By the Universal Principle of the Conservation of Perversity, the base of the floor lamp just barely doesn’t fit under the edge of the Comfy Chair:
Well, I can fix that!
The feet descend from the fuzzy felt feet on the plant shelves, with the hex head socket transmogrified into a circle to match the chair feet. The support structure grew a flat plate to ensure it doesn’t pull loose from the platform:
Print ’em out, stick the felt in place:
Lift the chair (maybe with a small prybar atop some plywood to protect the floor), position the feet, lower gently: done!
While the M2 was warm, I ran off another set for the other Comfy Chair, just for symmetry.
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:
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:
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):
Save the outline as an SVG:
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:
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:
OpenSCAD ignores SVG holes, which isn’t a problem for me, because I’d rather punch the bore, keyway, and so forth programatically.
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 …
Mini-lathes sold everywhere except the USA have hard-metric leadscrews with a 1.5 mm pitch, so they can cut metric threads without any trouble at all. USA-ian mini-lathes have hard inch leadscrews with a 1/16 inch pitch and require gymnastics to cut decent metric threads.
For inch threads:
For metric threads, it’s upside-down and converted:
Including a 21 tooth change gear at A or C in the train will get closer to metric threads, but the stud holding the B-C gears on my lathe imposes a minimum B gear size. Here’s a 1 mm thread with a 21-30-45-50 train:
You can interchange the AB and CD gear pairs, but the CD pair also has a minimum spacing:
If it worked, the 1 mm thread would be off by -125 ppm, which is surely close enough.
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):
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:
So shorten the tube attached to the head and deburr the cut:
The 45° fitting is too high and a 90° fitting is obviously too low, so cut a 20° slice out of a 90° fitting:
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:
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:
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?