Friday, April 30, 2010

My new heater construction

Now that it works, I should mention the changes to my heater, compared to the RepRap standard design. (See for the standard.)

Instead of the brass bolt for a barrel, I use a welding tip. It already has a 0.6mm hole at the tip, and it's easy to drill a 3mm or 1/8" hole at the top in a drill press. The smooth outer surface makes for good heat transfer from the nichrome wire.

I had several kinds of trouble threading it into the PTFE thermal barrier. First, I used a tap set to thread the PTFE, which created a good thread, but it expanded the hole above the brass, so that the melted plastic would expand too much, and be too wide to pull out, and too thick to push in. For my second try, I cut slots across the threads of a throwaway tip, and used that like a tap. It worked, but the threads were lower quality. The motor pushed the tip out of the PTFE threads.

My third try worked. I use a nut and fender washer to secure the tip. Then I hollowed out the PTFE in the shape of the nut, to keep it centered on the hole. Drill 3 small holes in the fender washer for 1/8" bolts that connect to the acrylic extruder frame.

The tip can be easily swapped for another, such as when I had to replace the tape with Kapton.

Thursday, April 29, 2010

A bit of success!

Printed my first object! Still have some fine tuning to do, but it prints. :) It was just a simple cube, but it came out nice. I did have to baby-sit the machine, though.

Sunday, April 25, 2010


I raised the temperature to 240C, and promptly fried the insulator tape I was using. ("Rescue Tape" is not good above about 220C) I had initially tried "Rescue Tape," a silicon-based tape I found at a local store to keep the nichrome heater from shorting to anything, and it worked well at 200C. But at 240C, it would try to shrink too much, and ended up splitting down the side, exposing the nichrome. So I gave up on that, and ordered some Kapton online, like I should have done initially.

So, a week later it arrives, and I rebuild the heater. Now it goes all the way to 240C, and the ABS starts flowing like honey in a squeeze bottle. Now it extrudes quite well, in fact, faster than the X axis can move. So I just need to fine-tune the variables, and start printing...

Thursday, April 15, 2010

always test your wiring

So I fix the heater barrel, which involved re-doing the heater element. I test resistance across the heater element, (8 ohms) and across the thermistor. Then I assemble everything and hook it to the controller. When I add power, the heater LED lights up even when the heater is off! :(
Turns out I have a short between a heater wire and the thermisor wire. Didn't test for that. Doh!

Sunday, April 11, 2010

Uh Oh

Well, it grips now. I pushed a bit of rubber between the bearing's post and the acrylic frame, and loosened the nut. Now it grips quite well, and doesn't get stuck on the teeth, like it did when too tight. Only problem is, it pushed the extruder heater barrel right out of the PTFE insulator. So.. on to the next problem.