The New Hotness

Up to this point, the Sherline has been drilling 3.5 inch hard drive platters to serve as as reflecting bases for the vacuum tubes:

LinuxCNC - Sherline Mill - Logitech Gamepad — LinuxCNC – Sherline Mill – Logitech Gamepad

The CNC 3018-Pro has a work envelope large enough for CD / DVD platters, so I mashed the Sherline fixture with dimensions from the vacuum tube code, added the 3018’s T-slot spacing, and conjured a pair of fixtures for a pair of machines.

Because I expect to practice on scrap CDs and DVDs for a while:

Platter Fixtures - CD on 3018 — Platter Fixtures – CD on 3018

And a 3.5 inch hard drive platter version:

Platter Fixtures - hard drive platter on 3018 — Platter Fixtures – hard drive platter on 3018

The holes sit at half the 3018’s T-slot spacing (45 mm / 2), so you can nudge the fixtures to the front or rear, as you prefer.

The alignment dots & slots should help touch off the XY coordinate system on the Sherline, although it can’t reach all of a CD. Using bCNC’s video alignment on the hub hole will be much easier on the 3018.

After fiddling around with the 3018 for a while, however, the CD fixture doesn’t have many advantages over simply taping the disc to a flat platen. Obviously, you’d want a sacrificial layer for drilling, but it’s not clear the OEM motor / ER11 chuck would be up to that task.

The OpenSCAD source code as a GitHub Gist:

	// Machining fixtures for CD and hard drive platters
	// Ed Nisley KE4ZNU February … September 2016
	// 2019-08 split from tube base models

	PlatterName = "CD"; // [3.5inch,CD]

	CNCName = "3018"; // [3018,Sherline]

	PlateThick = 5.0; // [5.0,10.0,15.0]

	RecessDepth = 4.0; // [0.0,2.0,4.0]

	//- Extrusion parameters must match reality!

	/* [Hidden] */

	ThreadThick = 0.25;
	ThreadWidth = 0.40;

	HoleWindage = 0.2;

	Protrusion = 0.1; // make holes end cleanly

	inch = 25.4;

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

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


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

	//———————-
	// Dimensions

	P_NAME = 0; // platter name
	P_ID = 1; // … inner diameter
	P_OD = 2; // … outer diameter
	P_THICK = 3; // … thickness

	PlatterData = [
	["3.5inch", 25.0, 95.0, 1.75],
	["CD", 15.0, 120.0, 1.20],
	];

	PlatterSides = 345; // polygon approximation

	B_NAME = 0; // machine name
	B_OC = 1; // … platform screw OC, use small integer for slot
	B_STUD = 2; // … screw OD clearance

	BaseData = [
	["3018", [5.0, 45.0], 6.0], // slots along X axis
	["Sherline", [1.16inch,1.16inch], 5.0], // tooling plate

	];

	//———————-
	// Drilling fixture for disk platters

	module PlatterFixture(Disk,Machine) {

	PI = search([Disk],PlatterData,1,0)[P_NAME]; // get platter index
	echo(str("Platter: ",Disk));
	Platter = [PlatterData[PI][P_ID],
	PlatterData[PI][P_OD],
	PlatterData[PI][P_THICK]];

	BI = search([Machine],BaseData,1,0)[B_NAME]; // get base index
	echo(str("Machine: ",Machine));

	AlignOC = IntegerMultiple(Platter[OD],10);
	echo(str("Align OC: ",AlignOC));
	AlignSlot = [3ThreadWidth,10.0,3ThreadThick];

	StudClear = BaseData[BI][B_STUD]; // … clearance

	StudOC = [IntegerMultiple(AlignOC + 2*StudClear,BaseData[BI][B_OC].x), // … screw spacing
	BaseData[BI][B_OC].y];
	echo(str("Stud spacing: ",StudOC));
	NumStuds = [2,1 + 2*floor(Platter[OD] / StudOC.y)]; // holes only along ±X edges
	echo(str("Stud holes: ",NumStuds));

	BasePlate = [(20 + StudOC.x*ceil(Platter[OD] / StudOC.x)),
	(10 + AlignOC),
	PlateThick];
	echo(str("Plate: ",BasePlate));
	PlateRound = 10.0; // corner radius

	difference() {
	hull() // basic plate shape
	for (i=[-1,1], j=[-1,1])
	translate([i(BasePlate.x/2 – PlateRound),j(BasePlate.y/2 – PlateRound),0])
	cylinder(r=PlateRound,h=BasePlate.z,$fn=4*4);

	for (i=[-1,0,1], j=[-1,0,1]) // origin pips
	translate([iAlignOC/2,jAlignOC/2,BasePlate.z – 2*ThreadThick])
	cylinder(d=4*ThreadWidth,h=1,$fn=6);

	for (i=[-1,1], j=[-1,1]) { // alignment slots
	translate([i*(AlignOC + AlignSlot.x)/2,
	j*Platter[OD]/4,
	(BasePlate.z – AlignSlot.z/2 + Protrusion/2)])
	cube(AlignSlot + [0,0,Protrusion],center=true);
	translate([i*Platter[OD]/4,
	j*(AlignOC + AlignSlot.x)/2,
	(BasePlate.z – AlignSlot.z/2 + Protrusion/2)])
	rotate(90)
	cube(AlignSlot + [0,0,Protrusion],center=true);
	}

	for (i=[-1,1], j=[-floor(NumStuds.y/2):floor(NumStuds.y/2)]) // mounting stud holes
	translate([iStudOC.x/2,jStudOC.y/2,-Protrusion])
	rotate(180/6)
	PolyCyl(StudClear,BasePlate.z + 2*Protrusion,6);

	translate([0,0,-Protrusion]) // center clamp hole
	rotate(180/6)
	PolyCyl(StudClear,BasePlate.z + 2*Protrusion,6);

	translate([0,0,BasePlate.z – Platter[LENGTH]]) // disk locating recess
	rotate(180/PlatterSides)
	linear_extrude(height=(Platter[LENGTH] + Protrusion),convexity=2)
	difference() {
	circle(d=(Platter[OD] + HoleWindage),$fn=PlatterSides);
	circle(d=Platter[ID] – HoleWindage,$fn=PlatterSides);
	}

	translate([0,0,BasePlate.z – RecessDepth]) // drilling recess
	rotate(180/PlatterSides)
	linear_extrude(height=(RecessDepth + Protrusion),convexity=2)
	difference() {
	circle(d=(Platter[OD] – 10),$fn=PlatterSides);
	circle(d=(Platter[ID] + 10),$fn=PlatterSides);
	}
	}

	}


	//———————-
	// Build it

	PlatterFixture(PlatterName,CNCName);

view raw Platter Fixtures.scad hosted with ❤ by GitHub

The New Hotness

CNC 3018-Pro: Platter Fixtures