Tuesday, 13 August 2019

CNC plotter pen holder

To help test my CNC proof of concept I have designed a couple of pen holders which I have 3D printed.


One utilises a modified ballpoint pen and the other fits a fine point marker pen.
At the moment I have only tested the one for the ballpoint.

Ballpoint Pen
I have cannibalised a couple of ballpoint pens to make one that has a spring tip. I took the inch long spring from a cheap retractable pen along with part of the ratchet mechanism.



The spring fits at the opposite end of the pen, pushing down towards the tip. I cut down the ink tube, a little at a time, until the spring, sitting on the ratchet, sitting on the tube, would fit in the pen and have about the same amount of give as I would put on the pen when writing.

The pressure was trial and error but as it worked first time, I guess it was not too difficult to judge.



The result of modifying the pen, is that all I need for the tool holder is a clamp. I just made it fit the same holes as the spindle would use on my budget Chinese CNC machine.

Parts:
1x M4 wingnuts
1x M4 A type (standard) washer
1x M4x40mm bolt


Marker Pen
The design for the marker pen is a bit more complex. I could not modify the pen, so the holder had to be spring loaded to get the right pressure.




Again, I used the roughly 1 inch long spring from a give away retractable ballpoint pen.





In this version the pen sits at an angle and pivots. It's only a little bit of movement but enough to keep the pressure on the pen tip.

Unlike the pen holder, the motion of this version means that the marker is not perfectly aligned, at all times, so this is OK for testing in place of a spindle but it is not ideal for detailed plotting.






This design took a few attempts to get the mechanism right. It's a bit larger than I would have liked but it had to be to accommodate the 13mm diameter of the marker pens that I had to hand. I will, most likely, use this on a larger machine.

Parts:
2x M4 wingnuts
2x M4 A type (standard) washers (optional)
2x M4x40mm bolts

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Downloads:
Pen holder STEP, Fusion 360 and STL files (Zip)
Marker holder STEP, Fusion 360 and STL files (Zip)
Licence attribution - small business exception

My designs in the Fusion 360 Gallery.
My models in the GrabCAD library.
My designs on YouMagine.com

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Shapecut Series:
Part 1 - Magic Eye to CNC
Part 2 - CNC proof of concept design
Part 3 - CNC controller enclosure

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