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

CNC Kitchen Sink Strainer

Our Young Engineer recently rented a house, now knows why our sinks have CNC-machined strainers, and asked for something better than the disgusting stainless mesh strainer in the kitchen sink.

Being a doting father, I turned out a pair to get a pretty one:

CNC Sink Strainer - overview — CNC Sink Strainer – overview

They’re made from the same scrap smoked acrylic as the ones in our sinks:

They’re definitely upscale from the (not watertight!) 3D printed version I built for a Digital Machinist column to explain OpenSCAD modeling:

This time around, though, I rewrote the subtractive design in GCMC, with helical milling for all the holes to eliminate the need to change tools:

Sink Strainer - tool path simulation - CAMotics — Sink Strainer – tool path simulation – CAMotics

They’re done on the Sherline, because it has real clamps:

CNC Sink Strainer - on Sherline — CNC Sink Strainer – on Sherline

Four tabs eliminated the need to reclamp the stock before cutting the perimeter, but I should have ramped, not plunged, through the final cut between the tabs:

CNC Sink Strainer - tab surface fracture — CNC Sink Strainer – tab surface fracture

The handles come from the same chunk of hex acrylic as before, eyeballed to length, tapped 8-32, and secured with acrylic adhesive.

The GCMC source code as a GitHub Gist:

	// Drill & mill sink drain strainer
	// Ed Nisley KE4ZNU — Digital Machinist 15.2 Spring 2020
	// polycarbonate or acrylic sheet
	// External clamps at corners
	// Origin at center of sheet

	//—–
	// Dimensions

	DiskOD = 80.0mm; // usual kitchen drain = 3-1/4 inch
	DiskRad = DiskOD/2;

	PlateThick = 6.0mm; // stock thickness

	MillOD = 3.170mm; // measured end mill OD

	HoleDia = 4.75mm; // 3/16 inch drain holes
	ScrewOD = 0.18in; // knob screw clearance

	NumRings = 3; // rings of drain holes
	RingSpace = 1.5 * HoleDia; // .. between rings

	MaxZCut = 0.25 * MillOD; // max cut depth

	MillSpeed = 1000mm; // horizontal feedrate

	NumTabs = 4;
	TabTilt = 45deg;
	TabLength = 5.0mm;
	TabThick = 0.5mm;

	SafeZ = 10.0mm; // above all obstructions
	TravelZ = 1.0mm; // within engraving / milling area
	MillZ = -(PlateThick + 0.5mm); // through disk into spoil board

	TwoPi = 2*pi();

	//—–
	// Mill one hole

	function MillHole(ctr,radius,turns) {

	goto([-,-,TravelZ]);
	goto(head(ctr,2) + [radius,-,-]);
	goto([-,-,0]); // kiss surface

	circle_cw(ctr,turns); // helix downward
	circle_cw(head(ctr,2)); // remove last ramp

	goto(ctr); // get elbow room
	goto([-,-,TravelZ]);

	}

	//—–
	// Start cutting!

	goto([-,-,SafeZ]);
	goto([0,0,-]);
	goto([-,-,TravelZ]);

	feedrate(MillSpeed);

	// Mill center screw hole

	comment("– Center hole");

	ctr = [0,0,MillZ];
	MillHole(ctr,(ScrewOD – MillOD) / 2,ceil(abs(ctr.z) / MaxZCut));

	// Mill hole rings

	comment("– Drain hole rings");

	repeat (NumRings; ri) {
	comment("Ring: ",ri);

	rr = DiskRad – ri*RingSpace; // ring radius
	comment(" radius: ",rr);

	nh = to_int(floor(TwoPirr / (2HoleDia))); // number of holes
	comment(" holes: ",nh);

	repeat(nh; h) {
	a = (h – 1) * TwoPi / nh; // angle of hole
	ctr = [rrcos(a),rrsin(a),MillZ]; // center point at ending Z
	MillHole(ctr,(HoleDia – MillOD)/2,ceil(abs(ctr.z) / MaxZCut));
	}
	}

	// Mill perimeter

	comment("– Perimeter");

	r = DiskRad + MillOD/2;

	goto([r,0,-]);
	goto([-,-,0]);

	ctr = [0,0,-(PlateThick – TabThick)];

	circle_ccw(ctr,ceil(abs(ctr.z) / MaxZCut)); // ramp downward
	circle_ccw(ctr,1); // remove last ramp

	goto([-,-,TravelZ]);

	comment("– Tabs");

	ta = 360deg / NumTabs; // between tabs
	tsa = to_rad(TwoPi((TabLength + MillOD) / (TwoPi r))); // subtended tab angle

	repeat (NumTabs; i) {
	comment(" # ",i);

	a = TabTilt + (i – 1)*ta; // tab center angle

	p0 = [rcos(a + tsa/2),rsin(a + tsa/2),MillZ]; // entry on ccw side
	p1 = [rcos(a + ta – tsa/2),rsin(a + ta – tsa/2),MillZ]; // exit at next tab

	if (0) {
	comment(" angle: ",a);
	comment(" entry: ",p0);
	comment(" exit: ",p1);
	}

	goto(head(p0,2)); // to entry point
	move(p0); // plunge through
	arc_ccw(p1,r);
	goto([-,-,TravelZ]);
	}

	goto([-,-,SafeZ]);
	goto([0,0,-]);

view raw Sink Strainer.gcmc hosted with ❤ by GitHub

All in all, a pleasant diversion from contemporary events …

2020-03-19

Metal-case 5T4 Vacuum Tube Opened

I’ve always wondered what’s inside a metal-case vacuum tube:

Dual rectifier tube 5T4 – metal case opened

The cutter last saw action on the EMT used in the MPCNC, so it’s intended for use on steel tubes. I thought about parting the case off in the lathe, but a tubing cutter sufficed for a first attempt, even if it couldn’t cut quite as close to the flange as I wanted.

A 5T4 tube is a full-wave rectifier with two sections:

Dual rectifier tube 5T4 – upright

Unsurprisingly, the guts resemble those of glass-envelope rectifier tubes in my collection, like this 5U4GB:

5U4GB Full-wave vacuum rectifier – cyan red phase

The metal case would be far more rugged than a glass bottle and, perhaps, the flange locked the tube into its socket against vibration.

The filaments surely weren’t thoriated, so it’s all good …

2020-02-06
MPCNC Drag Knife Holder: Lock Screw

While calibrating the MPCNC’s probe camera offset for the drag knife holder, this happened:

Drag Knife – vertical escape

Well, at least it’s centered on the target:

Drag Knife – vertical escape – detail

This happened a few times before, because my fingers don’t fit neatly inside the drag knife holder to tighten the lock ring:

Drag Knife – LM12UU ground shaft – assembled

[Update: The lock ring keeps the holder at a fixed position inside the 12 mm shaft and doesn’t affect the blade directly. When the ring works loose, the threaded holder can rotate to expose more blade and, in this case, stab deeper into the target. ]

So I turned & knurled an aluminum ring, then tapped a 3×0.5 mm hole for a lock screw plucked from the Drawer o’ Random M3 Screws:

Drag Knife – lock screw – side

A view looking along the screw shows a bit more detail around the spring:

Drag Knife – lock screw – front

The general idea is to set the blade extension, then tighten the lock screw to hold it in place, without relying on the original brass lock ring, shown here while cutting a boss for the spring:

Drag Knife – turning spring recess

The lock screw’s knurled handle just barely kisses the NPCNC’s black tool holder ring, so my guesstimated measurements were a bit off. Clamping the knife holder one itsy higher in the tool holder solved the problem.

I cranked on 300 g of spring preload and, squashed like that, the spring’s rate is now 75 g/mm. Cutting at Z=-1 mm should suffice for laminated paper slide rule decks.

The original sizing doodle:

Drag Knife Holder – lock screw ring doodle

The short 18 mm section clears the inside of the LM12UU bearing, although it could be a millimeter shorter. The 19 mm section comes from the 3/4 inch aluminum rod I used, skim-cut to clean it up.

If I ever remake this thing, it needs a major re-think to get all the dimensions flying in formation again.

2020-01-21
Mini-Lathe, Maxi-OD

This came about while tinkering up a shade for a repurposed LED downlight:

PVC fitting – boring setup

It’s a 4 inch DWV pipe coupling I bored out to fit the LED housing, which was ever so slightly larger than the pipe OD.

Cutting it off required as much workspace as the poor little lathe had:

PVC fitting – cutoff setup

Ignore the toolpost handle across the top. What’s important: the cutoff blade poking out of the QCTP, above the orange carriage stop lock lever, extending just far enough to cut through the coupling’s wall before the compound hits the coupling. The compound slide is all the way out against the cross-slide DRO, rotated at the only angle putting the tool where it needs to be and clearing the end of the coupling.

It ended reasonably well:

PVC fitting – LED floor lamp

But, in retrospect, was hideously bad practice. Next time, I’ll make a fixture to hold the fitting on a faceplate.

2019-12-13
MPCNC Drag Knife Holder: Showing More Blade

Attempting to cut laminated cardstock decks for the Homage Tektronix Circuit Computer required a bit more blade extension than my LM12UU holder made available:

Drag Knife – LM12UU ground shaft – assembled

Shortening the 12 mm shaft wasn’t going to happen, so I knocked a little bit off the blade holder to give the knurled lock ring slightly more travel:

Drag Knife Holder – shortening stop

The lathe cutoff blade is a bit to the right of the new cut, but you get the general idea: not a whole lot of clearance in there.

2019-12-12
Mini-Lathe DRO Battery Life

The Mini-Lathe DROs eat a 390 alkaline coin cell a year, more or less:

Mini-Lathe DRO – battery life

The other DRO’s cell was 10 mV higher, so it might have survived another few weeks. I’ll call it a year, as the OEM cells failed half a year after I got the thing and these are the second set.

The last time I did this, I wedged a thin foam sheet below the display PCB to put a bit more pressure on the (+) contact tab sticking down from the middle of the plate:

Mini-Lathe DRO – battery compartment

The (-) contact is a pad on the PCB below the battery compartment. The glaring metal reflector is part of the curved cell retainer.

I still wish the DROs didn’t collide with the compound slide, but you can get used to anything if you do it long enough.

2019-12-11
Printer Filament Millifiori

I finally decommissioned my old Thing-O-Matic, as it’s been far surpassed by the current generation of dirt-cheap Prusa-style 3D printers, and must now figure out what to do with about 10 kg of 3 mm ABS filament. Yes, 3 mm filament from back in the Bad Old Days.

Also back in the day, our Larval Engineer made millifiori creations in glass (at school) and polymer clay, building up the final piece from murrine canes, which suggested a similar technique using filament strands:

Filament Millefiori – 160C pipe – slice detail

Well, maybe it’s not exactly art …

Just to see how it might work, I packed a random length of conduit with filament snippets and jammed a thermocouple into the middle:

Filament Millefiori – packed conduit

Which went into the shop’s sacrificial Dutch oven over low heat:

Filament Millefiori – conduit heating

For lack of anything smarter, I slowly heated it to 250 °C, well above what the Thing-O-Matic used for extrusion, let it soak for a few minutes, then let the tube cool on the counter.

Some persuasion with a hammer and drift punch extracted the fused filament:

Filament Millefiori – 250C results

Obviously, the concept needs more work, but the bottom side looks promising:

Filament Millefiori – 250C results – bottom

Wrapping the bundle with silicone tape should keep the filament from sticking to the tube and provide uniform compression:

Filament Millefiori – 235C silicone wrap

I forced it into the tube and wrapped the whole affair with aluminum foil to confine the hot ABS stench:

Filament Millefiori – 235C heating

I held this one at 235 °C for a few minutes, cooled, unwrapped, and discovered the silicone wrap worked as expected:

Filament Millefiori – 235C thermocouple blob

OK, the blob on each end wasn’t expected, but at least the thermocouple came out with gentle persuasion. The compressed filament looked like it should be edible:

Filament Millefiori – 235C results

The molten filament oozed out of the wrap inside the tube, over there toward the right.

The filament snippets have a distinct curvature, brought on by years spent snuggled around a spool’s core, so I wondered if they could be straightened by application of somewhat less heat. Wikipedia lists the glass transition temperature for various ABS compositions as around 105 °C, so I packed the tube with more snippets and affixed the thermocouple with silicone tape:

Filament Millefiori – 100C setup

Wrap with foil, heat to 100 °C, let cool, and they’re definitely straighter than the unheated white strand at the bottom:

Filament Millefiori – 100C results

Having learned my lesson with a thermocouple inside the strands, the straightened strands get a looser silicone wrap with the thermocouple secured to the outside of the bundle:

Filament Millefiori – 160C setup

Heat to 160 °C:

Filament Millefiori – 160C setup

Let cool and (easily!) slide the compressed bundle out of the tube:

Filament Millefiori – 160C cooling

The silicone wrap definitely mushed the strands together, as shown by the larger diameter on the uncompressed end:

Filament Millefiori – 160C results

Bandsawing the bundle reveals nicely fused filaments inside, along with melty ends that stuck out of the wrap:

Filament Millefiori – 160C cut end

Thinking shorter lengths might pack better without straightening, I faced the ends of a thick aluminum pipe and stuffed as many snippets into it as would fit. This is the point where a real artist would arrange the filaments in a pleasing pattern, if not a picture, but I was content with a random layout:

Filament Millefiori – 160C pipe – cable in pipe

That’s what the ends looked like after heating to 160 °C: somewhat glazed, reasonably fused, but certainly not compacted. The other end pointed upward and definitely felt the heat:

Filament Millefiori – 160C pipe – cable melty end detail

With a PCV pipe “collet” holding the cable / cane / murrina in the chuck, I faced the end:

Filament Millefiori – 160C pipe – cable facing

After taking this picture, I came to my senses and bandsawed the slice instead:

Filament Millefiori – 160C pipe – cutoff tool

Parting the slice in the lathe might have worked, but it just seemed like a really really bad idea when I looked at the setup.

A PVC pipe spacer kept the slice lined up in the chuck jaws while facing the bandsawed end:

Filament Millefiori – 160C pipe – slice facing

The slice and the cable:

Filament Millefiori – 160C pipe – slice and cable

Although the filament snippets fuse together without a silicone tape compression wrap, the gaps collect plenty of swarf during the cutting & facing:

Filament Millefiori – 160C pipe – cable end detail

The snippets along the outside, closest to the pipe, obviously got hotter than the ones in the middle and fused more solidly.

The pipe has a 35 mm ID for an area 136 times larger than a 3 mm filament. I packed about 100 snippets into the pipe, a 0.73 packing fraction, which looks to be in the right ballpark for the high end of the Circle Packing Problem. If they were straighter, maybe a few more would fit, but twisting the lot into a cable seemed to align them pretty well.

Perhaps filling the gaps with pourable epoxy before cutting the slices would help? A completely filled interior might require pulling a good vacuum on the whole thing.

A hexagonal pipe would produce slices one could tile into a larger sheet.

All in all, a useful exercise, but … it ain’t Art yet!

2019-08-29