Posts Tagged Mini-lathe
Cheese Slicer Rebuild
Posted by Ed in Home Ec, Machine Shop on 2018-11-05
The cheese slicer frame looked much better after sandblasting with 220 aluminum oxide grit:
Cheese slicer – sandblasted
The flower bed outside the Basement Laboratory door seems a bit dusty, though.
Slathering it with JB Weld steel-filled epoxy went reasonably well:
Cheese slicer – JB Weld curing
JB Weld is much much more viscous than the clear XTC-3D I used last year and the final coating, while smoother than what you see here, has too many sags and dents to say “good job”. I didn’t bother coating the upper tips, because the epoxy will wear off from my morning KP.
The aluminum roller turned on those bare stainless steel screws in the tray, with the threads chewing into the roller bore. While the epoxy was curing, I drilled out the roller to remove most of the ridges:
Cheese slicer – drilling roller
Cut a pair of stainless screws slightly longer than the old screws, then turn the threads off to make a shaft:
Cheese slicer – screw reshaping
The lathe spindle runs in reverse, so the cutting force tends to tighten the screw in the nuts. The big old South Bend lathe had a screw-on chuck and didn’t really like turning backwards.
The new screws won’t win any beauty prizes, but they get the job done:
Cheese slicer – screw shafts
Turn a Delrin rod to a press fit in the drilled-out roller:
Cheese slicer – turning Delrin bearing
Part it off, repeat, ram them into the roller, then drill to a loose fit around the smooth-ish screw shafts:
Cheese slicer – drilling Delrin bearing
Reassemble in reverse order:
Cheese slicer – rebuilt
Looks downright industrial, it does.
Stipulated: this makes no economic sense, apart the simple fact we appreciate utensils that just work.
Doorknob Repair
Posted by Ed in Home Ec, Machine Shop on 2018-10-22
The outer doorknob on the kitchen pantry became very loose and sloppy, with the screw holding the inner knob on the shaft remaining snug. Obviously, something else was wrong inside the door.
A spring clip should retain the outer knob in the escutcheon:
Doorknob – worn retaining flange – detail
The flange holding the clip has worn away, letting the clip fall loose. A side view shows the problem:
Doorknob shaft – worn retaining flange
Yes, the knob’s chrome plating is in sorry shape after six decades of wear. I’d rather keep using a solid knob, instead of force-fitting some contemporary half-assed / cost-reduced junk into the door.
Reference: beausage. I say it “beau-sage”, the beauty that comes from usage.
The shaft consists of three triangular rods, with the setscrew on the inner knob pressing against the smaller rod to lock all three of them in place and eliminate all rattle & play:
Doorknob shaft – detail
A tapered pin (!) locks the three shaft rods into the outer knob:
Doorknob shaft – tapered pin
Some doodling, most of which turned out to be irrelevant, captured the essential dimensions and suggested how to replace the flange:
Doorknob – dimension doodles
The stock is 11/16 inch O-1 oil-hardening rod, forever to remain unhardened:
Doorknob – retainer ring boring
I drilled a few holes to get up to 1/2 inch, the largest drill bit I have and just barely clearing the the boring bar.
With the hole bored out to fit the end of the knob, cut it off:
Doorknob – retainer ring cutoff
Trial-fit the ring on the knob with the spring clip:
Doorknob – retainer trial fit
Reinstall the shaft, tap in the retaining pin, then epoxy the ring in place with the knob supported from below to eliminate having to fiddle with the spring clip:
Doorknob – retainer ring epoxy
Add a few dots of oil here & there, reinstall the parts in reverse order, and the knob works perfectly again. Still looks heavily used, of course, but that’s OK.
They definitely don’t make ’em like that any more …
Presta Valve to Schraeder Hole Adapter
Posted by Ed in Machine Shop, Recumbent Bicycling on 2018-08-02
The front rim on my Tour Easy developed a distinct bulge, of the sort usually caused by ramming something, but I’m not Danny McAskell and the bulge got worse over the course of a few weeks, suggesting the rim was deforming under tire pressure. Having ridden it upwards of 35 k miles with plenty of trailer towing and too much crushed-stone trail riding, the brake tracks were badly worn and it’s time for a new rim.
An Amazon seller had an identical (!) rim, except for the minor difference of having a hole sized for a Schraeder valve stem, rather than the Presta valves on the original rims. One can buy adapters / grommets, but what’s the fun in that?
The brake track walls are 1.5 mm thick on the new rim and a scant 1.0 mm on the old rim, so, yeah, it’s worn.
A few measurements to get started (and for future reference):
Presta to Schraeder Adapter – dimension doodle
If you don’t have an A drill, a 15/64 inch drill is only half a mil larger and, sheesh, anything close will be fine.
Introduce a suitable brass rod to Mr Lathe:
Presta-Schraeder Adapter – parting off
Break all the edges and drop it in place:
Presta-Schraeder Adapter – installed
One could argue for swaging the adapter to fit flush against the curved rim, but commercial adapters don’t bother with such refinements and neither shall I.
The 7.0 mm length got shortened to fit flush with the center of the rim:
Presta-Schraeder Adapter – valve stem installed
It’s brass, because the rim is heaviest on the far side where the steel pins splicing the ends live, and, with the tube & tire installed, the rim came out almost perfectly balanced. Which makes essentially no difference whatsoever, of course.
The shiny new rim sports shiny new reflector tape (from the same stockpile, of course).
That was easy …
MPCNC: Ground Shaft Pen Holder
Posted by Ed in Machine Shop on 2018-04-18
Drilling a pair of holes into a length of ground steel shaft turned it into a holder for a Sakura Micron pen:
DW660 Pen Holder – printed plastic vs ground steel
The aluminum ring epoxied to the top keeps it from falling completely through the linear bearing.
The hole sizes are the nearest inch drills matching the pen’s hard metric sizes:
Ground 12 mm rod – Sakura pen drill diameters
While I was at the lathe, I turned another layer of epoxy on the printed holder down to a consistent 11.95+ OD. It fits the bearing nearly as well as the steel shaft, although it’s not quite as smooth.
The steel version weighs about 20 g with the pen, so it applies about the same downforce on the pen nib as the HP 7475A plotter. The force varies from about 19 g as the Z axis moves upward to 23 g as it move downward, so the stiction amounts to less than 10% of the weight:
DW660 Pen Holder – ground shaft
However, the more I ponder this setup, the less I like it.
When the Z-axis moves downward and the nib hits the paper, it must decelerate the weight of the pen + holder + ballast within a fraction of a millimeter, without crushing the nib. If the pen moves downward at 3000 mm/min = 50 mm/s, stopping in 0.3 mm requires an acceleration of 4.2 m/s² and a 20 g = 2/3 oz mass will apply 0.08 N = 0.3 oz to the nib. Seems survivable, but smashing the tip a few hundred times while drawing the legends can’t possibly be good for it.
Also, the tool length probe switch trips at 60 (-ish) g, which means the pen can’t activate the switch. Adding a manual latch seems absurd, but you can get used to anything if you do it enough.
Quilting Ruler Pivot Pin Sharpening
Posted by Ed in Home Ec, Machine Shop on 2018-02-18
Mary mentioned the pivot pin supplied with a quilting ruler tended to hang up on the layers of fabric and batting in the quilt squares she’s been making. A quick look showed the pin bore a remarkable resemblance to an ordinary thumb tack:
Ruler Quilting Pivot Pin – as delivered
I reset the pin shaft perpendicular to the head, grabbed a small brass tube in the lathe tailstock, inserted pin in tube, grabbed the head in the chuck, ignored a slight radial offset, and attacked the pin with fine files and sandpaper:
Ruler Quilting Pivot Pin – sharpened
The lathe chuck seemed the easiest way to firmly hold the head; I rotated the chuck by hand while filing.
Most of the remaining scratches go mostly parallel to the pin, but it really didn’t work much better than before. We decided polishing the pin wouldn’t improve the situation enough to make it worthwhile.
That’s the difference between sharp and keen, which cropped up with the cheap ceramic knife from a while ago. The point may penetrate the fabric, but the shaft can’t get through the tight weave.
She’s now using a scary thin and pointy embroidery pin, having successfully rebuffed my offer to mount it in a suitable base.
M2 Thermistor Rebuild
Posted by Ed in Electronics Workbench, Machine Shop on 2018-02-07
The MAXTEMP error killing the M2 while printing the bar clamp mounts (probably) came from a short in the thermistor pellet that lowered the thermistor resistance and raised the calculated temperature. I manually heated the extruder and, although the temperature stabilized at 250 °C, the history plot showed irregular downward jogs from increasing resistance. Whenever this constellation of symptoms appears on the M2 forums, I always recommend ordering another thermistor or two, so …
Start by turning a 1/8 inch OD brass tube down to 3.00 mm, parting off a suitable length, facing the ends:
M2 – thermistor brass tube turning
Countersink the ends just for pretty.
The tube should be a slip fit in the hot end:
M2 – hot end thermistor – turned brass tube
While I had the hot end on the bench, I scuffed the nozzle to remove (most of) the baked-on crud:
M2 – nozzle silicone – cleaned nozzle
The plan is to seal the thermistor bead inside the tube with JB Weld epoxy, which I’ve verified (!) to work at extrusion temperatures, depending on the epoxy to insulate the wiring and immobilize all the pieces.
Harvest the original wire harness from the defunct thermistor, solder to the bead, lay out guide lines:
M2 – thermistor – assembly 1 layout
Slobber epoxy over everytyhing, fill the tube, insert bead into tube, stabilize with tape:
M2 – thermistor – assembly 1 curing
Verify connectivity through the thermistor and isolation from the brass tube, then return upstairs to warm up thaw out while the epoxy cures.
At this point, the observant reader should be thinking “Uh, Ed, that bead looked a tad large. Are you absolutely sure … ?”
Halfway up the basement stairs I realized I’d meticulously entombed a 10 kΩ thermistor, not the 100 kΩ thermistor used in the M2’s hot end. You can easily verify the resistance, as I did, with a quick web search; I have hella-good SEO for some specific topics.
Back to the lab …
Fortunately, JB Weld has a pot life over an hour, so extract the wrong bead, unsolder, install the right thermistor using snippets of insulation harvested from the original wiring, realign components:
M2 – thermistor – assembly 2 layout
Reapply epoxy:
M2 – thermistor – assembly 2
Re-verify resistances, return upstairs, fast-forward through the night, have another good idea …
Lathe-Turned Drugs
Posted by Ed in Home Ec, Machine Shop on 2018-02-03
For reasons not relevant here, I had to wake up a New Old Stock bottle of an eye drug dispensed as a suspension in a small bottle:
Lathe turned drugs
A few hours at 50 RPM and it’s all shook up.
Blowback