Getting comfy required a bank shot off the familiar chord equation to find the radius of a much larger circle producing the proper depth between the known width. The recess then comes from subtracting a hotdog from a lozenge exactly filling the wood pocket.
Ironing Weight Finger Grip – recess chord
A pair of grips takes just under two hours to print while requiring no attention, which I vastly prefer to tending the Sherline.
The wood pocket is 7 mm deep and the grips stand 6.5 mm tall, leaving just enough room for three blobs of acrylic adhesive to hold them together. After squishing the grips into their pockets, a pair of right angles aligned everything while the adhesive cured:
Ironing weight – grip adhesive curing
Mary asked for a longer weight for a place mat project, with a slightly narrower block to compensate for the additional length:
Ironing weight – seam ironing B
The grip and pocket were the same size, so it was just a matter of tweaking the block size and cutting more wood.
All in all, a quick project with satisfying results!
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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.
Other than demonstrating that it’s possible to laser-engrave a 3 mm deep pocket in a ¼ inch thick piece of scrap paneling, the process didn’t have much to recommend it:
Holly Coaster – mirror flaws
So I re-did the layout to put the 3 mm mirror in 3 mm thick plywood:
Holly Coaster – overview
The coaster has a self-adhesive cork pad on the bottom, which required an intermediate adhesive layer holding the aluminized Mylar reflector on the bottom of the mirror to brighten the colored areas.
The LightBurn layout shows all the pieces:
Holly Mirror Coaster – LB layout
The plywood cuts with the good side down, although “good” is certainly a judgement call with B/BB grade plywood. I cover the good side with blue painter’s tape to reduce scorch marks. In a real application, you’d do some sanding and finishing, probably before cutting; in this case, I want to see what happens to bare wood in coaster duty.
Engrave and cut the mirror with the backing upward:
I colored the engraved areas with fat-tip permanent markers, despite knowing the alcohol will crack the acrylic. In real life, you’d use spray paint, probably with laser-cut tape masks.
The adhesive layer extends 2 mm beyond the mirror perimeter to stick onto the bottom face of the plywood:
Holly Coaster – adhesive placement
Peeling off the paper reveals the adhesive tape stuck to the back side of the mirror:
Holly Coaster – adhesive exposed
Apply the similarly embiggened aluminized Mylar to the adhesive:
Holly Coaster – mylar placed
Cutting the holly shape directly from the original foot-square adhesive sheet lets me tuck smaller shapes into the remaining uncut areas. In a production environment, however, joining the Mylar and adhesive (perhaps using pre-cut squares), then cutting them as one sheet would definitely simplify the process.
Then peel-n-stick a cork disk (thus explaining why the plywood is exactly 4 inch OD) on the bottom:
Holly Coaster – edge view
I’ve been aligning the cork by feel, which explains the half-millimeter overhang along the right side. Inexplicably, I have yet to justify an alignment fixture.
After the first two snowflake coasters, it finally penetrated my thick skill that putting a 1 mm hole in the flake cut from the center of the plywood would convert it into a decorative window hanging:
Snowflake Hanger – plywood
Admittedly, I may be using the word “decorative” in a manner you had not previously encountered, but work with me on this.
Cutting a similar flake from transparent acrylic looks better:
Snowflake Hanger – blue acrylic
Transparent acrylic turned out to be, well, too transparent, so I set up a LightBurn layout to “engrave” a light frosting on the flake before cutting it out:
Snowflake Hangers – engraving in situ
That worked for all subsequent flakes, but I had to do something about the first few flakes. After realizing that the time to engrave an object depends only on its width, I set up a rectangle with the proper parameters, snugged two forlorn flakes next to each other, and fired the laser:
Snowflake Hangers – retroactive engraving
I thought using cardboard was a Good Idea™ for a stable backing, but lightly vaporizing the top layer produced an unbelievable amount of filth:
Snowflake Hangers – frosted
I had to scrub those poor flakes with dish detergent and a toothbrush to get them even close to their former pristine state; the blue one may never recover.
Anyhow, frosted flakes look good if you don’t look closely:
Snowflake Hangers – frosted
The grid pattern comes from the window screen in direct sunlight; the vertical bars are DIY BirdSavers.
The LightBurn layout produces 120 mm coasters to fit my 20 ounce mugs:
Snowflake Coaster 120 mm – LB Layout
You get two hanging flakes: one plain plywood and one frosted acrylic!
The Smell of Molten Projects in the Morning 
