Category: Machine Shop

Mechanical widgetry

Makergear M2 Improved Platform: Solid State Relay and Thermistor

I’d originally planned to drive the new HBP with a boost converter from the 24 V supply brick, but that didn’t quite work out. The arrival of a 36 V brick from halfway around the planet solved that problem, but the RAMBo platform heater’s 15 A ATO fuse restricts it to 24 V and I don’t quite trust that MOSFET for high current applications, either.

Sooo, I went full-frontal Cupcake with a solid state relay screwed to a pair of existing holes (!!!) in the M2’s frame:

M2 – SSR for Improved HBP

Note: that’s a DC-to-DC SSR, not the more common DC-to-AC SSR. Basically, it’s an up-armored optically isolated MOSFET, not a triac, and, yes, capitalizing acronyms and initalisms can be contentious.

Because the RAMBo’s MOSFET now drives the piddly current required to activate the SSR, I rewired the power to apply the M2’s 19.5 V brick to all three inputs by adding two red jumpers on the right side of the Phoenix plugs:

M2 HBP SSR Wiring

The M2’s hulking 12 V brick now resides in the Basement Warehouse’s Power Supply Annex.

The HBP cable comes in from the right side and the 36 V supply arrives through the Powerpole connectors in the lower right. Tucking the ferrite slug on the 19.5 V supply behind the wire loom prevents the cable from pulling the Phoenix connectors out of the RAMBo board at an inopportune moment.

The original M2 HBP wiring got uncomfortably warm carrying the 10+ A for that platform. It would probably work OK at a lower current, but I’d already put Powerpole connectors on the new HBP. So I ran that cable outside the loom and abandoned the original pair inside.

The SSR switches the +36 V wire, leaving the HBP at 0 V when it’s not activated: supply hot → SSR → HBP → supply common. That makes no practical difference, but it feels like a Good Idea. Also, the Kapton tape across the SSR terminals should be barely adequate to prevent contact with random conductive clutter; I’m channeling the true spirit of DIY 3D printing…

I don’t have a connector matching the M2’s 100 kΩ platform thermistor, either, so I just ran the new cable down the outside of the loom and conjured up a two-pin socket for the header on the RAMBo board:

Improvised 2-pin header socket

Plug it all together, tweak the startup G-Code to properly trip the Z-min switch at its new location, and it Just Works:

M2 Improved HBP – alignment test

Those are thinwall open boxes that came out 5±0.03 mm tall across the array, so the platform is just about as level / aligned as necessary for my simple needs.

The Z-min switch will move to get rid of that stupid block epoxied to the platform, so I didn’t record the G-Code tweakage…

2013-10-11
Makergear M2 Improved Platform: Mechanical Adjustments

The PCB under the improved flat-top glass platform has three soldered-in-place M3 screws that fit the M2’s Y stage support:

M2 – Improved HBP – bottom view

I applied a tiny rat-tail file to the holes until they became a free sliding fit for the screws.

The wave springs are mostly decoration, as the silicone rubber disks now take the compression load from the screws, and the platform is quite rigidly mounted.

The new platform eliminates the M2’s original aluminum support spider, the aluminum heater & heat spreader, and the corner supports & clips, all of which add up to about 780 g. I didn’t bother changing the Y axis acceleration to match, as all those numbers seem rubbery.

Minus the support spider, the platform rides much lower on the Z axis stage than the M2’s platform. Unfortunately, the Z-min switch clamped to the top of the rear Z-axis guide rod can’t get any higher, even after rearranging the cable and fiddling with the LED:

M2 – Z min limit switch

As a first-pass hack, I moved the switch to the rear of the X gantry and applied Gorilla Tape to hold it in place:

M2 – Z-min switch at rear X gantry

That required a small block to raise the platform enough to activate the switch before hitting the nozzle. I epoxied a snippet of brass rectangle tube to the left edge of the platform, directly under the switch lever:

M2 – Improved HBP – rear switch tab

The awkward position activates the switch with the platform as far to the rear as possible, so that you can’t inadvertently drag the dangling switch lever across the block in the wrong direction.

I think it’s stupid, too, but it let me bring up the printer and make sure all the electronics kept working. The next step was to relocate the switch to a more rational place

2013-10-10
Tour Easy: Handlebar Wrap

After more than a few years, the handlebar grips on my Tour Easy are rather worn, so I recently wrapped them with cheerful red and yellow silicone tape.

Back in the day, you wrapped with cork tape and had to worry about the direction on each side. Silicone tape fuses into a solid mass and the orientation shouldn’t matter; that’s a Good Thing, because I’m not sure what direction would be correct in this situation.

The yellow section covers the SRAM twist grip, which means it has a moving joint at each end. I suspect the tape will pull back from the larger part of the grip and form an unsightly lump just behind it.

It’s certainly much grippier than I expected…

(The small pushbutton switch is the PTT for the amateur radio HT that does voice and APRS/GPS.)

2013-10-08
Humanoid Finger

Just for fun, I printed out Anthromod’s Kickstarter Hand finger:

Anthromod Finger – parts on M2 platform

If I were doing it, I’d add 1.75 mm alignment holes in each part, but clamping each phalange in both directions came out close enough:

Anthromod Finger – clamping

The tolerances were a bit tight and it required some trimming before all the joints flexed freely. I used short segments of 3 mm orange filament for the knuckle hinges and heat-staked the ends, rather than having to trim a trio of 3 mm screws:

Anthromod Finger – detail

After making three short rubber bands by tying and trimming loops from a longer band, the finger curled up just like yours:

Anthromod Finger – curled

The overall quality isn’t as good as I’d like: there’s a bit of uplift on the edges and corners. If I print another one, I want to try less than 0.2 infill and less cooling.

2013-10-07
Sonicare Essence: Re-taping the Case

Much to my astonishment, the ordinary adhesive tape holding the Sonicare Essence power toothbrush together lasted for a bit over a year. As the tape splits along the gap in the case, the coil driving the brush head begins vibrating inside its nest, making a truly horrendous racket.

The new fix looks a bit odd, but works fine:

Sonicare Essence – red tape

The tape comes from Mad Phil’s stash and is, I think, splicing tape for reel-to-reel 1/4 inch recording tape: it has zero stretch, infinite strength, and adhesive that’s obviously lasted forever. The inside of the spool says “NOPI Made in Germany”, which doesn’t lead anywhere useful, although the NOPI name does seem to appear in a tape context.

After a year, the replacement NiMH cells are doing fine, still operating about once a day for three weeks from a 24 hour charge.

2013-10-04

3D Printed PCB Stiffening Bracket

The brassboard PCB for the Hall effect blinky light is too bendy for the SMD parts to survive much debugging, particularly with all the wires hanging off the edges, so I whipped up a stiff mounting bracket that captures the whole thing, with a flange that fits in the work stand arms:

PCB Test Frame - solid model — PCB Test Frame – solid model

I ran some self-tapping 4-40 hex-head screws into the holes while the plastic was still warm on the M2’s platform:

PCB stiffener with screws on M2 platform

Six screws seem excessive and I’ll probably wind up using just the middle two, but there’s no harm in having more holes and fittings than you really need.

The flange fits neatly into the board holder on the Electronics Workbench, above all the construction clutter:

The nice thing about having a 3D printer: when you need an object like this, a couple of hours later you have one!

The OpenSCAD source code, slightly improved based the results you see above:

// Test support frame for Hall Effect LED Blinky Light
// Ed Nisley KE4ZNU - Sept 2013

ClampFlange = true;

//- Extrusion parameters - must match reality!

ThreadThick = 0.25;
ThreadWidth = 0.40;

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

Protrusion = 0.1;

HoleWindage = 0.2;

//- Screw sizes

inch = 25.4;

Tap4_40 = 0.089 * inch;
Clear4_40 = 0.110 * inch;
Head4_40 = 0.211 * inch;
Head4_40Thick = 0.065 * inch;
Nut4_40Dia = 0.228 * inch;
Nut4_40Thick = 0.086 * inch;
Washer4_40OD = 0.270 * inch;
Washer4_40ID = 0.123 * inch;

//- PCB sizes

PCBSize = [46.5,84.0,1.0];
PCBShelf = 2.0;

Clearance = 4*[ThreadWidth,ThreadWidth,0];

WallThick = IntegerMultiple(4.0,ThreadWidth);
FrameHeight = 5.0;

ScrewOffset = 0.0 + Clear4_40/2;

OAHeight = FrameHeight + Clearance[2] + PCBSize[2];

FlangeExtension = 3.0;
FlangeThick = IntegerMultiple(1.5,ThreadThick);
Flange = PCBSize
			+ 2*[ScrewOffset,ScrewOffset,0]
			+ 2*[Washer4_40OD,Washer4_40OD,0]
			+ [2*FlangeExtension,2*FlangeExtension,(FlangeThick - PCBSize[2])]
			;

echo("Flange: ",Flange);
NumSides = 4*5;

//- Adjust hole diameter to make the size come out right

module PolyCyl(Dia,Height,ForceSides=0) {			// based on nophead's polyholes

  Sides = (ForceSides != 0) ? ForceSides : (ceil(Dia) + 2);

  FixDia = Dia / cos(180/Sides);

  cylinder(r=(FixDia + HoleWindage)/2,h=Height,$fn=Sides);
}

//- Put peg grid on build surface

module ShowPegGrid(Space = 10.0,Size = 1.0) {

  RangeX = floor(100 / Space);
  RangeY = floor(125 / Space);

	for (x=[-RangeX:RangeX])
	  for (y=[-RangeY:RangeY])
		translate([x*Space,y*Space,Size/2])
		  %cube(Size,center=true);

}

//- Build it

ShowPegGrid();

difference() {
	union() {									// body block and screw bosses
		translate([0,0,OAHeight/2])
			color("LightBlue")
			cube(PCBSize + Clearance + [2*WallThick,2*WallThick,FrameHeight],center=true);
		for (x=[-1,1], y=[-1,0,1]) {
			translate([x*(PCBSize[0]/2 + ScrewOffset),
						y*(PCBSize[1]/2 + ScrewOffset),
						0])
				color("Orchid") cylinder(r=Washer4_40OD,h=OAHeight,$fn=NumSides);
		}
		if (ClampFlange)
			translate([0,0,Flange[2]/2])
			color("SeaGreen") cube(Flange,center=true);
	}

	for (x=[-1,1], y=[-1,0,1]) {				// screw holes and washer recesses
		translate([x*(PCBSize[0]/2 + ScrewOffset),
					y*(PCBSize[1]/2 + ScrewOffset),
					-Protrusion])
			rotate((x-1)*90)
			PolyCyl(Tap4_40,(OAHeight + 2*Protrusion));
		translate([x*(PCBSize[0]/2 + ScrewOffset),
					y*(PCBSize[1]/2 + ScrewOffset),
					OAHeight - PCBSize[2]])
			PolyCyl(1.2*Washer4_40OD,(PCBSize[2] + Protrusion),NumSides);
	}

	translate([0,0,OAHeight/2])					// through hole below PCB
		cube(PCBSize - 2*[PCBShelf,PCBShelf,0] + [0,0,2*OAHeight],center=true);

	translate([0,0,(OAHeight - (PCBSize[2] + Clearance[2])/2 + Protrusion/2)])	// PCB pocket on top
		cube(PCBSize + Clearance + [0,0,Protrusion],center=true);
}

2013-10-02

Monthly Science: Silica Gel Status Report

The last of the silica gel from one bulk can went into a mesh bag:

Silica gel beads in mesh bag

That kept a batch of fresh-baked crackers crisp during several humid days. It started out at 110 g net = 112 g gross (with bag and ties), rose to 115 g after a day, then to 117 g by the time we were done with the crackers. That’s about 5 g of water = 4.5% by weight, so those charts say the humidity should be under 10 %RH, which agrees with the fading blue dot on the humidity indicator card I dropped in the can.

When the bag gets up to 130 g = 30 %RH, then it’ll be time for a recharge… or, more likely, a refill from one of the remaining three cans.

2013-10-01

Category: Machine Shop

Makergear M2 Improved Platform: Solid State Relay and Thermistor

Makergear M2 Improved Platform: Mechanical Adjustments

Tour Easy: Handlebar Wrap

Humanoid Finger

Sonicare Essence: Re-taping the Case

3D Printed PCB Stiffening Bracket

Monthly Science: Silica Gel Status Report