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Tag: Sherline

Sherline CNC mill

Sherline: Diamond Drag Engraving Tool Holder

Although I shouldn’t have used a hardened shaft for the case, the rest of the diamond drag tool holder worked out well enough:

Sherline Diamond Drag Holder – assembled

The dimension doodle shows what’s inside and gives some idea of the sizes:

Sherline Diamond Drag Holder – dimension doodles

From left to right, it’s an M6×1.0 setscrew to adjust the spring preload, a spring harvested from a cheap clicky ballpoint pen, a machined cap, a 3 mm rod (which should be a hardened & ground shaft, but isn’t) surrounded by a pair of LM3UU linear bearings, a machined coupler, and the stub of a diamond engraving tool’s shank.

Tapping 15 mm of M6×1.0 thread inside of the case took an unreasonable amount of grunt. Next time, brass.

The setscrew gets a little boss to hold the spring away from the adjacent threads in the case:

Sherline Diamond Drag Holder – setscrew spring boss

The little machined cap has a somewhat longer spring guide to prevent buckling:

Sherline Diamond Drag Holder – shank cap spring guide

The spring fits snugly on the slightly enlarged section inside the last few coils, with the rest being a loose fit around the guide. When the spring is fully compressed, it’s just slightly longer than the guide and can’t buckle to either side.

The cap gets epoxied onto the 3 mm rod with some attention to proper alignment:

Sherline Diamond Drag Holder – shank cap alignment

The other end of the rod has a 3 mm thread, which would be a serious non-starter on a hardened rod.

The shortened diamond tool shank gets epoxied into the gizmo connecting it to the now-threaded rod, again with some attention paid to having it come out nicely coaxial:

Sherline Diamond Drag Holder – diamond tool alignment

The LM3UU bearings got epoxied into the case, because I don’t have a deep emotional attachment to them.

Unscrew diamond tool, push spring onto cap, drop rod through bearings, crank setscrew more-or-less flush with the end of the case, screw diamond in place with some weak threadlock, add oil to rod, work it a few times to settle the bearings, and it’s all good.

A quick spring rate measurement setup, with a brass tube holding the diamond point off the scale pan:

Sherline Diamond Drag Holder – installed

The spring rate works out to 230 g + 33 g/mm for deflections between 1.0 mm (263 g) and 3.5 mm (346 g), so it’s in the same ballpark as the diamond tools on the MPCNC and CNC 3018.

Note: WordPress just “improved” their post editor, which has totally wrecked the image alignment. They’re all set to “centered” and the editor says they are, but they’re not. It’s a free blog and I’m using one of their ancient / obsolete / unsupported themes, so I must update the theme. Bleh.

2020-03-26

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

HON Lateral File Cabinet Foot Repair

We bought the best-looking (pronounced “least bashed”) pair of hulking five-drawer industrial-strength HON Brigade Lateral File Cabinets from the local ReStore outlet’s assortment for Mary’s quilting fabric stash. They came with a steep discount, barely fit inside the Forester, caused minor interior trim damage, and should organize her entire stash.

One cabinet lost a foot nut at some point in its 16 year history:

HON Lateral File – foot hole – weld nugget filed

The surviving foot nuts sported two weld nuggets apiece:

HON Lateral File – OEM front foot

The hole had the remains of one nugget at the top left and looks like a manufacturing defect to me. Of course, we’re (at least) the second owners and the usual lifetime warranty no longer applies.

I can fix that.

Bandsaw a 1×¾ inch rectangle from 3/8 inch aluminum plate to match the surviving foot nut (which is steel, but aluminum will suffice for our needs). Break the edges, clamp in the Sherline, and mill a square protrusion to match the square-ish hole:

HON Lateral File – square nut – rough cut

Drill a 17/64 inch hole (looser than the nominal F drill, because I’m a sissy) for a flat-head bolt from the Drawer o’ 3/8-16 Bolts, tap, and clean up.

A trial fit showed the nugget had to go before the nut would come even close to fitting flat into the hole:

HON Lateral File – foot hole – grinding

The sheet metal around the hole had absorbed at least one mighty blow pushing the entire surface inward behind the front edge. To compensate, recess the nut’s front edge and slope the sides with a Dremel wheel to let the bottom face sit level:

HON Lateral File – square nut – taper grinding

Another trial fit showed the need for more recess:

HON Lateral File – square nut – deeper cut

Another spate of grinding made it sit mostly level on the decidedly non-level surface around the hole:

HON Lateral File – square nut – ready to install

The beveled corners fit inside the swaged hole corners.

Grind paint / crud off the sheet metal and roughen the surface for good epoxy griptivity:

HON Lateral File – foot hole – ready for install

Stand the cabinet top-side-down to make the bottom level. I wish the basement had one more course of block, but it’s not to be.

Butter the nut with JB Weld epoxy, plunk it in place, apply excess epoxy to make a fillet around the edges, apply duct tape to guy the top of the bolt level-ish, and let it cure:

HON Lateral File – square nut – epoxy curing

After the epoxy stiffened enough to hold its position, remove the bolt, file a crude ¼ inch hex, and saw a screwdriver slot to make it match the other feet:

HON Lateral File – new foot hex head

Not the fanciest job I’ve ever done, but it now behaves just like the other ones and it’s all good. The HON Storage Files FAQ points to a Troubleshooting Guide showing how to level the thing with a hex socket from inside the bottom drawer.

The flat heads on those bolts are basically 25 mm OD steel plates calling for fuzzy felt bumpers on the Sewing Room’s wood floors. When properly leveled, the front will be ⅛ inch higher than the rear. Although they suggest a pencil should roll toward the back, the top sheet metal on this one may be sufficiently warped to confuse the issue; I have a long level well suited to the task.

The original dimension doodle includes metric offsets for cutting with a ¼ inch end mill:

HON Foot nut – dimension doodles

All in all, a satisfying day in the Basement Shop …

2020-02-24
ACM Poughkeepsie Presentation: Algorithmic Art

In the unlikely event you’re in Poughkeepsie this evening, I’ll be doing a talk on my Algorithmic Art for the Poughkeepsie ACM chapter, with a look at the HPGL and G-Code transforming math into motion:

Superformula – triangle burst – detail

The PDF of the “slides” lacks my patter, but the embedded linkies will carry you to the blog posts & background information:

ACM – Algorithmic Art – 2020-01-27 Download

See you there! [grin]

2020-01-27
Homage Tek CC Cursor: Pivot Milling
A test to mill the pivot hole in 0.5 mm PETG sheet worked perfectly:

Tek CC – cursor pivot hole milling

The cutter is a 3.175 mm = 1/8 inch router bit, one of a ten-pack that came with the CNC 3018 and to which I have no deep emotional attachment, held in a collet in the Sherline. The hole is 5.5 mm to fit an eyelet. The PETG is taped to a thin plywood scrap.

The hole happened by feeding G-Code manually into LinuxCNC, after touching off XYZ=0 at the center of the pivot and jogging up a bit:
```
g0 y-1.1625
f1000
g0 z0.5
g2 p5 z-1.5 i0 j1.1625
```
Yes, I engraved the hairline using a diamond drag tool on the CNC 3018, cut the cursor outline with a drag knife on the MPCNC, then milled the pivot hole on the Sherline. This seems way over the top, even to me, but that’s just how the tooling worked out right now.

In actual practice, I’d probably mill a stack of cursors and pivot holes on the Sherline in one setup, then engrave the hairlines in a suitable fixture. I think I know enough to fit a spring-loaded diamond drag bit into the Sherline’s 10 mm ID spindle or, worst case, conjure a block for the Z-axis carrier in place of the entire spindle mount.

At least now I can remember what I did to make the hole.
2020-01-22
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
CNC 3018-Pro: Milling the CD Fixture

It turns out that the outer diameter of CD platters isn’t quite as perfectly controlled as you (well, I) might imagine, although the differences between CDs from different sources amounts to perhaps ±0.1 mm. Of course, instantly after putting the tape-down fixture into use, the next few discs atop my stack of scrap CDs were just large enough to not quite fit.

The Sherline’s workspace can’t maneuver the holder’s perimeter around the spindle, so embiggening the OD calls for the rotary table. The general idea is to clamp the center of the fixture to the rotary table, run a small end mill about 0.1 mm into the fixture’s OD, spin the table one revolution, and be done with it.

Of course, the rotary table’s 3/8-16 threaded center hole doesn’t match the fixture’s 6 mm center hole: we need an adapter. Start with a 1 inch long 3/8-16 stainless steel hex bolt, center drill the end, peel off the hex head, then turn to 6 mm OD, going down far enough so the threads don’t stick up out of the table too much:

CNC 3018-Pro – CD fixture milling – bolt turning

The Sherline uses 10-32 screws, so poke a #16 drill 15 mm into the bolt to get maybe 25% thread depth (because it’s a blind hole into stainless steel for an application requiring minimal strength and I hate breaking taps), tap 10-32, clean out the hole, and call it All Good:

CNC 3018-Pro – CD fixture milling – rotary table adapter

Find the trim plate from an old faucet to reach around the central boss, stack up enough flat washers to meet the nut, snug a Sherline spherical nut + washer set (because it’s within reach), chuck up a 1/8 inch mill, and have at it:

CNC 3018-Pro – CD fixture milling

The fixture sits atop an aluminum plate cut to fit a smaller version of the table riser, but this requires zero fancy alignment. The 6 mm adapter centers the fixture on the rotary table and the cutter sits at a fixed radius from the center wherever it contacts the fixture rim; just spin the table and it cuts a neatly centered circle.

A test fit showed the oversize discs fit perfectly:

CNC 3018-Pro – CD fixture milling – test fit

Bonus: a nice new adapter for the rotary table!

2019-09-13