Bobbin Storage Trays

Long ago, I gave Mary a box of 100 empty bobbins for her Kenmore 158 sewing machine, with the intent she would never again have to unwind a bobbin to put new thread on it. This worked so well I did the same thing for her Juki, with the result she needed somewhere to store all those filled bobbins.

Her work table has a shallow drawer, so we tried this out:

Bobbin Storage Case - installed
Bobbin Storage Case – installed

They’re a matched set cut from 1.5 mm TroCraft Eco:

Bobbin Storage Case - cutting overview
Bobbin Storage Case – cutting overview

Watching all those little rectangles fall out just never gets old:

Bobbin Storage Case - cutting detail
Bobbin Storage Case – cutting detail

I ran off a test tray in ordinary chipboard that works just as well, but lacks the pleasant appearance and feel of the TroCraft. Clear 1.5 mm acrylic would probably work, at the cost of requring a much neater glue job where the dividers meet the walls.

The spacing is a bit tight to pluck a bobbin from its slot between two others, but now she has enough space to arrange them as needed, with empty spaces around the most-used colors. I offered to carpet the drawer with bobbin trays, but she suggested waiting until these fill up.

The well-stuffed URL specifying the tray:*7&sy=12*7&h=20.0&hi=10.0&outside=0&bottom_edge=s&top_edge=S&back_height=0.0&radius=0.0&gripheight=30&gripwidth=00&handle=0&thickness=1.65&format=lbrn2&tabs=0&debug=0&labels=0&reference=00&inner_corners=corner&burn=0.04

Which can now be specified as the biggest QR code I’ve ever seen:

Bobbin Tray - TroCraft Eco QR code
Bobbin Tray – TroCraft Eco QR code

That makes my eyes hurt …

Laser-Cut Envelope Opener

As practice in using the laser to engrave a figure to a known depth, this seemed appropriate:

Envelope Opener - original
Envelope Opener – original

The black envelope opener on the right came in a long-ago surplus deal and worked really well, which I cannot say for the retail replacements I got a few years back.

The tan envelope opener on the left is an obvious case of IP theft, copying the size and shape using a scanned image:

Classic opener - knife blades - scan
Classic opener – knife blades – scan

The two blades seemed like good candidates, with the lower one winning the contest:

Kobalt 78010 Mini Utility Knife Blade mask
Kobalt 78010 Mini Utility Knife Blade mask

Although the pack of “mini utility knife blades” sports a Lowe’s Kobalt part number, they no longer carry that item. You can find plenty of identical blades elsewhere, so they’re not a rare collectible and I have plenty of backup.

Put the outline of the opener on a cut layer, put the blade on an engraving layer, orient appropriately, and make a mirror-image duplicate:

Envelope Opener - LB Layout
Envelope Opener – LB Layout

The original opener is a touch over 3 mm thick, so the settings engrave 0.25 mm into the surface to make a blade pocket, then cut the shapes from 1.5 mm TroCraft Eco:

Envelope Opener - cutting
Envelope Opener – cutting

After all the cutting was done, it looks about as you’d expect:

Envelope Opener - interior layout
Envelope Opener – interior layout

Slather with yellow PVA wood glue and apply too many clamps:

Envelope Opener - clamping
Envelope Opener – clamping

Next time around, I’ll round off the edges before assembly, but that’s in the nature of fine tuning:

Envelope Opener - detail
Envelope Opener – detail

The TroCraft sheet engraves so cleanly that, were I to go into mass production, I’d set up a fixture for grayscale engraving shaping the perimeters.

Obviously, this makes no economic sense, but it does produce a considerable amount of satisfaction, which is pretty much all that matters for such things.

World War II Dog Tag Layout

Quite some time ago, I hammered out G-Code to engrave ersatz dog tags for a Cabin Fever demo:

Cabin Fever Dog Tag
Cabin Fever Dog Tag

A dozen years later, making a World War II dog tag is a whole lot easier:

John Q Public - WWII dog tag
John Q Public – WWII dog tag

Well, “easier” if you allow laser engraving in white-on-black Trolase using a font intended to mimic a typewriter.

Close enough, methinks.

Which comes from a simple layout:

John Q Public - WWII dog tag - LB layout
John Q Public – WWII dog tag – LB layout

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
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:

WWII dog tag outline test
WWII dog tag outline test

It might come in handy for something, someday.

The LightBurn SVG layout as GitHub Gist:

Laser-Engraved Bentley Snowflakes

Algorithmic snowflakes make for interesting coasters and decorations:

Snowflake Hangers - frosted
Snowflake Hangers – frosted

But they lack the complexity of real snowflakes:

Wilson Bentley Photomicrograph of Dendrite Star Snowflake No. 842 - SIA-SIA2013-09114 - rescaled
Wilson Bentley Photomicrograph of Dendrite Star Snowflake No. 842 – SIA-SIA2013-09114 – rescaled

That’s from the Smithsonian collection of the Wilson Bentley snowflake photos from back in the 1890s, all of which are CC0 = Public Domain images.

So pick a nice image, say #842, clean it up a bit, and isolate the flake from the background:

Snowflake No. 842 - SIA-SIA2013-09114 - isolated
Snowflake No. 842 – SIA-SIA2013-09114 – isolated

Pick a threshold level to prettify the result:

Snowflake No. 842 - SIA-SIA2013-09114 - Threshold
Snowflake No. 842 – SIA-SIA2013-09114 – Threshold

Then engrave it into the back of an acrylic mirror scrap, so the darkest parts become most transparent:

Bentley 842 - engraved mirror - white background
Bentley 842 – engraved mirror – white background

Which looks better when seen against an illuminated background:

Bentley 842 - engraved mirror - color background A
Bentley 842 – engraved mirror – color background A

Well, I think it does:

Bentley 842 - engraved mirror - color background B
Bentley 842 – engraved mirror – color background B

Maybe four different snowflakes atop those squares?

Gotta get this ready for the next snow season …

Tailor’s Clapper: 3D Printed Finger Grips

With the pockets milled into the oak blocks, the next step is to insert a pair of comfy 3D printed finger grips:

Ironing weight - prototype grip
Ironing weight – prototype grip

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
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
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
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!

The OpenSCAD source code as a GitHub Gist:

// Oak ironing weight finger grips
// Ed Nisley KE4ZNU 2023-01
Layout = "Show"; // [Block,Grip,Show,Build]
//- Extrusion parameters must match reality!
/* [Hidden] */
ThreadThick = 0.25;
ThreadWidth = 0.40;
HoleWindage = 0.2;
Protrusion = 0.1; // make holes end cleanly
inch = 25.4;
function IntegerMultiple(Size,Unit) = Unit * ceil(Size / Unit);
ID = 0;
OD = 1;
// Dimensions
// Length along X axis
Block = [250.0,50.0,39.0]; // overall wood block
BlockRadius = 10.0;
CornerRadius = 10.0;
Kerf = 0.2;
Socket = [160.0,25.0,6.5]; // raw recess into block
SocketRadius = Socket.y/2;
WallThick = ThreadWidth; // Thinnest printed wall
Clearance = 0.5; // between grip and recess
GripBlock = Socket - [2*Clearance,2*Clearance,Clearance];
GripBlockRadius = SocketRadius - Clearance;
GripDepth = 5.0; // finger grip recess
GripRecess = [GripBlock.x - 2*WallThick,GripBlock.y - 2*WallThick,GripDepth];
GripRecessRadius = GripBlockRadius - WallThick;
GripChordRadius = (pow(GripDepth,2) + pow(GripRecess.y,2)/4) / (2*GripDepth);
NumSides = 4*8;
// Shapes
module WoodBlock() {
difference() {
for (i=[-1,1], j=[-1,1]) // rounded block
translate([i*(Block.x/2 - BlockRadius),j*(Block.y/2 - BlockRadius),-Block.z/2])
for (j=[-1,1]) // grip socket
translate([0,j*(Block.y/2 + Protrusion),0])
hull() {
for (i=[-1,1])
translate([i*(Socket.x/2 - SocketRadius),(Socket.y/2 - SocketRadius),0])
cylinder(r=SocketRadius,h=Socket.z + Protrusion,$fn=NumSides);
module Grip() {
difference() {
for (i=[-1,1]) // overall grip block
translate([i*(GripBlock.x/2 - GripBlockRadius),0,0])
hull() {
for (i=[-1,1]) // grip recess
translate([i*(GripBlock.x/2 - GripRecessRadius - WallThick),
GripChordRadius + GripBlock.z - GripDepth])
// Build them
if (Layout == "Block")
if (Layout == "Grip")
if (Layout == "Show") {
for (j=[-1,1])
translate([0,j*(Block.y/2 - GripBlock.z),0])
if (Layout == "Build") {
for (i=[-1,1])
translate([i*(Block.y/2 - GripBlock.z),0,0])

Tailor’s Clapper: CNC Pocketing

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
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
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
Tailors Clapper – Pocket Milling Path

Now, most folks would say the Sherline lacks enough speed and stiffness for trochoidal milling:

Ironing weight - 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
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.

The GCMC source code as a GitHub Gist:

// Ironing weight pocketing
// Ed Nisley KE4ZNU - 2023-01
// Library routines
// Useful constants
SafeZ = 10.0mm; // above all obstructions
TravelZ = 2.0mm; // within engraving / milling area
BlockHome = [0.0mm,0.0mm,TravelZ]; // Origin on surface at center of pocket
FALSE = 0;
// Overall values
Socket = [160.0mm,25.0mm,7.0mm]; // raw grip recess into block
RoundEnds = TRUE; // TRUE for smooth rounded endcaps
SocketRadius = RoundEnds ? Socket.y/2 : 10.0mm;
comment("SocketRadius: ",SocketRadius);
CutterDia = 6.32mm - 0.15; // actual cutter diameter - windage
MillStep = 0.25 * CutterDia; // stepover in XY plane
comment("CutterDia: ",CutterDia," MillStep: ",MillStep);
MillClean = MillStep/2;
PlungeSpeed = 150.0mm; // cutter Z plunge into work
MillSpeed = 600.0mm; // XY speed
if (CutterDia > SocketRadius) {
error("Cutter too large for corner radius");
CornerOC = head(Socket,2) - 2*[SocketRadius,SocketRadius];
comment("CornerOC: ",CornerOC);
Corners = RoundEnds ? // rear left CCW around slot
{-CornerOC/2, CornerOC/2} :
{[-CornerOC.x,CornerOC.y]/2, [-CornerOC.x,-CornerOC.y]/2, [CornerOC.x,-CornerOC.y]/2, CornerOC/2};
comment("Corners: ", Corners);
if (RoundEnds) {
SlotPerimeter = {[0.0mm,Socket.y/2,-Socket.z]}; // entry point at center rear
SlotPerimeter += {Corners[0] + [0.0mm,SocketRadius]};
SlotPerimeter += varc_ccw([-SocketRadius,-SocketRadius],SocketRadius) + SlotPerimeter[-1];
SlotPerimeter += varc_ccw([+SocketRadius,-SocketRadius],SocketRadius) + (Corners[0] + [-SocketRadius,0.0mm]);
SlotPerimeter += {Corners[1] + [0.0mm,-SocketRadius]}; // across front
SlotPerimeter += varc_ccw([+SocketRadius,+SocketRadius],SocketRadius) + SlotPerimeter[-1];
SlotPerimeter += varc_ccw([-SocketRadius,+SocketRadius],SocketRadius) + (Corners[1] + [+SocketRadius,0.0mm]);
else {
SlotPerimeter = {[0.0mm,Socket.y/2,-Socket.z]}; // entry point at center rear
SlotPerimeter += {Corners[0] + [0.0mm,SocketRadius]};
SlotPerimeter += varc_ccw([-SocketRadius,-SocketRadius],SocketRadius) + SlotPerimeter[-1];
SlotPerimeter += {Corners[1] + [-SocketRadius,0.0mm]};
SlotPerimeter += varc_ccw([+SocketRadius,-SocketRadius],SocketRadius) + SlotPerimeter[-1];
SlotPerimeter += {Corners[2] + [0.0mm,-SocketRadius]}; // across front
SlotPerimeter += varc_ccw([SocketRadius,SocketRadius],SocketRadius) + SlotPerimeter[-1];
SlotPerimeter += {Corners[3] + [SocketRadius,0.0mm]};
SlotPerimeter += varc_ccw([-SocketRadius,SocketRadius],SocketRadius) + SlotPerimeter[-1];
//--- Begin cutting
if (!RoundEnds) { // clear corners outward of main pocket
foreach(Corners; xy) {
comment("Plunge corner at: ",xy);
comment(" pocket");
cc_hole(xy,(SocketRadius - MillClean),CutterDia/2,MillStep,-Socket.z);
comment(" done!");
comment("Open slot");
TrochRadius = (Socket.y - CutterDia)/2 - MillClean;
TrochPath = {[-(Socket.x/2 - TrochRadius - CutterDia/2 - MillStep),TrochRadius],
[ (Socket.x/2 - TrochRadius - CutterDia/2 - MillStep),TrochRadius]};
comment(" clear landing zone");
xy = [TrochPath[0].x,0.0mm];
cc_hole(xy,Socket.y/2 - MillClean,CutterDia/2,MillStep,-Socket.z);
comment(" trochoid pocket milling");
-Socket.z, TrochRadius, MillStep);
comment("Clean slot perimeter");
tracepath_comp(SlotPerimeter,CutterDia/2,TPC_CLOSED + TPC_LEFT + TPC_ARCIN + TPC_ARCOUT);
# Ironing weight finger grip pocketing
# Ed Nisley KE4ZNU - 2023-01
Flags='-P 4 --pedantic' # quote to avoid leading hyphen gotcha
# Set these to match your file layout
gcmc $Flags \
--include "$LibPath" --prologue "$Prolog" --epilogue "$Epilog" \
"Ironing weight grip pocket.gcmc" > "Grip pocket.ngc"
view raw hosted with ❤ by GitHub

Ironing Weight, a.k.a. Tailor’s Clapper: Overview

Mary wanted some ironing weights, formally known as tailor’s clappers, to produce flatter seams as she pieced fabric together:

Ironing weight - flattened seam
Ironing weight – flattened seam

The weights are blocks of dense, hard, unfinished wood:

Ironing weight - seam ironing A
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
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
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
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.