The Smell of Molten Projects in the Morning

Ed Nisley's Blog: Shop notes, electronics, firmware, machinery, 3D printing, laser cuttery, and curiosities. Contents: 100% human thinking, 0% AI slop.

Tag: Repairs

If it used to work, it can work again

Kenmore Model 158: Foot Pedal Pivots

I got an email asking how the Kenmore Model 158 sewing machine’s foot pedal pivots worked. The notes on rebuilding the carbon disk rheostat and conjuring a Hall effect sensor show the innards, but here’s what you need to know to get there.

The pedal has a pair of pivots on the side closest to your foot, held in place with a small screw inside the two feet:

Kenmore 158 – Pedal pivot screw – in place

The screw fits into a notch in the unthreaded pin inserted from the side:

Kenmore 158 – Pedal pivot screw – disassembled

And that’s all there is to it!

Now, as happened to my correspondent, the pin can go missing, perhaps after the screw worked loose. Worst case, you’re looking at replacing both parts.

Being made in Japan (as ours were), the pedal has metric sizes: the unthreaded pin is 4 mm in diameter and 18 mm long and the setscrew has an M4×0.7 thread. You could replace the pin with an 18 mm (down to maybe 15 mm) long M4 screw. The threads would make a gritty pivot, but better than no pivot at all.

Better to get a longer M4 screw with an unthreaded section near the head, hacksaw it to the proper length, file to tidy up the cut end, maybe file a notch for the setscrew, and pop it in place. For tidiness, file off the slot / Philips / hex socket to eliminate the temptation to turn it out.

Worst case, a pair of plain old USA-ian 6-32 screws 3/4 inch long would make a sloppy fit. Don’t tell anybody I said so; that’d be barely better than nothin’ at all in there.

Lowe’s claims to have M4×0.7 setscrews (with a hex socket, not a slot) to secure the pin.

If my experience around here is any guide, however, Lowe’s / Home Depot / Walmart may claim to have metric hardware in stock, but the only way to know is to actually go there and rummage around in the specialty hardware section, inside the big steel cabinet with slide-out drawers filled with a remarkable disarray of ripped-open bags and misfiled parts.

Good hunting …

2019-08-11
NuTone 8663RP Bathroom Vent Fan: Effective Repair
My high hopes for the UHMW bushing supporting the impeller lasted the better part of a day, because direct contact between the impeller and the motor bearing produced an absurdly loud and slowly pulsating rumble:

Bath Vent Fan – bushing installed

My hope that the UHMW would wear into a quieter configuration lasted a week …

Back in the Basement Shop, some free-air tinkering showed the impeller produced enough suction to pull itself downward along the shaft and jam itself firmly against the motor frame. My initial thought of putting a lock ring around the shaft to support the impeller turned out to be absolutely right.

So, make a small ring:

Bath Vent Fan – small lock ring – c-drill

With a 4-40 setscrew in its side, perched atop the impeller for scale:

Bath Vent Fan – small lock ring – size

It just barely fits between the impeller and the motor frame:

Bath Vent Fan – small lock ring – installed

This reduced the noise, but the hole in the impeller has worn enough to let it rotate on the shaft and the rumble continued unabated. The correct way to fix this evidently requires a mount clamped to both the shaft and the impeller.

Fast-forward a day …

A careful look at the impeller shows seven radial ribs, probably to reduce the likelihood of harmonic vibrations. After a bit of dithering, I decided not to worry about an off-balance layout, so the screws sit on a 9 mm radius at ±102.9° = 2 × 360°/7 from a screw directly across from the setscrew in another slice from the 1 inch aluminum rod:

Bath Vent Fan – mount ring – tapping

Centered on the disk and using LinuxCNC’s polar notation, the hole positions are:
```
G0 @9.0 ^-90
G0 @9.0 ^[-90+102.9]
G0 @9.0 ^[-90-102.9]
```
As usual, I jogged the drill downward while slobbering cutting fluid. I loves me some good manual CNC action.

Put the mount on a 1/4 inch tube, stick it into the impeller, and transfer-punch the screw holes:

Bath Vent Fan – mount ring – impeller marking

Apparently, some years ago I’d cut three screws to just about exactly the correct length:

Bath Vent Fan – mount ring – test fit – bottom

I knew I kept them around for some good reason!

The 9 mm radius just barely fits the screw heads between the ribs:

Bath Vent Fan – mount ring – test fit – top

Some Dremel cutoff wheel action extended the motor shaft flat to let the setscrew rest on the bottom end:

Bath Vent Fan – mount ring – shaft flat

Then it all fit together:

Bath Vent Fan – mount ring – installed

The fan now emits a constant whoosh, rather than a pulsating rumble, minus all the annoying overtones. It could be quieter, but it never was, so we can declare victory and move on.

Dropping fifty bucks on a replacement fan + impeller unit ~~would~~ might also solve the problem, but it just seems wrong to throw all that hardware in the trash.

And, despite making two passes at the problem before coming up with a workable solution, I think that’s the only way (for me, anyhow) to get from “not working” to “good as it ever was”, given that I didn’t quite understand the whole problem or believe the solution at the start.

But it should be painfully obvious why I don’t do Repair Cafe gigs …
2019-08-08
Vacuum Tube LEDs: Failed Tape, Failed USB Cable

While packing the vacuum tube LEDs for the HV Open Mad Science Fair, I noticed the knockoff Arduino Nano inside one had come unstuck from the base. It seems the double-stick foam tape I’d used had lost its sticky:

Vacuum Tube LEDs – unstuck foam tape

Replacing it with my now-standard black 3M outdoor rated tape ought to solve the problem forever more.

For whatever it’s worth, the SK6812 RGBW LEDs have had exactly zero failures in the last two years or so; I finally turned off the test fixture.

Before reassembling the light, I plugged the USB cable into the bench supply and watched the Nano reset erratically. Careful poking showed the USB cable was intermittent, so I carved it up:

Failed USB cable – autopsy

As far as I can tell, the black wire (supply common) was cut mostly all the way through, with just a few strands remaining, before I peeled the insulation back.

A closer look at the solder joints doesn’t inspire much confidence in their QC:

Failed USB cable – solder joints

If those pads tarnished along with their solder blobs, the overmolded plastic isn’t the right stuff for the job. If they started life like that … ick.

I must up my cable spend, although I have no confidence doing so will improve the quality.

2019-08-02
NuTone 8663RP Bathroom Vent Fan Bushing

The NuTone 8663RP (for future reference) vent fan in the Black Bathroom began making horrible grinding sounds and, after a day or two, stopped turning. Pulling it out showed the impeller had slipped downward on the motor shaft:

Bath Vent Fan – impeller shift

Which meant the impeller was now resting on the steel frame:

Bath Vent Fan – impeller interference

Curiously, there’s no retainer under the impeller preventing it from sliding downward, other than good intentions and a friction fit. Nothing lasts, although it’s been working for the last two decades, so I guess it doesn’t owe me much.

My first thought was to build a steel or aluminum collar with a setscrew to hold the thing up, but I decided to try a simple bushing made of UHMW polyethylene between the motor and the impeller.

Turning it to the proper length required a test fit, then another session on a mandrel made from some aluminum tubing:

Bath Vent Fan – bushing trim

The snout came out just long enough to clear the motor frame, resting the impeller’s weight atop the bearing around the shaft:

Bath Vent Fan – bushing installation

It’s hard to see between the impeller blades, but there’s actually a bit of clearance underneath:

Bath Vent Fan – bushing installed

Which left just barely enough room on the top for the retaining clip:

Bath Vent Fan – shaft clip – detail

I had high hopes for the UHMW, but it seems any contact between the rotating impeller and the stationary bearing transmits enough sound to be annoying.

So I must break down and build a collar, although it’s off the critical path right now.

As far as I can tell from the pictures, dropping $50 on a new fan unit will get me exactly the same problem. Whether it would last for two decades before failing is an open question, but my experience with freezer fans suggests what we have is as good as it gets and making a bushing is the least-awful way to proceed.

2019-07-31
Walmart Wiper Selector: FAIL

After five years, I figured it’d be a Good Idea™ to replace the Forester’s wiper blades. Being in the Walmart at the time, I tried to use their helpful Wiper Selector gadget:

Walmart Wiper Selector

You’d think whoever is responsible for updating / replacing such things would have done so several times during the last eight years.

2019-07-28
Another Garden Hose Y Valve Autopsy

An outlet thread failed on yet another garden hose Y valve:

Garden Fittings – Failed Y valve – detail

Out of an abundance of curiosity, I battered the remaining parts out of the carcass:

Garden Fittings – Failed Y valve – autopsy

One of these days, we must buy an assortment of new fittings …

2019-07-27
HP 7475A Plotter: Ceramic-Tip Pen EOL

Ceramic-tip plotter pens draw wonderfully crisp lines:

Spirograph pattern – black ceramic pen – detail

Eventually, though, the fiber tip wears flush with the ceramic shell, becomes slightly indented, and ceases to make its mark in the world:

HP 7475A Plotter – Ceramic pen – worn tip

As the lady says, “Starting from zero, got nothing to lose”, so I applied a fine diamond file around the tip:

HP 7475A Plotter – Ceramic pen – filed tip

Well, all I can say is it seemed like a good idea at the time.

Alas, even the newly exposed fiber didn’t make much of a mark on the paper and, as you’d expect, the ragged ceramic tip dragged painfully across the paper. I assume the fiber had filled with fossilized dry ink.

A New Old Stock bag of fiber-tip pens emerged from the Big Box o’ Pens while I was flailing around:

HP 7475A Plotter – NOS Green pen package

I think the “812” in the lower right corner is a date code, most likely early in 1988, so the pens started their lifetime countdown at least three decades ago. They still work, though:

HP 7475A Plotter – NOS Green pens

The plotter appeared at HV Open’s Mad Science Fair, because everybody loves a plotter!

2019-07-25