Category: Machine Shop

Mechanical widgetry

Please Close The Gate Signage: Painted

It seems two months of sunlight will fade laser charred MDF down to its original state:

Please Close The Gate – unpainted faded

That’s through a thick layer of indoor urethane sealant slathered over MDF without any surface prep. Obviously, not removing the char had no effect on the outcome. On the upside, the urethane did a great job of protecting the MDF from rainfall.

So. Back to the shop.

Lacking wider masking tape, two strips of tape laid along a cut-to-suit slab of fresh MDF will serve as a paint mask:

Please Close The Gate – masked engraving

Belatedly I Learned: cut the tape close to the edge, then fold it under so the autofocus pen can’t possibly snag it en passant.

Shoot the entire surface with a couple of black enamel rattlecan coats:

Please Close The Gate – masked paint

Yes, the engraved areas look reddish, most likely due to another complete lack of surface prep. Perhaps brushing / vacuuming / washing would remove some of the char, but let’s see how it behaves with no further attention.

Peel the tape, weed the letters / antlers, slather on a coat of urethane, and it looks downright bold:

Please Close The Gate – sealed

Of course, if those two tape strips don’t exactly abut, the paint produces a nasty line:

Please Close The Gate – mask gap

Should you overlap the strips a wee bit to ensure cleanliness, the engraved surface will then have a noticeable (in person, anyhow) discontinuity due to the laser losing energy in two tape layers, which wouldn’t matter in this application. We defined the few paint lines as Good Enough™ for the purpose; a strip of absurdly wide masking tape is now on hand in anticipation of future need.

Burnishing the tape might have prevented paint bleed around the engraved areas:

Please Close The Gate – paint creep

But, given that I was painting raw / unfinished MDF with an unsmooth surface, burnishing probably wouldn’t produce a significantly better outcome.

By popular request, the new signs sit a few grids lower on the gates:

Please Close The Gate – fresh painted

Perhaps these will outlast the garden season …

2022-06-30
OMTech 60 W Laser: Air Assist Pump Filter

The air assist pump sits in the right rear of the OMTech laser’s main compartment:

OMTech 60W laser – Z motor – air pump

Where it is, of course, exposed to all the usual dust / fragments / fumes / smoke generated by laser cutting & engraving, enhanced by my attention to getting good air flow over the platform. The picture shows the base plate in as-delivered condition, which it will never resemble ever again.

The problem: any crud in the air can clog the pump or contaminate the laser focus lens.

Four screws into threaded holes hold the pump to the base plate, secured with jam nuts on the outside.

The air inlet is a round fitting centered on the bottom of the pump housing:

OMTech 60 W Laser Air Assist – pump inlet

You’ll note the out-of-focus crud scattered on the base plate.

The general idea is to drill a hole through the base plate, put a snorkel on the inlet, and have it inhale fresh, relatively clean, basement air from outside the cabinet. The trick will be not touching the base plate with anything solid, because the pump vibrates like crazy; its four squishy standoffs do a great job of isolating the tremors from the base screwed to the laser cabinet.

Having a few other things going on at the moment, I just laid two generous wads of cheesecloth where they can filter the bigger chunks out of the air stream:

OMTech 60 W Laser Air Assist – cheesecloth filter installed

The air flow meter says the pump still delivers 12 l/m to the nozzle, so the cheesecloth has no effect compared to four or five feet of 4 mm ID tubing.

A doodle summarizes the inlet fitting dimensions:

OMTech 60 W Laser Air Assist – pump inlet fitting measurements

That looks like a 3D printed disk with a snout for a short air hose should do the trick, with a thin gasket sealing the disk to the fitting.

Now I can throw that piece of paper out …

2022-06-29

Replacement Muntin Clips

Terminology I had to look up:

Window: something in a wall you can see through
Sash: a sliding panel in a window
Mullion: vertical post separating two windows
Muntin: strips separating glass panes in a sash

TIL: Muntin, which I’d always known was called a Mullion.

With that as preface, one of Mary’s quilting cronies lives in a very old house updated with vinyl windows sporting wood muntins arranged in a grille. The wood strips forming the grille end in plastic clips that snap into the sash, thereby holding the grill in place to make the window look more-or-less historically correct, while not being a dead loss as far as winter heating goes.

Time passed, sun-drenched plastic became brittle, and eventually enough clips broke that the grilles fell out. An afternoon quilting bee produced a question about the possibility of making a 3D printed clip, as the original manufacturer is either defunct or no longer offers that particular style of clip as a replacement part.

Well, I can do that:

The original is (obviously) the transparent injection-molded part in the upper left. The other two come hot off the M2’s platform, with the one on the right showing the support material under the sash pin.

The solid model looks about like you’d expect:

Window Muntin Clip - solid model — Window Muntin Clip – solid model

There is obviously no way to build it without support material, so I painted the bottom facet of the sash pin with a PrusaSlicer support enforcer:

Window Muntin Clip - PrusaSlicer — Window Muntin Clip – PrusaSlicer

The pin comes out slightly elongated top-to-bottom, but it’s still within the tolerances of the original part and ought to pop right into the sash. We’ll know how well it works shortly after the next quilting bee.

The doodle with useful measurements amid some ideas that did not work out:

Window Muntin Clip - Dimension Doodle — Window Muntin Clip – Dimension Doodle

The OpenSCAD source code as a GitHub Gist:

	// Window Muntin Clips
	// Ed Nisley KE4ZNU June 2022

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

	/* [Hidden] */

	ThreadThick = 0.25;
	ThreadWidth = 0.40;

	HoleWindage = 0.2;

	Protrusion = 0.1; // make holes end cleanly

	inch = 25.4;

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

	function IntegerMultiple(Size,Unit) = Unit * ceil(Size / Unit);

	//———————-
	// Dimensions

	ClipOA = [13.0,18.7,8.0];

	TongueAngle = 70;

	TongueOA = [14.0,10.0,1.8 – 0.2]; // minus Z windage for angular slices

	BuildGap = 5.0;

	//———————-
	// Useful routines

	module PolyCyl(Dia,Height,ForceSides=0) { // based on nophead's polyholes

	Sides = (ForceSides != 0) ? ForceSides : (ceil(Dia) + 2);

	FixDia = Dia / cos(180/Sides);

	cylinder(r=(FixDia + HoleWindage)/2,
	h=Height,
	$fn=Sides);
	}

	//———————-
	// Pieces


	module Shell() {

	// Clip base as 2D polygon
	// Magic numbers from measurements

	cx = ClipOA.x;
	cy = ClipOA.y;
	cz = ClipOA.z;

	ClipPts = [
	[0,0],[0,cz],[0.3,cz],
	[1.0,cz-1.0],[2.0,cz-2.3],[2.0,cz-3.0],[1.3,cz-3.5],
	[1.3,1.6],[17.4,1.6],
	[17.4,cz-3.5],[16.7,cz-3.0],[16.7,cz-2.3],[17.7,cz-1.0],
	[18.4,cz],[18.7,cz],[18.7,0.0],[0,0]
	];

	difference() {
	translate([-ClipOA.x,-ClipOA.y/2,0])
	rotate([90,0,90])
	linear_extrude(height=ClipOA.x,convexity=3)
	polygon(convexity=3,points=ClipPts);
	translate([-(ClipOA.x – 3.0/2 + Protrusion),0,0])
	cube([3.0 + Protrusion,ClipOA.y – 21.3,41.6],center=true);
	}
	}

	module Tongue() {

	tx = TongueOA.x;
	ty = TongueOA.y;
	tz = TongueOA.z;

	tt = ty – 2sqrt(2)tz; // width at top of tapers
	td = ThreadWidth; // min size of features

	intersection() {

	rotate([0,-TongueAngle,0]) {

	difference() {

	union() {
	hull() {
	for (j=[-1,1]) {
	translate([td/2,j*(ty – td)/2,td/2])
	cube(td,center=true);
	translate([td/2,j*(tt – td)/2,tz – td/2])
	cube(td,center=true);
	}
	translate([10.0,0,0])
	rotate(180/12)
	cylinder(d=ty,h=td,center=false,$fn=12);
	translate([10.0,0,tz – td/2])
	rotate(180/12)
	cylinder(d=tt,h=td,center=false,$fn=12);
	};

	translate([10.0,0,-5.2])
	rotate(180/12)
	cylinder(d=5.0,h=5.2,center=false,$fn=12);

	translate([10.0,0,-5.2])
	rotate(180/12)
	resize([0,0,2.0])
	sphere(d=5.0/cos(180/12),$fn=12);

	}

	if (false)
	translate([10.0,0,-10]) // stiffening hole
	rotate(180/6)
	PolyCyl(0.1,20,6);

	}


	}

	cube([2ClipOA.x,2ClipOA.y,2*IntegerMultiple(13.0,ThreadThick)],center=true);
	}


	}

	module Clip() {
	Shell();
	Tongue();
	}

	//———————-
	// Build it


	if (Layout == "Show") {
	Clip();
	}

	if (Layout == "Build") {
	Clip();
	}

view raw Window Muntin Clips.scad hosted with ❤ by GitHub

2022-06-28

Kenmore HE3 Washer: End of Life
After eighteen years and one basket / tub replacement, our venerable Kenmore HE3 clothes washer has reached End of Life:
Kenmore washer – eroded tub A
Kenmore washer – eroded tub B
Kenmore washer – eroded tub C
I had looked in there (between the door gasket and the tub) to find any foreign objects making the horrible noise and again, perhaps a week later, when I replaced the shock absorbers, after which the corroded spider in the back finally broke enough to let the basket flop around continuously during the spin cycle and erode the tub rim.

In round numbers, we heard the first sign of trouble three weeks ago: a very loud, but only occasional, KLONK due to protrusions on the side of the basket or the fractured part of the spider on its back hitting indentations in the tub. The KLONK remained intermittent during half a dozen loads, until it became pretty much continuous.

We installed the washer in early 2004, replaced the tub and basket in 2010, and it’s now 2022: the first spider failed after six years and its replacement lasted twelve. After nearly two decades, the tub and basket are no longer available from the usual appliance part sources, so (even if I wanted to) I cannot repair the washer.

Another washer, also a front-loader, also highly rated, will arrive shortly. For the first time ever, we bought an Extended Service Plan good for five years. The alert reader will note the difference between the first failure and the length of the plan, but reviews of similar new machines suggest having Lemon Replacement coverage. In this situation, I am willing to pay for the talismanic effect of coverage that may never pay off, if that makes any sense.
2022-06-27
Kenmore HE3 Washer Shock Absorber Shims

As part of diagnosing a Terrible Sound inside our two decade old washer, I replaced the OEM shock absorber struts with cheap knockoffs. Although it didn’t solve the problem (spoiler: another tub spider bites the dust), the experience may come in handy elsewhere.

The left rear (as seen from the front) shock stood in a pile of rust on the baseplate that came from a drip in the water feed nozzle to the detergent / bleach / whatever dispenser drawer. The affected parts are no longer available and I have never had any luck finding a replacement O-ring of the proper size, so I just pulled the nozzle out, ran a small bead of acrylic sealant around the O-ring, and squished it back in place:

Kenmore washer – dispenser nozzle seal

It’s the Y connection between the two black hoses, held in place on the dispenser by a relentless little clip. Release the two hose clamps, remove the hoses, pull it out, apply sealant, squish, reinstall in reverse order.

As for the shocks, don a pair of work gloves and turn the upper mount (on the tub) counterclockwise as you look along the shock. The tub has molded-in latches that make turning it the wrong way difficult, but not impossible.

With the shock loose, you can now try to turn the lower mounts counterclockwise as you look along the shock, but I had to deploy the BFW in very cramped quarters to get enough traction. This will likely wreck the little latches holding the mount in place, but you were going to replace it anyway.

The new left-rear latch snapped firmly into place:

Kenmore washer shock – left rear

Yes, that’s after I cleaned off as much of the rust as made sense.

The remaining three latches did not snap firmly into place, so I made shims to soak up the slop:

Kenmore washer shock – shim laser cut

They slip around the central pillar with clearance for the latches, although the thicker shim didn’t leave much engagement:

Kenmore washer shock – shim installed

They ranged from 0.8 mm down to 0.2, based entirely on feel, and I used PETG, LDPE, and polypropylene clamshell of the right thickness.

The left front got the thickest:

Kenmore washer shock – left front

Right front thinnest:

Kenmore washer shock – right front

And right rear in the middle:

Kenmore washer shock – right rear

The shims aren’t precisely lined up with the feet, because I couldn’t make that work out, but they definitely prevented the mounts from shaking in their boots during the spin cycle.

You will inevitably want to take the mounts off the shocks, which will prove surprisingly difficult. The two halves are identical, with triangular latches that snap together with no provision for release:

Kenmore washer shock – foot internals

Brute force applied with a small screwdriver may suffice, but don’t be surprised if strong words are required.

2022-06-24
Nothing Lasts, Chemical Edition

Cleanup after painting the hairlines involved opening the cap of the rarely used can of methyl ethyl ketone:

$MEK can - fractured cap$
MEK can – fractured cap

It seems white-tinted polyethylene deteriorates after a dozen years of exposure to concentrated MEK fumes, suggesting I don’t use nearly enough enamel paint.

The Container Stockpile disgorged a pair of pure polyethylene jars that should last another decade.

2022-06-22
Homage Tektronix Circuit Computer: Laser-Engraved Painted Hairline

Having established that laser-engraving the hairline fuses the protective film to the PETG cursor, I wondered if the bond would allow filling the hairline by painting it with good old Testors enamel:

Tek CC – Painted Hairline – finished

Which is, straight up, the best hairline I’ve ever made!

I use a fine-tipped paintbrush, but there’s no need for finesse:

Tek CC – Painted Hairline – mask detail

After the paint has cured a bit, peeling the film removes everything that isn’t inside the trench:

Tek CC – Painted Hairline – mask removal

The clouds on the clear side come from PETG vapor condensing on the transparent film protecting the bottom of the cursor.

A closer look through the cursor shows bubbles in the bottom of the trench, presumably from boiling PETG:

Tek CC – Painted Hairline – detail

The hairline measures 0.3 mm across and, unlike previous attempts, is perfectly consistent from end to end.

Now I can go into mass production:

Tek CC – Painted Hairline – production

I love it when a plan comes together …

2022-06-21