Heater Block For Glass Nozzle
This page page describes how to use a glass nozzle in a resistor heater block. The Glass Nozzles page describes how to use a glass nozzle with a nichrome wire heating element.
I never liked dealing with nichrome and agree with nophead's suggestion that the resistor heater blocks should be adopted as the official hotend. I also wanted to experiment with glass nozzles. One problem with glass nozzles is the poor conductivity of glass means that you want to deliver heat near the end of the nozzle so that the plastic doesn't harden and block the nozzle because the nozzle it much cooler than the heat chamber. When thinking about how this could be done, and rifling through the stuff he had on hand, I found an aluminium tube with 10mm OD and approx 8 mm ID (which matches rocket_scientist's glass nozzle OD. A quick ream with an 8mm hand drill, 3 cuts with a hacksaw and a bit of judicial squeezing with some pliers yielded this:
I cut 2 pieces of 20mm wide aluminium strip and drilled a 10mm hole through both of them that fitted the sleeve snugly.
I then drilled 2 4.8mm holes as close to the sleeve as possible. These holes only go about 3/4 of the way through. The hole is drilled the rest of the way with a 2.5mm drill. This gives room for the resistor lead but prevents the resistor from going all the way through (and gives a bit of extra strength to the strip which otherwise would be quite thin all the way across where the hole was drilled. Using a hand drill, and because I am bit of a hack, one of the holes actually sliced into the sleeve, but I realized that this is actually OK and when the resistor is installed, it will prevent the sleeve from slipping through (or the strips from slipping down).
Then I insulated the resistor leads by wrapping Kapton tape around them. A handy hint for doing this neatly is to peel a bit off the reel and then slice it off neatly with some scissors. Then put the resistor lead under the small piece of tape sticking up and press it onto the lead. Then rotate the resistor to tightly wind as much Kapton onto it as you like.
In the end you end up with very neat insulated leads as shown below. I'm using 2 15 ohm resistors which will be placed in parallel to give about 7.5 ohms.
This shows how the resistors sit in the holes that have been drilled for them.
This shows the pieces about to be assembled. Notice the additional holes for M4 bolts to clamp the alu strips together. You will also notice a small hole in line with the sleeve. The idea of this hole was to add a setscrew to prevent the strips slipping down the sleeve.
To measure the temperature I sandwiched a thermocouple between the two alu strips and then clamped it by tightening the clamping bolts. I found that after I had clamped it, the resistors had shorted on the block (the paint cracked off the ends). I fixed this be disassembling and wrapping a single layer of kapton around the body of the resistor too. You may want to do this right of the bat.
Now see it in action:
This seemed to work OK, but I am using PLA which sticks to glass pretty well. If you let the filament melt up the glass a bit, it becomes quite difficult to push the filament through until the plug moves down into the heated part. There is a bit of slack between the filament and the glass, so a useful addition would be a PTFE sleeve that fitted in the glass tube, but still fitted the filament. If you know of where to get such a tube at a reasonable price, please update this page with details.
[Update 17 Oct 2010] I came back the next morning and found that the resistors had again shorted against the block. The lesson from this: is clamping resistors is not a good idea. The insulating paint will crack and they will short against the block. I have used similar resistors in the heatblock that I routinely use on my Mendel and have not had any issues. These resistors were installed by drilling the hole slightly larger than it needed to be and wrapping the resistors in kitchen foil (another nophead idea). I found that it works well by just wrapping the narrow part of the resistor. I had done this in the past (just to make it easier to shove the wrapped resistor into the hole), but I see now that it is important because it protects the metal caps on the ends of the resistor.
The large surface area was also a problem. I found that it struggled to heat to 200 deg (Im using PLA, so it still extruded reasonably well, but this would probably have been a problem for ABS.
I also found that attempting to record all of this in the third person (as suggested by someone as a standard for the wiki) was painful at best and I have reverted to first person.
With these lessons in mind, I decided to build a Mk 2 Glass nozzle heater block. For this I wanted to use a block of aluminium rather than the strips that are available from my local hardware store. I went looking for a supplier of bars. I went to a local scrap/tool place (Paramount Browns). They didn't have any bars, but they did have a pair of aluminium vice jaws that were made from a fairly hefty block for $9 AU:
I got these and Jaws chopped a bit off the end for my block. I also went to get some more 1W resistors. This time I got 3.3 Ohm resistors so that I could use 2 in series and have the heater leads come out the same side of the block. To keep the block small, I put both resistors on the same side. I again drilled the holes for the resistors so that they interfered with the 10mm tube. This will hold the block steady on the tube.
The result is shown below. This heated fairly rapidly and extruded quite well too. This nozzle looks like it is slightly larger than the previous nozzle.