CNC 3018XL: Pilot V5RT Pen Holder

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

Pilot V5 and V5RT pens
Pilot V5 and V5RT pens

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:

9.52 mm shaft and bushings
9.52 mm shaft and 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:

,

  1. #1 by david on 2019-12-19 - 01:23

    What, no pics of the output? Inquiring minds want to ogle! Also, how do the retracts compare to the traditional as handwriting instruments?

    • #2 by Ed on 2019-12-19 - 07:50

      Gotta have some suspense in the story!

      Aaaand it took me a while to accumulate the evidence: better paper produces better results. [duh]

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