MPCNC: Tool Length Probe, Reshaped for Plotter Pens

It turns out old-school plotter pen nibs skid right off the rounded top of the switch lever:

MPCNC Tool Length Probe - plotter pen — MPCNC Tool Length Probe – plotter pen

You can’t see the nib inside the cap, but you get the idea.

Flattening the top and adding a snippet of masking tape produces a better outcome:

MPCNC - Reshaped Tool Probe switch — MPCNC – Reshaped Tool Probe switch

I aligned the flat section so it’s parallel to the platform when the switch activates.

Stipulated: plotter pens aren’t a good test for tool length probing, because they have a locating flange to ensure a consistent position in the pen holder and a rigidly controlled flange-to-tip length:

HP 7475A Plotter Pen Body - in holder — HP 7475A Plotter Pen Body – in holder

What’s going on here involves configuring and testing bCNC’s overall tool change process: not using cutting tools preserves both sanity and hardware!

Comments

3 responses to “MPCNC: Tool Length Probe, Reshaped for Plotter Pens”

2017-12-26

MPCNC: Spirograph Generator with Tool Changes | The Smell of Molten Projects in the Morning

[…] have a well-defined position in the holder and a pretty nearly constant length, you must have a tool length probe installed and […]
2017-12-28

MPCNC: Plotter Pen Holder Spring Constant | The Smell of Molten Projects in the Morning

[…] paper surface to compensate for any tabletop warp / bow / misalignment, plus any errors from the tool length probe. An eyeballometric scan against a straightedge shows pretty nearly no misalignment, which means the […]
2018-01-05

MPCNC: Corner Post Shims | The Smell of Molten Projects in the Morning

[…] Lowering the pen to Z=-0.25 should darken the traces a bit and reduce the effect of any inconsistencies in the tool length probe switch. […]