Soooo I need to change the wasteboard bed on my CNC and changing the layout to something a bit better for me so I need to plot the work area. There are lots of options but I wanted to use a sharpie and wanted to be straight up and down for where the spingle would do it's thing.

While I could have made something simple and rigid I had extra time so of course I made it more complicated. I made a 2 piece body that goes into the spindle so you can have a direct line. The body also helps lock in a 12mm spring to give the pen 10mm of play so its not entirely rigid. You may or may not want to use a half sized sharpie instead of a full length one (read the note at the en

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So to assemble you need a M6 x 30mm screw, a M5 x 15mm screw (this could actually be shorter) and a spring that fits over the M6, the one I had was 9mm diameter and roughly 12mm of compression. One of the pictures shows how to assemble but:

1. tap the holder hole with the M5 screw and the bottom of the body with the M6 screw
2. put the M6 screw through the bottom of the holder and then the spring over the excess of the screw hanging out the bottom
3. put the holder into the body and screw the M6 screw through until the hole in the holder is visible at the top of the slot in the body
4. put the lock screw into the side of the holder through the body hole slot. When you want to put a sharpie in you need to push the holder all the way into the body and then tighten the locking screw. If you did that right you should have 10mm of springy play

Depending on how much height you have to work with between your spindle and the surface you need to mark you might need to use a half sized sharpie which is what I had to do as I didn't have enough leverage to put the sharpie in (even though I had enough distance for a full sized sharpie if I did.

Update - Added a pencil sheath in case you want to use a pencil instead of a sharpie. Nothing fancy just a smaller tube that fits inside with a notch for it to rest against the locking screw

Special Note - If you don't have a spring there is a remix of this that uses magnets instead which might be an option for you.