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: Mini-lathe

Tweaking an LMS 5200 Mini-Lathe

M2 Thermistor Rebuild

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 …

2018-02-07
Lathe-Turned Drugs

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.

2018-02-03
Umbrella Strut Splinting, Round Two

Two more umbrella struts snapped and required the same repair, but, having drained all the suitable snippets from the Box o’ Brass Cutoffs, some lathe work was in order:

Umbrella strut splint – cutting

I used the carbide insert in the mistaken belief it’d be less grabby, then applied the cutoff tool.

Break the edges, slide splints over the ribs, slobber epoxy on the struts, slide splints into place, apply masking tape for a bit of compression & alignment, and let it cure:

Umbrella strut splint – curing

Three down, five to go …

2018-01-29
Lathe-Turned Almond Butter

Pure almond butter comes with the somewhat stilted admonition “Must stir product. Oil separation occurs naturally.” I’d just opened a new jar and was busily (and laboriously) stirring when I realized we have the technology:

Lathe-turned Almond Butter

I installed the chuck’s outside jaws to grab the jar lid.

About three hours at 50 rpm, the lathe’s slowest speed, did the trick. We now have the smoothest, creamiest, best-mixed almond butter ever.

In a month or so, I’ll chuck up an unopened jar to see how well it works without any manual intervention.

2018-01-07
T-shirt Shop Rags

Small wipes made from worn-out cotton t-shirts absorb most shop liquids, don’t overstay their welcome after short projects, and prevent the deep emotional attachment leaving swarf in the clothes washer. Scissors cutting gets tedious, so mooch a rotary cutter and slash away:

T-shirt shop rags

Synthetic fabrics don’t work nearly as well as cotton, so pay attention to the labels.

2017-10-28
Shortening a 2MT-to-1MT Morse Taper Sleeve

The hulking 1/2 inch Jacobs chuck is grossly oversized for most of the holes I poke in things spinning in the lathe. I already have several smaller Jacobs chucks for the Sherline’s 1 MT spindle, so I got some Morse Taper Sleeve Adapters for the mini-lathe’s 2MT tailstock. They’re longer than the “short” 2MT dead center:

1MT to 2MT adapter – vs 2MT dead center

Because they’re longer, the tailstock ram loses nearly an inch of travel it can’t afford.

So I hacksawed the taper just beyond the opening at the tang and faced off the ragged end:

1MT to 2MT adapter – facing

The steady rest jaws don’t match the Morse taper angle, but they’re way better than assuming the nose of the Jacob chuck can hold such an ungainly affair.

The short 1MT taper on the drill chuck doesn’t extend to the opening: when it’s firmly pushed into the socket, there’s no simple way to eject it. So, drill a small hole for a pin punch to pop it out:

1MT to 2MT adapter – center drilling

I hate hammering on tooling, which means I must eventually enlarge the hole to clear a 5 mm bolt, make a square-ish nut to fit inside the slot, and gimmick up a plug for the 1/4-20 socket in the 1MT taper (used by the Sherline mill drawbar). More work than I want to take on right now, but it’ll provide some Quality Shop Time.

If the truth be known, I also got a 3/8-16 thread to 2MT adapter for the mid-size Jacobs chuck seen in the pictures, thus eliminating the thread-to-1MT adapter and plugging the chuck directly into the tailstock. The 1MT adapter will come in handy for the least Jacobs chuck; although LMS has a 0JT-to-2MT adapter, the less I monkey with that tiny taper, the better off we’ll both be.

2017-10-20
Plotter Grit Wheel Bushings

As part of recommissioning the lathe tailstock, I made some bushings to adapt Dremel sanding ~~drums~~ bands to an 8 mm shaft (in imitation of the grit drive wheels on the HP plotter):

Plotter Y bushing – samples

They’re not all the same because the lad who’s building the plotter got to turn out his own bushings. We think the knurled version, with a setscrew to lock it on the shaft, will work better than adhesive-bonding the drum to the bushing.

The overall process starts with a rough 1/2 inch aluminum rod. Skim-cut to get a concentric surface and face the end smooth:

Plotter Y bushing – facing

Then knurl it:

Plotter Y bushing – knurling

The skim cut makes the aluminum rod a loose fit inside the sanding band, but the knurling enlarges the diameter enough to make it a firm press fit and I think it’ll have enough traction to stay in place.

FWIW, the wheels in the LittleMachineShop knurling tool seem pretty bad: the central holes aren’t quite concentric with the cutting edge, the bores are a loose fit on the mounting screws, the wheels are much narrower than the slots they ride in, so they wobble uncontrollably. It’s not a fatal flaw, but they definitely produce a sub-par knurl.

Face off the front, cut the knurling down at each end, then part it off:

Plotter Y bushing – cutoff

Clamp it in the Sherline mill, laser-spot the edges, set the origin in the middle, and center drill:

Plotter Y bushing – center drill

Drill and tap for a teeny M3 setscrew:

Plotter Y bushing – tapping

Clean out the chips, debur the hole, install the setscrew, and you’re half-done: do it again to get the second drive roller!

2017-10-19