Ed Nisley's Blog: Shop notes, electronics, firmware, machinery, 3D printing, laser cuttery, and curiosities. Contents: 100% human thinking, 0% AI slop.
It’s easier to remove the leadscrew while dismantling the carriage and apron, which requires removing the cover from the control box containing all the switches & knobs. Come to find out the “cover” actually holds all the gadgetry onto the headstock:
LMS mini-lathe – control box interior
I want to replace the Power indicator with something visible in normal shop light; judging from the connectors and overall brightness, it’s a neon bulb inside a green housing.
Anyhow, the four screws holding cover to the headstock weren’t identical:
LMS Mini-lathe – cover screws
I thought the oddball screw was deliberate, perhaps fastening that corner to a plastic frame of some sort, but it turned out to be a quick fix for a boogered tap job:
LMS Mini-lathe – mistapped cover hole
A bag of 4 mm knurled brass inserts will arrive in a while, after which I’ll drill out all four holes and epoxy inserts in their place. Might have to use stainless hardware, just for nice…
The mini-lathe arrives covered in oil and the chuck is no exception. Wrap it in a paper towel, spin it up, let it sling out (nearly all) of the excess oil:
I got an LMS adjustable carriage stop along with the mini-lathe to simplify cutting things to length. A few tweaks make it much less annoying to use:
LMS Mini-lathe – carriage stop – crude shim
The fluorescent red tape makes the handle stand out vividly against the general clutter. It lives in the shadow of the chuck, where an extended jaw could end its life, so some protective coloration seemed in order.
The screw threaded into the lower part holds it together, but, as with the carriage retaining plates, only the outer edge clamped onto the lower part of the bed. Three layers of credit card plastic fill the gap and allow just enough compression to go from “freely sliding” to “firmly clamped” in half a turn of the lever.
The washer lets the lever turn easily on the upper block.
Remove the screw and spring from the lever to lift and properly re-index it on the internal nut.
The spring on the adjusting screw seems too long and exceedingly stiff for the task at hand. The Big Box o’ Little Springs didn’t offer a suitable replacement, so adapting / making one goes on the to-do list.
It really needs a sliding pin just to the left of the lever screw to hold the lower block in alignment, but that’s definitely in the nature of fine tuning.
Eks gave the traverse crank a few twirls, told me the gear was engaging the rack entirely too tightly, and recommended shimming the apron:
LMS mini-lathe – apron shim
Of course, he was right.
Took two 18 mil shims to make it feel right, for whatever that’s worth.
That isn’t the prettiest solution, but it’ll suffice until the ways wear a bit more, things settle in, and I can cut a proper shim to surround the bolt holes across the entire bearing surface.
You can just make out the transparent plastic sheet that serves as a chip shield around the traverse gear shaft; kudos to LMS for that upgrade.
A chip shield tube / roof over the leadscrew is in order, too.
While mulling over the DRO situation, I clamped the compound rest to the cross slide, backed the knob to the limit of the backlash, and poked feeler gauges into the opening:
LMS mini-lathe – measuring compound backlash
The backlash turned out to be around 20 mil = 0.020 inch = 0.5 mm, which seemed excessive to me, so I fiddled around with the contents of the Big Box o’ Polypropylene Sheets (harvested from various clamshell retail packages), deployed the hollow punches, performed some deft scissors work, and made some shims:
LMS mini-lathe – compound knob shims
Eventually, one of ’em offered a Good Enough combination of reduced backlash and E-Z turning to suffice for now. The proper solution involves facing off / rebuilding the fat metal washer on the right to put the bore at right angles to the bearing surfaces, but that’s another project.
The final backlash ended up around 4 mils, with a bit of drag due to the slightly irregular metal washer on the left preventing anything tighter. The cross slide knob also has a bit of backlash, but the thinnest sheets are a bit too thick.
Polypropylene isn’t the right plastic for a bearing, but it’s cheap, readily available, easily worked, and served as a bring-along project at Squidwrench…
The Little Machine Shop 5200 lathe package includes DROs on the cross slide and compound cranks. The readouts report the position of the crank, not the slide position, which isn’t a major problem on a lathe.
Unfortunately, the compound collides with the DRO on the cross slide:
LMS Mini-lathe – compound vs DRO
That is a major problem on a lathe.
When you can’t turn the cross slide more than 45° from parallel with the bed, you cannot set the compound to the (typical) 29° degrees required for (traditional) thread cutting. That’s measured perpendicular to the bed, so it would be 61° on the compound rest scale, if the scale went that high:
LMS Mini-lathe – compound way
This mess doesn’t have a trivial fix, because the DRO body under the (non-removable) display doesn’t quite clear the compound screw:
LMS Mini-lathe – compound vs DRO – bottom
As nearly as I can tell, removing the entire DRO is the only way to slew the compound beyond 45°, but the DRO replaced the usual manual scale around the cross slide knob, so there’s no analog backup.
The DRO mounts to the cross slide with three screws, so you can’t rotate it 90° to the side to get better clearance:
LMS mini-lathe – DRO mounting screws
The other four screws presumably mount the DRO encoder housing to the outer shell.
The setscrew sticking up from the sleeve anchors it to the cross slide shaft. The slit milled into the shaft captures the end of the setscrew:
LMS mini-lathe – cross slide leadscrew shaft
The knob slides over the shaft, with a screw in the end holding it in place by friction against a split lockwasher; you can apply enough torque to turn the knob under the lockwasher in either direction.
Removing the DRO doesn’t produce more cross slide travel, because the DRO body sits flush with the back side of that large disk.
I think the cross slide knob collides with the compound DRO, but I put it all back together without any further exploration.
Actual 6 inch DROs based on linear encoders seem to run $40-ish and other folks have fitted them to their mini-lathes. Verily, I don’t do much threadcutting, so I’ll just put this mess on the far back burner.
That DRO ticks me off every time I look at it, though…
About the third time I removed the mini-lathe’s change gear cover by deploying a 4 mm hex wrench on its pair of looong socket head cap screws, I realized that finger-friendly knobs were in order:
LMS Mini-lathe cover screw knobs – installed
A completely invisible length of 4 mm hex key (sliced off with the new miter saw) runs through the middle of the knob into the screw, with a dollop of clear epoxy holding everything together:
LMS Mini-lathe cover screw knobs – epoxied
The 2 mm cylindrical section matches the screw head, compensates for the 1.5 mm recess, and positions the knobs slightly away from the cover:
I built three of ’em at a time to get a spare to show off and to let each one cool down before the next layer arrives on top:
LMS Mini-lathe cover screw knobs – on platform
The top and bottom surfaces have Octagram Spiral infill that came out nicely, although it’s pretty much wasted in this application:
LMS Mini-lathe cover screw knob – Slic3r first layer
I have no explanation for that single dent in the perimeter.
The cover hangs from those two screws, which makes it awkward to line up, so I built a shim to support the cover in the proper position:
LMS Mini-lathe cover support shim – Slic3r preview
Nope, it’s not quite rectangular, as the change gear plate isn’t mounted quite square on the headstock:
LMS Mini-lathe – cover alignment block
I decided when if that plate eventually gets moved / adjusted / corrected, I’ll just build a new shim and move on. A length of double-sticky tape holds it onto the headstock.
Mounting the cover now requires only two hands: plunk it atop the shim, press it to the right so the angled side settles in place, insert screws, and it’s done.
A short article by Samuel Will (Home Shop Machinist 35.3 May 2016) pointed out that any chips entering the spindle bore will eventually fall out directly into the plastic change gears and destroy them. He epoxied a length of PVC pipe inside the cover to guide the swarf outside, but I figured a tidier solution would be in order:
The backside of the shield has three M3 brass inserts pressed in place. I marked the holes on the cover by the simple expedient of bandsawing the base of the prototype shield (which I needed for a trial fit), lining it up with the spindle hole, and tracing the screw holes (which aren’t yet big enough for the inserts):
LMS mini-lathe – cover hole template
Yeah, that’s burned PETG snot around 10 o’clock on the shield. You could print a separate template if you prefer.
The various diameters and lengths come directly from my lathe and probably won’t be quite right for yours; there’s a millimeter or two of clearance in all directions that might not be sufficient.
Don’t expect the cover hole to line up with the spindle bore:
LMS mini-lathe – view through cover and spindle
I should build an offset into the shield that jogs the holes in whatever direction makes the answer come out right, but that’s in the nature of fine tuning; those holes got filed slightly egg-shaped to ease the shield a bit to the right and it’s all good.
Heck, having the spindle line up pretty closely with the tailstock seems like enough of a bonus for one day.
The OpenSCAD source code as a GitHub Gist:
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The Smell of Molten Projects in the Morning 