A Box of Bits and Bobs

A box of bits and bobs that will be a 3d Printer

My recent iteration of a Prusa Mendel that made the 'box of bobs'

Well almost a year since my last post... better late than... well whatever. I've been working slowly, ploddingly, but unfortunately not documenting much because work has been so sporadic on this.

Extruder drive-screw

It seems there is only one way to mount the dremeled transport screw. That is with the nut in the gear. The gear it self imparts a slight twist to the filament, if the head of the screw is in the gear it's counter-clockwise. If the nut is in the large gear it is clockwise. This may seem trivial, but I found with changing the spin direction I got a more consistent extrusion flow. With counter-clockwise spin it was really inconsistent. I have to assume this is because the hole the filament goes down is slightly fluted from using a drill bit to clean the print... or from the drilling of the PEEK barrier. This still needs more testing though, I have another duplicate extruder almost setup. Maybe I can replicate the results with the other extruder.

Transport screw testing

This transport screw has been working well, much better than the other hobbed bolts I had made. This way of making the drive screw is a lot more consistent and quicker to make.  I'm making a cut area of about 22mm, this way the bolt can be put in either direction, with the head in the gear, or the nut in the screw. The head in the gear seems like it makes more sense to me... I tried a cut area of 20mm, this works, but when I added two washers just behind the large gear a small amount of uncut threading could be seen in the idler wheel hole, 22mm seems to be just right.

Transport Screw on drill press

http://www.thingiverse.com/thing:9291
I remade Elk's Transport Screw

July Fixes

So I started thinking about the endstop problem I was having while using the teacup firmware. I had wired my endstops to be normally open, when everyone else... on the planet... wired theirs to be normally closed.  a G28 would send whatever axis away from the minimum (the second part of homing), and when I closed the switch would stop because it looked like it finally got away from the minimum. Then I found this mechanical endstop schematic, and I wondered if maybe I had a tiny stroke last year... at 28. It seems I couldn't connect anything properly. 

And I found the speed issue I had yesterday was because MAXIMUM_FEEDRATE_E was set too low. Here is the now more... sensible diff.

July 2011 Updates

       I found that the firmware I had been using would require too much work going forward and I started a switch to using the Teacup Firmware.  Here's a diff of the changes I made.  I mostly made some small changes to my hardware to match closer to the firmware standard.  It seems to work great, except for a few middling things I still have to figure out, speeds are off.  This also means that I can switch to other host software and I'm presently using the 0025 release of Replicatorg.  Reprap Host worked well enough, but I can debug a lot easier with Replicatorg and it has included Skeinforge for a while.  Skeinforge is the one thing I don't think I'm changing anytime soon.  I also found in the course of this updating that I'm terrible at electronic design... well I suppose I'm better than I was... because I found the problems. I was terrible, I'm somewhat better now.  I had wired my heated bed in silly way, sharing the 5v- with the 12v+, the resistors were wired in two parallel sets of series resistors, which is now completely in series 12+ and 12-.  I also had added a 5v line to each of the minimum limit sensors... unnecessary with physical switches.  I cleaned up some wiring and fixed the pwm board to add some diodes and change out a transistor.

       Earlier in the month I bought a groove mount thermal barrier from makergear.com, which I found is based just about 30 minutes north of here... cool shit, on both points. I don't see any reason why to use any other design for a thermal barrier for a while. It's a great design and having tried it with PLA and ABS.  It works, and works well... I'm buying 10 once I have some money.

Back to Work.

Printing parts for a geodesic dome