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: Improvements

Making the world a better place, one piece at a time

Harbor Freight Slitting Saw Arbor
A three-pack of 100-tooth 2 inch cutoff saw blades followed me home from Harbor Freight a while ago. Although they’re intended for a craptastic HF tabletop saw, I thought they might come in handy on the Sherline for slicing lengths of brass tubing. The reviews for the saw indicate the blades are no good for steel, barely adequate for brass, and dandy for wood; they have nowhere near enough teeth for a screw cutoff blade.

None of the arbors in my collection fit a blade with a 3/8 inch hole, so a bit of lathe work produced one while the 3D printer cranked out a GPS+audio case:

Cutoff saw arbor in Sherline toolholder

The shaft is 3/8 inch drill rod and the collars are 3/4 inch drill rod, both of O1 oil-hardening steel that will remain forever unhardened, fitting into a Sherline endmill toolholder. I drilled-and-bored the collars to a slip fit on the shaft, then epoxied the rear one in place:

img_2156 – Cutoff saw arbor – parts

I drilled a 0.6 inch deep blind hole in the shaft and tapped it 10-32 all the way down for a 1/2 inch SHCS. A bag of assorted 10-32 taps produced a bottoming tap that came in handy, but I put tapping in the same category as parallel parking: I’ll walk half a mile to not parallel park the van. Couldn’t avoid it this time.

The flat on the shaft came from a bit of hand filing, which was easier than setting up the mill.

The front collar’s undercut ensures just the rim contacts the blade. The photo shows the vanishingly thin layer of epoxy on the rear collar that mooshed out as I clamped the stack together:
- Fixed (rear) collar
- Waxed paper with a 3/8 inch hole punched in the middle
- Cutoff blade
- Split lockwasher for a bit of space
- Loose (front) collar
- Socket head cap screw
After the epoxy cured, a pass through the lathe skimmed off that thin epoxy layer and trued up the fixed collar face to eliminate the last bit of wobble. The radial runout remains just enough so that one tooth tings before the others engage, but I’m not entirely convinced that’s due to the (minimal) shaft-to-blade clearance.

In use, putting the split lockwasher between the loose collar and the SHCS provides a little clamping compliance.

At some point, I’m sure this thing will come in handy…
2012-08-03
Trouser Hangers: The Good, The Bad, and The Ugly

So I finally looked at why one of the trouser hangers made a nasty gritty noise. Turns out that, no suprise, when you rub steel against steel long enough, it wears away:

Trouser hanger – abraded steel

Another hanger had a huge roller that worked wonderfully well:

Trouser hanger – elaborate roller

That one was obviously over-engineered, but a simple roller also works well:

Trouser hanger – simple roller

They cheapnified this one just a bit too much, because it’s not quite a roller any more:

Trouser hanger – ineffective roller

A bit of rummaging turned up enough hangers with working rollers, so it’s all good now…

2012-07-29
Sherline Z-Axis Home Switch Spacer
Sherline Z Axis home switch spacer

After drilling that PCB, I noticed that the Z axis saddle locking lever (which also functions as the backlash adjustment) had come loose. It turns out that if you don’t tighten the thumbscrew or it works loose, then the locking lever can turn with the leadscrew and, at the very top of the Z axis travel, can walk off the leadscrew thread.

A snippet of rectangular brass tubing epoxied to the top of the Z axis saddle solves that problem by removing 3/32 inch of precious travel. A slip of brown waxed paper (yes, harvested from the new Y axis leadscrew wrapper) kept the epoxy off the dovetail.

Just for consistency, I removed 0.09 inch from the Z axis home offset, but that really won’t make any difference.
```
HOME_OFFSET = 6.84
HOME = 6.5
```
Now, I’d put the switch in that position because the saddle jams against the preload nut exactly at the end of the switch button travel. Now I can crush the switch by manually running the Z axis beyond its Home position …
2012-07-27
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
Jacking Up The Microscope

Microscope with machinists jack

The stereo zoom microscope over the electronics bench lives on the end of long support arm that tends to be just slightly wobbly. Part of the problem is that the far end is anchored on the sponge-backed laminate flooring I put atop the bench, but it’d be slightly wobbly even with a firm base on the plywood bench top.

So I prop up the microscope with a machinist’s jack and it’s all stable & good.

This one happens to be from an ancient Starret 190 set that I accumulated along with some other tooling, but any of the cheap imitations would work just as well.

The two bubble level vials help get the microscope axis exactly perpendicular to the bench surface, which makes the difference between good overall focus and a blurred image with a single line in focus. Here the jack is vertical and the microscope is tilted slightly toward the edge of the bench; the jack has a pivot below its knurled top plate.

2012-07-02
K-26 Metal Detector: Sensor Coil Rewinding

There ought to be a survey marker pin at the front corner of the lot where it’d come in handy for locating the edge of the yet-to-be-contracted driveway paving, but if it’s there it’s been pushed below ground level. So I mooched a homebrew metal detector based on the Elenco K-26 PCB…

K-26 Metal Detector PCB

The kit included 45 feet of 22 AWG enamel wire that should have become a 5 inch diameter coil with 30 turns, but the as-built detector had a coil wrapped around a 1 foot diameter cardboard form. The coil inductance sets the oscillation frequency, which turned out to be around 300 kHz: far below the nominal 1000 kHz. So I wound 40 turns of 22 AWG magnet wire around an old CD-ROM spindle case (which is, quite coincidentally, just over 5 inches in diameter), and taped it atop the cardboard form.

The datasheet recommends a nonmetallic handle, so I swapped in a plastic umbrella support for the original metal mop (?) handle.

Rewound homebrew metal detector

The K-26 schematic looks like a common-base Colpitts oscillator, with only the most utterly absolutely vital essential components:

K-26 Schematic

In round numbers, the oscillation frequency varies inversely with the number of turns:

F = 1/(2π√(LC)) (for a simple tank)

L = stuff × N² (stuff = various constants & sizes)

F = stuff / N

The rewound coil oscillated at 350 kHz, so I spilled off a few turns at a time to produce these results and a tangle of wire on the floor:

L – µH Freq – kHz

330 350

186 535

107 711

65 840

42 1140

For the record, the coil in the photo corresponds to the last line and has 12 turns.

Contrary to what the instructions imply, trimpot P1 does not adjust the oscillation frequency. It tweaks the transistor bias for best oscillation, so it’s more of an amplitude control than anything else. I adjusted P1 while watching an oscilloscope connected across the negative battery terminal and the emitter of Q1, but you could probably use a small sniffer loop to good effect.

It draws about 2 mA, so the battery should last quite a while; labeling the switch positions should help a lot.

The oscillator produces an unmodulated carrier, so I tuned a Kenwood TH-F6A HT in LSB mode for maximum squeal. Any variation in L changes the carrier frequency and thus the pitch of the demodulated audio; an earbud just barely in one ear makes this almost tolerable.

As you should expect from the picture, that metal detector lashup is mightily microphonic, to the extent that touching a blade of grass wobbles the audio pitch and bumping the cardboard plate against an object can detune the whole affair. A bit more attention to rigid coil mounting would certainly help, but this isn’t the most stable of designs to begin with and I doubt anything will help very much at all.

The coil can detect a chunk of rebar sticking out of the ground at a range of maybe half a foot, but it’s not clear how well it will cope with buried treasures (like, oh, let’s say a survey marker pin). In any event, I must mow the grass down there before going prospecting.

2012-06-26