Slip On Lead Holder

As I’m a rookie at all things CNC I’m often surprised by what my machine does vs what I thought it would do. This can be painful when cutting a $60 sheet of ply.

I built this magnetic, spring loaded , slip on lead holder to help me pre-mark my cut paths.

It’s designed to fit over a Makita collet nut and can be installed over a 1/4 or 1/8 bit so no tool change is needed just attach the doodad and print. The spring loaded lead can handle about 3mm of Z movement.

As the crown test shows it has a a bit of wobble but less than the endmill width so I don’t care for prototyping and locating hold down screws.


You might avoid some pain by either dry running a job or cutting it in foam first. It can take a bit to get it in mind that the machine has no thought capability and will do exactly as told, good, bad, or indifferent.

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Use a piece of 3/4" plywood to set your z height above your material and then run the gcode. This lets you air cut to verify path.

Yeah I do the dry runs as well but being able to visualize the part in front of me is helpful. I can draw it on the actual workpiece and often see things that weren’t apparent in the drawings.

Foam would be great but I rarely keep it around. I may try some of the fanfold stuff in the future but storage is tight.

Would a “chalk chuck” allow similar functionality and easier erasure? (assuming erasure is needed)


I actually tried chalk first but the ablation on the chalk was too fast. It would work for about 30 linear feet before the chalk wore down past the springs range. This was for the thinner 1/2" sticks that I stole from the kids art set.

5.6mm HB leads get a bit worn down but seem to last long enough for the jobs I’m running. I found keeping the pencil less sharp worked better as the greater surface area wears down slower and also doesn’t score the wood. As long as I don’t have an oopsie on my design the pencil line will get cut. anyway. Otherwise I guess it better be a painted piece or I have some erasing / sanding ahead of me.


We used to mark out large scenic backdrop paintings using chalk wedged in the end of split bamboo. Think Dick Van Dyke’s scene at the start of Mary Poppins, but we just did outlines. The chalk would float to the top of the paint (depending on the paint and process being used) so you could paint large areas, the chalk lines would float up for the details, then you just flog the chalk off with a home-made “feather duster” made of muslin strips stapled to a wood scrap handle.

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Ok I built the pencil holder so now its your turn Tom… I’d love to attach your Marry Poppins flogging gizmo to my Lowrider… Wait that may have come out wrong.