Monthly Aphorism: On Improvements

  • You can rub and you can rub, but you can’t shine shit.

Eks tells me that was one of his grandmother’s favorite sayings.

He introduced me to the concept of a “used-car polish”: high shine over deep scratches. Sometimes, that’s exactly what the job requires.

There’s also the notion of making a silk purse from a sow’s ear (attributed variously to Jonathan Swift and Anon), which someone actually did: render the ear down to a gel, extrude thread, loom cloth, and sew up a purse. Yes, it can be done, but there’s a practical limit in there somewhere.

Contrary to what you might think, this has nothing to do with a certain Thing-O-Matic. A bit of laparoscopic surgery on our front yard just revealed that our septic leach field has filled with gunk; it’s 56 years old and hadn’t been pumped for two decades before we bought the place. The next week or two should be interesting: I can do the diagnosis, but I can’t handle this repair.

Stepper Extruder Calibration Objects: Barbie Style

After a few ranging shots, I printed coasterman’s calibration set. Much to my surprise, they came out very nicely… after the obligatory bit of tuning.

Everything printed at 40 mm/s, 0.33 mm layer thickness, 220 °C first layer / 210 °C all other layers, 120 °C aluminum platform. The first layer prints at 25% of normal speed/feed atop an aluminum plate covered with a thin layer of ABS. I’m still tweaking temperatures, first layer speeds, and ABS thickness on the plate.

All the pix have been contrast-stretched and lightly sharpened to bring out the detail. You’re going to start seeing a lot of Barbie style objects, because I want to use up that pink filament, OK?

The single-wall open box has an actual filament width of 0.55 mm, suggesting a w/t of 1.7. The Cool plugin throttled the speed down to 15 sec/layer and it’s just about perfect.

Calibration - Thin wall box
Calibration - Thin wall box

Here’s what it looked like in progress:

Calibration - Thin wall box - extruding
Calibration - Thin wall box - extruding
Calibration - 50 mm tower
Calibration - 50 mm tower

I simply didn’t believe the 50 mm tower would print until I saw it emerge intact. This is with 2 extra shells and 25% fill, at 15 sec/layer. The suck-in along the right edge comes from laying down the perimeter shell before doing the fill: that’s where the nozzle departs inward after finishing the perimeter. The distance to the fill was less than the Reversal threshold, so the stepper extruder didn’t reverse.

A few passes with the perimeter width/thickness tester resulted in a block that fits into the slot all eight ways with w/t=1.75 (with some orientations, mmm, much tighter than others, I’ll admit). The fill w/t=1.5 is obviously too low, because the top layer got overcrowded even with 25% fill on the internal layers.

The suck-out at the left corner shows where Reversal starts inhaling filament on alternate layers.  This was with 35 rpm and 100 ms, which seems too aggressive. It’s not bad-looking, mind you; I touched up the sides of the block with a bit of sandpaper to smooth out the tallest ridges.

Calibration - Perimeter Width
Calibration - Perimeter Width

The second classic 20 mm solid box looked good at w/t=1.75 and fill w/t=1.65, apart from the corner that pulled off the ABS and grew a tab that messed up half the layers. That’s what caused me to junk the ABP; about which, more later. The first one came out with the top looking a bit thin at fill w/t = 1.75.

Calibration - 20 mm solid box
Calibration - 20 mm solid box

The first hollow box just didn’t work at all, because setting w/t=1.75 built a single shell wall and the overhung top didn’t connect to the walls.

Calibration - 20 mm hollow box - failure
Calibration - 20 mm hollow box - failure

Changing to w/t=1.5 produced a reasonably good result, although the lid didn’t quite attach to the walls across the long diagonal. I always drop a scrap ball bearing inside to prove it’s hollow in there.

Calibration - 20 mm hollow box - success
Calibration - 20 mm hollow box - success

The Oozebane tests looked great, even though I’m not using Oozebane: a stepper extruder pretty much eliminates the need for that plugin. The front one had a few strings at 85 ms / 75 ms, the back one was clean at 100 / 75, but the fill got strangely thin.

Calibration - Oozebane test
Calibration - Oozebane test

Skeinforge 39 handles bridge layers oddly: no extra shells, fill parallel to one axis, and I really didn’t have it set up right. The holes look OK, albeit with poor contact with the fill.

Calibration - Precision - top
Calibration - Precision - top

The aggressive overhang didn’t work at all, but the 45 degree slope looks passable if you’re not too fussy. Small overhangs may be OK, but you really can’t do them without support material underneath.

Calibration - Precision - bottom
Calibration - Precision - bottom

All in all, the combination of a stepper extruder, spring-loaded filament tensioner, and an ABS-coated aluminum platform seems to produce good results. Maybe I can finally start printing useful objects…

However, as we all know, cranking out good calibration cubes doesn’t guarantee anything else will print the same way…

More Alkaline Battery Corrosion

The X10 RF Remote Control in the kitchen stopped working, which could mean only one thing: a set of dead AAA cells.

A negative terminal in the battery compartment showed the expected corrosion:

X10 Remote battery terminals
X10 Remote battery terminals

The corrosion evidently pushed the cell away from the terminal just enough to starve the remote.

The cells, on the other paw, looked just fine:

Battery negative terminals
Battery negative terminals

They’d been in there a year, sported a date code that’s still a few years in the future, and had a 1.3 V loaded output. Looks like that little bit of corrosion gave me enough of a heads-up to get the cells out before they rotted.


Thing-O-Matic: Wade/ScribbleJ Filament Tensioner

Putting a geared stepper motor on the MK5 filament drive produced greatly improved print quality, which meant I could finally print ScribbleJ’s version of the classic Wade Filament Tensioner and expect that it’d come out right. It’s a rather large lump of plastic that printed quite nicely on an aluminum plate.

Wade-ScribbleJ Filament Tensioner on plate
Wade-ScribbleJ Filament Tensioner on plate

The whole thing looks like this when it’s all assembled and adjusted:

Complete Geared Stepper Extruder
Complete Geared Stepper Extruder

[Update: The motor comes directly from the usual eBay supplier. You won’t find another one like it, but this is directly from the label…

  • 38 mm case
  • Minebea-Matsushita 17PM-K150-P1V
  • No. T6824-02


You can see the two thermal switches near the bottom of the picture. The 100 °C switch is inside the acrylic frame on the Thermal Riser, the 40 °C switch is just taped to the filament tensioner’s base. The former is OK, the latter isn’t as secure as it should be. FWIW, Riser temperatures run around 70 °C during normal extrusion, albeit in a chilly Basement Laboratory without covers on the TOM’s windows.

A better view of the shaft bearings and filament position:

Filament tensioner - overview
Filament tensioner - overview

The four long screws are 1.5 inch 4-40 from my heap, although 2 inch screws would give more room for adjustment. Some folks mount the screws the other way around, with the nuts pressing on the springs and little knobs on the nuts. I gave up on the washers to get a bit more adjustment range.

The springs came from my Big Box o’ Little Springs, sporting absolutely no pedigree at all. They’re not quite completely compressed, so there’s a bit of push left in them to handle filament diameter variations (which is the whole point of this exercise). I added four nuts (between the shaft bearing plate and the idler block) to keep the idler block from resting against the drive gear when there’s no filament in place: inserting a new filament became much easier.

Somewhat to my surprise, the entire filament drive gear assembly is free-floating and self-aligning within the housing:

Filament drive gear detail
Filament drive gear detail

I enabled the option to put a 5 mm diameter cleanout hole in the bearing housing, which turned out to be absolutely essential for monitoring the location of the drive gear inside all the machinery. You can barely see the hole in the first picture, on the left side of the curved section.

A floating shaft means the 7-tooth motor drive gear’s position must line up with wherever the 51-tooth filament drive gear happens to be. There’s not much room to adjust the motor gear, but a few iterations sorted out the proper number and placement of all the filament drive shaft washers, nuts, and bearings.

Filament drive gear - shaft spacing
Filament drive gear - shaft spacing

You (well, I) really really must put a flat on the shaft and use full-strength Loctite to hold the setscrew in place. I used an all-thread M6x40 bolt because that’s what I had on hand, but a partially threaded M6x50 bolt would provide better support for the bearings, more clearance for the spacers, and look a lot better; it’d require a custom-turned bushing instead of the nut against the big gear, though.

Flatted filament drive shaft
Flatted filament drive shaft

I initially used low-strength Loctite. Word: a loose drive gear setscrew can convince you that Skeinforge’s Reversal plugin isn’t working after you make many changes with worsening results. Those fast reversals loosen the setscrew in short order.

The diameters of the 7- and 51-tooth herringbone gears determine the center-to-center distance between the motor shaft and the extruder shaft. Alas, two of the motor mounting bolts wind up directly behind the larger gear. I marked the gear adjacent to the bolt heads and drilled a hole that just barely admits the hex wrench:

Stepper Extruder - motor mount access hole
Stepper Extruder - motor mount access hole

If you knew where that hole was supposed to be, you could print it right into the gear, but I haven’t a clue as to how you might algorithmically determine the precise location on the as-printed gears.

The modified OpenSCAD source produces two recesses for the bolt head and nut, but I just applied an end mill to the head side of the finished idler block. There’s no room for the bolt head between the block and the motor mounting plate.

Idler housing with recessed bolt
Idler housing with recessed bolt

Of course, I modified the OpenSCAD code along the way:

  • Changing the bearing size moved the base: use front_bearing_r in the routine that punches the holes
  • Add a complete outer surface on the idler block; I thought I might want a flat metal plate to distribute the stress.
  • Add bolt head / nut recesses for idler block pulley shaft
  • Include base_wall_h in the calculation for idler_max_h
  • Tweaked spacing to get idler bolt heads out of the walls
  • Extend motor wall rightward to cover all of the base plate
  • Adjust base hole positioning: -10 / +4.0, not -10 / +3.5
    • But not all instances of 3.5 must change, I think
  • Filament offset may need further tweakage
  • Other miscellaneous tweaks

Not all of those changes made it to the printed object shown here; if I ever print another one, they’ll be included. Use at your own risk!

The OpenSCAD source, which is almost entirely ScribbleJ’s work:

//  MK5 Wade's-Style Tensioner
// (C)2011, Christopher "ScribbleJ" Jansen
// Released under the BSD license.

// Modifications: Ed Nisley - KE4ZNU - Mar 2011

// Parametric Settings

// 1 = on, 0 = off
extend_shaft = 1 ;		// 0 will allow a bridge over the front of the motor hole
make_stepper_holes = 1;	// 1 will create mounting holes for a stepper mount.
make_dc_holes = 0;		// 1 will create mounting holes for a MK5 DC motor.
motor_shaft_supports = 1;	// 1 will create angle supports to the motor shaft. (See options below for support angle/size)
generate_for_viewing  = 0;	// 1 creates the model suitable for viewing.  0 creates the model suitable for printing.

cleaning_hole_d = 5;		// The diameter of a cleaning hole to punch.  (0 = no cleaning hole)
cleaning_hole_r = cleaning_hole_d/2;
cleaning_hole_angle = 75;	// Angle offset from 9 o'clock position (i.e. directly left)

hole_protrusion = 0.05;	// surface clearance for holes and suchlike

hole_windage = 0.4;			// allowance for small hole shrinkage

// _r = radius, _d = diameter, _h = height

// REAR BEARING = bearing closest to motor
rear_bearing_d = 17.0 + hole_windage;
rear_bearing_r = rear_bearing_d/2;
rear_bearing_h = 6.0;

// EXTRA SHAFT = include an extra length of motor shaft.  This is useful
// for giving your idler bolts enough room depth-wise.
extra_shaft = 5;

// FRONT BEARING = bearing furthest from motor  (Technically, front bearing diameter must be >= than rear to print properly... so
// there are many places in the code that we assume the front bearing is the largest d.
front_bearing_d = 17.0 + hole_windage;
front_bearing_r  = front_bearing_d/2;
front_bearing_h = 6;

// EXTRA FILAMENT = extend the length of the filament column.  This is useful
// for giving your idler bolts enough room height-wise.
extra_filament = 40;

filament_margin = 3.0;	// How wide is shaft on either side of filament?
filament_d = 4;			// How wide is filament shaft hole?
filament_r = filament_d/2;

// FILAMENT OFFSET = How far from the center of the motor axis your MK5 plastic pusher gear thingy
// or hobbed bolt groove is.
filament_offset = 6;

// MOTOR WALL = "rear" wall of tensioner.
motor_wall_h = 5;  		// thickness of wall
motor_bolt_d = 3.0 + hole_windage;		// diameter of motor mounting bolts
motor_bolt_r  = motor_bolt_d/2;
motor_bolt_h = motor_wall_h;
motor_bolt_hex_d = 6.3 + hole_windage;	// diameter of motor mounting bolt hex caps
motor_bolt_hex_r  = motor_bolt_hex_d/2;
motor_bolt_hex_h = 3;			// height of hex caps
motor_dropbolts   = 2.0;		// distance to sink bolts into wall
motor_boltmargin = 5;			// Distance to allow between bolts and edges of wall.
motor_shaft_width = 5;			// How thick is the wall around the motor shaft?
motor_shaft_support_width = 10;	// How thick are the motor supports (if any)?
motor_shaft_support_angle = 0;	// if non-0, will create three supports spaced apart this many degrees.
								// 0 creates a single support if enabled above.

// 31 is distance from center to bolt holes... do not chang this without changing hardcoded numbers
// in the motor bolt generating module.
motor_wall_w = 31 + (motor_boltmargin * 2) + motor_bolt_d;
motor_wall_d = 31 + (motor_boltmargin * 2) + motor_bolt_d;

// IDLER BEARING = the bearing that holds the plastic against the hobbed bolt/MK5 plastic pusher.
// You should include about an extra 2mm over your actual bearing measurements here so it can spin freely.
idler_bearing_d = 19 + 3;
idler_bearing_r  = idler_bearing_d/2;
idler_bearing_h = 6 + 2;
h_i = idler_bearing_h/2;
idler_bearing_bolt_d = 5;	// This is the size of the bolt holding the bearing in place.
idler_bearing_bolt_r = idler_bearing_bolt_d/2;

idler_bolt_d = 3.0 + hole_windage;		// This is the size of the (4) bolts holding the idler block in place.
idler_bolt_r  = idler_bolt_d/2;
idler_bolt_margin = 4;	// How much room to allow between bolt holes and edge of block.
idler_bolt_hex_d = 7.0 + hole_windage;
idler_bolt_hex_r  = idler_bolt_hex_d/2;
idler_bolt_hex_h = 5;         // Arbitrarily large to be sure to punch through supports/shaft.
idler_dropbolts   = 2.0;           // Try negative numbers here to catch your nuts on the supports.

idler_wall = 2.5;			// thickness of wall to left of idler bearing

idler_recess_dia = 9.0 + hole_windage;		// recess idler shaft bolt head & nut
idler_recess_r = idler_recess_dia/2;
idler_recess_depth = 3.0;

// BASE = the bottom part that bolts onto the hot end.
base_wall_h = 6;		// How thick or tall is the base.
base_bolt_d  = 3.0 + hole_windage;		// Size of bolts used to hold base -- rest of base settings are same as motor wall settings above.
base_bolt_r   = base_bolt_d/2;
base_bolt_hex_d = 6.3 + hole_windage;
base_bolt_hex_r  = base_bolt_hex_d/2;
base_bolt_hex_h = 5;
base_dropbolts = 1.5;
base_boltmargin = 6;
base_filament_offset_x = 6;

// 30/14.0 is distance from center to bolt holes...
// do not change this without changing hardcoded numbers
//  in the base bolt generating module.
base_w = 30 + (base_boltmargin*2) + base_bolt_r;
base_d  = 14.0 + (base_boltmargin*2) + base_bolt_r;

// base_z_extra is used for configurations where base wall or motor wall
//  would be unprintable due to differential in height.
// shrinks or grows the base to fit.
base_z_extra = ((idler_bearing_h/2) + rear_bearing_h + motor_wall_h) - ((base_d/2) + 3.5);
base_filament_offset_z = -3.5;  // How far the filament hole is from the bolts furthest from the motor.
base_d_use = base_d + base_z_extra;

// make up difference between bottom of wall and base... not really necessary but more support more better.
motor_wall_extra = front_bearing_r + (extra_filament/2) + base_h - (motor_wall_d/2);

// Calculate maximum space for idler block.
idler_max_h = idler_bearing_d + extra_filament + ((-base_bolt_hex_h+base_dropbolts)*2) - base_wall_h;
half_idler_max_h = idler_max_h/2;
idler_bolt_y = half_idler_max_h - idler_bolt_r - idler_bolt_margin;

//idler_max_w = .55 * idler_bearing_d;
idler_max_w = idler_bearing_r + idler_wall;			// enforce wall thickness on right side

idler_max_d = extra_shaft+front_bearing_h+idler_bearing_h+rear_bearing_h+((-motor_bolt_hex_h+motor_dropbolts)*2);
half_idler_max_d = idler_max_d/2;
idler_bolt_z = half_idler_max_d - idler_bolt_r - idler_bolt_margin;

echo(str("Idler block size: ",idler_max_d," x ",idler_max_h," x ",idler_max_w));
echo(str("Idler bolt spacing: ",2*idler_bolt_z," x ",2*idler_bolt_y));

// This module generates the bolt pattern for the idler, trying to fill the maximum space available.
	// echo(idler_bolt_r, idler_bolt_d, idler_max_d, idler_bolt_z, half_idler_max_d);
	// echo(idler_bolt_r, idler_bolt_d, idler_max_h, idler_bolt_y, half_idler_max_h);

	translate([idler_bolt_z,idler_bolt_y,0]) cylinder(r=idler_bolt_r, h=40);
	translate([idler_bolt_z,-idler_bolt_y,0]) cylinder(r=idler_bolt_r, h=40);
	translate([-idler_bolt_z,idler_bolt_y,0]) cylinder(r=idler_bolt_r, h=40);
	translate([-idler_bolt_z,-idler_bolt_y,0]) cylinder(r=idler_bolt_r, h=40);

		translate([idler_bolt_z,idler_bolt_y,0]) cylinder(r=idler_bolt_hex_r, h=idler_bolt_hex_h,$fn=6);
		translate([idler_bolt_z,-idler_bolt_y,0]) cylinder(r=idler_bolt_hex_r, h=idler_bolt_hex_h,$fn=6);
		translate([-idler_bolt_z,idler_bolt_y,0]) cylinder(r=idler_bolt_hex_r, h=idler_bolt_hex_h,$fn=6);
		translate([-idler_bolt_z,-idler_bolt_y,0]) cylinder(r=idler_bolt_hex_r, h=idler_bolt_hex_h,$fn=6);


// This module generates an idler block, filling the maximum space available.
module IDLER()
		translate([0,0,(idler_max_w/2)-(.25 * idler_bearing_bolt_d)]) cube([idler_max_d, idler_max_h, idler_max_w], center=true);
		translate([0,0,(-.5 * idler_bearing_bolt_r) + idler_max_w]) rotate([0,180,0]) IDLERBOLTS();
		#rotate([0,90,0]) cylinder(h=idler_max_d+1, r=idler_bearing_bolt_r,center=true);
		#rotate([0,90,0]) cylinder(h=idler_bearing_h, r=idler_bearing_r, center=true);
		translate([(idler_max_d/2 - idler_recess_depth),0,0])
		  #cylinder(r=idler_recess_r,h=(idler_recess_depth + hole_protrusion),$fn=10);
		translate([(-idler_max_d/2 + idler_recess_depth),0,0])
		  #cylinder(r=idler_recess_r,h=(idler_recess_depth + hole_protrusion),$fn=10);
	echo(str("IDLER BEARING BOLT LENGTH REQUIRED (longer is OK): ", idler_max_d, "mm"));

// This module creates the motor shaft hole pattern.
	// idler bearing
	cylinder(h=idler_bearing_h, r=rear_bearing_r, center=true);
	// front bearing
	translate([0,0,h_i]) cylinder(h=front_bearing_h, r=front_bearing_r);
	if(extend_shaft == 1)
		translate([0,0,h_i]) cylinder(h=front_bearing_h+(extra_shaft/2)+50, r=front_bearing_r);
	// rear bearing
	translate([0,0,0 - h_i - rear_bearing_h - (extra_shaft/2) - motor_wall_h])
		cylinder(h=         rear_bearing_h + (extra_shaft/2) + motor_wall_h, r=rear_bearing_r);

	echo(str("MOTOR SHAFT/BOLT LENGTH REQUIRED (longer is OK): ", front_bearing_h+idler_bearing_h+rear_bearing_h+motor_wall_h+(extra_shaft/2), "mm"));
	echo(str("MOTOR SHAFT LENGTH FROM REAR OF MOUNT TO FILAMENT:", motor_wall_h+(extra_shaft/2)+rear_bearing_h+(idler_bearing_h/2), "mm"));

// This module creates an MK5 mount motor hole pattern with optional hex insets for bolt heads/nuts.
module MK5_MOTORHOLES(include_dc = 1, include_stepper = 1, include_hex = 1)
	// The hardcoded numbers in the module below are simply the coordinates of the motor holes,
	// relative to the center of the motor shaft.

	if(include_stepper == 1)
		translate([15.5,15.5,-motor_dropbolts-hole_protrusion])	cylinder(r=motor_bolt_r, h=motor_bolt_h+(2*hole_protrusion));
		translate([15.5,-15.5,-motor_dropbolts-hole_protrusion])	cylinder(r=motor_bolt_r, h=motor_bolt_h+(2*hole_protrusion));
		translate([-15.5,-15.5,-motor_dropbolts-hole_protrusion])	cylinder(r=motor_bolt_r, h=motor_bolt_h+(2*hole_protrusion));
		translate([-15.5,15.5,-motor_dropbolts-hole_protrusion])	cylinder(r=motor_bolt_r, h=motor_bolt_h+(2*hole_protrusion));

		if(include_hex == 1)
			translate([15.5,15.5,motor_bolt_h-motor_dropbolts-hole_protrusion])	cylinder(r=motor_bolt_hex_r, h=motor_bolt_hex_h + (2*hole_protrusion), $fn=6);
			translate([15.5,-15.5,motor_bolt_h-motor_dropbolts-hole_protrusion])	cylinder(r=motor_bolt_hex_r, h=motor_bolt_hex_h + (2*hole_protrusion), $fn=6);
			translate([-15.5,-15.5,motor_bolt_h-motor_dropbolts-hole_protrusion])	cylinder(r=motor_bolt_hex_r, h=motor_bolt_hex_h + (2*hole_protrusion), $fn=6);
			translate([-15.5,15.5,motor_bolt_h-motor_dropbolts-hole_protrusion])	cylinder(r=motor_bolt_hex_r, h=motor_bolt_hex_h + (2*hole_protrusion), $fn=6);

	if(include_dc == 1)
		translate([0,-15.5,-motor_dropbolts])					cylinder(r=motor_bolt_r,h=motor_bolt_h);
		rotate([0,0,-60])  translate([0,-15.5,-motor_dropbolts]) 		cylinder(r=motor_bolt_r,h=motor_bolt_h);
		rotate([0,0,-120]) translate([0,-15.5,-motor_dropbolts])	cylinder(r=motor_bolt_r,h=motor_bolt_h);
		rotate([0,0,-180]) translate([0,-15.5,-motor_dropbolts])	cylinder(r=motor_bolt_r,h=motor_bolt_h);
		if(include_hex == 1)
			translate([0,-15.5,motor_bolt_h-motor_dropbolts])					cylinder(r=motor_bolt_hex_r,h=motor_bolt_hex_h, $fn=6);
			rotate([0,0,-60])  translate([0,-15.5,motor_bolt_h-motor_dropbolts]) 	cylinder(r=motor_bolt_hex_r,h=motor_bolt_hex_h, $fn=6);
			rotate([0,0,-120]) translate([0,-15.5,motor_bolt_h-motor_dropbolts])	cylinder(r=motor_bolt_hex_r,h=motor_bolt_hex_h, $fn=6);
			rotate([0,0,-180]) translate([0,-15.5,motor_bolt_h-motor_dropbolts])	cylinder(r=motor_bolt_hex_r,h=motor_bolt_hex_h, $fn=6);

// This module creates MK5 hot-end hole patterns with optional hex heads for the bolts/nuts.
module MK5_BASEHOLES(include_MK5boltheads = 1, include_filament = 1, include_hex = 1)

	// The hardcoded numbers in the routine below are simply the coordinates of the base holes,
	// relative to the filament hole.
	if(include_filament == 1)
		translate([0,0,100/4]) cylinder(r=filament_r, h=100,center=true);

	translate([-15,4.0,-base_dropbolts-hole_protrusion]) cylinder(r=base_bolt_r,h=base_h+(2*hole_protrusion));
	translate([-15,-10,-base_dropbolts-hole_protrusion]) cylinder(r=base_bolt_r,h=base_h+(2*hole_protrusion));
	translate([15,4.0,-base_dropbolts-hole_protrusion]) cylinder(r=base_bolt_r,h=base_h+(2*hole_protrusion));
	translate([15,-10,-base_dropbolts-hole_protrusion]) cylinder(r=base_bolt_r,h=base_h+(2*hole_protrusion));

	if(include_MK5boltheads == 1)
		translate([17,9.5,-hole_protrusion]) cylinder(r=3, h=4);
		translate([17,-15.5,-hole_protrusion]) cylinder(r=3, h=4);
		translate([-17,9.5,-hole_protrusion]) cylinder(r=3, h=4);
		translate([-17,-15.5,-hole_protrusion]) cylinder(r=3, h=4);

	if(include_hex == 1)
		translate([-15,4.0,base_h-base_dropbolts-hole_protrusion]) cylinder(r=base_bolt_hex_r,h=base_bolt_hex_h+(2*hole_protrusion), $fn=6);
		translate([-15,-10,base_h-base_dropbolts-hole_protrusion]) cylinder(r=base_bolt_hex_r,h=base_bolt_hex_h+(2*hole_protrusion), $fn=6);
		translate([15,4.0,base_h-base_dropbolts-hole_protrusion]) cylinder(r=base_bolt_hex_r,h=base_bolt_hex_h+(2*hole_protrusion), $fn=6);
		translate([15,-10,base_h-base_dropbolts-hole_protrusion]) cylinder(r=base_bolt_hex_r,h=base_bolt_hex_h+(2*hole_protrusion), $fn=6);


// This module generates the mounting part of the Wade's-style tensioner.
// The generated item is centered on the motor shaft in X,Y and the filament in Z.
module MOUNT()


		translate([0,0,-1 * (motor_wall_h/2)])
			cylinder(h=front_bearing_h + idler_bearing_h + rear_bearing_h + extra_shaft + motor_wall_h, r=front_bearing_r+motor_shaft_width, center=true);
			translate([base_filament_offset_x,0,0]) cube([filament_d + (2 * filament_margin),   front_bearing_d + extra_filament,  front_bearing_h + idler_bearing_h + rear_bearing_h + extra_shaft + motor_wall_h], center=true);

			if(motor_shaft_supports == 1)
				translate([0,0,(motor_wall_h/2)]) {
					cylinder(	h=front_bearing_h + idler_bearing_h + rear_bearing_h + extra_shaft,  r1=(motor_wall_w/2),  r2=front_bearing_r+motor_shaft_width, center=true);
					rotate([0,0,90]) translate([0,50,0]) cube([motor_shaft_support_width, 100, front_bearing_h + idler_bearing_h + rear_bearing_h + extra_shaft], center=true);
					cylinder(	h=front_bearing_h + idler_bearing_h + rear_bearing_h + extra_shaft,  r1=(motor_wall_w/2),  r2=front_bearing_r+motor_shaft_width, center=true);
					rotate([0,0,90-motor_shaft_support_angle]) translate([0,50,0]) cube([motor_shaft_support_width, 100, front_bearing_h + idler_bearing_h + rear_bearing_h + extra_shaft], center=true);
					cylinder(	h=front_bearing_h + idler_bearing_h + rear_bearing_h + extra_shaft,  r1=(motor_wall_w/2),  r2=front_bearing_r+motor_shaft_width, center=true);
					rotate([0,0,90+motor_shaft_support_angle]) translate([0,50,0]) cube([motor_shaft_support_width, 100, front_bearing_h + idler_bearing_h + rear_bearing_h + extra_shaft], center=true);

		translate([0,motor_wall_extra/-2,((motor_wall_h/-2) + rear_bearing_h+(extra_shaft/2)+motor_wall_h+(idler_bearing_h/2)) * -1])
			  union() {
				cube([motor_wall_w, motor_wall_d+motor_wall_extra, motor_wall_h], center=true);
				translate([base_filament_offset_x - (motor_wall_w - base_w)/2 + motor_wall_w/4,0,0])
				  cube([motor_wall_w/2,motor_wall_d+motor_wall_extra, motor_wall_h],center=true);

		translate([filament_offset, -1* (front_bearing_r + (extra_filament/2) + (base_h/2)), base_filament_offset_z])
			  cube([base_w, base_h, base_d_use], center=true);
			// extend filament shaft
			translate([0,(front_bearing_d + extra_filament + base_h)/2, 0])
			  cube([filament_d + (2 * filament_margin), front_bearing_d + extra_filament, base_d], center=true);


	// Punch motor holes
	translate([0,0,-1*((idler_bearing_h/2) + (rear_bearing_h) + (motor_wall_h) + (extra_shaft/2))])
	  # MK5_MOTORHOLES(include_stepper=make_stepper_holes, include_dc = make_dc_holes);
	// Punch motor shaft
	// Punch idler bolt holes
	translate([filament_offset - filament_margin - (filament_r) + idler_dropbolts,0,0])
	  rotate([90,90,90]) # IDLERBOLTS();
	// Punch baseplate holes
	translate([filament_offset, -1* (front_bearing_r + (extra_filament/2) + base_h), 0])
	  rotate([-90,180,0]) # MK5_BASEHOLES();
	// Punch idler bearing clearance
	translate([filament_offset + idler_bearing_r - filament_r, 0,0])
	  cylinder(h=idler_bearing_h + front_bearing_h + rear_bearing_h + extra_shaft + hole_protrusion, r=idler_bearing_r, center=true);
	// Punch cleaning hole
	rotate([-1 * cleaning_hole_angle,-90,0])


if(generate_for_viewing == 1)
	translate([filament_offset + idler_bearing_r,0,0]) rotate([0,90,0]) IDLER();
else if(generate_for_viewing == 0)
	translate([15.5+motor_boltmargin+motor_bolt_r+2.5,    0,   (motor_wall_h+(extra_shaft/2)+rear_bearing_h+(idler_bearing_h/2))]) MOUNT();
	translate([(idler_max_d/-2)-2.5, 0, (-.5 * idler_bearing_bolt_r) + idler_max_w]) rotate([180,0,0]) IDLER();

Just. Do. It.

Thing-O-Matic: Manual Wipe and Splodge

The first step of a good print requires nailing the extrusion to the build platform. The Skeinforge Splodge plugin seems to thicken the first part of each filament on the first layer, which is not helpful. So I turned that off and added a few lines to start.gcode that do a much better job.

I also disabled the Wipe plugin, because you really can’t wipe the nozzle after the first few layers without having some part of the Z stage clobber the object. Rather than enable Wipe for just the first layer, I put a manual wipe in start.gcode, too.

The relevant sections look like this; they fit after the homing sequence at the end of the file:

(--- manual wipe ---)
G0 X54 Y-57.0 Z15	(move above wipe start)
G0 Z8   			(down to wipe level)
M6 T0				(wait for temperature settling)
M101				(Extruder on, forward)
G4 P4000			(take up slack, get pressure)
M103				(Extruder off)
G4 P4000			(Wait for filament to stop oozing)
G0 Y-40				(wipe nozzle)
(--- manual splodge)
G0 X-50 Y-55		(to front left corner)
G1 Z0.50			(just over surface)
M108 R2.0			(set stepper extruder speed)
M101				(start extruder)
G4 P2000			(build up a turd)

Depending on a myriad imponderable factors, the manual wipe sequence flips off either a huge tangle or a tiny strand. That’s why I used a 4 second delay: it’s long enough to leave the extruder pressure in a consistent state no matter how it starts.

The manual splodge location depends on your platform layout; I’m thinking of putting it entirely outside the build area. It must be somewhere near the front left corner, because Skeinforge starts each new layer from that direction. Two seconds of extrusion at 2 rev/min forms a blob with a generous contact patch, although the nozzle must plow through the side on its way out.

Note that I leave the extruder running at the end of start.gcode, which means that it’s printing all the way to the outline. That won’t interfere with any part of the object, because (by definition) the first layer of the object lies entirely within the outline.

The Outline plugin puts a single filament around the entire object, allowing me to measure the actual nozzle height and extrusion width on the first layer. More on that later.

The final result looks like this:

Manual Splodge with Companion Cube
Manual Splodge with Companion Cube

Notice that the splodge turd isn’t firmly glued to the platform, but the thread leading to the outline sticks like it was glued and the outline comes out perfectly formed. That’s the whole idea in a nutshell: paste the thread down from a stationary nozzle, then start moving with the turd acting as an anchor.

Trying to start pasting the filament with the nozzle moving doesn’t work well, as witness the left edge of the outline around these test pieces:

ABS coating on aluminum build plate
ABS coating on aluminum build plate

Admittedly, that was with a DC extruder, but the same principle applies to stepper extruders.

MK5 Extruder: Thermal Riser Temperatures – Operating

Thermal Switches in place
Thermal Switches in place

My Parts Heap disgorged a somewhat larger TO-5 heatsink (a Thermalloy 228B, which they no longer make) with three fins and a collar having enough spring to fit tightly around the Thermal Riser Tube. It was intended for transistors on PCBs with horizontal air flow, but I hoped it would be more effective than the smaller heatsink that comes stock with the TOM.

There’s certainly some air flow through the heatsink at the top of the arches, but I have no way of measuring that. The picture there shows another, much flatter, heatsink that I’d been using to cool the Thermal Riser after I found out how hot it was getting near the top.

This heatsink didn’t get a thermocouple mount epoxied to it and, given my experience with the first set of measurements, I didn’t bother stuffing a thermocouple between the fins.

The Thermal Switch Block now has a 100 °C NC Thermal Switch epoxied to it and, barely visible to the lower right, a 40 °C NO Switch is taped to the Z stage in the corner of the acrylic support base. The switch cable looks like this:

Themal Switches - prepped and mounted
Themal Switches - prepped and mounted

With the meter’s T1 thermocouple bead behind the 40 °C switch and T2 tucked into the Thermal Switch Block, the results look thusly:

Thermal Riser and Z stage Temperature Graph - block top
Thermal Riser and Z stage Temperature Graph - block top

The core went to 220 °C this time, with the ABP at 120 °C, and I started extruding at 20 minutes when the temperature had stabilized. The Switch Block temperature promptly dropped 6 °C as room-temperature filament entered the top of the Thermal Riser Tube at 2 rev/min × 10 cm drive dia × π = 63 mm/min ≈ 1 mm/sec.

The previous test showed that the Thermal Switch Block stabilized at 90 °C and I think this one will be about the same, despite the larger heatsink, although the while-extruding temperature hovers around 70 °C. That’s better than 90 °C, so I’ll keep monitoring it and see how it plays in warmer weather inside a cozy build chamber. Obviously, having the Extruder ram cool filament into the Thermal Core holds the temperature down.

Given those numbers, a 110 to 120 °C NC switch would be better; I’m sure one will eventually appear in my usual surplus sources. With a 30 °C margin and an assumed rise of 7 °C per 25 °C Thermal Core increase, the switch will trip when the Core passes 225 + (4 × 25) = 325 °C. That’s rather toasty, but the alternative seems to be having a switch that kicks out on a hot day.

As expected, the Z stage temperature passed 40 °C at 10 minutes and the (yellow) Low Overtemperature LED blinked on. I wasn’t too surprised at that; the previous test had a cold ABP. I’ll move that switch to the top of the acrylic arch, taped against the base of the Filament Drive frame where it can measure the effect of the Thermal Riser on the plastic base. That picture shows the potential for high temperatures at that spot.

The original data:

Thermal Riser and Z stage Temperatures - block at top
Thermal Riser and Z stage Temperatures - block at top

MK5 Extruder: Thermal Riser Temperatures 2

Switch block - top
Switch block - top

Using pretty much the same setup as before, I put the Thermal Switch Block at the top of the MK5 Thermal Riser Tube and the little heatsink at the bottom. The heatsink sat between the bolt head and left just enough room that I could snake the thermocouple bead into the brass tube, so these temperatures should be much more representative of the actual Thermal Riser.

After getting everything stuck together, I discovered that I’d interchanged the thermocouple leads. Rather than fixing that, take note that the T1 and T2 datasets represent different objects, but the same physical position: T1 on the bottom, T2 on the top.

I skipped the staged warmup, cried “Fire the Thing-O-Matic!” and ran it to 225 °C while recording temperatures every 5 minutes along the way. The graph looks like this:

Thermal Riser Tube Temperature Graph - block on top
Thermal Riser Tube Temperature Graph - block on top

They’re not quite exponentials, because the Core temperature gets flattened at the top, but they’re still pretty.

The top-to-bottom temperature differential has increased to 35 °C, although the top temperature still hits 90 °C. I think there are countervailing forces at work:

  • The thermocouple is in better contact with the Heatsink: the bottom of the tube really is hotter with the Heatsink at that end.
  • The Thermal Block gives a better measure of the top-of-Tube temperature, because that thermocouple is intimately connected to the Block. The Tube top is about the same temperature, but the previous Heatsink temperatures were lower.

In short, I trust these readings a bit more than the previous ones.

But, as before, the Switch Block is still too hot for a 100 °C Thermal Switch. The next step is to add a somewhat larger heatsink from my Parts Heap and see what happens.

The original data:

Thermal Riser Temperatures - block at top
Thermal Riser Temperatures - block at top