Saturday, April 2, 2011

This is my largest print to date. It measures 10" by 10" by 3" and was printed in two parts that took more than 24 hours each. Even so, it is still just the front half of the teeth of an orca whale.
I found several people online took photos of the same orca skull in a museum, and was able to use all those photos to reconstruct the positions of the teeth, since each photo had a different angle. Unfortunately, I haven't found any CT scans or the like, which might have given me better quality data, so the jawbone here is pretty simplified.
I initially used that model to create a 3D whale model for rendering in Carrara, but I wanted to see what it would look like at full scale, so I printed it. I printed the first part in November, and it had some rough spots in the overhang area. A few weeks ago, I printed the second half, using what I've learned since then, and the result is much nicer, except it got stuck a few times, so I had to restart it in the middle.

Monday, January 10, 2011

I haven't had much to write about, but I have been printing stuff. Check out the designs I've shared on Thingiverse
In addition to the clear PLA I started with, I'm also now printing with black. The black PLA has been uneventful, to the point where I just warm up the machine and start printing. Some prints take 8 hours or more, but I don't have to babysit them anymore. :-) That lets me get more ambitious, like a 20-hour print I'm in the middle of now. I just slept through the first part of it. To date, I've had about 30 successful prints. At some point I had heard that the acrylic I used as a build surface deteriorates after as few as 20 prints, but I don't see any evidence of that with PLA. (My build still has some scars from when I was trying ABS.) The PLA keeps a good bond to Acrylic while printing, (it needs to so it doesn't move around) but I slide a spatula-shaped Xacto knife underneath, and the whole model pops up when I get enough leverage. The acrylic is left pretty clean. This works even on large 8" models.

Saturday, October 30, 2010

I printed a whale tooth I found on Thingiverse: (Whale Tooth) because I thought it looked cool and would really test the capabilities of my machine and software tools. (Which is great for working out the kinks.) I'm happy to report success! The RepRap java tool couldn't handle the STL file, so I used Skeinforge. to create the GCode. I had to customize Skeinforge a bit before it worked right. It wanted to send Z moves in the same line as an X-Y move, and that clashed with the different speeds required. It still doesn't do acceleration right, which messed up a few layers when the X stepper skipped a few steps.

Tuesday, October 26, 2010

The secret to my success

Here you can see my extruder's hot-end. The bottom part is a standard welding tip, which already had a 0.6mm hole in it. I drilled it out to 3mm (well, 1/8" really.) almost to the tip, so there's maybe 1-2mm left for the nozzle. Around that is wrapped the nichrome wire for heating, with a thermistor near the tip. Kapton tape surrounds it all for insulation and to keep it all in place. The welding tip goes through a fender washer and into a nut which keeps it in the washer. The washer has 3 holes drilled for the long bolts (black thread in photo) that attach it to the extruder. The white PTFE insulator sits between the washer and the extruder. I carved out a hex nut-shaped hollow in the PTFE so everything stays centered, and in a pinch I could unscrew the nut using the insulator. Leakage between the insulator and the nut is minimal. (Only noticeable when disassembled.)
The latest change to get things working is I added a bunch of Kapton tape around the washer so it stops acting like a heatsink. I found that the PLA was cooling too much, (especially when it stopped while moving between layers after the extruder was warm,) and creating a plug in the top half of the welding tip. If I pulled out the filament, the portion between the pinch wheel and in the PTFE was a little stringy (it would stretch as I pulled) but the part below that, in the area of the nut and washer, was a perfect 3mm cylinder, which terminated in the really melted part.

And here's my first success with PLA! It's a small stand for my Droid phone, which holds it in portrait position. It fits a bit tight, but that's because I haven't had a chance to calibrate the extruder settings.

Monday, October 25, 2010

Print complete!

It finished, with only a little help here and there. Success! Now on to fine-tuning. But first, some sleep.

Printing! (crosses fingers)

As I write, I'm printing layer 7 of my best print so far.. Here's hoping!
I added Kapton tape to insulate the big washer that mounts the heater to the extruder, so it doesn't cool down so much. I'm extruding at 200C, with some minor back slipping of the stepper, but it's extruding pretty well.

Saturday, October 16, 2010

or so I thought

I can't get consistent feed from PLA. There were a few times it would feed perfectly for a few minutes, but now I can't even duplicate that much. Eventually, it gets jammed up in the extruder barrel. Frustrating. I can get it to squirt a foot or two of extruded plastic before it starts jamming. Then I have to either push it out with extreme pressure, or drill it out. If I'm really careful, and a bit lucky, I can pull a plug out and then squeeze out the remainder with a metal rod. I even re-built the hot end twice, with no improvement. :-(