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