Any way to get the magnetic touchplate to work with a pen?

Mostly Printed CNC - MPCNC Troubleshooting
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I’m trying to get my MPCNC to do pen plotting. The regular V1 Engineering touch plate works fine when I’m dealing with router bits, but with rollerball and gel ink pens like the Sakura Gelly Roller, it’s got an issue. I’m guessing the ball part of the pen is suspended in its own mechanism at the end of the ink, so regardless if the rest of the tip is ferrous or not, it never actually comes into contact with the touchplate. There isn’t much pen tip exposed, just about 1-2mm, and I can’t remove the plastic cap since that’s holding the tip in for refilling.

Low-budget artistic rendering is below:

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image1302×683 46.8 KB

I’m not sure how to approach this here - the best thing I can think of is to remove the Gcode block in Estlcam that mandates probing at job start, getting Z dialed in to just the tip of the touchplate, and setting the job to start at 0.5mm and manually going from there. Unless there’s some kind of conical magnet that will fit on the 1 or 2mm of exposed metal tip on a Gelly Roll.

Has anyone else tried this?

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I have never tried to probe a pen. I would just do it like you would with the crown gcode. You jog it down so it’s close or barely touches and run the gcode.

If you have a pen mount with a spring, you can have more leeway on the starting Z.

3

Gotcha, I was thinking it might be on or close to that. I have a spring loaded holder that I’m jury rigging into place.

I’ve got this as my start gcode in Estlcam - should I comment out the G38, G1, and M0 lines near the bottom to ensure it doesn’t probe and just starts?

G21
G90
G94
G92 X0 Y0
M0 (MSG Attach probe)
G38.2 Z-110 F200 P0.5 (probe down set thickness )
G1 Z10 F900
M0 (MSG Remove probe)
M62 P1 (If used start spindle pin27 )

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This is the starting Z from the crown file:

G21
G90
G94
G92 X0 Y0 Z0
G1 Z10 F900
G00 X0.0000 Y0.0000 Z0.0000 F2400
G00 Z5.0000 F900

You need that G92 including the Z0 so it zeroes Z at the current position.

The G1 Z10 is good to raise the pen up so it doesn’t draw during travel.

Although, those G00s don’t make much sense.

So, I guess this is probably good:

G21
G90
G94
G92 X0 Y0 Z0
G1 Z10 F900

That Z10 could be a Z5. 10mm is probably more clearance than necessary.

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5

Maybe you could 3d print a pen body that is the same length as your pen and insert a wire down the middle of it that probes the touch plate. Then build a jig so your pen and fake pen are always the same height as each other in the tool holder, and first probe with the fake pen and then swap to the real pen. It would be more work, but might allow you to probe reasonably accurately.

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6

Make a touch probe with a endstop spring sensor. Or a small push button?

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7

I can’t find it on Thingiverse or Printables, but years ago I printed an mpcnc pen mount that had a probe point added that you wrap with aluminum duct tape to use as a probe/switch. The mount flexes and acts as a switch, so you don’t need any connection at the point of the pen.

Found it - MPCNC Add-on Pen Holder with Touch Plate by Jason Bentler.

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