Introduction: Spring Loaded CNC Penholder for Rapidograph Technical Pens

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Here's my first Instructable for a CNC Penholder. It features a very simple setup, yet safe for your precious pen tips, especially if you want to use a Rapidograph technical pen with its tips priced at about 20€.

Rapidographs are excellent for use in CNC plotter as they work best when the tip is set perpendicular to the drawing surface and most important they're not changing their lineweight with altering pressures on the pen.

Step 1: Things You Will Need

REQUIRED MATERIALS FOR PENHOLDER ASSEMBLY

- aluminium tube, 10mm inner diameter, 12mm outer diameter, about 100mm long

- aluminium tube, 13mm inner diameter, 15mm outer diameter, about 125mm long

- matching end plugs for the tubes, one per tube (you can also mill some out of MDF or some other scrap like i did)

- a spring from a ballpoint pen, mine is 4mm in diameter and about 32mm long

- some electrical tape

- the Rotring Rapidograph pen (don't worry, this will not be harmed in the process)

Step 2: Assembly

1) Unscrew your Rapidograph so you just have the pen tip stuck in the ink cartridge. This will fit nicely in the 10mm inner diameter tube. Enhance the fit by wrapping some electrical tape around the rear part of the cartridge until there's no wobble left.

2) Do the same with the smaller tube. It should fit snuggly with no play or wobble into the bigger one, but be careful to ensure that it can slide freely up an down in the other.

3) drill holes for the spring in the end plugs. One in the top of the smaller plug and one in the bottom of the bigger plug. Be careful not to drill completely through the plugs, just about 5mm deep to secure the position of the spring. The diameter of the holes depends on your spring, it should be as big as the spring needs to be stuck in the plugs. If you want you can secure the spring with some glue in the plugs.

4) Put everything together. You can spray a tiny amount of WD40 or such between the moving parts for even smoother sliding.

Step 3: You're Done!

Depending on your machine, you could need an adapter ring to fit your spindle mount. I milled mine out of MDF, just like the end plugs.

When drawing, set your Z zero point with the pen about 1-2mm depressed into the holder when touching the paper. This will ensure that the tip is in constant contact even when the ground is not completely flat and that a constant force is applied to the tip.

Here you can see a video of the pen holder in action. By the way, i use the freeware gcodetools for Inkscape to turn vector drawings into gcode.