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

HP Scope Probe Flange Repair

Quite some time ago I manage to break the finger flange on one of my scope probes and, what with it being made of an un-glueable engineering plastic, a simple repair job failed quickly. It’s entirely round and a perfect lathe project, but … this is easier:

You can see remnants of that failed repair just below the fracture:

HP scope probe flanges - repair disk — HP scope probe flanges – repair disk

Some epoxy around the rim of the flange, plus filling the missing sector, looks about as grubby as you’d expect:

HP Scope Probes - rear — HP Scope Probes – rear

That’s a tiny zit at about 1 o’clock which came off with fingernail pressure.

From the business end, it actually looks pretty snappy:

HP Scope Probes - front — HP Scope Probes – front

I’m mildly tempted to preemptively reinforce the other probes…

The OpenSCAD source code joins two parts with coincident faces, but it worked out OK for once:

// Tek Scope Probe Flange
// Ed Nisley KE4ZNU November 2013

//- Extrusion parameters must match reality!
//  Print with 2 shells and 3 solid layers

ThreadThick = 0.25;
ThreadWidth = 0.40;

HoleWindage = 0.2;

Protrusion = 0.1;			// make holes end cleanly

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

//----------------------
// Dimensions

FlangeOD = 16.0;
FlangeID = 8.75;
FlangeThick = IntegerMultiple(1.25,ThreadThick);

DiskOD = FlangeOD + 4*ThreadWidth;
DiskThick = FlangeThick + 4*ThreadThick;

NumSides = 8*4;

//----------------------
// 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);
}

module ShowPegGrid(Space = 10.0,Size = 1.0) {

  Range = floor(50 / Space);

	for (x=[-Range:Range])
	  for (y=[-Range:Range])
		translate([x*Space,y*Space,Size/2])
		  %cube(Size,center=true);

}

//----------------------
// Build it

ShowPegGrid();

	difference() {
		union() {
			translate([0,0,2*ThreadThick])
				cylinder(r=DiskOD/2,h=DiskThick,$fn=NumSides);			// main repair part
			cylinder(r1=(DiskOD - 2*ThreadWidth)/2,r2=DiskOD/2,h=2*ThreadThick,$fn=NumSides);
		}
		translate([0,0,(DiskThick - FlangeThick)])				// flange clearance
			PolyCyl(FlangeOD,2*FlangeThick,NumSides);
		translate([0,0,-DiskThick/2])
			PolyCyl(FlangeID,2*DiskThick,NumSides);
	}

2013-11-13

Arduino Pro Mini Knockoff: Solder FAIL
Although it’s not obvious, the two blue 2431 Ω resistors just above the toroid are a divider that scales the switched battery voltage (from the p-MOSFET on their left) by 50% and sends it to input A0 on the Arduino Pro Mini board:

Hall effect sensor – toroid CCW field

The firmware can use that input to dim the LEDs when the voltage drops below some preset threshold and, eventually, turn them off completely.

Figuring the actual battery voltage is straightforward:
- get 10 bit ADC value with analogRead()
- multiply by actual V_CC (measured at 4.96 V for this board)
- divide by actual voltage divider ratio (measured at 3.78/7.57)
Which, of course, reported the battery voltage was 4.116 V. Huh?

After spending far too much time poking the code with a sharp stick, I wired the divider to the (previously unused) A6 and A7 inputs and dumped the raw ADC counts for all three. The answer should be somewhere near 763, but the three values came out around 215, 667, and 750. Huh?

The A0 value is totally bogus, so I finally looked at the Arduino Pro Mini board:

Arduino Pro Mini clone – chip overview

Hmmm. It turns out A0 is the second pin back on the left side:

Arduino Pro Mini clone – unsoldered leads

Double hmmm. An even closer look:

Arduino Pro Mini clone – unsoldered A0 lead

Well, that was obvious after I figured out where to look…

I slathered flux on all the pins, touched each one with a soldering iron, and it’s all good.

This is a knockoff Arduino Pro Mini board from eBay, of course, and the rest of the boards in that lot were OK. Their QC inspection almost certainly boils down to running the Blink sketch: if the LED blinks after the power goes on, ship it!

Blink doesn’t verify the analog inputs, which turn out to be wrapped around that corner of the package.
2013-11-11
Kitchen Spatula Handle Anchoring

Shortly after we bought this kitchen scraper spatula (or whatever it’s called), the handle pulled out of the blade and left it sitting in a bowl of batter. That turned out to be unsurprising, given that neither side of the interface has any mechanical locking features. I rinsed the batter off, stuck some urethane glue inside, rammed the handle in place, and hoped for the best. Lacking any mechanical interlock and not bonding to either surface, the adhesive didn’t improve the situation.

So I recently added a pair of stainless 4-40 setscrews standing just proud of the handle’s surface that should dig into the blade and hold it in place:

Spatula handle enhancement

Another item for the shopping list…

2013-11-10
Samsung Quiet Jet Vacuum: Floor Brush Wheels

After rebuilding the front end of the Samsung vacuum’s floor brush, I’d hoped that was the end of it; other than replacing the brush strips every now and again, it’s been cooperative. Recently, however, one of the wheels popped off, which revealed the minimal mechanism holding them in place:

Samsung Quiet Jet – floor brush wheel interior

Those four delicate latches have worn themselves and the hub to the point where they ride over the edge at the slightest provocation. I pulled both wheels off and packed three turns of insulated wire (one turn is visible in the photo, as it was an iterative process) around the outside of the clips, with the intent of restoring enough force to hold the wheels in place until we exhaust the lifetime supply of bags I bought for the thing…

2013-11-09
3D Printed Bike Helmet Mirror Mount: Two Years Later

A bit over two years ago, I hoped my design for a bike helmet mirror mount would prove to be more durable than the fragile commercial mirrors I’d given up on:

Helmet mirror mount – 3D model – Fit layout

Having just tightened the teeny screws that hold the joints in place for the first time since I glued it to the helmet, I’d say it’s working fine. The 2-56 elevation setscrew has worn a slight dent in the arc and the 3-48 azimuth screw worked slightly loose; the mirror didn’t fall apart, but the position wasn’t as stable as it should be.

If I ever re-do the design, I’ll try adding a recessed metal (brass?) strip along the top of that arc, as that’s the most finicky adjustment. Perhaps a shoe under the setscrew would be better?

Two years of road grit show up clearly against the yellow plastic, though:

Bike helmet mirror mount – two years

For the record, those 2-56 setscrews require 35 mil hex keys; as Eks reminds me, any design requiring those screws is just crazy talk.

2013-11-05
Brita Water Pitcher: Reinforced Lid Screws

While I had the epoxy for the last step in the eyeglass frame repair, I fixed the lid on the never-sufficiently-to-be-damned Brita filter pitcher, as it had just tossed one of its miniature screws somewhere on the kitchen floor.

Nothing too challenging and, as nobody else ever sees this side of the lid, not very pretty:

Brita Pitcher – reinforced lid screws

I probably should have added a brass reinforcement strip around the cracked plastic mounts, but JB Weld epoxy should be strong enough for this job all by itself. Assuming, that is, it can maintain a grip on the plastic; I’m hoping the various fractures will lock it in place.

2013-11-03
Silhouette Eyeglass Repair: Broken Temple Mount

The left temple mount of Mary’s five-year-old and staggeringly expensive titanium Silhouette glasses snapped. Here’s the intact right earpiece and the broken piece from the left temple (the lens is upside-down on the paper):

Silhouette frame – broken temple part

They’re just about ideal glasses, with nothing more than two lenses and three metal bits, but that means simple repairs don’t come easily. The Official Repair Price was about $120 to install a whole new earpiece, so, seeing as how she had these customized for computer work and wouldn’t be wearing them when anybody else was around, I got the job…

First off, mask the lenses with Parafilm to avoid scuffs:

Silhouette glasses – lens protection

Then cut out the broken part shown in the first picture. It’s attached to the lens with a U-shaped bit of transparent plastic that fits into the frame holes and captures its two peg legs; I used flush-cutting pliers to carve away the plastic bar on the inside of the lens.

The lens mount fragment is flat-out not reparable, but the broken end of the earpiece lies flush against the lens and is roughly circular. Even better, a 1/16 inch brass tube from the Little Box o’ Cutoffs fit the temple end perfectly: OD = 62 mils, ID = 35 mils.

The Little Box o’ Tiny Screws produced a pair of stainless steel screws (intended for the hinges in ordinary eyeglass temples) that also fit the holes in the lens and were precisely the right length, so the overall plan came together. The screws seem a bit over 1 mm diameter and I don’t have a nut for them, but epoxy is my co-pilot…

Line up and drill a pair of 47 mil clearance holes in that piece of 62 mil OD brass tubing, leaving barely 7 mil behind on each side:

Drilling brass tube

I may have to frame that picture…

Much to my astonishment, drilling those two holes worked on the first try. I’d chamfered the end with a #1 center drill while mulling over how all this would work out.

File off the screw heads to leave a thin plate:

Silhouette frame – temple mount parts

A dry fit shows how everything hangs together:

Silhouette frame – temple trial fit

The intact earpiece holds the lens at the proper angle on a flat surface, so as long as I can keep the repair parts in place on the lens, the temple angle will take care of itself.

I scuffed up the broken end of the earpiece to encourage a good epoxy bond, bent the edges of those flat plates around the tube, and cleaned everything with acetone. Tiny dabs of JB Weld epoxy hold the screws and the temple piece in the tube, with those little machinist’s squares encouraging the lenses to stay put:

Silhouette frame – mount curing

A day later, lay the lenses face down so the screws point straight up and dab on more JB Weld:

Silhouette frame – lens mount curing

Those dots aren’t quite as round as I’d like, but they’re the better part of 2 mm OD and I’m not complaining much. Note the nice fillet around the temple piece at end of the tubing.

Pause another day for curing…

Then file off the rough edges and peel off the Parafilm. It’s a bit on the garish side, but Mary preferred the Steampunk look over a crude paint job, particularly because it’s invisible from her side of the lens:

Silhouette frame – repaired

There, now, that wasn’t so hard after all…

2013-10-31