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.

Author: Ed

MPCNC Diamond Engraver: LM3UU Bearings, First Pass

Gripping a diamond engraver in a collet chuck worked well enough, but the MPCNC’s pen holder lacks sufficient downforce and lateral stiffness. The bit has a chrome-ish plated 3 mm shank, so I tinkered up a mount for a pair of LM3UU linear bearings from the LM12UU drag knife holder:

Diamond Scribe – LM3UU – Rev 1 – point view

The shank isn’t exactly a precision part, but a few licks with a diamond file knocked off enough of the high spots so it slides reasonably well through the bearings. The bearing alignment is more critical than a simple 3D printed plastic part can provide, so a real version may need bearings in a metal shaft press-fit into the plastic; brute-forcing the bearings into alignment sufficed for now.

The butt end of the shank press-fits into a disk held down with three springs, similar to the LM12UU mount:

Diamond Scribe – LM3UU – Rev 1 – top view

It draws Guilloché patterns just fine:

Diamond Scribe – LM3UU – Rev 1 – first light

I don’t like how the spring-around-screw motion works, even if it’s OK for small excursions.

2019-06-17
Monthly Image: Turkey Hen and Chicks

Mary saw a fox trotting behind the garden, gripping a (dead) turkey chick in its jaws, with the hen in hot pursuit. The fox dropped the chick, circled the pine grove, picked up the chick, and departed stage right. The hen eventually led her remaining chicks into the yard, but gathered them underneath while watching for danger:

Turkey hen with chicks – alert

She settled down for a few minutes:

Turkey hen with chicks – resting

With the fox safely departed, she released the chicks:

Turkey hen with chicks – emerging

Then they returned to foraging, with one chick trying out its wings:

Turkey hen with chicks – dispersing

Two days earlier, she led nine chicks through the yard; we think the fox picked off a chick a day. She lost two more during the next four days, suggesting they rapidly improve their ability to scamper out of harm’s way.

2019-06-15
Monthly Science: Water Bottle Refill History
This year’s Northern Star Quilt Guild show in the O’Neill Center at WCSU gave me an opportunity to update last year’s data points, although not quite in the way I expected.

The overview:

Gym water bottle refill station B – overview

The left display is rotting out:

Gym water bottle refill station B – left

The center display seems undamaged:

Gym water bottle refill station B – center

The right display took a direct hit:

Gym water bottle refill station B – right

So the middle station refilled 3025 = 10460 – 7435 bottles, roughly eight bottles a day, every day, for a year. Seems like a lot of refilling, doesn’t it?

Unfortunately, I didn’t take pictures of the other watering hole last year, but here’s what it looks like now:

Overview:

Gym water bottle refill station A – overview

Left:

Gym water bottle refill station A – left

Center:

Gym water bottle refill station A – center

Right:

Now, it’s entirely possible I have the two stations reversed, in which case I have numbers for all three displays:
- Left = 242 = 4758 – 4516
- Center = 633 = 8068 – 7435
- Right = 800 = 9689 – 8889
Does a bottle or two a day, every day, for a year, seem more reasonable? Hard to say, so, with a bit of luck, we’ll have more data next year.

For science!
2019-06-01

MPCNC Drag Knife: LM12UU Linear Bearing

The anodized body of the drag knife on the left measures exactly 12.0 mm OD:

Drag Knife holders - detail — Drag Knife holders – detail

Which happy fact suggested I might be able to use a standard LM12UU linear bearing, despite the obvious stupidity of running an aluminum “shaft” in a steel-ball bearing race:

Drag Knife - LM12UU holder - solid model — Drag Knife – LM12UU holder – solid model

The 12 mm section extends about halfway through the bearing, with barely 3 mm extending out the far end:

Drag Knife - LM12UU - knife blade detail — Drag Knife – LM12UU – knife blade detail

Because the knife body isn’t touching the bearing for the lower half of its length, it’ll probably deflect too much in the XY plane, but it’s simple enough to try out.

As before, the knife body’s flange is a snug fit in the hole bored in the upper disk:

Drag Knife - spring plate test fit — Drag Knife – spring plate test fit

This time, I tried faking stripper bolts by filling the threads of ordinary socket head cap screws with epoxy:

Ersatz stripper bolts - epoxy fill — Ersatz stripper bolts – epoxy fill

Turning the filled section to match the thread OD showed this just wasn’t going to work at all, so I turned the gunked section of the threads down to about 3.5 mm and continued the mission:

Drag Knife - LM12UU holder - assembled — Drag Knife – LM12UU holder – assembled

Next time, I’ll try mounting the disk on telescoping brass tubing nested around the screws. The motivation for the epoxy nonsense came from the discovery that real stainless steel stripper bolts run five bucks each, which means I’m just not stocking up on the things.

It slide surprisingly well on the cut-down screws, though:

Drag Knife - applique templates — Drag Knife – applique templates

Those appliqué templates came from patterns for a block in one of Mary’s current quilting projects, so perhaps I can be of some use whenever she next needs intricate cutouts.

The OpenSCAD source code as a GitHub Gist:

	// Drag Knife Holder using LM12UU linear bearing
	// Ed Nisley KE4ZNU – 2019-04-26

	Layout = "Show"; // [Build, Show, Puck, Mount, Plate]

	/* [Extrusion] */

	ThreadThick = 0.25; // [0.20, 0.25]
	ThreadWidth = 0.40; // [0.40]

	/* [Hidden] */

	Protrusion = 0.1; // [0.01, 0.1]

	HoleWindage = 0.2;

	inch = 25.4;

	function IntegerMultiple(Size,Unit) = Unit * ceil(Size / Unit);

	ID = 0;
	OD = 1;
	LENGTH = 2;

	//- Adjust hole diameter to make the size come out right

	module PolyCyl(Dia,Height,ForceSides=0) { // based on nophead's polyholes
	Sides = (ForceSides != 0) ? ForceSides : (ceil(Dia) + 2);
	FixDia = Dia / cos(180/Sides);
	cylinder(r=(FixDia + HoleWindage)/2,h=Height,$fn=Sides);
	}

	//- Dimensions

	// Basic shape of DW660 snout fitting into the holder
	// Lip goes upward to lock into MPCNC mount

	Snout = [44.6,50.0,9.6]; // LENGTH = ID height
	Lip = 4.0; // height of lip at end of snout

	// Knife holder & suchlike

	KnifeBody = [12.0,15.9,2.0]; // flange epoxied to top of diamond shaft, with epoxy fillet

	WallThick = 4.0; // minimum thickness / width

	Screw = [4.0,8.5,8.0]; // holding it all together, OD = washer

	Insert = [4.0,6.0,10.0]; // brass insert

	Bearing = [12.0,21.0,30.0]; // linear bearing body

	Plate = [KnifeBody[ID],Snout[OD] – WallThick,KnifeBody[LENGTH] + WallThick]; // spring reaction plate
	PlateGuide = [4.0,4.8,Plate[LENGTH]]; // … guide tubes

	PuckOAL = max(Bearing[LENGTH],(Snout[LENGTH] + Lip)); // total height of DW660 fitting
	echo(str("PuckOAL: ",PuckOAL));
	Key = [Snout[ID],25.7,(Snout[LENGTH] + Lip)]; // rectangular key

	NumScrews = 3;

	ScrewBCD = 2.0*(Bearing[OD]/2 + Insert[OD]/2 + WallThick);

	NumSides = 9*4; // cylinder facets (multiple of 3 for lathe trimming)

	module DW660Puck() {

	translate([0,0,PuckOAL])
	rotate([180,0,0]) {
	cylinder(d=Snout[OD],h=Lip/2,$fn=NumSides);
	translate([0,0,Lip/2])
	cylinder(d1=Snout[OD],d2=Snout[ID],h=Lip/2,$fn=NumSides);
	cylinder(d=Snout[ID],h=PuckOAL,$fn=NumSides);
	intersection() {
	translate([0,0,0*Lip + Key.z/2])
	cube(Key,center=true);
	cylinder(d=Snout[OD],h=Lip + Key.z,$fn=NumSides);
	}
	}
	}

	module MountBase() {

	difference() {
	DW660Puck();

	translate([0,0,-Protrusion]) // bearing
	PolyCyl(Bearing[OD],2*PuckOAL,NumSides);

	for (i=[0:NumScrews – 1]) // clamp screws
	rotate(i*360/NumScrews)
	translate([ScrewBCD/2,0,-Protrusion])
	rotate(180/8)
	PolyCyl(Insert[OD],2*PuckOAL,8);
	}
	}

	module SpringPlate() {
	difference() {
	cylinder(d=Plate[OD],h=Plate[LENGTH],$fn=NumSides);

	translate([0,0,-Protrusion]) // knife holder body
	PolyCyl(KnifeBody[ID],2*PuckOAL,NumSides);

	translate([0,0,Plate[LENGTH] – KnifeBody[LENGTH]]) // flange, snug fit
	PolyCyl(KnifeBody[OD],KnifeBody[LENGTH] + Protrusion,NumSides);

	for (i=[0:NumScrews – 1]) // clamp screws
	rotate(i*360/NumScrews)
	translate([ScrewBCD/2,0,-Protrusion])
	rotate(180/8)
	PolyCyl(PlateGuide[OD],2*PuckOAL,8);
	}
	}

	//—–
	// Build it

	if (Layout == "Puck")
	DW660Puck();

	if (Layout == "Plate")
	SpringPlate();

	if (Layout == "Mount")
	MountBase();

	if (Layout == "Show") {
	MountBase();
	translate([0,0,1.6*PuckOAL])
	rotate([180,0,0])
	SpringPlate();
	}

	if (Layout == "Build") {
	translate([0,Snout[OD]/2,PuckOAL])
	rotate([180,0,0])
	MountBase();
	translate([0,-Snout[OD]/2,0])
	SpringPlate();
	}

view raw Drag Knife LM12UU holder.scad hosted with ❤ by GitHub

2019-05-29

Baofeng Big Battery Capacity

I bought a pair of third-party 3800 mA·h batteries for the Baofeng UV-5RE Plus (whatever that means) radios on our bikes. Oddly, the packs carry the same “Model BL-5” identification as 1800 mA·h batteries shipped with the radio:

Baofeng BL-5 Batteries – 1.8 and 3.8 Ah

The obviously mislabeled “Baofeng” battery eliminator also sported a 3800 mA·h label:

Baofeng Battery Eliminator – overview

I conjured a “test fixture” from a clamp, copper sheet, and copper tape snippets:

Baofeng battery – test setup

Which produced interesting results:

Baofeng BL-5 3800 mAh packs – Ah – 2019-05

The 250 mA load = 15 hour rate seemed reasonable to simulate radios spending most of their time in power-save mode, but the packs still delivered only 2.8 A·h.

The packs also claim an unnaturally precise 28.12 W·h, but they’re still underperformers at 20 W·h:

Baofeng BL-5 3800 mAh packs – 2019-05

Anyhow, I can run the radios for a week without (worrying about) running out of juice during a ride.

2019-05-27
MPCNC Drag Knife: PETG Linear Bearing
Having reasonable success using a 12 mm hole bored in a 3D printed mount for the nice drag knife holder on the left, I thought I’d try the same trick for the raw aluminum holder on the right side:

Drag Knife holders – detail

The 11.5 mm body is long enough to justify making a longer holder with more bearing surface:

Drag Knife Holder – 11.5 mm body – Slic3r preview

Slicing with four perimeter threads lays down enough reasonably solid plastic to bore the central hole to a nice sliding fit:

Drag Knife – 11.5 mm body – boring

The top disk gets bored to a snug press fit around the flange and upper body:

Drag Knife – 11.5 mm body – flange boring

Assemble with springs and it pretty much works:

Drag Knife – hexagon depth setting

Unfortunately, it doesn’t work particularly well, because the two screws tightening the MPCNC’s DW660 tool holder (the black band) can apply enough force to deform the PETG mount and lock the drag knife body in the bore, while not being quite tight enough to prevent the mount from moving.

I think the holder for the black knife (on the left) worked better, because:
- The anodized surface is much smoother & slipperier
- The body is shorter, so less friction
In any event, I reached a sufficiently happy compromise for some heavy paper / light cardboard test shapes, but a PETG bearing won’t suffice for dependable drag knife cuttery.

Back to the laboratory …
2019-05-24
M20 Camera Operation

A reader asked how the M20 camera mount on my bike works with respect to the camera’s clock; this description explains a few things missing from the original writeup.

SJCAM M20 Mount – Tour Easy side view

Do you have to set the time & date at start of every ride?

The internal clock shuts down about ten seconds after you pull the battery. If-and-only-if you swap batteries fast enough, it’ll keep time forever. Screw up once and it snaps back to Epoch Zero.

“Car mode” automagically begins recording when USB power goes on, but the manual advises:

TIP: When using your camera as a dashcam, use a car charger cable and remove the internal battery to make sure it does not die out while you travel.

That’s because the M20 continues to run from its internal battery when USB power drops. After recording an hour of a parking lot or your garage wall, the battery dies and so does the clock.

Of course, without the internal battery, the clock dies ten seconds after you turn off the car.

The internal battery has many days of capacity with the camera turned off (whew!), so I conjured the case & PowerCore battery tray to handle our normal rides. The internal battery keeps the clock alive overnight and during the rain we’ve had for the last week, the PowerCore supplies juice during the ride, and I recharge the PowerCore every few weeks.

The M20 doesn’t draw charging current when I turn it on, but poking the PowerCore’s status button also turns on its outputs, whereupon the M20 decides it should begin charging and, bonus, draw power from the PowerCore during the entire ride. The M20 finishes charging while we ride, but the PowerCore continues supplying power and, when I turn the M20 off, the PowerCore sees no current draw and shuts itself off.

Only a geek could love a lashup like that, but it works around the M20’s broken clock and removes its battery maintenance hassle.

2019-05-22