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

Window Latch Cam Rebuild

One of the living room window latches stopped working and, although the correct response would be to simply replace it, the window sash already had six holes surrounded by paint scars suggesting this wasn’t the first failure.

The latch as built:

Window latch cam – as built

The stamped steel spring holder was loose on the handle arm’s square pot-metal post, due to obviously poor factory swaging during assembly. Unseen below the plate is a cam molded into the handle intended to slide the white latch plate with the stamped post (over on the left) guiding the plate around the curved track and into the recess.

I don’t have a “before” picture of the cam, but it had completely worn away against the various steel parts. The task boiled down to replacing it with something more durable, which turned out to be a reshaped M3 brass screw:

Window latch cam – test fit

The Sherline setup to remove the worn cam, with the screw in place for a test fit:

Window latch cam – Sherline setup

The vise loosely clamps the handle, mostly for alignment, with the step block clamp holding it firmly in place.

The lever arm looked like this after poking the endmill into it a few times to clear the rubble, then using a smaller endmill as a drill to get a flat-bottomed recess:

Window latch cam – milled hole

Obviously, that was accomplished with eyeballometric alignment and manual jogging.

Reshaping and trimming the screw with Tiny Lathe produced a suitable cam-like object:

Window latch cam – screw installed

I planned to epoxy it in place, but AFAICT there is no way for it to go anywhere, so I just reassembled everything in reverse order:

Window latch cam – reassembled

I brutally swaged the square post with an automatic center punch cranked to maximum throttle while forcing the spring holder firmly atop the stack. The latch now moves smoothly and everything stays properly aligned.

While that was going on, the window sash had wood pins pounded into the errant screw holes with wood epoxy filling the gaps. Aligning the latch, drilling holes in the proper spots, and screwing the latch in place proceeded as expected.

That wasn’t easy, but now I can install plastic film over those windows for the winter.

2026-10-14
Countersunk Screw Recess Fillers

For reasons not relevant here, a friend must fill several pre-drilled countersunk flat-head screw holes with brass plugs suitable for M5 screws. These proof-of-concept samples give the general idea, with the red blotch on the left marking the first attempt:

Shelf flush screw fillers – samples

He gets to make as many as needed …

The flat-head screws have an 82° included angle, so the lathe compound angle must be 41°. Tiny Lathe lacks sufficient reach to accomplish that on the front side, but cutting the back of the brass rod with the spindle running in reverse will work:

Shelf flush screw fillers – lathe setup

The quick-change tool post is aligned parallel with the lathe bed to put the tools at the proper angle.

It turns out 41° is about as far as the compound will go:

Shelf flush screw fillers – compound angle setting

This, readers of long memory may recall, is the mini-lathe with the cross-slide DRO interfering with the compound enough to prevent it from cutting ordinary 60° screw threads, which is why the angle tops out at 42° instead of 60° in both directions.

The filler needs a 5.1 mm hole for EZ clearance, which is straightforward:

Shelf flush screw fillers – drilling

That was the first attempt after I got the compound angle worked out, which is why it eventually got the red mark. You want to drill on a flat end after countersinking with a center drill. It’s also good practice to drill only a few diameters deep, rather than trying to gun-drill sufficient hole for half a dozen fillers with one poke.

Run the spindle in reverse to cut the 41° angle on the back side:

Shelf flush screw fillers – backside cutting – detail

Run the spindle forward to separate the finished filler with a cutoff tool:

Shelf flush screw fillers – parting off

The length isn’t critical, so holding a millimeter scale against the right side of the tool and eyeballing the distance from the end of the taper should suffice.

Filing to polish, deburring to finger-frendliness, and similar activities are in the nature of fine tuning.

Now for some Quality Shop Time!

2026-10-09
Bike Helmet Mirror: Always Have A Spare

As fate would have it, the telescoping stalk on Mary’s helmet mirror broke off at the ball mount a few days after I assembled another spare mirror:

Helmet Mirror Ball Mount – broken shaft

That’s the point where all the stress concentrates, but the stalk lasted almost exactly six years and didn’t owe me anything.

So I clamped the mirror+shaft+ball from a spare into the mount on her helmet, and she rode off as planned.

Once again being down to a single spare, I drilled a few more 10 mm balls:

Helmet Mirror Ball Mount – ball drilling

Cleaning up the end of the broken shaft let me shove it into a drilled ball:

Helmet Mirror Ball Mount – repaired – drilled balls

The insert and random screw came from the stub end of the broken shaft: ramming it into the cleaned-up end makes the job look Good Enough™.

Clamp the repaired stalk into the spare mount, drop the drilled balls & lathe fixture back in their bag, and maybe it’ll be another six years before they’re needed.

Life is good!

2026-08-25
Mini-Lathe 100 TPI Stacked Change Gear

Before turning the PVC conduit to the proper diameter for the Shopvac hose adapter, I set up a 20-50-32-80 change gear train for a 100 TPI finish. While the urethane adhesive cured in the hose, I fed the BC gear pair into my change gear generator:

Mini-lathe stacked change gears – 32-50T – solid model

It’s ready for the next time I cut something down to size:

Mini-lathe 100 TPI change gears

One reference suggests a 256 TPI finish for “general turning”, which works out to 20-80-20-80:

Mini-lathe stacked change gears – 20-80T – solid model

That’s just crazy talk, because the BC washer overlaps the D gear teeth:

Mini-lathe 256 TPI change gears

If all else fails and I really need a 256 TPI finish, lathes are pretty good at making washers.

2026-07-31
Shopvac Hose Adapter
Adapting a previous adapter to put a much longer hose on the Least Shopvac now lurking under the bandsaw / Sherline / lathe workbench:

Spiral Hose – 1.25in nozzle adapter – installed

The tapered adapter drags the OpenSCAD code into the BOSL2 era:

Spiral Hose – 1.25in nozzle adapter – solid model

The ID of the hose determined the OD of the lathe-turned PVC tube inside the 3D printed adapter, so a straight pipe would just slide right into both parts.

It would be possible to skip the 3D printing and make the adapter from a single piece of PVC:
- Turn one end of the conduit to fit the hose ID
- Maneuver the lathe compound to the required 1.05° half-angle
- Turn the taper to fit the crevice tool
- Clean up the original OD between the two sections
Just turning the whole pipe to a smaller OD and sliding the taper on was definitely easier, particularly given the mini-lathe’s cramped quarters with the compound nearly parallel to the bed.

A generous helping of JB PlasticBonder urethane adhesive bonds the PVC pipe inside the vacuum hose and the tapered adapter.

The as-printed taper perfectly fits the crevice tool shown in the picture and is one wrap of electrical tape smaller than another crevice tool of “the same size”. The Finesse variable handles that situation, should it matter to you.

The OpenSCAD source code:
```
// Shopvac spiral hose to 1.25 in nozzle
// Ed Nisley - KE4ZNU
// 2026-07-25

include <BOSL2/std.scad>

Finesse = 0.2;             // [-0.5:0.1:0.5]

// PVC pipe liner final OD
PipeOD = 28.5;

/* [Hidden] */

NumSides = 4*3*4;
$fn=NumSides;

Protrusion = 0.1;           // make holes end cleanly
HoleWindage = 0.2;          // make holes large enough to fit

//----------------------
// Dimensions

TAPER_MIN = 0;
TAPER_MAX = 1;
TAPER_LENGTH = 2;

Tool = [30.0,31.1,30.0] + [Finesse,Finesse,0];

FlangeOD = 37.0;
FlangeLength = 5.0;

//render()
difference() {

    union() {
        cyl(FlangeLength,d=FlangeOD,anchor=BOTTOM) position(TOP)
          cyl(Tool[TAPER_LENGTH],d1=Tool[TAPER_MAX],d2=Tool[TAPER_MIN],anchor=BOTTOM);
      }

    down(Protrusion)
      cyl(2*Tool[TAPER_LENGTH] + FlangeLength,d=PipeOD + HoleWindage,anchor=BOTTOM);

}
```
2026-07-30
Dremel Collet Chuck Handle
With the set of Dremel collets organized, I made a quartet of handles for them:

Dremel Collet Chuck Handle – group portrait

The idea came from the June/July 2026 Machinist’s Workshop, wherein I learned Dremel nuts / chucks fit on a 0.275 inch = 9/32 inch 40 TPI threaded body, drilled through 11/64 inch.

Making such a thing involved some pleasant lathe time:

Dremel Collet Chuck Handle – lathe work

The business end of the body has a slight taper to (ideally) match the collets:

Dremel Collet Chuck Handle – threaded body recess

However, the collets have tapers ranging from 20° to 35°, so I defined a 60° center drill to be Good Enough™ and got a free taper while drilling the central hole.

The collets sit in the taper:

Dremel Collet Chuck Handle – collet installed

Tightening the nut closes the collet:

Dremel Collet Chuck Handle – threaded body – nut installed

The article described a nicely turned wooden handle, but a somewhat uglier 3D printed handle is fine with me:

Dremel Collet Chuck Handle – solid model – top view

Which comes from a few lines of OpenSCAD code:
```
difference() {

  cyl(h=HandleLength,d=HandleOD,anchor=BOTTOM,texture=Knurling,tex_size=[3.0,6.0],tex_taper=0.08) position(TOP)
    cyl(h=3.0,d=HandleOD,circum=false,rounding2=2.0,anchor=BOTTOM);

  down(Protrusion) {
    cyl(h=15.0,d=ShaftOD + HoleWindage,chamfer2=2.0,circum=true,anchor=BOTTOM);
    cyl(h=2*HandleLength,d=ShaftID + HoleWindage,circum=true,anchor=BOTTOM);
  }

}
```
The variables match the threaded body to my fingers:
```
Protrusion = 0.1;           // make holes end cleanly
HoleWindage = 0.2;          // make holes large enough to fit

ShaftOD = 6.9;       // collet closer thread - 40 TPI 0.275 OD
ShaftID = 4.3;       //  … internal clearance

HandleOD = 15.0;
HandleLength = 45.0;
Knurling = "trunc_diamonds";
```
The motivation for all this was to put the smallest taps in a holder suitable for delicate jobs. The smallest chuck on my real tap driver bottoms out on an M3 tap and can’t grip the M2 tap:

Dremel Collet Chuck Handle – M3 vs M2 taps

I try very hard to not tap small holes, but sometimes you gotta do what you gotta do and now I’m better prepared.

Incidentally, the first threaded body I made absolutely did not fit the Dremel nuts. After eliminating everything else, I discovered I’d set up the lathe change gears with a 20-65-45 train, rather than the 20-65-50 train required for 40 TPI with the lathe’s 16 TPI leadscrew.

Protip: Even the best threading job (which I didn’t do on any of those things) can’t make a 36 TPI screw fit into a 40 TPI nut.
2026-07-16
Monitor Arm Tilt Adjustment: Bad Part Repair

The tilt (it’s really “pitch”, but I can’t make a case for being that pedantic) adjustment on a recently arrived monitor stand / arm was nonfunctional, because the metal clamp had been bent about a millimeter too narrow to fit the plastic core. This is how it should look:

Monitor tilt adjustment – installed

As delivered, the plastic core was 32-ish mm wide and the gap at the base of the metal clamp was 31 mm, so the clamp arms stuck out at an angle on both ends of the core .

Because the cap screw bottomed out on the threads in the far side of the clamp, it couldn’t be tightened enough to force the clamp arms against the core.

Well, if the core is a millimeter too large for the clamp, shortening it should solve the problem; I can always shorten the screw if it comes to that.

Quick! To the mini-lathe:

Monitor tilt adjustment – lathe setup

Shaving half a millimeter from each side:

Monitor tilt adjustment – shaved

Twirling a deburring bit in each hole got rid of the swarf.

Rather than trimming the cap screw, a pair of fender washers keep it from bottoming out. With the core fitting into the clamp, the arms grip the core firmly on both sides with plenty of friction:

Monitor tilt adjustment – tweaked

I’ve bought this brand of arm before and the most recent pair have definitely been cheapnified from earlier ones. Because only one had a bad tilt clamp, the OEM may be in the middle of a changeover and shipped it with mismatched parts.

I wonder how many stands / arms get returned because they just don’t work?

2026-03-13