Today we have a quick fix and a short post in our continuing saga of learning to use a punch card knitting machine. In our first post of this series, we cleaned and set up a Brother KH-881 knitting machine. In our second post, we learned to create punch cards on Dura-Lar paper with Silhouette Cameo 3 craft cutter. In this post we’ll use 3D printing to solve the micro-problem of keeping the marker aligned in the craft cutter.
Here’s the problem: Because of the type of paper we need to use for the punch cards, we have to use Sharpie markers instead of the pens that came with the Silhouette. (The craft cutter both cuts and draws, and we’d like to do both so that we can label our cut punch cards.) However, the Sharpies don’t fit snugly into the machine, and this casuses errors in alignment when printing. Putting tape around the marker to make it larger helped a little, but was ultimately unreliable. We tried to fix the problem with a Chomas Creations Silhouette Cameo Marker Holder that we bought online, but the marker holder was still too big for our Ultra-fine point Sharpie markers. Then we realized we have a whole bunch of 3D printers… maybe we 3D print something to fit exactly?
What we need is a hollow cylinder to fit around the pen, to make it slighly larger and thus fit snugly in the pen housing. We decided to make the pen fit into the maker holder instead of directly into the machine, because the marker holder was so nice and has a little adjustment screw that we find useful. Here’s how we made this simple object in OpenSCAD:
All this code does is create a cylinder and then remove a cylinder from inside it. The inside of the maker holder has straight sides, but the pen itself tapers a bit; thus the interior “cylinder” has two radii, making it a slightly angled truncated cone. We also added “wiggle” terms so that we could iterate the design until the fit was exact, both around the Sharpie and inside the marker holder.
We used an Ultimaker 2+ Extended to print the piece. We have a lot of 3D printers but for accuracy we always go to the Ultimakers! The blue piece in the picture below is our final print. With the addition of the blue spacer, the Sharpie fits perfectly in the marker holder:
Below are pictures of the test drawings we did before and after we added the spacer; tests #14 and #15 are before, and all the others are after.
With the alignment problem fixed, we’ve gone on to try getting text to work… more on that in a future post!
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