The short answer is I found that 1/2" CPVC piping fits perfectly down a 1/2" PVC repair coupler such that it will smoothly slide in and out with little resistance. Also, that the interior diameter of 1/2" CPVC piping is a great size for sharpies and other pens. Now on to the longer explanation.
First, start with a 1/2" PVC expandable repair coupling shown at top. If you unscrew the back completely the center portion will push out with a bit of force. That bottom left piece in the picture is what you want, the rest can be tossed. Note that the internal diameter of this repair coupling is larger than a normal 1/2" PVC pipe. Otherwise I would just use regular PVC pipe
The reduced end is the same outside diameter as any given 1/2" PVC pipe. I found a fitting that fit over that end, but had a smaller internal diameter, than 1/2" PVC, in the threaded portion. This reduced diameter keeps the CPVC pipe from sliding right out every time the machine lifts to do another letter. You can glue this on, but a good friction fit might be all you ever need.
Next I took a short section of 1/2" CPVC and stuck a sharpie in it. Regular sharpies fit perfectly. The thin tip guys took a few wraps of painters tape to get them snug, and pencils took a quite a bit of tape. Once shoved in the CPVC you can use a dab of glue in the back to keep them from ever going anywhere. Hot glue, 5 min epoxy, what ever you have on hand. Once the writing utensil is fixed inside, slide it into the the back end of expansion coupler and it should stick out the front.
Like I said, I don't have a shapeoko yet, so I did a hand test. The weight of the sharpie alone was enough pressure to do a great job writing. because the CPVC is just barely smaller than the expansion coupler, it keeps everything straight and true while you move the device around.
Make sure the writing utensil sticks out enough to clear the tip of the device.
Why go to all this work when people have used a rubber band to good success? This is true, but letting the weight of the pen set the pressure is more consistent. You can be pretty sloppy with the Z values and still get good results. Also, this method should make swapping out pens very quick. I have the idea to do multi colored pictures and the like.
- 1/2" CPVC pipe. Only sold in 10ft sections at my stores, but it was less than 4 dollars. That will hold a lot of pens!
- 1/2" PVC expansion repair coupler. 3 bucks at Lowes. Make sure the CPVC fits nicely inside
- 1/2" PVC threaded fitting. <1 dollar. You could use a cap and drill a hole large enough to let the pen poke through, but this threaded thing worked well for me.
- Lots of sharpies, pens, colored pencils, and what ever else you want to draw with.
Again, I dont have a shapeoko, but the outside of that disassembled expansion piece is a consistent diameter. I imagine that wouldn't be too hard to chuck up in place of the spindle, or as a side add on. That way you could slide a marker in at any time and get drawing.
The threaded portion of that stop fitting I used could be cut down to save space, and I may end up doing that when I implement it into my future tool. When the CPVC is inside the coupler there is a tiny bit of wiggle. I don't know how badly that will impact the drawing, but a single wrap of painters tape seemed to stop it completely. Mileage may vary with use, I am not sure.
My experience with the different sharpie types showed that their own weight was more than enough to leave a good mark. The pencil on the other hand was a bit light. You can cut extra CPVC sections and fill them with weight. Fill one end with hot glue, put measured amounts of sand, BBs, fishing weights, or what ever, then seal it up with more glue. These will then just drop on top after the pencil has been loaded. I doubt I will be using a pencil much, but it could be cool to have shapeoko draw me colored pencil art!
Let me know what you think, or if you have any suggestions for improvement.