Ed Nisley's Blog: Shop notes, electronics, firmware, machinery, 3D printing, laser cuttery, and curiosities. Contents: 100% human thinking, 0% AI slop.
Back in 1998, we bought this house “with contents” and spent the next year sorting the heap. Among the treasures was a half-size clipboard with a black Dymo label on the clamp:
N9991W clipboard – front
And what’s obviously an airplane checklist on the back:
N9991W clipboard – back
I looked up N9991W back then and didn’t find anything useful; it was early on with the Internet, so perhaps the records weren’t so readily available. Time passed, our daughter grew up using the clipboard for this-and-that, and it accumulated the usual scuffs and doodles.
It’s a Piper Cherokee 140 built in 1967 and, after nigh onto half a century, it looks just fine, doesn’t it?
There’s no way to know how that clipboard came to rest in what was to become our basement, probably no later than the mid-1980s, but it’s good to know they’re both still around.
May it continue to land with the shiny side up and the rubber side down…
The entire Kenmore Model 158 sewing machine tilts on a pair of pivots extending from the rear of the base, just below the top surface. Mary’s slightly more recent machine has all-steel pivots:
Kenmore 158 – steel pivot pin
The older crash test dummy machine has two-part pivots, with a plastic housing molded around a steel pin:
Kenmore 158 – plastic pivot pins
Obviously, plastic was the wrong material for the cross pins that rest in the base, leading to the all-steel redesign. Sears no longer stocks replacement parts for those pins, sooo …
Both machines have a large plastic base that’s gradually disintegrating. The plan is to embed the machine frames in countertops, with those cross pins resting on plastic plugs set flush with the surface.
The frame sockets aren’t quite 1/4 inch in diameter; the rest of the hardware uses hard metric sizes, so they’re most likely 6 mm. A 15/64 inch (5.95 mm) drill bit fits snugly and a length of 0.228 inch (5.79 mm) drill rod fits loosely. The round pins are 18 mm long from the shoulder.
The square section is 8.5 mm wide, 9.5 mm tall, and 16 mm long. I have no idea what that mysterious tab on the end is supposed to do.
The cross pins are 5 mm diameter, a scant 15 mm end-to-end, stand 3 mm proud of the central block, and are centered 11 mm out from the edge of the block. I’d make them longer, to distribute the machine’s weight over more of the plugs in the countertop when it’s tilted back.
I can’t duplicate the newer forged steel pins and, for sure, they’re not good candidates for 3D printing. Perhaps:
Saw off 16 mm of 3/8 inch (9.5 mm) square stock
Blind drill 16/64 inch for the 0.228 main pin
Cross drill #12 for a 3/16 inch pin
Epoxy everything together
File off the sharp edges
For the moment, the crash test dummy sits happily on the three legs that the designers thoughtfully cast into its frame.
The handwheel on the Kenmore Model 158 sewing machine has a shiny knurled knob in the middle:
Kenmore 158 handwheel – knob
Turning the knob clockwise screws the knob inward and clamps a friction clutch that locks the handwheel to the main shaft; the motor belt drives the handwheel, the handwheel drives the shaft, and the shaft drives everything inside the sewing machine.
Remove the small screw, turn the knob counterclockwise to remove it, and you see the clutch:
Kenmore 158 – handwheel clutch – detail
Yes, the black stamped metal part is the clutch.
Those three projections around the exterior limit the knob’s travel to a bit under 1/3 turn, with the little screw you just removed traveling between two of the projections. When you reinstall the knob:
Turn it until it’s snug
Insert and tighten the screw
Done!
The two dogs in the middle project outward from the shaft notches: the bases engage the notches, the tips bears on the knob’s inner surface. Tightening the knob compresses the dogs, presses the clutch against the handwheel, and locks everything together.
It’s entirely possible to install the clutch backwards and, while it’ll come pretty close to working, it’s not quite right.
Having a NEMA 23 stepper fit almost exactly into the spot vacated by the sewing machine’s AC motor was too good to pass up:
Kenmore 158 – NEMA 23 stepper – on adapter
So I wired a power supply to an M542 stepper driver brick, connected the pulse output of a function generator to the brick’s STEP inputs, swapped motor leads until it turned the proper direction (CCW as seen from the shaft end), and turned the function generator knob:
Kenmore 158 – NEMA 23 stepper test
The object was to find the step frequency where the motor stalls, for various winding currents and supply voltages. The motor won’t have enough torque to actually stitch anything near the dropout speed, but this will give an indication of what’s possible.
With a 24 V DC supply and 1/8 microstepping (40 k step/s = 1470 RPM):
1.00 A = 11 k step/s
1.91 A = 44 k/s
2.37 A = 66 k/s
3.31 A = 15 k/s
With a 36 V DC supply and 1/8 microstepping:
1.91 A = 70 k/s
3.31 A = 90 k/s
With a 36 V DC supply and 1/4 microstepping (40 k step/s = 2900 RPM):
1.91 A = 34 k/s
2.37 A = 47 k/s
2.84 A = 47 k/s
3.31 A = 48 k/s
The motor runs faster with a higher voltage supply, which is no surprise: V = L di/dt. A higher voltage across the winding drives a faster current change, so each step can be faster.
The top speed is about 3500 RPM; just under that speed, the motor stalls at the slightest touch. That’s less than half the AC motor’s top speed under a similarly light load and the AC motor still has plenty of torque to spare.
90 k step/s at 1/8 microstepping = 11 k full step/s = crazy fast. Crosscheck: 48 k step/s at 1/4 microstepping = 12 k full step/s. The usual dropout speed for NEMA 23 steppers seems to be well under 10 k full step/s, but I don’t have a datasheet for these motors and, in any event, the sewing machine shaft provides enough momentum to keep the motor cruising along.
One thing I didn’t expect: the stepper excites howling mechanical resonances throughout its entire speed range, because the adapter plate mounts firmly to the cast aluminum frame with absolutely no damping anywhere. Mary ventured into the Basement Laboratory to find out what I was doing, having heard the howls upstairs across the house.
She can also hear near-ultrasonic stepper current chopper subharmonics that lie far above my audible range, so even if the stepper could handle the speed and I could damp the mechanics, it’s a non-starter for this task.
Given that the AC motor runs on DC, perhaps a brute-force MOSFET “resistive” control would suffice as a replacement for the carbon disk rheostat in the foot pedal. It’d take some serious heatsinking, but 100 V (or less?) at something under 1 A and intermittent duty doesn’t pose much of a problem for even cheap surplus MOSFETs these days.
That would avoid all the electrical and acoustic noise associated with PWM speed control, which counts as a major win in this situation. Wrapping a speed control feedback loop around the motor should stiffen up its low end torque.
The “Garden” trace comes from a waterproof Hobo datalogger buried a few inches underground, beneath a thick layer of chipped leaf mulch. The “Patio” trace comes from the center of the cramped space below the concrete patio, buried flush with the bare dirt floor. The “Water” trace is the temperature at the incoming water pipe from the town water main, which passes 150 feet under the front yard.
Calculated eyeballometrically, the temperature rose 7 °F in about a month.
The datalogger in the garden came from the “cold cellar” veggie storage buckets, so I don’t have a year-long record. On the other paw, it looks like the patio temperature will be a pretty good proxy for the minimum garden temperature.
I hand-cleaned the Hobo CSV files and fed the results into a Gnuplot script that’s replete with the cruft of ages:
#!/bin/sh
#-- overhead
export GDFONTPATH="/usr/share/fonts/truetype/"
ofile=Temperatures.png
echo Output file: ${ofile}
#-- do it
gnuplot << EOF
#set term x11
set term png font "arialbd.ttf" 18 size 950,600
set output "${ofile}"
set title "Ground Temperatures"
set key noautotitles right center
unset mouse
set bmargin 4
set grid xtics ytics
set timefmt "%m/%d/%Y %H:%M:%S"
set xdata time
set xlabel "Date"
set format x "%Y-%m-%d"
set xrange [:"07/15/2014"]
set xtics font "arial,12"
#set mxtics 2
#set logscale y
#set ytics nomirror autofreq
set ylabel "Temperature - F"
#set format y "%4.0f"
#set yrange [30:90]
#set mytics 2
#set y2label "right side variable"
#set y2tics nomirror autofreq 2
#set format y2 "%3.0f"
#set y2range [0:200]
#set y2tics 32
#set rmargin 9
set datafile separator ","
#set label 1 "Garden" at "05/31/2014",25 left font "arialbd,10" tc lt 3
#set arrow from 2.100,110 to 2.105,103 lt 1 lw 2 lc 0
plot \
"Garden.csv" using 2:3 with lines lt 3 lw 1 title "Garden",\
"Patio.csv" using 2:3 with lines lt 2 lw 1 title "Patio",\
"Water.csv" using 2:5 with lines lt 4 lw 1 title "Water",\
EOF
A small and defunct laser pointer emerged from the back of the workbench. There being no way to repair the thing, I filed a slit in the soft aluminum case and peeled it back to extract the guts:
Gutted laser pointer
The corrosion on the spring adequately explains the “defunct” situation; that’s the – terminal for a trio of LR44 watch batteries. The + terminal is the glossy (aluminum flashed?) molded shape with the threads, which friction-jams into the outer tube with a tiny spur for “good” contact.
Hotwiring a power supply to the appropriate terminals shows that the laser still works fine, even if the contacts are shot.
The ribbed gray plastic ring on the business end of the laser adjusts a focusing lens. Behind that lies a cylindrical lens that corrects the beam’s astigmatism. It was a nice pointer, back in the day … and might work its way into an art project, if I ever get finished with the practical stuff.
Here’s what happened when I shut down comments on posts older than a few days:
Softsolder Daily Spam Catch – 2014-04 to 2014-06
Apparently the spammers’ scripts can’t keep up with a short window and most comments happen in a few days, so this seems like a workable compromise. I know for a fact that spammers also employ humans to type comments, but that model doesn’t scale well at all.
Akismet disposes of most spam automatically, but presents me with a list of comments that it can’t classify. That list amounts to 10% of the daily catch, meaning I had to process that much junk every day just to keep up. I don’t know why Akismet can’t classify total gibberish as obvious spam and automatically delete it, but that’s how Akismet works.
As mentioned in the sidebar, send me a note to comment on an older post.
The Smell of Molten Projects in the Morning 