2) was about 11 degrees higher than the 3 colour version. The temperatures at time = 0 (therefore ambient) were around 25 deg C for the first test and 23 degrees for the second so despite a 2 degree drop in ambient, the recorded temperatures for the 5 colour version were significantly higher. The fact that the temperature at the top of the heat sinks for the 5 colour version is higher than both ambient and the 3 colour version, reinforces my belief that the smaller lower fins are not as efficient at dissipating heat.
What I don’t know is what the temperature of the filament would be at the “T1” position other than that it would be higher than was measured on the outside of the tube. The Tg temperature for PETG is around 80 deg C as far as I can ascertain. This is purely speculation but taking an arbitrary value of 10 degrees C as the difference between the outer temperature as measured and the inner (filament) temperature at that point, then the filament could reach 80 deg C using the 5 colour version but only 68 deg C using the 3 colour version. So effectively reaching the Tg temperature with the 5 colour but staying below it with the 3 colour version. Thanks to Rob Miller for pointing that out and I think these tests back that up.
The next logical step was to try a higher air flow fan. Of course, if the limiting factor is the surface area of the heat sink fins, then increasing the air flow may have limited benefits. However, it is worth a try……
The highest flow rate 50mm 24V fan that I can find is 20cfm. Apologies if you see it referred to as 22 cfm – that’s what I thought it was but when I checked, it’s actually 20 cfm. So to get a higher flow rate, I had to go to 60mm which meant making a 50 to 60 mm adaptor. It was only after I had designed it that I discovered there are numerous designs on thingiverse that I could have used – oh well….
By the way, if using a 60mm fan works, this works then I’ll have to redesign this hot end mounting arrangement as it was an absolute pig to assemble.
The other little issue is that the fan blows directly down onto the hot end which is only “protected” from the draught by 3 layers of fire blanket type insulation. Also the heater is fitted in the centre of the hot end so would normally be directly under the fan. It seems that RepRap.me had thought of that and their “official” mount has a tube running down the centre to mask the air flow from the heater. So I used that idea and expanded on it slightly. Here is a picture of my mount, with the 50 to 60 mm adaptor fitted.
The top of the tube is the same diameter as the fan motor, then it tapers down so that the heater cartridge would just fit inside the bottom of the tube.
These OpenScad screen shots maybe show it better.
On the basis that more is better (when will I ever learn?) I sourced two fans. The first was 50.4 cfm and the second was a whopping 84.4 cfm. In hind site, I should have taken more notice of the noise level, the first being 54dBA and the second 66dBA compare to the one I have been using which is 40.5 dBA.
Anyway, here it is with the first (50 cfm) fan fitted.
Then I attempted to run the first test again but didn’t get far before I ran into a heater fault. After 4 minutes, the hot end had only got up to 183 deg C and was struggling to go any higher. I attempted to re-tune the heater PID with this big fan running but to no avail. Just too much air. Actually I’m glad it didn’t work because even if it had, there is no way that I could have lived with that noise level.
So, I’ve ordered two more fans of much more modest air flow (and noise level). One is rated at 27cfm which is about 35% higher flow rate than the 50mm fan I’m currently using and at 39dBA, is actually quieter. The other is 33 cfm so about 65% higher flow rate but is slightly noisier at 44dBA.
Quite what I’ll do with the other fan, I don’t know. Maybe a leaf blower? As for the whopping 84cfm fan that I didn’t even fit I’m open to (polite) suggestions.
So part 3 of this blog will follow. If the increased air flow dosn’t work, then for me at least, I’ll be limiting any printing with the 5 colour Diamond to PLA.