Tuesday, May 29, 2007


Adventures in RepStrapping: Days 2 and 3

I decided to combine days 2 and 3 for this post because day 2 was not particularly productive, and I didn't have much to show for my efforts. :) Day 3 definitely made up for it, however. Below is a picture of the machined parts I was able to make today:

extruder machined partsextruder drive screw
Yes, I know the PTFE tube looks like crap - that stuff has a nasty tendency to pick up any grease and dirt within a five mile radius :) The studding was quite difficult for me to machine. The steel in it is quite tough, and I had a lot of difficulty getting any tools to take a good bite out of it. I eventually found that the edges of a file work pretty good (especially the corners) for digging into the threads and starting a smooth groove. Once the threads are gone, it becomes a lot easier. I had significant difficulties in soldering the 3mm cable to the drive screw, so I'm trying JB Weld instead. I'll know tomorrow if it is holding well.

The acorn/dome nut for the extruder nozzle was surprisingly easy to machine - I was extremely afraid of snapping the 0.5mm drill bit I had (because I had only one), and the drill chuck I have for my lathe was too big to hold the bit. I ended up using my jeweler's drill (I'm sure a Dremel would work just as well), used a center punch to gently indent the inside of the nut (it was easier on the inside - concave surface), then held the jeweler's drill in hand to drill the hole - it was exceptionally easy, as the metal there is VERY thin. I also decided to grind a groove for the thermistor in the nut instead of a hole, since the thermistor I got (part #527-DKF104N5 from Mouser.com) has leads on either end instead of both leads at one end:

thermistorextrude head thermistor groove

The nichrome wire I got from www.pelicanwire.com is unfortunately unshielded, so I decided that since I was already going to cover the first few threads of the heater with PTFE tape, I might as well cover the middle with a few layers of it as well, since PTFE is not electrically conductive. I used three or four layers of the tape on the middle of the studding to make sure that the nichrome doesn't poke through easily and short against the studding, then wrapped it in JB Weld:
extruder heaterheater element done

For completeness' sake, here is a pic of the thermistor attached to the dome nut with JB Weld:
thermistor done

Tomorrow I will assemble all of the pieces, and hopefully will have a functioning extruder!

I was also able to make a functioning Power/Comms board yesterday, and it passed testing OK, and I made a Universal Controller Board that failed communications testing halfway through, causing me to spend the next 5 hours troubleshooting it. As soon as I figure out what went wrong, I'll post what happened so that others don't make the same mistake (I'm suspecting it might be a firmware issue, and I'll try new firmware once I'm done writing this post).

Well, it's time for me to get back to soldering and testing the circuit boards... If all goes well, tomorrow will be an exciting day!

Very nice. Some of the most detailed images I've seen of the extruder assembly. The blue plastic shows up a lot better in photos than the white.
Brilliant! Great work and greater documentation! :-)
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