Tag: Mini-lathe

Tweaking an LMS 5200 Mini-Lathe

Machine Shop, Oddities

123 Block Links: Cap Screw Head Pins

Contemplating a project using a small saw in the Sherline suggested that attaching the workpiece to the side of a 123 block would simplify the machining. My blocks have a centered quintet of 3/8-16 tapped holes through the 2×3 side, all the remaining holes are untapped, and it has no smaller holes. The hole spacing doesn’t match the Sherline tooling plate, but the T-nut slots in the underlying table would suffice.

Rather than run long 10-32 screws through the entire block, It Would Be Nice to use short screws from, say, the nearest holes:

123 Block Links - assembled
123 Block Links – assembled

I cannot possibly be the first person to have this idea, but the obvious keywords don’t produce any useful results on The Intertubes, other than a link to a different (and far more complex) block with counterbored holes of various sizes.

Update: Jason found a video about building those blocks and somebody else built some pins similar to mine. Nope, I’m definitely not the first person to have this idea!

Further doodling produced some useful dimensions:

123 Block Links - SHCS head pin doodle
123 Block Links – SHCS head pin doodle

The holes through the blocks probably came from a 5/16 inch drill, the 75% thread depth diameter for the 3/8-16 taps used on the threaded holes. They’re distorted, full of debris, and hardened enough to kill a file, so I eventually settled on 8.2 mm pins that pass through most of the holes.

The socket head screws seat at the pin axis, because the pin diameter is scary close to the counterbore diameter and I didn’t see much point in finesse. I started with a half-inch aluminum rod and peeled it to size, because it simplified the clamping and I have a bunch of them.

The pins are 3/4 inch long to leave a little space on either side of the 1 inch deep holes. I started with comfort marks along the length of the rod:

123 Block Links - laser alignment
123 Block Links – laser alignment

Center-drill so the clearance drill doesn’t skitter off the top:

123 Block Links - center drilling
123 Block Links – center drilling

The counterbore calls for a 0.204 inch = #6 drill, just slightly larger than the #7 clearance drill for a 10-32 screw:

123 Block Links - counterbore
123 Block Links – counterbore

I touched off the counterbore flutes on the sides of the hole, then drilled downward half the 12.8 mm actual rod diameter:

123 Block Links - 10-32 SHCS test fit
123 Block Links – 10-32 SHCS test fit

Lower the counterbore into the hole again, relax the vise enough to let the rod slide, jog the spindle to X = -25.4 mm, and tighten the vise again:

123 Block Links - index setup
123 Block Links – index setup

I figured I needed four pins, tops, so make half a dozen to be sure:

123 Block Links - all c-bored
123 Block Links – all c-bored

Stick the rod in the mini-lathe chuck, add some comfort marks, and prepare to peel it down to 8.2 mm:

123 Block Links - lathe setup
123 Block Links – lathe setup

Having done the lathe work during a Squidwrench remote meeting, I have no pictures of the process, but it goes a little something like this:

  • Peel off 0.5 mm at a time, stopping just beyond the mark on the left
  • Mark 3/8 inch on each side of the hole center
  • Face the end
  • Chamfer the rim with a file
  • Clean up the body hole and counterbore
  • Part the pin off a bit to the left of the mark
  • Remove the rod
  • Chuck the pin with the cut off end outward
  • Face to the mark
  • Chamfer
  • Repeat for all six pins
  • Done!

It’s tedious, but not particularly difficult.

Futher doodling suggested the need for threaded pins to join two blocks together.

Machine Shop, Recumbent Bicycling

Tour Easy: Extended V-brake Noodle

Although our Tour Easy recumbents use ordinary (*) V-brakes, their frame geometry doesn’t route the rear cable quite the way the brake designers expected. Mary’s Medium-Small frame always had its rear brake cable resting against the frame tube, where it bent slightly as she applied the brakes:

Tour Easy rear V-brake layout
Tour Easy rear V-brake layout

That’s looking up from under the rear wheel, with the bike on a workstand, and, yeah, it’s pretty grubby down there.

The squashed rubber boot suggests the brake arms are too close together, but that’s where they must be to hold the brake pads in the proper position, even with new pads and big spacer washers. As a result, the cable stop over on the right at the end of the noodle rests against the frame and dings the paint.

My first thought was to add some length to the end of the noodle inside the stirrup, so I made an adapter with the ID on the noodle end matching the OD on the fitting end:

V-brake - larger noodle - end stop adapter
V-brake – larger noodle – end stop adapter

Which worked poorly, because the noodle has a straight section leading up to the fitting inside the stirrup; any additional length pushes the noodle curve against the stirrup pivot and cants it out of line:

Tour Easy rear V-brake noodle
Tour Easy rear V-brake noodle

I’ve been avoiding the fallback plan of building a bigger noodle for years, but finally combined a foot of 3/32 inch brass tubing, a tube bender spring, and various large-diameter round-ish objects from the Basement Warehouse Wing:

V-brake - larger noodle - bending
V-brake – larger noodle – bending

I annealed the tube by running a torch along its length until the color changed to the obvious “I’m hot enough” copper color, then let it air-cool while I did something else. Brass work-hardens quickly and required two more annealings while finishing that smooth curve; as far as I know, brass doesn’t harden with the heat-and-quench cycle used for steel.

A little more lathe work produced a replacement fitting:

V-brake - larger noodle - end stop
V-brake – larger noodle – end stop

The hole is barely one diameter deep, but I think it’ll align the tube well enough for my simple needs. The failure will most likely involve having the cable chew through the inward side of the mis-aligned tube, which should become obvious in short order.

The fitting on the OEM noodle seems to be crimped in place, but I figure my version is unlikely to fall off in normal use:

V-brake - larger noodle vs OEM
V-brake – larger noodle vs OEM

Lined up thusly, you can see the reduced straight section behind my fitting and the much larger sweep out to the cable stop.

The OEM noodle had a (presumably) PTFE liner, so I adapted a length of PTFE brake cable liner by mashing the end with various conical objects until it kinda-sorta looked like the cable stop might capture the ragged flange:

V-brake - larger noodle - PTFE liner
V-brake – larger noodle – PTFE liner

Reassembling in reverse order produces a comforting sight:

V-brake - larger noodle - installed
V-brake – larger noodle – installed

Despite appearances, the new noodle sits below the frame and well above the chain in normal use. In the most extreme small-small cross gearing position the chain barely clears it, but the takeup arm on the rear derailleur starts clattering enough to remind us not to do that.

Brass is certainly not as strong as stainless (?) steel, although I think it ended up in a reasonably hard condition after all the bending. I’m certain neither of us can squeeze the brake lever enough to come anywhere close to causing a problem.

Making a noodle was easier than I expected and, in a month or so, we’ll see how it behaves under actual riding conditions.

(*) “Ordinary” as of many decades ago, because the design dates back to the mid-70s, when Fast Freddy Markham broke 65 mph on a rather customized Easy Racers Gold Rush.

Electronics Workbench

Audio Amp vs. Bananas

A low-end audio power amp destined for a pair of ancient-yet-still-serviceable speakers arrived, but attempting to poke wires through the side holes of the banana jacks showed they were oriented in random directions. Back in the day, banana jacks had D-shaped shafts fitted into D-shaped panel holes, but those days are gone.

A few minutes with screwdriver, wrench, and (tiny) punch sufficed to line up the holes for E-Z poking:

Fosi audio amp - jack alignment
Fosi audio amp – jack alignment

Despite the new convenience, I decided to solder banana plugs to the speaker wires, leading to the discovery my few remaining plugs came from the very bottom of the usability barrel:

Cheap banana plug - solder side
Cheap banana plug – solder side

I have no idea how one might affix a wire to that blank stub, but poking a small center drill into the brass lump produces an easily solderable recess:

Cheap banana plug - center drilled
Cheap banana plug – center drilled

Dab with flux, tin, insert wire, add solder, repeat with all four plugs, and I’m set with a boomin’ system.

Home Ec, Machine Shop, Software

Torchiere Lamp Shade 2

Three and a half years later, the shade on the living room’s other torchiere lamp crumbled at a touch:

Torchiere Lamp Shade 2 - crumbled
Torchiere Lamp Shade 2 – crumbled

Because I live in the future and had solved this problem in the past, eight hours of print time produced a second shade:

Torchiere Lamp Shade 2 - on platform
Torchiere Lamp Shade 2 – on platform

I sliced the same STL file with PrusaSlicer to get G-Code incorporating whatever configuration changes I’ve made to the M2 over the years and include any slicing algorithm improvements; the OpenSCAD code remains unchanged.

The as-printed shade had pretty much the same crystalline aspect as the first one:

Torchiere Lamp Shade 2 - no epoxy
Torchiere Lamp Shade 2 – no epoxy

Smoothing a layer of white-tinted epoxy over the interior while spinning it slowly in the mini-lathe calmed it down enough for our simple needs, although the picture I tried to take didn’t show much difference.

That was easy …

Machine Shop

Dial Test Indicator Mount Finishing

While pondering a project requiring a slitting saw, I discovered the clamp on the dial test indicator magnetic mount I’d picked up a while ago didn’t quite fit the 5/32 inch = 4 mm stem on the indicator. The clamp ring is obviously punched from sheet, then formed into its final shape, as the holes are somewhat un-round. Running the proper drill through the holes removed a minute sliver of steel:

Dial test indicator mount - redrilling
Dial test indicator mount – redrilling

And then it fit just fine:

Dial test indicator mount - in use
Dial test indicator mount – in use

Although it looks like I’m in the process of sawing the ball off the indicator, I’m really measuring the runout, which turned out to be maybe 5 mils = 0.13 mm. The blade is likely too small for what I’m thinking of using it for, so the pondering continues.

The two bigger holes in the clamp fit the equally standard 3/8 inch = 9.5 mm stems just fine, so it’s just another one of those tools where I get to finish the last few percent of their manufacturing.

Machine Shop, PC Tweakage

KeyboardIO Atreus: LED Diffuser

After staring at the RGB LED I installed in my Atreus keyboard for a while, I converted the stub of a ¼-20 nylon screw into a light diffuser:

Atreus keyboard - LED diffuser
Atreus keyboard – LED diffuser

It stands slightly proud of the surface plate so I can extract it without dismantling the whole keyboard again:

Atreus keyboard - LED diffuser installed
Atreus keyboard – LED diffuser installed

I’ll eventually make a better-looking diffuser from a recently arrived translucent acrylic rod, but this will reduce the accumulation of fuzz inside the keyboard until the matching Round Tuit arrives.

Machine Shop

Makergear M2: New Filament Drive and Guide Tube Adapter

After replacing the M2’s nozzle, I also installed a spare filament drive:

Makergear M2 filament drive R3 - installed
Makergear M2 filament drive R3 – installed

That’s the V4 R3 version, although I bought it from Makergear rather than fight with all the support required to get a proper bearing opening.

The long M4 screw and spring apply a constant force to the filament against the drive gear, rather than the constant position from the default (and much shorter) stock screw. The lever arm does have some springiness, but not much travel, so IMO the spring works better with the fine teeth in the drive gear.

This drive has a 5 mm hole at the top for the stock PTFE guide tube, which I long ago replaced with ¼ inch OD HDPE tubing to reduce the friction required to get the filament off the spool and into the hot end. The rather hideous hot-melt glue blob holding a ¼ inch ID tube onto the previous drive never failed enough to bother me, but a little lathe action produced a much better adapter:

Makergear M2 filament drive R3 - guide adapter
Makergear M2 filament drive R3 – guide adapter

It’s a chunk of ⅜ inch = 9.5 mm Delrin rod with a 2.4 mm hole through that 5 mm spigot for easy extraction of a gear-mashed 1.75 mm filament. The other end has a 6.5 mm hole drilled 20 mm deep to hold the guide tube.

Looks downright dressy, it does!