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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

Mini-Lathe Metric Threading: 42 Tooth Gear
Going from a 21 tooth gear to a 42 tooth gear means you must reduce the remaining train ratio by a factor of two for a given thread pitch. Here’s a 42-50-45-60 train, with the same -125 ppm error as the 21-50-60-40 train and no screw / washer clearance issues between the A screw and the C gear:

Mini-Lathe change gears – 1 mm – 45-50-45-60

The original 60-40 CD pair has a 3:2 ratio, the 45-60 CD pair is 3:4, so that’s where the factor-of-two reduction happens.

The first pass at the solid model included a debossed legend:

Mini-lathe 42 tooth change gear – Slic3r

With a printed gear in hand, I realized the legend must be embossed below the surface, so as not to rub against an adjacent gear; better modeling is in order.

The general idea is to set Inkscape’s (known-good) gear generator to the correct gear parameters (module 1 → 3.14 mm circular pitch, 20° pressure angle):

Inkscape Gear Generator dialog

Save the outline as an SVG:

Inkscape Gear Generator result

If you do like I did and neatly position the gear at the bottom-left origin, all SVG viewers will show only the Quadrant I arc, probably because Inkscape sets the SVG file to display it that way. I’ve made that mistake before and maybe, someday, I’ll remember.

Load the SVG into OpenSCAD, which will find the entire gear, no matter where it falls in the coordinate space, and spike it at the origin:
```
linear_extrude(8.0,center=false,convexity=5) 
 import(file="/the-source-directory/Mini-Lathe/Change Gear - 42 teeth.svg",center=true);
```
The linear_extrude( … center=false … ) keeps the bottom of the blank at Z=0. The import( … center=true … ) puts the 2D shape at the XY origin. Because OpenSCAD centers the bounding box, gears with an odd number of teeth will be ever so slightly off-center, which would matter a whole lot more in a fancier machine tool than a mini-lathe.

All of which produces a tidy 3D gear blank:

Mini-lathe change gear – 42 tooth – SVG import

OpenSCAD ignores SVG holes, which isn’t a problem for me, because I’d rather punch the bore, keyway, and so forth programatically.

But that’s another story …
2020-05-14
Mini-Lathe Metric Threading: 32 Tooth Gear

While not strictly necessary for metric threading on a USA-ian mini-lathe, a 32 tooth gear can produce reasonable approximations, so I printed a pair from a Thingiverse collection:

Mini-lathe 32 tooth change gear – Slic3r

The model was designed for a slightly different mini-lathe, as it includes a short boss and thinner plate, but it did fit on the shaft:

Mini-Lathe change gears – 1 mm – bad 32 60 65 55

The gear mesh seemed odd, though, and comparing it with a standard 30 tooth gear and a different printed 32 tooth gear (about which, more later) showed it was definitely not compatible:

Mini-lathe change gears – 32 30 odd 32

Yes, the 32 tooth Thingiverse gear on the right is slightly smaller than the stock 30 tooth gear in the middle.

The larger 32 tooth gear (on the left, above) meshes better:

Mini-Lathe change gears – 1 mm – 65 55 32 60

Both of those trains have a 600 ppm error, so they’re definitely suboptimal compared to the results with a 21 tooth gear in the train.

The real reason you need a 32 tooth gear is for exact 25, 50, and 100 TPI threads with a 1/16 inch leadscrew. I don’t foresee much need for those around here, but you can never have too many change gears …

2020-05-13
Garden Rake Cross Bolt

Mary’s long-suffering garden rake pulled apart while we were flattening a section of what will become something like a lawn next to the garden:

Garden rake – shank and ferrule

For whatever reason, there’s no cross bolt holding the shank into the ferrule, like there should be on any tool subject to pulling force.

After marking the wide spot on the shank, a couple of good shots with a two pound hammer flattened the ferrule around it well enough to start a hole with a 3/16 step drill:

Garden rake – cross drilling

Go through the far side with a 13/16 inch drill for a generous 5 mm fit, drop a bolt into the hole while it can’t get away, tighten the nyloc nut, and it’s all good:

Garden rake – cross bolt

In fact, it’s better than it ever was, because now the shank can’t pull out until the ferrule falls off the handle. Which could happen, but I’m not averse to another bolt.

Admittedly, it’s not a stainless steel socket head cap screw, because that’d just about double the value of the rake. The handle is in such bad shape that the bolt will probably outlast the wood …

Done!

Update: The consensus says I totally missed the Ritual Invocation of the Epoxy, so:

Garden rake – epoxy fill

Now all is right with the world …

2020-05-11
Floor Lamp Height vs. Reach: Plumbing Fitting

Update: Welcome Adafruit! The reshaped elbow shown here eventually got threaded adapters for the tubing and an awful paint job.

The floor lamp with the invisible / non-tactile controls moved to a different chair, where it didn’t have quite enough reach and too much height. Knowing what was about to happen, I spliced a JST-SM connector into the wire inside the tube:

Floor Lamp – base wiring JST-SM connector

After trimming off all the extraneous bits, the larger half of the connector (male pins) fits through the tubing and the smaller half (female sockets) barely fits through the bottom bushings.

It turns out half-inch copper pipe fittings (ID = 15.9 mm) almost exactly fit the tubing (OD = 15.7 mm):

Floor Lamp – copper 45° elbow

A quick test showed the 45° (actually, it’s 135°, but we’re deep into plumbing nomenclature) positioned the lamp head too high and with too much reach:

Floor Lamp – gooseneck exercise

So shorten the tube attached to the head and deburr the cut:

Floor Lamp – tube deburring

The 45° fitting is too high and a 90° fitting is obviously too low, so cut a 20° slice out of a 90° fitting:

Floor Lamp – copper 90° elbow – 20° cutout

Cut a snippet of brass tubing to fit, bash to fit, file to hide, buff everything to a high shine, silver-solder it in place, and buff everything again:

Floor Lamp – copper 90° elbow – 20° fill strip

The 5/8 inch aluminum rods serve to stiffen the fitting, smooth out the torch heating, and generally keep things under control.

Wrap the obligatory Kapton tape around the butt ends of the tubes to fill the fitting’s oversize hole, put everything together, and it’s just about perfect:

Floor Lamp – copper 70° elbow – installed

I immobilized the fitting with black Gorilla tape, but it really needs something a bit more permanent. One of these days, maybe, a pair of setscrews will happen.

The additional reach required a little more counterweight on the far side for security, so I added the broken stub of a truck leaf spring. It should be secured firmly to the base plate, but no tool I own can put a dent in those three pounds of spring steel. Maybe it’ll merit a fancy enclosure wrapped around the base?

2020-05-09
Reversible Belt Buckle: Setscrew

The post in my reversible belt buckle popped out again, a year after punching it back in place, so it’s time to do a better job.

Grab the buckle in the Sherline vise, center on the post hole, and drill a #38 = 2.58 mm hole:

Reversible Belt Buckle – cross drilling

Tap it M3×0.5, clean out the hole, tap the post + spring back in place, dab threadlocker on the shortest M3 setscrew from the assortment, snug down on the post, and reinstall the belt:

Reversible Belt Buckle – M3 setscrew installed

Looks like it grew there, doesn’t it?

Now, as my buddy dBm will remind me, the real problem is too much weight in the saddle, but this fix should move the symptoms elsewhere …

2020-05-08
Tek Circuit Computer: Cursor Hairline Scraping

Engraving a PETG sheet with a diamond drag engraver on the Sherline and filling the scratch produces a good-looking hairline, but there’s a tradeoff between having the protective sheet pull the paint out of the scratch and having the crayon scuff the unprotected surface. This time around, I scribbled the crayon through the protective film, let it cure for a few days, then scraped the surface to level the paint and see what happens.

First, an unscraped cursor:

Tek CC – Cursor red lacquer – plain – overview

Peeling the transparent protective film:

Tek CC – Cursor red lacquer – plain – partial peel

The hairline is solidly filled:

Tek CC – Cursor red lacquer – plain – peeled

Scribbling another cursor the same way, then scraping the protective film to flatten the shredded edges:

Tek CC – Cursor red lacquer – scraped – overview

The hairline remains filled, but not as completely:

Tek CC – Cursor red lacquer – scraped – partial peel

A closer look:

Tek CC – Cursor red lacquer – scraped – peeled

Scraping the crayon off the film removes a substantial amount of paint from the hairline, but, on the upside, the protective film does exactly what it says on the box and the PETG surface remains pristine.

Both hairlines are, at least eyeballometrically, Just Fine™ for their intended purpose.

2020-05-06
End of the Thing-O-Matic

After nine years, it’s come to this:

End of the Thing-O-Matic

The Thing-O-Matic got me started in 3D printing (and blogging!), provided an education in many useful subjects, and has long since outlived its usefulness.

A view from happier times:

Thing-O-Matic Overview

Its components will live on in other projects.

One of those bittersweet moments, fer shure …

2020-05-04