Machine Shop, Science

MPCNC: Modified Drag Knife Adapter Spring Constant

The bars on the original MPCNC drag knife / plotter pen adapter had a 100 g/mm spring constant:

MPCNC - Plotter pen force test
MPCNC – Plotter pen force test

Making the bars slightly thicker improved their print-ability:

MPCNC knife adapter mods - OpenSCAD model
MPCNC knife adapter mods – OpenSCAD model

The reddish tint marks the new bars, with their location carefully tweaked to be coincident with the stock STL.

Shoving the pen into the scale with 0.1 mm steps produces another unnervingly linear plot:

Modified MPCNC pen adapter - Spring Constant data
Modified MPCNC pen adapter – Spring Constant data

Real plotter pens want about 20 g of force, so this isn’t the holder you’re looking for.

A bunch of plots at Z=-1.0 mm turned out well with the ballpoint pen insert, though:

MPCNC Modifed pen adapter - first plots
MPCNC Modifed pen adapter – first plots

The globs apparently come from plotting too fast for conditions; reducing the speed to 1500 mm/min works better.

4 thoughts on “MPCNC: Modified Drag Knife Adapter Spring Constant”

  1. Tell me more about this scale with all the nice physical buttons. Does it annoyingly turn itself off or does it stay on? :-)

    1. Got it from Harbor Freight long ago, had to figure out the counting function on my own, and it’s worked ever since.

      It shuts down after a minute, which is surprisingly long.

      I’d probably get something similar from Amazon, if only because Harbor Freight is the Home of Single-Use Tools. In your part of the world, you’re on your own! [grin]

  2. Pingback: MPCNC: Jogging Keypad for bCNC | The Smell of Molten Projects in the Morning
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