Category: Machine Shop

Mechanical widgetry

Tailor’s Clapper: CNC Pocketing

Separating the interior contour of the finger grip from its overall shape let me reduce the woodworking to a simple pocketing operation:

Start by aligning the finished block to put the joint between the pieces parallel to the X axis, then touch off at the center:

Ironing Weight - alignment — Ironing Weight – alignment

A pair of clamps screwed to the tooling plate act as fixtures to align the block when it’s flipped over to mill the other pocket.

Just to see how it worked, I set up a GCMC program to produce a trochoidal milling pattern using the sample program:

Tailors Clapper - Pocket Milling Path — Tailors Clapper – Pocket Milling Path

Now, most folks would say the Sherline lacks enough speed and stiffness for trochoidal milling:

Ironing weight - trochoidal milling — Ironing weight – trochoidal milling

Aaaand I would agree with them: chugging along at 24 in/min = 600 mm/min doesn’t put the 10 k RPM spindle speed to good use. Fortunately, oak doesn’t require much in the way of machine stiffness and the trochoid path does ensure good chip clearance, so there’s that.

If I had to do a lot of trochoid milling, I’d tweak the GCMC sample code to short-cut the return path across the circle diameter, rather than air-cut the last half of every circumference.

The code starts by emptying a circular pocket so the trochoid path begins in clear air, rather than trenching into solid wood.

Eventually it finishes the pocket:

Ironing weight - grip pocket — Ironing weight – grip pocket

After the trochoid finishes, one climb-milling pass around the perimeter clears the little ripple between each trochoid orbit.

Flip it over, clamp it down, touch off the middle, and do it all again.

The next step is filling those pockets with a pair of comfy grips.

The GCMC source code as a GitHub Gist:

	// Ironing weight pocketing
	// Ed Nisley KE4ZNU – 2023-01

	//—–
	// Library routines

	include("/opt/gcmc/example/cc_hole.inc.gcmc");
	include("varcs.inc.gcmc");
	include("tracepath_comp.inc.gcmc");
	include("trochoidal.inc.gcmc");

	/*
	include("tracepath.inc.gcmc");
	include("engrave.inc.gcmc");
	*/

	//—–
	// Useful constants

	SafeZ = 10.0mm; // above all obstructions
	TravelZ = 2.0mm; // within engraving / milling area

	BlockHome = [0.0mm,0.0mm,TravelZ]; // Origin on surface at center of pocket

	FALSE = 0;
	TRUE = !FALSE;

	//—–
	// Overall values

	Socket = [160.0mm,25.0mm,7.0mm]; // raw grip recess into block

	RoundEnds = TRUE; // TRUE for smooth rounded endcaps

	SocketRadius = RoundEnds ? Socket.y/2 : 10.0mm;
	comment("SocketRadius: ",SocketRadius);

	CutterDia = 6.32mm – 0.15; // actual cutter diameter – windage
	MillStep = 0.25 * CutterDia; // stepover in XY plane
	comment("CutterDia: ",CutterDia," MillStep: ",MillStep);
	MillClean = MillStep/2;

	PlungeSpeed = 150.0mm; // cutter Z plunge into work
	MillSpeed = 600.0mm; // XY speed

	if (CutterDia > SocketRadius) {
	error("Cutter too large for corner radius");
	}

	CornerOC = head(Socket,2) – 2*[SocketRadius,SocketRadius];
	comment("CornerOC: ",CornerOC);

	Corners = RoundEnds ? // rear left CCW around slot
	{-CornerOC/2, CornerOC/2} :
	{[-CornerOC.x,CornerOC.y]/2, [-CornerOC.x,-CornerOC.y]/2, [CornerOC.x,-CornerOC.y]/2, CornerOC/2};
	comment("Corners: ", Corners);

	if (RoundEnds) {
	SlotPerimeter = {[0.0mm,Socket.y/2,-Socket.z]}; // entry point at center rear
	SlotPerimeter += {Corners[0] + [0.0mm,SocketRadius]};
	SlotPerimeter += varc_ccw([-SocketRadius,-SocketRadius],SocketRadius) + SlotPerimeter[-1];
	SlotPerimeter += varc_ccw([+SocketRadius,-SocketRadius],SocketRadius) + (Corners[0] + [-SocketRadius,0.0mm]);
	SlotPerimeter += {Corners[1] + [0.0mm,-SocketRadius]}; // across front
	SlotPerimeter += varc_ccw([+SocketRadius,+SocketRadius],SocketRadius) + SlotPerimeter[-1];
	SlotPerimeter += varc_ccw([-SocketRadius,+SocketRadius],SocketRadius) + (Corners[1] + [+SocketRadius,0.0mm]);
	}
	else {
	SlotPerimeter = {[0.0mm,Socket.y/2,-Socket.z]}; // entry point at center rear
	SlotPerimeter += {Corners[0] + [0.0mm,SocketRadius]};
	SlotPerimeter += varc_ccw([-SocketRadius,-SocketRadius],SocketRadius) + SlotPerimeter[-1];
	SlotPerimeter += {Corners[1] + [-SocketRadius,0.0mm]};
	SlotPerimeter += varc_ccw([+SocketRadius,-SocketRadius],SocketRadius) + SlotPerimeter[-1];
	SlotPerimeter += {Corners[2] + [0.0mm,-SocketRadius]}; // across front
	SlotPerimeter += varc_ccw([SocketRadius,SocketRadius],SocketRadius) + SlotPerimeter[-1];
	SlotPerimeter += {Corners[3] + [SocketRadius,0.0mm]};
	SlotPerimeter += varc_ccw([-SocketRadius,SocketRadius],SocketRadius) + SlotPerimeter[-1];
	}


	//— Begin cutting

	goto([-,-,TravelZ]);
	goto(BlockHome);

	if (!RoundEnds) { // clear corners outward of main pocket
	foreach(Corners; xy) {
	comment("Plunge corner at: ",xy);
	feedrate(PlungeSpeed);
	goto(xy);
	move([-,-,-Socket.z]);
	comment(" pocket");
	feedrate(MillSpeed);
	cc_hole(xy,(SocketRadius – MillClean),CutterDia/2,MillStep,-Socket.z);
	goto([-,-,TravelZ]);
	comment(" done!");
	}
	}

	comment("Open slot");

	TrochRadius = (Socket.y – CutterDia)/2 – MillClean;
	TrochPath = {[-(Socket.x/2 – TrochRadius – CutterDia/2 – MillStep),TrochRadius],
	[ (Socket.x/2 – TrochRadius – CutterDia/2 – MillStep),TrochRadius]};

	comment(" clear landing zone");
	xy = [TrochPath[0].x,0.0mm];
	feedrate(PlungeSpeed);
	goto(xy);
	move([-,-,-Socket.z]);
	feedrate(MillSpeed);
	cc_hole(xy,Socket.y/2 – MillClean,CutterDia/2,MillStep,-Socket.z);
	goto([-,-,TravelZ]);

	comment(" trochoid pocket milling");

	feedrate(MillSpeed);
	trochoid_move(TrochPath[0],TrochPath[1],
	-Socket.z, TrochRadius, MillStep);
	goto([-,-,TravelZ]);

	comment("Clean slot perimeter");
	feedrate(MillSpeed);
	goto([-,-,-Socket.z]);
	tracepath_comp(SlotPerimeter,CutterDia/2,TPC_CLOSED + TPC_LEFT + TPC_ARCIN + TPC_ARCOUT);

	goto([-,-,TravelZ]);
	goto(BlockHome);

view raw Ironing weight grip pocket.gcmc hosted with ❤ by GitHub

	#!/bin/bash
	# Ironing weight finger grip pocketing
	# Ed Nisley KE4ZNU – 2023-01

	Flags='-P 4 –pedantic' # quote to avoid leading hyphen gotcha


	# Set these to match your file layout

	LibPath='/opt/gcmc/library'

	Prolog='prolog.gcmc'
	Epilog='epilog.gcmc'

	#—–

	gcmc $Flags \
	–include "$LibPath" –prologue "$Prolog" –epilogue "$Epilog" \
	"Ironing weight grip pocket.gcmc" > "Grip pocket.ngc"

view raw pocket.sh hosted with ❤ by GitHub

2023-02-02

Tailor’s Clapper: Laser-Cut Woodwork

Creating the rounded-rectangle shape of a tailor’s clapper in LightBurn, then cutting it out, doesn’t pose much of a challenge:

Ironing weight – cutting oak plank

That was a prototype cut from an oak plank with some fairly obvious splits. It turned out OK, but ¾ inch oak is obviously right at the limit of my 60 W laser’s abilities:

Ironing weight – laser cut edges

The “production” clappers came from a nicer plank that was just barely long enough:

Ironing weight – laser cuts – top

The cut, at 2 mm/s and 70% power, just barely penetrates the plank:

Ironing weight – laser cuts – bottom

Unlike the top picture, I put the plank on the knife-edge supports, resulting in the small charred lines perpendicular to the cut.

The edges came out thoroughly charred:

Ironing weight – laser cuts – edges

Spread yellow wood glue smoothly on one piece, stick another to it, then align and clamp:

Ironing weight – clamping

I offset the cut 1 mm outside the nominal shape to allow Mr Belt Sander to remove the char while reducing the block to size. Obviously, there is no real tolerance, other than that it must fit Mary’s hand, and they all came out nice and straight.

Some of the char seems embedded deep in the wood grain and leaves a dark mark despite removing the extra millimeter:

Ironing weight – seam ironing B

Contrary to what I feared, the characteristic wood-stove odor dissipated after a day or two: they’re entirely inoffensive. Which was fortunate, as the slightest odor would cause them to fail incoming inspection.

The longer weight on the far left came from a plank with a conspicuous knot on one end. The stress from supporting that branch while the tree grew apparently made the wood much denser, as the same 2 mm/s 70% cut setting barely made it halfway through the plank. I finished the job by cutting the outline with Tiny Bandsaw™, which didn’t proceed any faster than the laser and left a much less uniform path for Mr Belt Sander.

I’d definitely consider making any future tailor’s clappers by laminating three half-inch oak planks that would be much easier to cut, but my woodpile doesn’t have anything like that.

The wood remains unfinished, as part of its job is to absorb moisture from steam-ironed fabric (which is not happening in the photo). Applying stains / sealers / finishes would definitely improve the wood’s appearance, but wreck its performance. Around here, function always outweighs form.

2023-02-01
Ironing Weight, a.k.a. Tailor’s Clapper: Overview

Mary wanted some ironing weights, formally known as tailor’s clappers, to produce flatter seams as she pieced fabric together:

Ironing weight – flattened seam

The weights are blocks of dense, hard, unfinished wood:

Ironing weight – seam ironing A

One can buy commercial versions ranging from cheap Amazon blocks to exotic handmade creations, but a comfortable grip on a block sized to Mary’s hands were important. My lack of woodworking equipment constrained the project, but the picture shows what we settled on.

The general idea is a rounded wood block with 3D printed grips:

Ironing Weight Finger Grip

All other clappers seem to have a simple slot routed along the long sides, presumably using a round-end or ball cutter, which means the cutter determines the shape. This being the age of rapid prototyping, I decided to put the complex geometry in an easy-to-make printed part inserted into a simple CNC-milled pocket.

The first pass at the grip models:

Ironing Weight Finger Grip – slicer preview

Both recesses came from spheres sunk to their equators with their XY radii scaled appropriately, then hulled into the final shape. Customer feedback quickly reported uncomfortably abrupt edges along the top and bottom:

Ironing Weight – maple prototype

We also decided the straight-end design didn’t really matter, so all subsequent grips have rounded ends to simplify milling the pocket into the block.

With the goal in mind, the next few posts will describe the various pieces required to make a nice tailor’s clapper customized to fit the user’s hand.

2023-01-31
Acrylic Engraving Dust

The MDF signs I made last year disintegrated pretty much on the expected schedule, so it’s time for something more durable:

Please Close The Gate – acrylic engraving

The idea is to engrave both sides of a 3 mm orange acrylic sheet, shoot it with rattlecan black paint, and declare victory. The second step awaits warmer weather, but at least I’m doing my part to prepare for the new gardening season.

Vaporizing that much acrylic produces a fair bit of debris:

Please Close The Gate – acrylic dust on laser head

Some dust / vapor accumulates / condenses on the honeycomb platform beyond the orange sign, but most of it gets through to the baffle on the exhaust duct:

Please Close The Gate – acrylic dust on exhaust port

A closer look shows it really does grow out from the perimeter of each hole:

Please Close The Gate – acrylic dust on exhaust port – detail

Now, if that doesn’t trip your trypophobia, nothing will …

A few passes with the trusty Electrolux vacuum’s dust brush brought the visible surfaces back to normal.

By now, the duct fan blades have surely layered on a good coating, too, which shall remain undisturbed until I find a better reason to open the duct.

2023-01-27
Brick Wall in Z-Scale

A LightBurn forum discussion about problems making Z-scale (1:220) bricks led me to trying a few ideas on the way to figuring out what was going wrong.

Each brick is about 1.0×0.5 mm, so an entire wall doesn’t cover much territory:

Z-scale bricks – assortment

Yes, those are millimeters along the scale.

The kerf on my 60 W CO₂ laser seems slightly wider than the “mortar” lines should be, so I made a layout with the vertical lines slightly inset from the horizontal ones:

Z Scale Brick Wall – LB layout

That let the kerf complete the lines without burning into the adjacent bricks:

Z Scale Brick Wall – laser lines

The cuts are obviously too wide (and deep!), but just for fun I colored the chipboard with red marker and rubbed a pinch of flour into the lines:

Z Scale Brick Wall – color and flour

Which looks chunky, but not terrible, for what it is. Maybe concrete blocks would look better?

The next attempt started with a raster bitmap scaled at 254 dpi = 10 pix/mm, so that single-pixel “mortar” lines between 10×5 pixel bricks would be 0.1 mm wide:

Raster Z-Scale Bricks

Scanning the image at 100 mm/s makes each pixel 1 ms “wide” and, because the power supply risetime is on the order of 1 ms, the laser won’t quite reach the 10% power level across the vertical lines:

Raster Z-Scale Bricks – LB layer settings

The raster lines come out lighter and (IMO) better looking:

Z Scale Brick Wall – raster lines

The horizontal lines are darker because the beam remains on at 10% across their full length, but the overall result seems much closer to the desired result.

The original poster will use a diode laser and, combining all the ideas we came up with, now has a path toward making good, albeit invisibly small, bricks.

His modeling (and coloring!) hand is strong!

2023-01-26
Bobbin Rock

Mary handed me a bobbin with a trouble report: it fit into the bobbin holder either way, but would go into the sewing machine either poorly or not at all.

Based on past experience with this lot of bobbins (*), I expected to find a burr inside the steel hub left behind by the saw cut creating the drive dog slot, so this came as a surprise:

Bobbin Rock – overview

A closer look:

Bobbin Rock – detail

That pebble was jammed in place so firmly I needed a pin punch: a small screwdriver wasn’t enough.

It came new from the factory like that, which makes one wonder just exactly what the factory floor looks like.

More likely, the bobbins spend their last few hours in a vibratory polisher and that little rock just crept with all the walnut shell kibble.

Works fine now, so we’ll call it a win.

(*) I gave her a lot of 100 to ensure she never had to unload a bobbin to keep her new Juki well-fed.

2023-01-23
Ersatz Library Card: Fixed

Sharper eyes than mine pointed out I misspelled Poughkeepsie, so I took advantage of the opportunity to make the whole thing look better:

Library card tag – revised front

It turns out the low-surface-energy tape stuck like glue to the acrylic tag (because that’s what it’s designed for) and peeled right off the laminating film on the printed paper. So I stuck some ordinary adhesive film to the back of the new paper label, left its protective paper on the other side, cold laminated the film+paper, laser-cut the outline, peeled off the back side of the laminating film with the protective paper, and stuck the new adhesive to the LSE tape still on the tag.

I have no idea how well this will work out in the long term, what with two adhesive layers bonded to each other, but this whole thing is in the nature of an experiment.

2023-01-19