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

Sheath Your Blades!

Trigger warning: gore.

A week ago I milled a stack of cursor blanks, then engraved a test hairline on a scrap cursor to make sure everything was ready:

Cursor V-bit setup

After raising the spindle a few inches, I reached across the table, peeled the tape, and, as I pulled my hand back with the finished cursor, snagged the back of my left index finger on the V bit.

So. Much. Blood.

Urgent Care PA: “You may have nicked the tendon. Get thee hence to the Hospital Trauma Center.”
Trauma Center MD: “See that white fiber down in there? That’s the extensor ligament. Looks OK and should heal fine.”
Me: “Urp.”
Trauma Center MD: “Unless you’re one of the 20% who get an infection.”
Me: “Unless I’m one of the few who contract an MRSA infection, then just up and die.”
Trauma Center MD: “Well, yes, there’s that. If the wound swells or smells bad, come back here quickly.”

Dutchess County is now on the trailing edge of the Omicron wave, but the Trauma Center is attached to the Emergency Room and had a steady stream of customers arriving by ambulance. While being entirely content to not be their most urgent case, I had plenty of time to examine the wide variety of instruments parked in the room with me:

Nameless Hospital Cart

I’m on a ten-day regimen of surprisingly inexpensive Amoxicillin + Clavulanate Potassium capsules, which is apparently what it takes to knock down a potential infection these days.

Five days later, it looks like I should pull through:

Lacerated Left Index Finger

So I hereby swear a mighty oath on the bones of my ancestors to always sheath my blades. You should, too.

But we all knew that last week, didn’t we?

2022-02-17
Dremel Flex Shaft Oiling

While using a Dremel cutoff wheel to shape a lathe bit, the flexible shaft sounded not quite noisy, if slightly less smooth than before, so easing some oil into the drive shaft might be a Good Idea. The springy shaft slides out of the motor end without disassembly, but, just for completeness, I took a look inside the handpiece:

Dremel flex shaft – handpiece internals

Before removing the two obvious screws holding the handpiece together, remember to remove the steel ring at each end. The tail ring is obvious:

Dremel flex shaft – tail ring

The nose ring wasn’t where I expected it, but released easily after the obvious mistake revealed itself:

Dremel flex shaft – nose ring

The steel shaft spun freely in its bearings and the matching end of the flex drive shaft had plenty of grease:

Dremel flex shaft – drive detail

So I just reassembled everything in reverse order. The trick is to line up the existing indentations in the outer sheath with the bumps inside the handpiece shell:

Dremel flex shaft – housing detail

After all that, spreading a few drops of high-speed spindle oil along the spring drive shaft seemed appropriate.

Didn’t make the least bit of difference to the sound, but I feel better.

2022-02-01
Tektronix AM503: Balance Pot Bushing

One of the Tekronix AM503 current probe amplifiers arrived without the panel bushing for the Balance trim pot. Back in the day, you could presumably order part number 350-0301-02 and have it delivered (most likely) by your local Tek representative:

Balance pot panel bushing – Tek part listing

Those days are over.

A few minutes produced a doodle with pretty-close measurements:

Balance pot panel bushing – dimension doodle

The as-built bushing turned out just a smidge too long, so make yours a scant eighth of an inch. Maybe the Tek dimension is the overall length?

An SLA resin printer might crank out such a thing, but it’s well below the looks-good / fits-well resolution limit of an ordinary fused-filament printer.

Applying the mini-lathe to a 1/4 inch white acrylic rod produced a reasonable facsimile:

Tek AM503 Balance pot bushing – front

The side view:

Tek AM503 Balance pot bushing – side

Acrylic is definitely the wrong material for the job, but it came readily to hand while pondering the Shelf o’ Rods. Acetal would be better, as you could easily trim off the aforementioned excess length with a knife.

All’s well that ends well:

Tek AM503 Balance pot bushing – installed

A dab of white acrylic adhesive around the raw opening holds the bushing in place and it looks good enough to me.

The motivation for this boils down to having the bushing center the pot twiddler required to set the balance, which I must do every time I fire up the amps, even after waiting for the half-hour required to stabilize them at their operating temperature.

2022-01-27
Bafang Battery Charge Port: Autopsy

My friends in Raleigh sent a small box with the various tools I made, along with the scorched Bafang battery charge port. As it turned out, none of the tools were useful and the real fix required opening the battery cover enough to remove and replace the charge connector.

A view looking straight into the connector, with the side contact on the top of the image:

Bafang Battery Charge Port – damage overview

Gutting the connector shows why my homebrew shell drill wasn’t going to work:

Bafang Battery Charge Port – components

There’s not much left of the central pin: the nugget hanging on its side is much larger than I expected. Most of the pin melted into that nugget, with a bonus droplet on the near side.

The rectangular chunk (upper right) is the switch terminal, with the tab from the side contact (on the right) welded to it.

Fortunately, none of the mayhem (including a few small sparks during the connector replacement) damaged the battery management circuitry or triggered a shutdown, so the reset tool wasn’t needed.

It’ll make a great 3D printing show-n-tell exhibit, in the unlikely event I ever do an in-person talk …

2022-01-26
Verizon FiOS Battery Replacement

Being that type of guy, a red LED glowing in the far corner of the basement attracts my attention:

Verizon FiOS – replace battery

Back in the day, Verizon didn’t make it obvious that the customer is responsible for replacing the battery keeping the ONT alive during power failures. I expect VZ would eventually let me know the battery was dead, remind me I was on the hook for the replacement, then offer to send a tech around with a Genuine VZ Battery to maintain reliable service.

It’s an ordinary 12 V 8 A·hr sealed lead acid battery and, yes, it’s been in there for a while:

Verizon FiOS – OEM battery date

However, being that type of guy, I just happen to have a box of not-dead-yet SLA batteries waiting for recycling:

UPS SLA 2021-10-22

They’re three years younger than the VZ battery …

2022-01-25
Folding Step Stool Re-seating

The top step of a folding step stool we’ve been (ab)using forever finally wore out, mostly because it was covered in vinyl and intended as a seat. We always used it as a step, despite knowing you should never stand on the top rung of a ladder: “Do not stand on or above this level”.

I tossed the ripped vinyl and warped particle board, cut a random chunk of wood-textured paneling (which Came With The House™) to fit, match-drilled four holes, and it looks OK:

Folding step stool – reseated

The original seat / step / whatever used press-fit studs with a flat flange covered by the vinyl, but I just slammed 10-32 tee nuts into the paneling:

Folding step stool – tee nut installed

That’s a ring of low-strength threadlock around the inside of the nut; I do not expect the screws to come out ever again.

I cut the screws to length with a Dremel cutoff wheel using a slightly shortened tee nut as a fixture:

Folding step stool – screw shortening fixture

Not visible: the vacuum hose clamped to the vise sucking up all the abrasive + metal dust.

Good for an hour of Quality Shop Time™ on a cold winter morning!

2022-01-21
Tektronix AM503: Special Adapter and Failed BNC Bullet

The Tektronix AM503 manual specifies a Special Adapter to inject a signal directly into the input connector in place of the A6302 Hall probe:

Tektronix AM503 Special Adapter

The intricate Amphenol plug might still be available at some phenomenal cost, but I’m willing to just jam a pair of wires into the AM593 connector and be done with it.

I combined a pigtail BNC sporting a male connector, two 51 Ω resistors in parallel, two snippets of 18 AWG wire (an exact match for the 40 mil connector pins!) with the ends filed smooth, and some heatshrink tubing to make a roughly equivalent adapter:

Tek AM503 – Crude Special Adapter

Because the pigtail didn’t quite reach the function generator, I joined it to a longer cable with a BNC bullet, whereupon a slight tug ripped the guts out of the bullet:

BNC Bullet – failed

A closer look:

BNC Bullet – parts

The center hole comes into play with their equally craptastic BNC tee connectors.

Comparing this bullet with others from the same eBay lot shows the outer shell didn’t get quite enough crimp around the metal ring. Because it’s not an electrical connection, I eased some epoxy onto the internal shoulder where that ring seats, then slid the guts back in place.

Yak shaving in full effect!

2022-01-20