Category: Machine Shop

Mechanical widgetry

Laser Cutter: Letter Page Fixture

Making 200×200 mm layered paper “pictures” involved cutting the square blanks from 8½×11 Letter sheets, putting those blanks in a fixture to hold them flat, then cutting the layer patterns:

Layered Paper cutting fixture – in use

That worked well enough, but it occurred to me that I should cut the patterns directly into the Letter sheet, with a couple of tabs on each edge holding the square to the sheet so it didn’t fall free.

A cardboard prototype showed this would actually work, at least after I fixed the tab width to keep them from just evaporating:

Pyrotechnics – metallized paper fixture

The top and bottom strips of tape hold cardboard bars that flatten the slightly curled metallic paper. The tape on the sides holds the cardboard flat to the knife bars across the laser platform.

A few adjustments later, I had an MDF version:

Letter paper fixture – cardboard vs MDF

Which fits atop the bars even better:

Letter paper fixture – on knife bars

Cutting colored paper definitely makes for cheerful chaff!

The two bar magnets hold the fixture in place on the steel platform rim. The aluminum knife bars stand slightly proud of the steel, so there’s a 1.4 mm chipboard shim glued under the fixture to put it flat on the bars.

The opening is 10 mm smaller than the Letter sheet to support it all around. The recess is 1 mm larger than the sheet to allow for slight size variations, with an MDF ring flattening the sheet:

Letter paper fixture – sheet in place

The four targets in the corners correspond to targets in the LightBurn template suitable for Print and Cut alignment:

Letter sheet template – LightBurn layout

The alert reader will note the fixture targets on the MDF fixture sit juuuust slightly to the right of where they are in the template. It turns out the targets cannot be grouped with anything else (or even each other), because when you select a target on the template for Print and Cut the center of the selection must match the location of the physical target on the fixture.

However, it’s convenient to have the rest of the template grouped into a single lump, so it’s painfully easy to select and move only the template while leaving the targets behind. It seems while setting up to mark & cut the template, I managed to click-n-drag the group a few millimeters to the left.

I eventually used Print and Cut to align the template and target with the corners of that MDF frame, re-engrave the targets at the correct locations, and scribble over the misplaced targets. If I don’t tell anybody, they’ll never know.

The LightBurn SVG layout as a GitHub Gist:

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view raw Letter sheet fixture – LightBurn.svg hosted with ❤ by GitHub

2025-03-26
Laser-Cut Vole Trap Boxes
We deployed low-effort vole trap boxes a few weeks ago, only to discover no voles checked in, most likely due to wintertime gardens consisting of bare earth. I had weighted the boxes with convenient rocks that pretty much crushed them flat during rainstorms.

So I converted a few dozen square feet of cardboard into better-looking boxes and transferred the traps:

Vole Finger Box – large

That one has a rat trap inside.

Smaller boxes hold mouse traps:

Vole Finger Box – small

Two pairs of 4 mm holes on the bottom flanges fit some spare irrigation pipe holddowns to, yes, hold them down, with those rotten planks keeping their lids in place.

They’re lightly customized “Electronics Boxes” held together by hot-melt glue. The jawbreaker URLs will get you started:
- Large
- Small
Cardboard remains the wrong material, but my stockpile remains well-stocked.
2025-03-24
TEC Drawing Kit: Reconditioned Cover

Our Young Engineer recently rebuilt the cover of a “vintage” drawing kit, with fabric pockets for protractors & scales and real leather hinges, thereby raising a long-procrastinated project to the top of my to-do list:

TEC Drawing Set – top old

I know my father used it when he took drafting after high school in 1929. His penmanship and drawing ability were up to par well before that.

The inside sports a TEC logo:

TEC Drawing Set – open old

Some searching revealed it’s a No. 718 Drafting Set from the Technical Supply Company of Scranton and appeared in their 1913 catalog:

TEC Brand Catalog p68

The printing on the inside of the flap differs, but the logo has TEC in the middle.

My father did not attend college and, in the teeth of The Great Depression, $26.50 was certainly too spendy for his family:

CPI Calculator – 1929 to 2025

When the catalog was printed in 1913, No. 718 cost the equivalent of $862.82. Nowadays, similar sets once again cost about twenty bucks on eBay, which tells you something about economics.

None of that information changes what I know.

Having recently touched a roll of Kraft-Tex while shelving some boxes, this seemed reasonable:

TEC Drawing Set – top new

It lacks pockets for the tools I’ve added:

TEC Drawing Set – scales new

In retrospect, I should have used two leather snaps, but three would be excessive.

I folded the Kraft-Tex flat across a steel scale to make the first folds around the base, then finger-crimped folds at the top of the base with subsequent crisping around the scale:

TEC Drawing Set – open new

The underside of the original case seemed stable:

TEC Drawing Set – case bottom

This may be sacrilege, but I saw no point in peeling the bottom just to cover it up,so I stuck the Kraft-Tex in place with a rectangle of adhesive sheet.

It doesn’t look the same, but it still gives me a warm feeling.

It still has the tiny wrench needed to adjust all its screws:

TEC Drawing Set – wrench

It’s on 0.1 inch graph paper and is 40 mil = 1 mm thick, should you want to make your own. The blades taper down to essentially a knife edge, which is why it’s made from hard blue steel.

I remember being fascinated by that little pig when I was a pup.

Putting some scraps to good use, I stuck a cushion in the anvil for the next time I punch down a leather snap:

Leather Snap kit – cushioned anvil

The LightBurn SVG layout as a GitHub Gist:

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view raw TEC Drafting Set cover – LightBurn layout.svg hosted with ❤ by GitHub

2025-03-21

LED Strip Lights: Window Moulding Mounts

The object of the game being to tilt the LED strip lights at (maybe) 30° to put more light higher on the wall and further out on the ceiling, with the overriding constraint of no visible holes. Given their eventual home atop the window moulding along the front wall of the ~~Living~~ Sewing Room, these seemed adequate:

LED Bar Lamp Mount - solid model — LED Bar Lamp Mount – solid model

The hole on the angled part fits an M4 brass insert and the recessed holes capture the washer-like head of a sharp-point lath screw.

Two pairs applied to the lights sitting atop the Fabric Cabinets served to verify the fit:

LED strip light - moulding mount - on cabinet — LED strip light – moulding mount – on cabinet

They’re held firmly by the aluminum extrusion and don’t need a bigger footprint to remain stable.

So I made another six, stuck on ⅞ inch strips of aluminized Mylar (cut from a bag in much better condition), and drilled holes where they can’t be seen:

LED strip light - moulding mount - installed — LED strip light – moulding mount – installed

It’s almost too bright in there with 3 × 40 W of LED lights washing the wall and ceiling:

LED strip light - moulding mount - lit — LED strip light – moulding mount – lit

I don’t like the cold 6000 K color temperature, but Mary doesn’t mind it. They fill the Sewing Table with shadowless / glareless light, although that kind of light makes the place look like a store.

I think moving the strip lower and away from the wall could hide the entire mount from view.

Contrary to what I expected, the Mylar reflectors must be at least an inch tall to avoid Baily’s Beads seen from across the room:

LED strip light - short reflector — LED strip light – short reflector

With all that in mind, we’ll run these for a while to shake out any other improvements.

The OpenSCAD source code as a GitHub Gist:

	// LED light bar mounts
	// Ed Nisley – KE4ZNU
	// 2025-03-16

	include <BOSL2/std.scad>

	Layout = "Show"; // [Show,Build,ScrewMount,BarMount]

	BaseAngle = 30; // [0:50]

	/* [Hidden] */

	ID = 0;
	OD = 1;
	LENGTH = 2;

	Protusion = 0.1;
	NumSides = 3*4;
	Radius = 1.5;

	$fn = NumSides;

	MouldWidth = 18.0; // nominal (3/4) * INCH, but lots of paint slop
	MouldScrew = [4.7,12.0,2.6]; // clearance, head OD, head thick

	Insert = [4.0,5.5,6.0 + 3.0]; // heat-set brass without pilot end

	BarClip = [33.0,15.0,11.0]; // snaps around led base

	ScrewBlockOA = [MouldWidth,MouldScrew[OD] + 2*Radius + 2.0,10.0];

	BarBlockOA = [BarClip.xcos(BaseAngle),15.0,BarClip.xsin(BaseAngle) + 2*ScrewBlockOA.z];

	Gap = 2.0 + max(ScrewBlockOA.y,BarBlockOA.y);

	//———-
	// Define shapes

	module ScrewMount() {

	difference(){
	cuboid(ScrewBlockOA,anchor=BOTTOM,rounding=Radius,except=[FRONT,BOTTOM,LEFT]);

	up(ScrewBlockOA.z – MouldScrew[LENGTH])
	zrot(180/NumSides)
	cylinder(d=MouldScrew[OD],h=MouldScrew[LENGTH] + Protusion);

	down(Protusion)
	cylinder(d=MouldScrew[ID],h=2*ScrewBlockOA.z);
	}

	}

	module BarMount() {

	difference() {
	cuboid(BarBlockOA,anchor=CENTER,rounding=Radius,edges=RIGHT);
	yrot(BaseAngle)
	cube([3BarBlockOA.x,2BarBlockOA.y,BarBlockOA.z],anchor=BOTTOM);
	yrot(BaseAngle)
	cylinder(d=Insert[OD],h=2*Insert[LENGTH],anchor=CENTER);
	}

	}

	module Mount() {

	union() {
	right(ScrewBlockOA.x/2) back(ScrewBlockOA.y/2)
	ScrewMount();
	right(BarBlockOA.x/2) fwd(BarBlockOA.y/2) up(BarBlockOA.z/2)
	BarMount();
	}

	}

	//———-
	// Build things

	if (Layout == "ScrewMount")
	ScrewMount();

	if (Layout == "BarMount")
	BarMount();

	if (Layout == "Show")
	Mount();

	if (Layout == "Build") {
	yflip_copy(Gap) Mount();

	}

view raw LED Bar Lamp Mount.scad hosted with ❤ by GitHub

2025-03-19

LED Strip Lights: Shade Adhesive

This is a quick-and-ugly test to see how well aluminized Mylar will work as a reflective shade for some LED light bars eventually washing the Living / Sewing room ceiling with enough light to brighten the Sewing Table:

LED strip light – Mylar reflector – ugly fit

The key question: how well adhesive adheres Mylar to the pleasantly warm aluminum extrusion serving as the heatsink for 40 W of LEDs:

LED strip light – Mylar reflector – adhesive strips

Perhaps surprisingly, those ½ inch strips come from an A4 sheet by way of a paper cutter.

As with the Mylar shades over the COB LED strips in the laser, the LEDs remain through the aluminized layer:

LED strip light – Mylar reflector – overexposed

The LED bars will be directly visible, so bouncing the direct light against the wall reduces glare and puts it to good use.

The Mylar strips are 1 inch wide, cut with a utility knife against a straightedge, although ⅞ inch seems adequate. The last LED over on the right sits at the endcap, so I will (try to) tuck the Mylar ends under the caps for a cleaner fit.

The bars have two 4 foot strips of LEDs in series, with a lump of circuitry buried in the aluminum extrusion that seems be a bridge rectifier and a small electrolytic capacitor. There’s not nearly enough capacitance to knock down the 120 Hz flicker and I have an uneasy expectation of stroboscopic effects on the sewing machines.

This is a test. […] This is only a test.

Now, to model angle brackets fitting the strips to the window moulding.

2025-03-17
Subpixel Zoo: Wall Hanging

Having herded all the denizens of the Subpixel Zoo into one LightBurn workspace, framing them seemed appropriate:

SubPixel Zoo – wall hanging

We had some 18×24 inch frames which fit a standard construction paper size. The paper colors aren’t nearly as vivid as a real artist would want, but they’ll suffice for my simple needs.

Lay out a template and decide 180 mm blocks fill the frame:

SubPixels – LightBurn 18×24 template

Offse the blocks 2 mm outward for cutting clearance and make a fixture:

SubPixels – LightBurn 18×24 fixture

The outer rectangle matches a blank sheet of corrugated cardboard cut by hand to fit the platform. The inner rectangle marks a line around the 18×24 inch position of the paper, giving me a mark within which I can center the paper well enough by eyeballometric approximation.

Cutting the blocks and marking the lines produces the template:

SubPixel Zoo – laser fixture and chaff

It’s held in place by four finger-crushingly strong magnets. If I ever do this again, I’ll throttle back on the power for the corner targets, because the laser cannot reach the top speed marking the outline, so it cut through the top layer of cardboard at the targets.

The layers for the 8×8 versions have 170 mm blocks with all the colors properly separated:

SubPixels – LightBurn 8×8 layers

Embiggen the blocks to 180×180 mm, rotate them to their new orientation, then snap them into copies of the new template:

SubPixels – LightBurn 18×24 layers

I can only envision these things in the landscape orientation that will fit the laser platform, but you could build them in their final portrait orientation and rotate the result.

I put the template pattern in the middle of the LightBurn workspace and use Print and Cut to align the fixture with the corner targets. Then it’s just a sequence of laying a sheet of paper on the fixture, selecting the corresponding layout, hitting P to snap the layout to the center of the workspace, and Firing The Laser.

It’s not nearly as pretty as Mary’s quilts, but now I have a wall decoration of my very own.

2025-03-13
Wire Shelf Shims
Another trivial laser cutter project:

Wire Shelf Shim – top view

I’m finally assembling the shelves for the last of the boxes cluttering the basement floor. Because the top of the wire shelf grid sits 4 mm below the top of the shelf rails, surely for some good reason, that pale strip is a 6 mm shim raising the grid just enough to let the boxes slide easily off without having to lift them over the rail.

It’s a pair of 3 mm thick MDF strips stuck together with tapeless sticky (a thin adhesive layer on backing paper), with the same adhesive holding the shim to the rail while I lay them down and plunk the shelf grid on top:

Wire Shelf Shim – side view

I made two sets of shims to fit the support rod spacing, with lengths carefully chosen to match two stacks from my Big Box o’ MDF Cutoffs, all 10 mm wide to fit the shelf rails:

Wire Shelf Shim – laser cutting

Admittedly, not all of the neatly rounded corners came through, due to slight variations in MDF sizing / Print-and-Cut alignment / whatever, but it’s a nearly zero waste way to turn stock into strips.

Each shelf needs 14 shims = 28 strips and I’m here to tell you if I had to bandsaw 140 little strips for each of three sets of shelves, well, I:
- Probably wouldn’t ever get around to making them
- Definitely would grumble about lifting those boxes, forever
Watching that thing never gets old …
2025-03-12