Swing Arm Sorrow and Tight Fits

First up for today’s post are yesterday’s prints: http://i.imgur.com/9pljC5I.jpg

I haven’t done any prints today, as I needed to take care of some other things.

A core feature of any plastic based 3D printer is the feed mechanism, the part of the printer that pushes the strand of plastic through the extruder nozzle. On the Solidoodle 3, this is handled through a motorized drive gear, with a swing arm connected that uses a spring to push a bearing into the other side of the plastic, holding it tight against the drive gear. Inconsistent plastic extrusion can be caused by any number of problems related to this feed mechanism, including poor voltage control to this motor, the motor over or under turning, excess dust and plastic shavings caught in the gear teeth, or a poorly positioned swing arm.

While I have greatly reduced the number of print failures with the changes mentioned in previous posts, I find I am still running into the same issue that has been plaguing me for a while: The nozzle stops extruding plastic mid-print. Sometimes it will fix itself and get going again, sometimes it stops for good.

In the previous post I mentioned calibration, which sounds fancy but is really just marking your plastic with a sharpie so you can measure how much it extrudes. Before I figured this out, I had been just watching the output, which often seemed consistent to me. Using this sharpie trick, I could watch the plastic going in, and it became obvious that often when the gear was spinning, the plastic was not going down. This narrows my problem with inconsistent extrusion a ton: I am not having voltage problems, or electronics overheating, inconsistent heat on the nozzle, or anything else, the problem is my gear is often not catching on the plastic very well.

Now that I have a more focused problem to solve, I can look into what causes that. One cause is dust on the gear head. When the gear grinds against plastic without extruding it, some plastic get pulled off by the gear, and stuck in its teeth. This issue I resolve by taking a q-tip, dipping it in acetone, and running it against the gear.

I still get failures even after freshly cleaning the gear, that leaves me with two other potential problems to look at: snags in the plastic feed, difficulty pulling the plastic from the spool, or the swing arm not properly holding the bearing against the gear, either too tight or too loose.

I was able to greatly improve the first problem by moving my plastic spool to a shelf above the printer. The second problem is what I am focusing my efforts mostly on. Those efforts so far have mostly been me fiddling with the swing arm, adjusting the tightness of the spring holding it in.

When I did these adjustments Friday night, I was able to get a good 16 hours of printing straight before any mishaps: 8 hours on the 20 DS game holder, 2 hours on an iPad stand, and 6 hours on a large deer head. This long length of time makes me wonder, maybe it was the plastic spool that got caught?

The second part of this blog post is about a new issue I had not noticed before,, because my prints haven’t been as functional. The sizing of things is not perfect. When I printed the 10 card DS case in black, the cards fit, but it was an extremely tight fit, and they were tough to get out. When I printed the 20 card case in transparent plastic, I scaled it up by 2%, hoping it would have enough slack to hold them. This case was a far tighter fit than the black case! When I printed the iPad stand, it was three pieces that fit together, I used the model in this link http://www.thingiverse.com/thing:29631. The center piece was far off enough in size that I could not fit it into the holes. I have not done much investigation into this problem yet, as I’m still trying to raise my print success rate. One theory I have here is that the different color plastics I am using all melt and flow at slightly different rates, leaving thicker extruders with the transparent plastic than with others. I can modify the nozzle and print settings, but I am not at the point I want to start doing that yet. Luckily I ordered some white ABS plastic to get what will hopefully be a less problematic color, and can get things ironed out on that before coming back to the fancier materials.




Joseph Stankowicz is a software engineer who has worked in the video games industry for over eight years. The last two years have had a heavy focus on Unity development, where he helped ship over eleven titles to iOS and Android platforms. He also is really excited about 3D printing, and keeps his Solidoodle 3 printing out stuff as often as possible. You can view his LinkedIn profile here http://www.linkedin.com/pub/joseph-stankowicz/60/294/420

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