Build a spring loaded pencil plotter bit for around $9

Here’s a video of the finished result

I’m gearing up to do a routing job on a piece that I’ve put quite a few hours into and it’s a piece with several tight curves that I am loading in as an image and then drawing the path. I have basically zero room for error. So while I could run the bit around the top and watch it, I really wanted a way to trace the exact center point of the bit and verify it will follow the outline of the piece the way I need it to.

There are quite a few DIY pen holders out there but it seemed to me that many of them were complicated, required fabricating 3D printed pieces or building fixtures that then required running with an offset.

I was looking at mechanical carpenters pencils on amazon and came across this one that showed the dimensions of the barrel at 5mm … almost perfect for a 1/4 inch collet.

So here are the steps to turn this $9 carpenters pencil into a 1/4 inch plotter bit that gives you a spring loaded pencil.

  1. Using a heat gun or torch heat up the plastic housing above where the barrel comes out of the pencil body. It should slip out easily once you’ve softened the body.

  2. There is a small plastic tube that sits above a small spring. I didn’t need this tube but if your router has a deeper ceiling above the collet you might use it to ensure there is tension on the spring.

  3. Remove the spring from the barrel. You’ll want to break the pencil lead so that it’s about 1/3 the length then insert it down into the sleeve. We now need something to go between the spring and the top of the pencil lead so that it applies the spring tension to the lead. What I found to be a perfect solution was a hollow point pellet for a bb gun/pellet rifle. The rear side of the pellet slips over the lead and the rounded side mates up with the spring perfectly. But, if you don’t have one or can’t get one, try to find something reasonably small that will sit between the spring and the lead without catching and it should work.

  4. Now at 5mm it’s too narrow to secure in a 1/4 inch collet. I used some aluminum shielding tape and put 2 wraps around the barrel to build it up. This part you have to sort of adjust until it’s right but you want it to just barely fit into the collet so that you will be able to tighten it.

  5. I placed the barrel into the collet and pushed it up until there was some tension on the spring from where the spring contacted the ceiling of the router. Tighten it down and now you should be able to apply a little pressure and see the lead move up and down.

The pencil I linked to comes with 6 additional leads. I feel like this is a cheap, fairly easy way to get an accurate plotter if you want to test trace your paths. It’s not ideal for actual plotter work I wouldn’t think because there’s a limit to how far you can run before you’ll need to re-sharpen and then once there’s no tension on it you’ll need to put a new length of lead in. Hope this helps you or gives you an idea!


I love this idea.
Wonder if there is a good way to fit lead into the MCEtcher.

Actually, the vinyl cutter looks closer. If you find the lead in the diameter of the cutter shaft it would be pretty straight forward.

Ooooo… this could be fun. Keeping it sharp could be a bit of a pain. Or I guess it could be some character if you are using for more artistic uses.

Ah yes, I meant the Sting ray, not the MCEtcher.

Yeah I haven’t tested it to see how quickly it loses the point yet. The pencil comes with a little sharpener though