Monday, December 5, 2011

Saturday Setbacks

I ended Saturday significantly farther behind than I started it.  That’s how these things go sometimes.  You just hope you learn something in the process, so that next time you can make new and more glorious mistakes.
I started with trying to use a few unbroken scraps of that clear PLA that I was about to throw away.  I figured I could make a few linear bushings or something with it.
Unfortunately I got into some areas where the diameter exceeded 3.2mm (it varied from 2.65 to 3.25mm, wow) and that was too big to fit through the hotend – and while it was jammed, what was left in the bottom apparently scorched and clogged the nozzle.
So I disassembled the extruder and spent quite a lot of time with a torch burning crud out of the nozzle, and with drill bits in hand scraping junk out of the shaft.  After 3 tries I was sure I had things sorted, and…it wouldn’t heat. I found I had broken the wire into the heatcore, just where it enters the ceramic.  Argh.
I had a J-Head sitting around that I’d intended to use on my new printer, so I installed that.  I’d never used resistor block heaters before.  I had little luck with it – it seemed like it was extruding OK but it also seemed to have little thermal mass, so when I started to go fast with it (over about 80mm/s) the extrusion started to peter out until it slowed down again.  It’s possible that I was doing something wrong, people on IRC assure me that they use J-Heads without trouble, but for now I don’t have the time to mess with it.
EDIT: I now believe that the J-Head is innocent – I later discovered that my extruder idler was broken.
I got out a spool of 28 gauge bare nichrome, broke the ceramic up with pliers to get down to the bare M6 threaded insert, wrapped it tightly with kapton, and wound a new core.  The 28 gauge needed two wraps to get to 5.6 ohms so I made a kapton/wire/kapton/wire sandwich, and covered the whole thing with leftover ceramic paste.  This eventually got me going.
I also had the thermistor fall of the bottom of the HPB during a print, which caused the HPB to get very hot and scorch and partially melt the extruder I was printing.  As a result I came up with the idea of drilling a hole in the center of the top platform and feeding the thermistor up through that, and laying it down in a groove carved out from the hole and putting a piece of kapton over that.  This allows the HPB to lay directly on the top platform which should increase performance (no loss to the air) – it did make the reading on the thermistor more accurate than I’ve ever seen it before.
I did manage to make a little progress by the end of the day Sunday – the frame build instructions are about done, I have a batch of Sanguinololu CPUs with bootloader and Marlin burned to them, I did finally get that extruder printed, my printer is slightly improved (and therefore all future printers will be improved)

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