Tag: CNC

Although that collet pusher works fine, the locking pin holder often teleported itself inside the vacuum cleaner. It recently reappeared on the far end of the main workbench, a good 15 feet away from the Sherline as the swarf flies. This, to misquote Churchill, is an impertinence up with which I shall not put.

Herewith, a replacement offering several advantages:

• Won’t fit up the vacuum’s snout
• Easy to grip
• Perfect pin alignment
• 3D printing FTW!

It’s a flat block resting on the flat top of the pulley, with a nice arc matching the pusher’s OD. A small hole for the pin at exactly the right altitude makes the whole thing rock-solid stable: it slides firmly into position.

The 3D model looks like you’d expect:

The finger grips were just for pretty, as you don’t need that much traction to extract the thing.

A similar view of the real object with the bottom surface up and some flash around the edges:

The as-printed block put the pin about 0.2 mm above the spindle hole, so I rubbed it on Mr Belt Sander (with the power off) until it fit. I printed the block on the aluminum plate platform; the Z height home setting evidently needs a tweak. However, the hole was exactly the correct distance from the top surface: flipping the block over fit perfectly.

The OpenSCAD source code:

// Collet extractor locking pin holder for Sherline spindle
// Ed Nisley - KE4ZNU - Feb 2011

include </home/ed/Thing-O-Matic/lib/MCAD/boxes.scad>
include </home/ed/Thing-O-Matic/lib/MCAD/units.scad>

PusherOD = 17.35;					// Shell of collet pusher

PulleyOD = 65.5;					// For 3k rpm head

PinHoleCtr = (3/16) * inch;			// pin hole center above pulley surface
PinDia = 2.50;						// pin is about #40 drill
PinHoleDepth = 10.0;				// hole depth from PusherOD

HoleWindage = 0.55;					// Approximate extrusion width
Padding = 0.1;						// A bit of spacing to make things obvious

HolderWidth = 2 * PusherOD;						// Overall holder width
HolderProtrusion = 15;							// sticks out beyond pulley
HolderLength = PulleyOD/2 + HolderProtrusion;	//	... length
HolderThickness = 2*PinHoleCtr;					//	... thickness
HolderRounding = HolderWidth/5;					// corner rounding

GripLength = 0.70 * HolderWidth;	// grip notch
GripWidth = 0.25 * GripLength;
GripIndent = HolderProtrusion/2;

difference() {

// main slab

  translate([-HolderLength/2,0,0])
	roundedBox([HolderLength,HolderWidth,HolderThickness],HolderRounding,true,$fn=4*8);

// pin hole

  translate([-(PusherOD/2 + PinHoleDepth/2 - Padding),0,0])
  rotate([0,90,0])
	cylinder(r=PinDia/2,h=(PinHoleDepth + Padding),center=true,$fn=8);

// upper grip

  translate([-(HolderLength - GripIndent),0,(HolderThickness/2)])
  rotate([90,0,0])
	cylinder(r=GripWidth/2,h=(GripLength - GripWidth),center=true);

  translate([-(HolderLength - GripIndent),((GripLength - GripWidth)/2),(HolderThickness/2)])
	sphere(r=GripWidth/2,$fn=10);

  translate([-(HolderLength - GripIndent),-((GripLength - GripWidth)/2),(HolderThickness/2)])
	sphere(r=GripWidth/2,$fn=10);

// lower grip

  translate([-(HolderLength - GripIndent),0,-(HolderThickness/2)])
  rotate([90,0,0])
	cylinder(r=GripWidth/2,h=(GripLength - GripWidth),center=true);

  translate([-(HolderLength - GripIndent),((GripLength - GripWidth)/2),-(HolderThickness/2)])
	sphere(r=GripWidth/2,$fn=8);

  translate([-(HolderLength - GripIndent),-((GripLength - GripWidth)/2),-(HolderThickness/2)])
	sphere(r=GripWidth/2,$fn=8);

// spindle shaft

  cylinder(r=(PusherOD/2)+HoleWindage,h=(HolderThickness + 2*Padding),center=true);

}

This is a variation of Thing 6384: an aluminum plate sitting atop the Automated Build Platform’s bare heat spreader, minus the belt. HIs truly ingenious idea was to cover the plate with a thin layer of ABS to ensure adhesion: an ABS filament bonds very well to ABS!

I started with a big sheet of 3/32 inch aluminum, a bit thinner than the 1/8 inch sheet he used, which is what I had in the Parts Heap. Bandsawed three chunks to rough shape, squared up the edges on the Sherline with manual CNC:

That was complicated by the Sherline’s cramped work envelope. The 5/8 inch lathe bit on the right sits at exactly right angles to the X axis and serves as the reference plane. To make it happen:

• Stack the three plates, clamp to table aligned against lathe bit
• Whack off the far edge
• Put clean edge against lathe bit
• Whack off another edge
• Measure / scribe 120 mm from each new edge (thus the blue stripes)
• Align & cut

That actually worked quite well, although you’d think the angular error would build up as I rotated the plates. I checked and tweaked the angle after the first cut and it was all good.

Then drill six clearance holes for the socket head cap screws holding the heater plate to the ABP; a #1 drill gave a few mils clearance, which is all it needs. The holes are 4 mm in from the edges of the 120 mm square, with the two middle ones at, yes, 60 mm.

However, there’s not much meat between the edge of the plate and the holes: call it 1.1 mm. If you do this, using 122 mm plates would produce less scary-close results. That’s why I like manual CNC for this stuff: no need to lay it out, tap in the numbers and it just Works.

My APB heater has a static drain connected to the heat spreader, so I milled a 2 mm recess around the right-hand screws to clear the lugs, wires, and Wire Glue blob. The silicone wiper gets its own cutout, which I made a snug fit so that the rubber would push the plate against the screw heads and hold it in place.

I machined recesses on only one plate, so I could incorporate any changes in the other two. The initial setup was atop a scrap plastic sheet which, as it turned out, wasn’t particularly flat. The edges of that not-quite-complete hole on the left were nasty-sharp.

Then clean off the ink with xylene, scrub the plate with a 220-grit sanding sponge, and it looks really nice. Impossible to photograph a uniform gray surface, though: the autofocus goes nuts.

While all that was going on, I’d dumped some MEK into a polyethylene jar along with a handful of calibration cubes and similar debris. I used MEK, rather than acetone, because it’s somewhat less aggressively flammable while still being a good solvent for ABS. Right now, the gunk has the consistency of thin honey, which may be too thick to spread easily; I’m still figuring this out. I apply the gunk with a folded coffee filter: scrape the puddle around to cover the whole plate, then let it dry. This is best done outdoors, except that right now it’s well below freezing out there.

Here’s what the film looks like under the start of a quartet of dodecahedrons I ran off to see if they stuck properly:

The bottom surface looks like it was machined: dead flat,nice edges, good thread definition. The parts stick like they were glued to the surface, with no tendency to pull up at the corners.

The Outline thread shows some adhesion trouble for the first 10 mm or so. After that, it’s nailed right to the ABS film. That’s why I use Outline, at least until I figure out a better way to start the thread.

After I finish the next two plates, I’ll have a somewhat quick-change build platform: pull the hot plate off (holding it with pliers!) and slap a new one on. Not as convenient as the ABP, but much better for building precision parts like gears and extruder motor mounts.