Ed Nisley's Blog: Shop notes, electronics, firmware, machinery, 3D printing, laser cuttery, and curiosities. Contents: 100% human thinking, 0% AI slop.
The Google Pixel 3a camera, unlike the camera in my older Google Pixel XL, takes spectacularly good images through a widefield 5X eyepiece on the stereo zoom microscope:
0.5 1.0 mm ball pens – 0.7 mm lead pencil
That’s hand-holding the phone against the eyepiece while manipulating it with the other hand. Definitely not the most stable arrangement, but the camera copes well with slight motions. I really need a gripping hand for the camera, to free up another for the microscope’s focus knob.
The cartridge is a nice 6 mm cylinder, eminently transformable into a plotter pen:
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
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
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
The other end had a maker’s logo, but I don’t recognize it:
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
A trial fit with the pen cartridge:
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
The screw bears on a split collar turned and drilled from a Delrin rod:
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:
A trial fit showed the snout was a bit too long for comfort:
Pilot V5RT holder – snout test fit
Making something shorter doesn’t pose much of a challenge:
Pilot V5RT holder – trimming snout
Another trial fit shows it’s spot on:
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
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
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.
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The tiny engravings don’t photograph well, because they’re floating atop the transparent disc and the rainbow patterns from the data layer, but they still come out OK even when scaled to fit on a hard drive platter:
So I bought some LM12UU linear bearings from a nominally US-based eBay seller and received a suitably marked bag:
eBay – LM8UU bearings in LM12UU bag
They looked a bit on the skinny side:
eBay – LM8UU bearing
It seems somebody in the supply chain wasn’t paying attention, which isn’t surprising given the its ability to deliver ten hunks of reasonably precise machining to my mailbox for a buck-and-a-half apiece.
As it happens, I already have far too many LM8UU bearings and, after some unavailing back-and-forth with the seller, eBay customer service determined neither of us was “at fault” and refunded the whole order.
Being in no particular hurry, I ordered the next lot from halfway around the planet. Apparently, I’m now known throughout the land:
eBay – drop-ship addressing
Another label atop that one sported my actual address, with a matching Orange Connex tracking number barcode. Turns out OC is a “a joint venture between a leader in Chinese private equity investment, CITI CPE, and the a [sic] pioneer of global e-commerce platform, ebay”.
AFAICT, containers of “direct from China” packages arrive in the belly of a cargo airplane, get a sticker with their final destination, and enter the US postal system. It’s not clear buying from a “US seller” changes anything, as many of those packages come from addresses matching a building next to an airport.
This came about while tinkering up a shade for a repurposed LED downlight:
PVC fitting – boring setup
It’s a 4 inch DWV pipe coupling I bored out to fit the LED housing, which was ever so slightly larger than the pipe OD.
Cutting it off required as much workspace as the poor little lathe had:
PVC fitting – cutoff setup
Ignore the toolpost handle across the top. What’s important: the cutoff blade poking out of the QCTP, above the orange carriage stop lock lever, extending just far enough to cut through the coupling’s wall before the compound hits the coupling. The compound slide is all the way out against the cross-slide DRO, rotated at the only angle putting the tool where it needs to be and clearing the end of the coupling.
It ended reasonably well:
PVC fitting – LED floor lamp
But, in retrospect, was hideously bad practice. Next time, I’ll make a fixture to hold the fitting on a faceplate.
Attempting to cut laminated cardstock decks for the Homage Tektronix Circuit Computer required a bit more blade extension than my LM12UU holder made available:
Drag Knife – LM12UU ground shaft – assembled
Shortening the 12 mm shaft wasn’t going to happen, so I knocked a little bit off the blade holder to give the knurled lock ring slightly more travel:
Drag Knife Holder – shortening stop
The lathe cutoff blade is a bit to the right of the new cut, but you get the general idea: not a whole lot of clearance in there.
The Smell of Molten Projects in the Morning 