The outline traces a scanned image of my father’s tag, fitting a few hand-laid splines around the curves:
John Q Public – WWII dog tag – spline curves
I generated a random serial number based on my father’s draftee status (he was in his early 30s during his South Sea Island tour) and state of residence; my apologies to anyone carrying it for real. His blood type was A and (I think) the religion code marks him as “Brethren”, a common group in my ancestry.
Given the outline, various plastics, and a laser, other effects become possible:
Separating the interior contour of the finger grip from its overall shape let me reduce the woodworking to a simple pocketing operation:
Ironing Weight Finger Grip
Start by aligning the finished block to put the joint between the pieces parallel to the X axis, then touch off at the center:
Ironing Weight – alignment
A pair of clamps screwed to the tooling plate act as fixtures to align the block when it’s flipped over to mill the other pocket.
Just to see how it worked, I set up a GCMC program to produce a trochoidal milling pattern using the sample program:
Tailors Clapper – Pocket Milling Path
Now, most folks would say the Sherline lacks enough speed and stiffness for trochoidal milling:
Ironing weight – trochoidal milling
Aaaand I would agree with them: chugging along at 24 in/min = 600 mm/min doesn’t put the 10 k RPM spindle speed to good use. Fortunately, oak doesn’t require much in the way of machine stiffness and the trochoid path does ensure good chip clearance, so there’s that.
If I had to do a lot of trochoid milling, I’d tweak the GCMC sample code to short-cut the return path across the circle diameter, rather than air-cut the last half of every circumference.
The code starts by emptying a circular pocket so the trochoid path begins in clear air, rather than trenching into solid wood.
Eventually it finishes the pocket:
Ironing weight – grip pocket
After the trochoid finishes, one climb-milling pass around the perimeter clears the little ripple between each trochoid orbit.
Flip it over, clamp it down, touch off the middle, and do it all again.
The next step is filling those pockets with a pair of comfy grips.
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Mary wanted some ironing weights, formally known as tailor’s clappers, to produce flatter seams as she pieced fabric together:
Ironing weight – flattened seam
The weights are blocks of dense, hard, unfinished wood:
Ironing weight – seam ironing A
One can buy commercial versions ranging from cheap Amazon blocks to exotic handmade creations, but a comfortable grip on a block sized to Mary’s hands were important. My lack of woodworking equipment constrained the project, but the picture shows what we settled on.
The general idea is a rounded wood block with 3D printed grips:
Ironing Weight Finger Grip
All other clappers seem to have a simple slot routed along the long sides, presumably using a round-end or ball cutter, which means the cutter determines the shape. This being the age of rapid prototyping, I decided to put the complex geometry in an easy-to-make printed part inserted into a simple CNC-milled pocket.
The first pass at the grip models:
Ironing Weight Finger Grip – slicer preview
Both recesses came from spheres sunk to their equators with their XY radii scaled appropriately, then hulled into the final shape. Customer feedback quickly reported uncomfortably abrupt edges along the top and bottom:
Ironing Weight – maple prototype
We also decided the straight-end design didn’t really matter, so all subsequent grips have rounded ends to simplify milling the pocket into the block.
With the goal in mind, the next few posts will describe the various pieces required to make a nice tailor’s clapper customized to fit the user’s hand.
Anything would be better than just taping some gel filters to the front of the bare photodiode package:
Laser output – photodiode kludge
Right?
I heaved the slab of ½ inch black acrylic left over from the Totally Featureless (WWVB) Clock into the laser cutter and, two passes at 90% power later, had a somewhat lumpy 32 mm donut with an 11 mm hole in the middle. Because acrylic is opaque to the IR light from a CO₂ laser (which is why it cuts so well) and black acrylic is opaque to visible light (which is what the photodiode is designed for), this is at least as good as an aluminum housing and much easier to make.
Chuck the donut into Tiny Lathe and bore out the hole:
PIN-10D photodiode filter holder – boring ID
When it’s a snug fit to ½ inch brass tube (about the same size as the photodiode’s active area), flip it around, and bore the other size out to fit the photodiode case.
Ram the tube in place, grab the large recess, and center the tube:
[Edit: Got that backwards: I bored the big recess first.]
Skim most of the OD down, then, because I am a dolt forgot to put a spacer in there, flip it around again, get it running true (the chuck aligns the flat side):
Even though they’re pretty much transparent to thermal IR, a focused IR laser beam cuts them just fine. The little tab at 6 o’clock (remember round clocks with hands?) keeps the cut circle from falling out.
Drill & tap for an M3 setscrew to hold the photodiode in place:
PIN-10D photodiode filter holder – parts
Put them all together:
PIN-10D photodiode filter holder – assembled
I must conjure a better mount for the thing, because this is way too precarious:
PIN-10D photodiode filter holder – test install
Early results suggest it works better than the previous hack job, without ambient light sneaking around the edges of the filter pack.
The red-dot pointer on the OMTech laser cutter has the same problem as my laser aligner for the Sherline mill: too much brightness creating too large a visual spot. In addition, there’s no way to make fine positioning adjustments, because the whole mechanical assembly is just a pivot.
The first pass involved sticking a polarizing filter on the existing mount while I considered the problem:
OMTech red dot pointer – polarizing filter installed
The red dot pointer module is 8 mm OD and the ring is 10 mm ID, but you will be unsurprised to know the laser arrived with the module jammed in the mount with a simple screw. Shortly thereafter, I turned the white Delrin bushing on the lathe to stabilize the pointer and installed a proper setscrew, but it’s obviously impossible to make delicate adjustments with that setup.
Making the polarizing filter involves cutting three circles:
OMTech red dot pointer – polarizing filter
Rotating the laser module in the bushing verified that I could reduce the red dot to a mere shadow of its former self, but it was no easier to align.
Replacing the Delrin bushing with a 3D printed adjuster gets closer to the goal:
Pointer fine adjuster – solid model
Shoving a polarizing filter disk to the bottom of the recess, rotating the laser module for least brightness, then jamming the module in place produces a low-brightness laser spot.
The 8 mm recess for the laser module is tilted 2.5° with respect to the Y axis, so (in principle) rotating the adjuster + module (using the wide grip ring) will move the red dot in a circle:
Improved red-dot pointer – overview
The dot sits about 100 mm away at the main laser focal point, so the circle will be about 10 mm in diameter. In practice, the whole affair is so sloppy you get what you get, but at least it’s more easily adjusted.
The M4 bolt clamping the holder to the main laser tube now goes through a Delrin bushing. I drilled out the original 4 mm screw hole to 6 mm to provide room for the bushing:
Improved red-dot pointer – drilling bolt hole
The bushing has a wide flange to soak up the excess space in the clamp ring:
Improved red-dot pointer – turning clamp bushing
With all that in place, the dimmer dot is visually about 0.3 mm in diameter:
Improved red-dot pointer – offset
The crappy image quality comes from excessive digital zoom. The visible dot on the MDF surface is slightly larger than the blown-out white area in the image.
The CO₂ laser hole is offset from the red laser spot by about 0.3 mm in both X and Y. Eyeballometrically, the hole falls within the (dimmed) spot diameter, so this is as good as it gets. I have no idea how durable the alignment will be, but it feels sturdier than it started.
Because the red dot beam is 25° off vertical, every millimeter of vertical misalignment (due to non-flat surfaces, warping, whatever) shifts the red dot position half a millimeter in the XY plane. You can get a beam combiner to collimate the red dot with the main beam axis, but putting more optical elements in the beam path seems like a Bad Idea™ in general.
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Lacking a 4-jaw chuck for the lathe, this should suffice:
Coaster Epoxy Rim – chuck-in-chuck setup
Which is just the Sherline 4-jaw chuck chucked in the lathe’s 3-jaw chuck, with both chuck Jaw 1 positions lined up and marked on the acrylic disk fixture. The picture is a recreation set up after the fact, because I lack a good picture of the overall scene.
Now it’s easy enough to center the fixture, stick the coaster in place with reasonable accuracy, then tweak the Sherline chuck to center the coaster:
Coaster Epoxy Rim – turning setup
Because the bottom layer is a laser-cut disk, eyeballometrically aligning its edge to a simple pointer worked surprisingly well:
Coaster Epoxy Rim – locating mirror edge
Turning the OD down to match the bottom disk meant I could finally get decent results with zero drama:
Coaster Epoxy Rim – turned samples
From the bottom, this one has a 3 mm mirror, the 3 mm fluorescent green frame + petals, and a 1.6 mm top sheet:
If I never tell anybody, they’ll think the slightly granular look if the tape was deliberate; it looks OK to me.
And, for completeness, the crash test dummy from the start of this adventure:
Coaster Epoxy Rim – turned 6 petal black
I don’t know how to avoid the bubbles, as the usual torch-the-top and pull-a-vacuum techniques pop bubbles at the epoxy-air interface. These bubbles are trapped under the top acrylic sheet, even though I was rather painstaking about easing the layer down from one side to the other while chasing bubbles along.
Maybe I can define bubbles as Part of the Art?
Definitely fancier than chipboard, although not nearly as absorbent.
Because the Sherline mill can’t cut all the way around a 4 inch OD coaster clamped to its table, I set up the 4-jaw chuck on the rotary table and centered the nicely round fixture:
Coaster Epoxy Rim – centering fixture plate
Admittedly, the centering need not be so precise, but practice makes perfect.
A few sissy cuts demonstrated the tape lacked sufficient stickiness to hold the coaster in place against the milling cutter’s uplift. I managed to mill most of the perimeter with those clamps in place, moving each one from just ahead of the cutter to just behind the cutter.
That way lies both madness and organic damage.
There are better tapes and better adhesives, all trading off a really sticky fixture against difficulty extracting an undamaged part.
A more complex circular fixture with built-in mechanical edge clamps extending around a major part of the perimeter seems like entirely too much of a diversion for a couple of obscene-gerund coasters.
The Smell of Molten Projects in the Morning 