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.

Category: Machine Shop

Mechanical widgetry

Maximum PCB Platen: Hold-Down Screws

The whole point of tweaking the Sherline was to get it ready to drill the Wouxun KG-UV3D GPS+voice PCB. While setting up for that, I drilled two #5 holes in the maximum-size PCB platen for 10-32 socket head cap screws to hold it to the tooling plate:

Sherline with maximum PCB platen

The sloppy hole fit lets the platen align to the tooling plate with the outer two 6-32 screws on the back edge.

Most of the PCB boards I make aren’t nearly as wide as the platen, which means the new SHCS won’t get in the way. The screws require a nut (as a spacer) to keep them from bottoming out on the Sherline’s table underneath the tooling plate and the washers are just because I can’t do it any other way; I should just shorten the screws and store them with the platen.

Masking tape holds small PCBs to the platen reasonably well, probably because I use an unreasonably high 50 mil travel clearance. I have a defunct dehumidifier that might make a dandy low-volume vacuum pump to eliminate any lifting in the middle: a project that has been on the to-do list for far too long…

2012-07-23
Sherline Tooling Plate: Protecting the Tapped Holes

While I had the tooling plate off, I cleaned the crud out of the tapped holes and ran a handful of 1/4 inch stainless steel 10-32 setscrews just below the surface:

Sherline tooling plate with setscrews

They’re pretty much invisible, of course, but they’re all present. FWIW, you need a 3/32 inch hex wrench for 10-32 setscrews.

In the event that I gouge the aluminum surface (you can see the odd ding and blind hole) through a setscrew, I’ll regret doing this. Not having to remove the plate to dig swarf out of the last clamping hole after carefully aligning a part seems like a win.

2012-07-20
Sherline CNC Mill Y Axis Home Switch: To The Front!
Reassembling the mill provided an opportunity to move the Y axis Home switch from the rear of the axis to the front. The key discovery happened during the teardown: I can get the saddle off the Y axis dovetail by removing the gib, without sliding it off the front, which means a front switch can remain firmly glued in place.

A few random hunks of steel and a wire nut held the switch in position while the epoxy cured:

Mounting Y axis home switch

The switch actuator bottoms out with the saddle just touching the preload nut, so the saddle can’t dislodge the switch: the switch trips just before the saddle hits the nut, at which point all motion stops and the motor stalls.

Moving the switch means I can remove all the gimcrackery that poked the rear switch with the tooling plate in place; I was never happy with that setup. I also removed the small block that trapped the rear end of the Y leadscrew, under the assumption that, as I haven’t yet dropped anything on the leadscrew, I probably won’t. That adds about 1/4 inch to the maximum travel and allows the tooling plate to whack into the column.

The switch wire runs along the stepper cable, a tidy technique that hasn’t introduced any glitches into the shared Home signal from the X axis drivers:

Sherline mill – X and Y axis home switches

The Y axis now seeks the Home switch in the positive Y direction, so that stanza in Sherline.ini looks like this:
```
[AXIS_1]
TYPE = LINEAR
MAX_VELOCITY = 0.400
MAX_ACCELERATION = 5.0
STEPGEN_MAXACCEL = 10.0
SCALE = 16000.0
FERROR = 0.05
MIN_FERROR = 0.01
MIN_LIMIT = -0.5
MAX_LIMIT = 4.90
BACKLASH = 0.003
HOME_IS_SHARED = 1
HOME_SEQUENCE = 2
HOME_SEARCH_VEL = 0.3
HOME_LATCH_VEL = 0.016
HOME_FINAL_VEL = -0.4
HOME_OFFSET = 5.125
HOME = 5.0
```
2012-07-19
Reworking Sherline Anti-Backlash Nuts
The new Y axis anti-backlash nuts for the Sherline mill have a countersink on the end that fits into the saddle. The nut on the left is as-delivered (I bought two) and the nut on the right is after cleanup:

Sherline Y axis anti-backlash nuts – original vs cleared

The thread was munged enough to jam the leadscrew; it started fine from the knurled end, but wouldn’t emerge from the countersink. This being a left-hand thread, I couldn’t just run a tap through the nut, so clearing the thread required:
- Some tedious handwork to clear enough of a path until …
- I could force the nut over the old leadscrew, which re-formed the thread enough that …
- More tedious handwork could remove the debris and bent brass
After that, the OD of both nuts was slightly oversized: 0.316 inch, which didn’t fit in the 5/16 inch (0.3125) bore. So I mounted the nut on the old leadscrew, ~~took advantage of the fact that a left-hand thread gets tighter with cutting force from the lathe bit~~ [Edit: wrong! See comments], and turned it down just a hair:

Turning down anti-backlash nut OD

Purists will quibble that I should have used the four-jaw chuck. Turns out the three-jaw has under 1 mil of runout, which is as good as one could possibly want in light of the bearings.

The X axis nuts were fine, so I suspect a recent production run had a bit of a tooling problem.

[Update: The mail brings replacement nuts that look just fine. Must have been one of those glitches. No hard feelings!]
2012-07-18
They Don’t Make ‘Em Like They Used To: Hinges
Door hinge with pin punch hole

A hinge started squeaking, which required nothing more than a long pin punch, a soft hammer, and a dab of oil.

The unplated steel hinges in our house date back to the middle of the last century and all of them have a convenient hole in the bottom for a pin punch: much fancier than the raw edge of the folded frame and the butt end of the hinge pin. You drive the hinge pin upward with a few taps, lube it, and tap it back in again with a soft hammer (perhaps against a folded rag), and you’re done.

On the other side of door, however, lies one of our follies. For reasons that made perfect sense at the time, the hallway has five different shades of white paint:
- Flat walls
- Eggshell ceiling
- Gloss trim
- Semigloss front door
- Epoxy hinges
The hallway has three branches, two openings, and ten doors. The white really sets off the hardwood floors and doors, while brightening what would otherwise be a rather dim area, but never, ever again will we make that mistake.

On the other paw, the hinges came out well. I took them off all those doors and jambs, cleaned the steel, gave ’em two rattle coats of white epoxy, and reinstalled. Much nicer than contemporary “shiny brass” plating or raw steel.
2012-07-14
Wouxun KG-UV3D Battery Capacity

After I get the next GPS+voice interface running on the (yet-to-be-bought) Wouxun KG-UV3D radio, a pair of reasonably new 1A17KG-3 7.4 V 1.7 A·h lithium battery packs will be floating around with nothing to do; the GPS interface connects an external battery to the radio, so there’s no need for the OEM battery.

Before doing anything else, it’d be useful to know the actual capacity. The pack has flush terminals, so I snipped off two lengths of shield braid, jammed a wire into each one, and taped them in place:

Battery pack – braid contacts

That obviously wasn’t going to last, so I added some closed-cell foam:

Battery pack – foam compression

And then, ever so gently, crunched a clamp around the whole mess:

Battery Pack – clamped contacts

Crude, but workable, although the ragged start to the test showed I was too gentle. Another click of the clamp and everything settled down just fine:

Wouxun Pack

In round numbers, the pack delivers 1.6 A·h down to 7.0 V and then falls off very rapidly to the 6.0 V that ended the test.

A string of three red / amber LEDs adds up to 3×1.9 = 5.7 V. A dumb DC blinky light running from 7.4 V has 77% efficiency, which isn’t all that bad, and 70% at the start. A current-regulating switcher might give 85% to 90% at the cost of considerable circuit complexity and wouldn’t be feasible for four independent blinky channels.

The starting voltage, fresh from the charger, is just shy of 8.5 V, which is why I figured I could get away with 9 V from the external pack through the GPS interface. So far, so good.

Obviously, if those packs are to be useful, I must conjure up a better battery holder. Having already designed a battery-shaped case for the GPS interface, it should be easy enough to build a radio-shaped mount for the pack.

2012-07-11
Sherline Leadscrew Nut Removal
The Y axis on my Sherline CNC mill has developed about 8 mils of backlash, a bit more than seems reasonable. Some poking around shows that the anti-backlash nut is loose while in the middle of the leadscrew and snug while at either end, which suggests the leadscrew thread is also worn. That’s no surprise, as I didn’t figure out that having a bellows over the leadscrew was a Good Thing until, let us say, considerably later than I should.

If I must replace the leadscrew, I may as well take the whole XY assembly apart, clean everything, and replace the consumables. So I ordered a sack o’ parts from Sherline; they’re all cheap and readily available. The overall index has the exploded diagrams and the parts list for my mill boiled down to:
- 54161 Y axis leadscrew (9 inch)
- 50140 Y axis anti-backlash nut
- 50200 Y axis nut
- 50171 X axis leadscrew
- 50130 X axis anti-backlash nut
- 40890 X axis nut
- 50150 anti-backlash lock
The only gotcha: nowhere (that I can find, anyway) is it written how to get the leadscrew nuts out of the stage. It turns out that the holes through the stage aren’t uniform: the X narrower on the right and the Y on the front, so you must drive the X axis nut out to the left and the Y axis nut out to the rear. The counterbore is visible just behind the anti-backlash nut if you know what to look for, so you’re driving the axis nut away from the backlash nut.

On the X axis:

X axis leadscrew hole counterbore

On the Y axis:

Y axis leadscrew hole counterbore

Trust me on this: you cannot drive a 5/16 inch nut through a 19/64 inch counterbore. If you have a 19/64 inch transfer punch, that’s a dandy way to get the nuts out.

The easiest way to loosen the socket head cap screw holding the flex coupling to the leadscrew is to grab the coupling in a lathe chuck (with the leadscrew protruding into the headstock) and then apply the hex key:

Loosening leadscrew bolt

They used red (high-strength) Loctite on all the leadscrew bolts, as well as on the tapered joint between the leadscrew and the flex coupling, and on the bearing preload nut… so I will, too.
2012-07-10