Category: Machine Shop

Mechanical widgetry

USB Gooseneck: Unwinding

The USB gooseneck extension consists of a spring-steel helix with an aluminum filler strip to smooth the outside:

USB Gooseneck – filler unwound

A pin vise holds the intact part of the gooseneck.

The filler unwinds easily, but the spring required several bashes with a drift punch to loosen the first coil. The pin vise can’t apply enough grip to immobilize the spring, so you (well, I) bashed more-or-less radially outward, rather than at a tangent; that’s almost as difficult to do as to describe.

After enough bashing to get a grip with sturdy needlenose pliers, the spring unwound in short sections, again applying force radially to avoid turning the gooseneck in the pin vise:

USB Gooseneck – spring unwinding

The black helix aimed off to the side seems to be plastic from the USB shell injection-molded around the connector hardware.

Chopping the spring with the tip of a hardened diagonal cutter (don’t do this with a copper-wire dike!) and bashing the tail ends back around the wire core produced a passable result:

USB Gooseneck – reshaped ends

The black thing sticking out beyond the spring seems to be the jacket around the wires.

All the conductors are the same diameter, which ~~isn’t~~ shouldn’t be particularly surprising.

2017-02-03
Screw Cutting Fixture: Not Quite Right

A stack of PCB proto boards arrived from halfway around the planet and, in a rare preemptive strike, I made some holders before I need them:

PCB Protoboard – in holder

That called for trimming eight 4-40 screws, so I also tried a first pass at a screw cutting fixture:

Screw cutting fixture – 4-40 insert

That’s an ordinary 4-40 brass insert epoxied inside a drilled hole, with a snug 4-40 clearance hole on the other side.

If I needed slightly longer screws, they’d get a jam nut on the inside, but in this case I just tightened it firmly, ran the lathe in reverse, and cut against the far side to keep the screw from working loose:

Screw cutting fixture – in use

The insert is on the left side of the fixture, just under the screw head.

Unfortunately, my faith in epoxy bonding led me astray: there’s just not enough griptivity to lock the insert inside that drilled aluminum hole. Despite my taking sissy cuts, the cutting forces pushed the insert out of its hole. I completed the mission by cutting the last four screws by hand.

The original idea for the fixture would have me turning the fixture from steel and tapping the screw hole. That puts a lot of labor into something that may get chewed up fairly quickly, so I wondered if a brass insert would suffice.

Not in that orientation, it doesn’t. Putting the insert on the other side of the fixture (to the right, away from the chuck) would have the cutting forces pushing it into the fixture, which should have been obvious from the start. So it goes.

When I must cut a larger screw, I’ll redrill that fixture, put the insert on the other side, and see how that plays.

If I turned the fixture from steel with similar drilled similar holes, I could braze / silver solder the insert into the hole: that would prevent it from turning, even if the jam nut wasn’t quite up to the task.

2017-01-30
Kenmore 158 Foot Pedal: Fine Tuning
After a week of use, Mary decided the single additional graphite disk in each stack produced a too-high initial speed when the sewing machine started up; this being a matter of how it feels injects some of trial-and-error into the repair.

Shaving a graphite disk down from 0.8 to 0.4 mm seemed entirely too messy, so I snipped squares from 0.40 mm = 16 mil brass shim stock, nibbled the edges into a polygon, and filed the resulting vertexes to produce a (rough) circle:

Kenmore 158 Foot Pedal – 0.40 mm brass shims

Each stack looks like this:
- 1.5 mm graphite disk (double-thick)
- 0.30 mm brass (original part)
- 0.79 mm graphite disk
- 0.40 brass (new part)
- The rest of the stack
Protip: dump those shards onto a strip of wide masking tape, fold gently until it’s all corners, and drop in the trash. Otherwise, you’ll pull those things out of your shoes and fingers for months…

You can get cheaper nibbling tools nowadays; I’ve had mine for decades.
2017-01-25

60 kHz Preamp: Board Holder

A cleaned up version of my trusty circuit board holder now keeps the 60 kHz preamp off what passes for a floor in the attic:

The solid model became slightly taller than before, due to a serious tangle of wiring below the board, with a narrower flange that fits just as well in the benchtop gripper:

Proto Board - 80x110 — Proto Board – 80×110

Tidy brass inserts epoxied in the corners replace the previous raw screw holes in the plastic:

Proto Board Holder - 4-40 inserts and screws — Proto Board Holder – 4-40 inserts and screws

The screws standing on their heads have washers epoxied in place, although that’s certainly not necessary; the dab of left-over epoxy called out for something. The screws got cut down to 7 mm after curing.

The preamp attaches to a lumpy circle of loop antenna hung from the rafters and returns reasonable results:

WWVB - morning - 2017-01-16 — WWVB – morning – 2017-01-16

The OpenSCAD source code as a GitHub Gist:

	// Test support frame for proto boards
	// Ed Nisley KE4ZNU – Jan 2017

	ClampFlange = true;

	Channel = false;

	//- Extrusion parameters – must match reality!

	ThreadThick = 0.25;
	ThreadWidth = 0.40;

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

	Protrusion = 0.1;

	HoleWindage = 0.2;

	//- Screw sizes

	inch = 25.4;

	Tap4_40 = 0.089 * inch;
	Clear4_40 = 0.110 * inch;
	Head4_40 = 0.211 * inch;
	Head4_40Thick = 0.065 * inch;
	Nut4_40Dia = 0.228 * inch;
	Nut4_40Thick = 0.086 * inch;
	Washer4_40OD = 0.270 * inch;
	Washer4_40ID = 0.123 * inch;

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

	Insert = [3.9,4.6,5.8];

	//- PCB sizes

	PCBSize = [110.0,80.0,1.5];
	PCBShelf = 2.0;

	Clearance = 2*[ThreadWidth,ThreadWidth,0];

	WallThick = 5.0;
	FrameHeight = 10.0;

	ScrewOffset = 0.0 + Clear4_40/2;

	ScrewSites = [[-1,1],[-1,1]]; // -1/0/+1 = left/mid/right and bottom/mid/top

	OAHeight = FrameHeight + Clearance[2] + PCBSize[2];

	FlangeExtension = 3.0;
	FlangeThick = IntegerMultiple(2.0,ThreadThick);
	Flange = PCBSize
	+ 2*[ScrewOffset,ScrewOffset,0]
	+ 2*[Washer4_40OD,Washer4_40OD,0]
	+ [2FlangeExtension,2FlangeExtension,(FlangeThick – PCBSize[2])]
	;

	echo("Flange: ",Flange);
	NumSides = 4*5;

	WireChannel = [Flange[0],15.0,3.0 + PCBSize[2]];
	WireChannelOffset = [Flange[0]/2,25.0,(FrameHeight + PCBSize[2] – WireChannel[2]/2)];

	//- Adjust hole diameter to make the size come out right

	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);
	}

	//- Build it

	difference() {
	union() { // body block
	translate([0,0,OAHeight/2])
	cube(PCBSize + Clearance + [2WallThick,2WallThick,FrameHeight],center=true);

	for (x=[-1,1], y=[-1,1]) { // screw bosses
	translate([x*(PCBSize[0]/2 + ScrewOffset),
	y*(PCBSize[1]/2 + ScrewOffset),
	0])
	cylinder(r=Washer4_40OD,h=OAHeight,$fn=NumSides);
	}

	if (ClampFlange) // flange for work holder
	linear_extrude(height=Flange[2])
	hull()
	for (i=[-1,1], j=[-1,1]) {
	translate([i(Flange[0]/2 – Washer4_40OD/2),j(Flange[1]/2 – Washer4_40OD/2)])
	circle(d=Washer4_40OD,$fn=NumSides);
	}
	}

	for (x=[-1,1], y=[-1,1]) { // screw position indexes

	translate([x*(PCBSize[0]/2 + ScrewOffset),
	y*(PCBSize[1]/2 + ScrewOffset),
	-Protrusion])
	rotate(xy180/(2*6))
	PolyCyl(Clear4_40,(OAHeight + 2*Protrusion),6); // screw clearance holes

	translate([x*(PCBSize[0]/2 + ScrewOffset),
	y*(PCBSize[1]/2 + ScrewOffset),
	OAHeight – PCBSize[2] – Insert[LENGTH]])
	rotate(xy180/(2*6))
	PolyCyl(Insert[OD],Insert[LENGTH] + Protrusion,6); // inserts

	translate([x*(PCBSize[0]/2 + ScrewOffset),
	y*(PCBSize[1]/2 + ScrewOffset),
	OAHeight – PCBSize[2]])
	PolyCyl(1.2*Washer4_40OD,(PCBSize[2] + Protrusion),NumSides); // washers
	}

	translate([0,0,OAHeight/2]) // through hole below PCB
	cube(PCBSize – 2[PCBShelf,PCBShelf,0] + [0,0,2OAHeight],center=true);

	translate([0,0,(OAHeight – (PCBSize[2] + Clearance[2])/2 + Protrusion/2)]) // PCB pocket on top
	cube(PCBSize + Clearance + [0,0,Protrusion],center=true);

	if (Channel)
	translate(WireChannelOffset) // opening for wires from bottom side
	cube(WireChannel + [0,0,Protrusion],center=true);
	}

view raw Proto Board Holder.scad hosted with ❤ by GitHub

2017-01-24

Kenmore 158: Presser Foot Tweak

After watching Mary fiddle with the shrunken presser foot screw, I tapered the tip as a guide into the hole:

Presser Foot Screw – tapered tip

A hint-and-tip (which I cannot, alas, find again) suggested making bushings to simplify trimming screws in the lathe. A rim on the bushing aligns it with the front of the jaws, the screw threads into the central hole with a jam nut locking it in place, then you can turn / shape / file the end of the screw just beyond bushing with great support and a total lack of drama.

For the moment, I just aligned the screw in the tailstock drill chuck, crunched the three-jaw spindle chuck on the screw head, backed off the tailstock, took unsupported sissy cuts, and it was all good:

Presser Foot Screw – chuck alignment

Gotta make those bushings!

2017-01-22
Pot Lid Repair

For reasons not relevant here, we (temporarily) have a set of pots with glass lids. One of lids had a remarkable amount of crud between the glass and the trim ring under the knob, which turned out to be corrosion falling off the screw. Trying to remove the screw produced the expected result:

CKC Pot Lid – broken screw in handle

For whatever reason, they used an ordinary, not stainless, steel screw:

CKC Pot Lid – corroded screw

I figured I could mill the stub flat, drill out the remainder, install a new insert, and be done with it. The knob has a convex surface and, even though this looked stupid, I tried clamping it atop a wood pad:

CKC Pot Lid – precarious clamping

Two gentle cutter passes convinced me it was, in fact, a lethally stupid setup.

Soooo, I poured some ShapeLock pellets into a defunct (and very small) loaf pan, melted them in near-boiling water, and pressed the knob into the middle, atop some stretchy film to prevent gluing the knob in place:

CKC Pot Lid – ShapeLock bedding

That’s eyeballometrically level, which is good enough, and the knob sits mechanically locked into the room-temperature plastic slab. Clamping everything down again makes for a much more secure operation:

CKC Pot Lid – clamped ShapeLock fixture

A few minutes of manual milling exposes the original brass insert molded into the knob, with the steel screw firmly corroded in the middle:

CKC Pot Lid – screw stub milled flat

Center-drill, drill small-medium-large, and eventually the entire insert vanishes in a maelstrom of chips and dust:

CKC Pot Lid – OEM insert removed

Run a 10-32 stud into an insert, grab in drill chuck, dab JB Kwik around the knurls, press in place while everything’s still aligned in the Sherline, pause for curing, re-melt the ShapeLock, and the insert looks like it grew there:

CKC Pot Lid – new insert installed

Wonder to tell, a 1 inch 10-32 screw fit perfectly through the pot lid into the knob, with a dab of low-strength Loctite securing it. Reassemble everything in reverse order, and it’s all good:

CKC Pot Lid – repaired knob

Well, apart from those cracks. I decided I will not borrow trouble from the future: we’ll let those problems surface on their own and, if I’m still in the loop, I can fix them.

2017-01-19
Kenmore 158 Sewing Machine: Another Foot Pedal Rebuild

The pedal on Mary’s most recent Kenmore 158 lost its low-speed control, which meant I must add a few more graphite / carbon disks to the stacks:

Kenmore 158 – carbon disks

The contacts needed a bit of attention, too:

Kenmore 158 – carbon contact plates – detail

Contrary to what I found in the previous rheostats, these stacks end with a double-thick graphite disk backed up by a disk of brass shimstock, all of which needed cleaning, too. No broken disks, none severely eroded, no debris, just a general shortening of the stacks; I think the disks gradually turn into carbon dioxide.

Each stack has 42 graphite disks that average 0.79 mm thick, the double-thick disks measure 1.5 mm, and the brass shims are 0.30 mm = 12 mil. The punched contacts on those brass plates stand 0.95 mm proud of the surface.

With the big graphite plugs in place, the ceramic housing had 37 mm deep holes for the disk stacks. Subtracting the 0.95 mm contact leaves about 36 mm and, seeing as how the stacks add up to just under 36 mm overall, there’s barely room for one additional disk. I added one to each stack, buttoned the pedal up, and it works perfectly again.

Good thing I have a bag of those disks from the crash test dummy machine!

2017-01-15