The New Hotness

It turns out my all-time favorite Pilot Precise V5 Extra Fine stick pen also comes in a clicky-top retractable version:

The cartridge is a nice 6 mm cylinder, eminently transformable into a plotter pen:

Pilot V5RT holder - installed — Pilot V5RT holder – installed

A few minutes with a caliper provides key measurements for a snout surrounding the business end:

Pilot V5RT Pen Holder - snout dimension doodle — Pilot V5RT Pen Holder – snout dimension doodle

The green letters & numbers give the nearest drill sizes. The “T” values along the bottom are the tailstock turns (at 1.5 mm/turn) required to poke the drills to the indicated depths, eyeballed when the body just enters the hole.

Having recently decomissioned the Thing-O-Matic and harvested its ~~organs~~ parts, I have a vast collection of 3/8 inch = 9.52 mm shafts and matching bronze bushings:

Bronze bushings have low stiction, at least when they’re co-axial, and are much shorter than linear ball bearings.

I chopped off a 70 mm length of shaft and faced the raw end:

Pilot V5RT holder - facing shaft — Pilot V5RT holder – facing shaft

The other end had a maker’s logo, but I don’t recognize it:

Pilot V5RT holder - center drill — Pilot V5RT holder – center drill

I really wanted an 8 mm bore around the snout, but it just didn’t work out. The ring around the 7.5 mm counterbore shows where the larger drill just … stopped:

Pilot V5RT holder - drilled shaft — Pilot V5RT holder – drilled shaft

A trial fit with the pen cartridge:

Pilot V5RT holder - pen in shaft — Pilot V5RT holder – pen in shaft

The top of the shaft gets a somewhat longer knurled ring for the 3 mm SHCS holding the cartridge in place:

Pilot V5RT holder - knurling pen clamp — Pilot V5RT holder – knurling pen clamp

The screw bears on a split collar turned and drilled from a Delrin rod:

Pilot V5RT holder - drilling Delrin clamp — Pilot V5RT holder – drilling Delrin clamp

The “split” came from a simple saw cut across one side and I milled a flat spot in the knurling to seat the screw. As usual, the knurled ring got epoxied to the shaft.

The snout started as a 3/8 inch aluminum rod, drilled as shown in the sketch, with a (scant) 7.5 mm section to fit the shaft. The carbide insert left a nicely rounded shoulder that required trimming to fit snugly into the shaft:

Pilot V5RT holder - shaping snout seat — Pilot V5RT holder – shaping snout seat

The compound can handle the shallow angle required to shape the snout:

Pilot V5RT holder - tapering snout — Pilot V5RT holder – tapering snout

A trial fit showed the snout was a bit too long for comfort:

Pilot V5RT holder - snout test fit — Pilot V5RT holder – snout test fit

Making something shorter doesn’t pose much of a challenge:

Pilot V5RT holder - trimming snout — Pilot V5RT holder – trimming snout

Another trial fit shows it’s spot on:

Pilot V5RT holder - shaft snout pen test fit — Pilot V5RT holder – shaft snout pen test fit

The critical part is having the snout support the plastic around the pen tip to prevent wobbulation.

Epoxy the whole thing together, add a suitable spring, tighten the screws & nuts for the reaction plate, and it’s all good. I write with about 50 g of force for these pens, so a light preload seemed in order:

Pilot V5RT Pen Holder - initial downforce measurement — Pilot V5RT Pen Holder – initial downforce measurement

If I’d weighed the full-up shaft + snout + collar + cartridge, I’d know if the Y intercept matches that weight. It seems a little lighter, but I’m not taking the thing apart to find out.

The first version of the 3D printed holder (shown above) is a straightforward modification of the LM12UU diamond drag bit holder, but, after building enough of these things, I realized the circular reaction plate should be triangular to get more clearance in front of the Z-axis stepper motor when installing & removing the holder:

Pilot V5RT Pen Holder - solid model - show view — Pilot V5RT Pen Holder – solid model – show view

It also has a recess for the serrated top of the bearing, to prevent the knurled collar from clicking annoyingly as the Z-axis rises at the end of each stroke.

Now, to see how well it draws!

The OpenSCAD source code as a GitHub Gist:

	// Diamond Scribe in linear bearings for CNC3018
	// Ed Nisley KE4ZNU – 2019-08-9

	Layout = "Build"; // [Build, Show, Base, Mount, Plate]

	/* [Hidden] */

	ThreadThick = 0.25; // [0.20, 0.25]
	ThreadWidth = 0.40; // [0.40, 0.40]

	/* [Hidden] */

	Protrusion = 0.1; // [0.01, 0.1]

	HoleWindage = 0.2;

	inch = 25.4;

	function IntegerMultiple(Size,Unit) = Unit * ceil(Size / Unit);

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

	//- Adjust hole diameter to make the size come out right

	module PolyCyl(Dia,Height,ForceSides=0) { // based on nophead's polyholes
	Sides = (ForceSides != 0) ? ForceSides : (ceil(Dia) + 2);
	FixDia = Dia / cos(180/Sides);
	cylinder(r=(FixDia + HoleWindage)/2,h=Height,$fn=Sides);
	}

	//- Dimensions

	PenOD = 6.1; // pen refill shaft, max OD

	Bearing = [(3.0/8.0)*inch,16.0,10.6]; // linear bearing body, ID = shaft diameter

	BearingFlange = [Bearing[OD],17.2,1.0]; // flange around end of bearing

	Spring = [8.5,9.5,15.5]; // compression spring around shaft, LENGTH = uncompressed
	SpringRecess = 4*ThreadThick;

	WallThick = 4.0; // minimum thickness / width

	Screw = [3.0,6.75,25.0]; // holding it all together, OD = washer

	Insert = [3.0,4.2,7.9]; // brass insert
	//Insert = [3.0,5.0,8.0];
	//Insert = [4.0,6.0,10.0];

	Clamp = [43.2,44.0,34.0]; // tool clamp ring, OD = clearance around top

	LipHeight = IntegerMultiple(2.0,ThreadThick); // above clamp for retaining

	BottomExtension = 15.0; // below clamp to reach workpiece

	MountOAL = LipHeight + Clamp[LENGTH] + BottomExtension; // total mount length
	echo(str("Mount OAL: ",MountOAL));

	Plate = [PenOD + 4ThreadWidth,Clamp[ID] – 02*WallThick,WallThick]; // spring reaction plate

	echo(str("Screw length: ",Spring[LENGTH] + Plate[LENGTH] + Insert[LENGTH]));

	NumScrews = 3;
	ScrewBCD = Bearing[OD] + Insert[OD] + 2*WallThick;

	echo(str("Retainer max OD: ",ScrewBCD – Screw[OD]));

	NumSides = 9*4; // cylinder facets (multiple of 3 for lathe trimming)

	// Basic mount shape

	module CNC3018Base() {

	translate([0,0,MountOAL – LipHeight])
	cylinder(d=Clamp[OD],h=LipHeight,$fn=NumSides);
	translate([0,0,MountOAL – LipHeight – Clamp[LENGTH] – Protrusion])
	cylinder(d=Clamp[ID],h=(Clamp[LENGTH] + 2*Protrusion),$fn=NumSides);
	cylinder(d1=Bearing[OD] + 2*WallThick,d2=Clamp[ID],h=BottomExtension + Protrusion,$fn=NumSides);

	}

	// Mount with holes & c

	module Mount() {

	difference() {
	CNC3018Base();

	translate([0,0,-Protrusion]) // bearing
	PolyCyl(Bearing[OD],2*MountOAL,NumSides);

	translate([0,0,-Protrusion]) // bearing flanges
	PolyCyl(BearingFlange[OD],BearingFlange[LENGTH] + Protrusion,NumSides);

	translate([0,0,MountOAL – 1.5*BearingFlange[LENGTH]]) // sink into surface
	PolyCyl(BearingFlange[OD],2*BearingFlange[LENGTH],NumSides);

	for (i=[0:NumScrews – 1]) // clamp screws
	rotate(i*360/NumScrews)
	translate([ScrewBCD/2,0,MountOAL – Clamp[LENGTH]])
	rotate(180/8)
	PolyCyl(Insert[OD],Clamp[LENGTH] + Protrusion,8);
	}

	}

	module SpringPlate() {

	difference() {
	hull()
	for (i=[0:NumScrews – 1])
	rotate(i*360/NumScrews)
	translate([ScrewBCD/2,0,0])
	cylinder(d=Screw[OD] + 4*ThreadWidth,h=Plate[LENGTH],$fn=24);

	translate([0,0,-Protrusion])
	PolyCyl(Plate[ID],2*MountOAL,NumSides);

	translate([0,0,Plate[LENGTH] – SpringRecess]) // spring retainer
	PolyCyl(Spring[OD] + 4*ThreadWidth,SpringRecess + Protrusion,NumSides);

	for (i=[0:NumScrews – 1]) // clamp screws
	rotate(i*360/NumScrews)
	translate([ScrewBCD/2,0,-Protrusion])
	rotate(180/8)
	PolyCyl(Screw[ID],2*MountOAL,8);
	}

	}


	//—–
	// Build it

	if (Layout == "Base")
	CNC3018Base();

	if (Layout == "Mount")
	Mount();

	if (Layout == "Plate")
	SpringPlate();

	if (Layout == "Show") {
	Mount();
	translate([0,0,MountOAL + Plate[LENGTH] + Spring[LENGTH]])
	rotate([180,0,0])
	SpringPlate();
	}

	if (Layout == "Build") {

	translate([0,-0.75*Clamp[OD],MountOAL])
	rotate([180,0,0])
	Mount();
	translate([0,0.75*Plate[OD],0])
	SpringPlate();
	}

view raw Pilot V5RT Pen Holder.scad hosted with ❤ by GitHub

The New Hotness

CNC 3018XL: Pilot V5RT Pen Holder