Category: Machine Shop

Mechanical widgetry

Under-shelf Kitchen Light Bracket

Quite a while ago I’d added another LED strip to the under-cabinet light array, because the little cutting boards & suchlike on a wire shelf blocked the light, but fastened it in place with ugly wire ties.

Finally I found a Round Tuit on the desk for brackets mounting the strip directly to the shelf:

Kitchen Light Bracket - shelf blocks - solid model — Kitchen Light Bracket – shelf blocks – solid model

Ram a pair of brass inserts in the holes, screw the strip in place, snap the brackets between the wires, and it’s much better:

Kitchen Light Bracket - installed — Kitchen Light Bracket – installed

Stipulated: those wire ends look awful. Fortunately, they’re normally hidden by the cutting boards and suchlike on the shelf.

Although it looks precarious, the rounded sides (seem to) have enough grip on the wires to hold the LED strip in place. We’ll see how well that works in practice, but the idea was to avoid anything sticking up above the wires to collide with the stuff on the shelf.

The blocks emerge from a chunk of code glommed onto the original OpenSCAD program:

ShelfWireDia = 3.2;
ShelfWireOC = 1*inch;
StrutWireDia = 6.3;

ShelfBlock = [ShelfWireOC,LEDEndBlock.y,(0.8*ShelfWireDia + StrutWireDia/2)/cos(180/8)];
echo(ShelfBlock=ShelfBlock);

LEDHoleOffset = [ShelfBlock.x/2 - (6.0 + ShelfWireDia/2),6.0];  // from Y+ and X±
LEDHoleDia = 3.0;

ID = 0;
OD = 1;

M3Insert = [3.0,4.0,4.2];   // short M3 knurled insert

<<< snippage >>>

module ShelfBlocks(Side=1) {

  difference() {
    translate([0,ShelfBlock.y/2,ShelfBlock.z/2])
      cube(ShelfBlock,center=true);
   translate([Side*LEDHoleOffset.x,ShelfBlock.y - LEDHoleOffset.y,-Protrusion])
      rotate(180/8)
        PolyCyl(M3Insert[OD],M3Insert[LENGTH] + 2*ThreadThick,8);
    translate([-2*ShelfBlock.x,-StrutWireDia/4,0])
      rotate([0,90,0]) rotate(180/8)
        PolyCyl(StrutWireDia,4*ShelfBlock.x,8);
    for (i=[-1,1])
      translate([i*ShelfWireOC/2,-ShelfBlock.y,(StrutWireDia/2 + ShelfWireDia/2)/cos(180/8)])
        rotate([-90,0,0]) // rotate(180/8)
          PolyCyl(ShelfWireDia,3*ShelfBlock.y,8);
  }
}

<<< snippage >>>

if (Layout == "ShelfBlocks")
  for (i=[-1,1])
    translate([i*(ShelfBlock.x/2 + 3.0),0,0])
      ShelfBlocks(i);

Should’a done that years ago …

2023-10-26

Laser-Cut Specialty Wipes

For reasons not relevant here, Mary asked for a bunch of small cloth wipes cut to a particular size. A few minutes with LightBurn for rectangle-drawing and array-fiddling produces a useful result:

Laser-cut wipes – cutting

The part about peeling away what you don’t want just never gets old:

Laser-cut wipes – on honeycomb

It turns out this is even faster than rotary cutter action, because you need not worry about the old T-shirt sliding around while you’re slashing away at it. Bonus: a free 2 mm radius on all the corners!

Let the pieces air out for a day on the patio and they’re ready for use.

2023-10-25
Tiled Einstein Coasters

When life gives you a sheet of tiled einsteins:

Einstein tiling

You can make coasters:

Einstein tiled coasters

They’re rattlecan colored chipboard atop MDF atop cork, with the tiles cut from half a dozen sheets of einsteins. The lighter colors suffered from ineffective tape masking during cutting, producing more smudging than I’d like, but overall they look pretty good.

I was surprised at how dull the black surround turned out and how good the gray appears: rapid prototyping & iteration in full effect.

Unlike the layered paper version, these require a great deal of fiddly handwork.

I hope the MDF will prevent the premature warping afflicting the chipboard-on-cork coasters. Perhaps shooting the assembled coasters with a clearcoat would help, although you do want coasters to be a bit absorbent, lest they stick to wet cups / mugs / glasses in humid weather.

2023-10-24
Layered Paper: Einsteins

Go to the source and bring back a suitable number of tiled einsteins:

Einstein tiling

Import the bitmap into LightBurn, fiddle with the tracing until it lays down two lines along each border, apply a 1 mm inset to all the tiles, then scale & crop & delete to fit a 170 mm square:

Einsteins – LB paper – top layer

Cut one of those sheets, tape it to a sheet of white paper, fire up a calculator, generate a random number, write the first digit in the upper-left tile, and iterate to fill in all the tiles.

Duplicate that layout and delete all the tiles marked with a zero to get the next layer.

Iterate for all ten layers:

Einsteins – LB paper cuts

Set up the fixture, do the Print-and-Cut alignment, then cut all the layers with different colors:

Layered Paper cutting fixture – in use

Assemble the layers with some stick adhesive:

Layered Paper – Einsteins

Frame it and admire:

Layered Paper – Einsteins

It’s way busier than the quilt blocks, but I like it.

2023-10-23
Layered Paper: Mariner’s Compass Insets

Given the geometry of the Mariner’s Compass block:

Mariners Compass – top level shapes – LB layout

Applying increasing insets to that top level produces a beveled result:

Layered Paper – Mariners Compass – offsets – detail

Seen from a distance, you need oblique light to make any sense of it:

Layered Paper – Mariners Compass – offsets

It’s made from random sketch paper, rather than cardstock, and we all know how much the paper matters.

2023-10-20
Layered Paper: Cutting & Assembly Fixtures

Time spent making a fixture is never wasted time:

Layered Paper cutting fixture – in use

The general idea: securely hold a piece of paper flat while cutting it, so that it cannot move or warp, while letting the cut pieces fall out without snagging on anything underneath. The sheet holder I made a while ago worked reasonably well, but those thin metal blades tend to warp while cutting small patterns in restricted areas and the pieces definitely don’t fall free.

The simple fixture I use while assembling the paper layers consists of four rivnuts poking through a chipboard upper layer, with a craft paper layer around the rivnut washers on the bottom:

Layered Paper – alignment fixture

The cutting fixture uses a similar layout around a hole for freely falling chips:

Layered Paper cutting fixture – installed

Next time, I’ll remove those three bars across the hole, because the MDF doesn’t need any support. Nearly all the chips fell out, so the fixture worked as intended.

I trimmed the flange off the rivnuts so they would sit flat on the MDF:

Layered Paper cutting fixture – trimming rivnut flange

That’s the kind of job chuck stops really simplify.

The cutting fixture requires pre-cutting paper into 200 mm squares with four 5 mm corner holes, which can be done three-abreast on the platform bars, then putting each sheet in the fixture to cut the shapes. That’s not much of a disadvantage compared to messing up an unsupported sheet.

The cutting fixture has crosshair targets to align a LightBurn template using Print-and-Cut, thus eliminating the need to precisely locate the fixture on the platform. The finger-crushingly strong neodymium bar magnets do a fine job of holding the MDF in place on the steel platform.

The small cutout rectangle in the lower right corner frames the sheet number, done in binary code with 0 = 1 mm circle and 1 = 2 mm circle:

Layered Paper cutting fixture – layer binary code

That’s the underside view of a completed stack with the 5 mm lower-right fixture hole on the left and the code for layer 11 = 0b1011 reading backwards. The small 0 holes have two lobes showing the Print-and-Cut alignment was off by maybe 0.3 mm; the off-center hole was in the blank sheet.

Obviously, cutting tiny circles with a big laser at 300 mm/s doesn’t produce perfect results. You can see small wiggles in larger shapes:

Layered Paper cutting fixture – cut wobbles

Unless you’re trying hard to find a problem, you’ll never notice them.

2023-10-19
Layered Paper: Chimney Swallows Block

The Chimney Swallows block from page 128 of Beyer’s book:

Chimney Swallows – Beyer 128

The tool (blue & orange) and top cut (red) layers:

Chimney Swallows – LB layout

The long radial blue tool lines simplified selecting them when mirroring / duplicating the cut polygons around their symmetries. The orange tool circles aligned various midpoints / vertices / features during construction.

The inward curve along the outer edge started as a triangle with a node at about the middle of the curve. Deleting that node left the remaining two sides overlapped, but dragging one of them to match the curve worked OK. There’s probably a better way.

That curve defines the outer edges of the shapes along it, so I drew polygons from the corner intersections and dragged the outer edge to match the curve at high zoom.

The shape remains selected after dragging the side, which meant I could immediately apply a 1 mm inset to create the cut lines.

To my surprise, the swallow bodies are straight-sided polygons!

After taking advantage of all the symmetries, knock out the shapes defining each layer:

Chimney Swallows – LB paper cuts

The swallows look like F-117 Nighthawks to me:

Layered Paper – Chimney Swallows – Beyer 128

Maybe I have the colors wrong:

Layered Paper – Chimney Swallows – Beyer 128

Fly away!

2023-10-18