The New Hotness

A trio of Cutter Cutting Plotter Blade Holders arrived:

Despite the name, they’re not well-suited for drag knife blades, because they’re collets gripping a 2 mm shaft. The blade doesn’t rotate unless the plotter / cutter rotates the entire holder, which is actually a thing.

I got ’em because the snout of a common ball-point pen refill measures about 2 mm:

Collet pen holder - detail — Collet pen holder – detail

The glob around the tip comes from plotting too fast for conditions; about 1500 mm/min works better for continuous lines and 250 mm/min improves text.

The stock MPCNC adapter has a single recess suited for Genuine Plotter Pens, but the knurled lock ring on these cheapies sticks out far enough to make them wobbly. This being an inconvenience up with which I need not put, a few lines of OpenSCAD tweak the stock STL:

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

The original STL is ivory, new cuts are cyan, and additions are reddish.

The two support beams are now 1.6 mm = four thread widths, for improved slicing with a 0.35 mm nozzle and a higher spring constant.

It’s by-and-large indistinguishable from the old adapter:

MPCNC - Pen Holder Detail — MPCNC – Pen Holder Detail

Which I was using upside-down, because the flange fit better.

The MPCNC works reasonably well as a pen plotter with a genuine ballpoint pen:

The OpenSCAD source code as a GitHub Gist:

	// Adding clearance for eBay collet pen holder

	MPCNC_OD = 12.0; // pen holder OD (matches STL curvature)
	MPCNC_Z = 8.9; // Z offset of pen axis

	Pen_OD = 11.5; // actual pen body OD

	ID = 0;
	OD = 1;
	LENGTH = 2;

	Flange = [11.5,15.7,2.2]; // actual pen body flange

	Locknut = [16.0,16.0,2.8]; // knurled locknut
	Locknut_Offset = 4.5; // flange center to locknut

	Wall = [41.0,4 * 0.4,9.0]; // thicker walls for more spring and better fill

	$fn = 32; // default cylinder sides

	difference() {
	translate([-(101.3 + MPCNC_OD/2),-111.9,0]) // put pen axis above Y axis, flange centered on X axis
	import("/mnt/bulkdata/Project Files/Mostly Printed CNC/Accessories/Tool Holders/MPCNC_525_Drag_Knife-1860310.STL",
	convexity=5);

	if (true) // improve holder-to-mount fit if needed
	translate([0,60/2,8.90])
	rotate([90,0,0])
	cylinder(d=MPCNC_OD,h=60);

	translate([0,0,MPCNC_Z]) // improve flange slot clearance
	rotate([90,0,0])
	cylinder(d=Flange[OD] + 1.0,h=Flange[LENGTH] + 0.5,center=true);

	translate([0,Locknut_Offset – 0.5,MPCNC_Z]) // add locknut clearance
	rotate([-90,0,0])
	cylinder(d=Locknut[OD] + 1.5,h=Locknut[LENGTH] + 1.5,center=false);
	}

	# translate([-(27.0 + Wall.x/2),0,0]) { // embiggen walls for higher spring constant
	translate([0,-24.4,0])
	cube(Wall);
	translate([0,20.6 – Wall.y,0])
	cube(Wall);
	}

view raw MPCNC Drag Knife Adapter – Collet Pen Mod.scad hosted with ❤ by GitHub

The New Hotness

MPCNC: Modified Drag Knife Adapter