The Smell of Molten Projects in the Morning

Ed Nisley's Blog: Shop notes, electronics, firmware, machinery, 3D printing, laser cuttery, and curiosities. Contents: 100% human thinking, 0% AI slop.

Tag: Improvements

Making the world a better place, one piece at a time

Thing-O-Matic: Filament Melt Zone
The 0.5 mm nozzle came off the hot end with surprisingly little effort; the high-temperature lube did its job! I dismantled the tensioner, clipped the filament at the top of the drive wheel, and extracted it (with the red PTFE insulation / guide tube) through the bottom of the Thermal Core. Getting the filament out of the tube required the gentle suasion of a pin punch, but eventually I found this:

Filament melt zone – overview

Although you can’t tell from the picture, the filament seems completely melted for about 20 mm, well-softened for another 20 mm, and soft for about 10 mm. Here’s a detail of the transition from well-softened to soft to hard:

Filament melt zone – detail

Notice how the notches from the drive wheel gradually fade out over about 10 mm, whereupon the filament expands to fill the PTFE tube. You can’t see the shallow depression from an air pocket offscreen at about 30 mm, but it suggests the filament isn’t quite molten from 20 mm onward. Given that the distance from the nozzle tip to the top of the Thermal Core is about 40 mm, all this makes sense, particularly when you figure the filament was stationary as the Core cooled off after the last print: the melted-to-melty sections are inside the Core and the softened section is just above the Core.

In round numbers, the Thermal Core supplies enough heat through the PTFE tube to fully melt the filament for about 20 mm above the nozzle when printing at 2 rev/min. The effective drive diameter is 9.6 mm, so 1 rev = 9.6 π = 30 mm and the Core must melt 60 mm/min = 1 mm/s. This is obviously a grossly nonlinear situation, but if you get only 20 mm of molten filament at 1 mm/s, the maximum speed can’t be much more than 4 mm/s or so.

The rest of the Thing-O-Matic’s mechanics set an upper limit for, say, printed octopi at 80 mm/s and 4 rev/min = 2 mm/s, but the extruder will definitely be the limiting factor for speeds over, say, 150 mm/s. Not much risk of that happening here, I’d say.

I’ve settled on Reversal for 125 ms at 25 rev/min, so the retraction distance is:
```
1.6 mm = (30 mm/rev) (0.125 s) (25 rev/min) / (60 s/min)
```
That’s somewhat smaller than the 3 mm of pushback I’ve seen when swapping filaments in mid-print, but it’s in the right ballpark.

Now, to install the 0.4 mm nozzle and recalibrate the software yet again…
2011-12-17
RCA Alarm Clock Dimming

Mary prefers dim digits on the bedroom alarm clock, far below what the usual DIM switch setting provides. I’d slipped a two-stop neutral density filter in front of our old clock’s VFD tube, but the new one has nice green LED digits that ought to have a tweakable current-setting resistor behind the switch. Indeed, a bit of surgery revealed the switch & resistors:

RCA clock – DIM switch and resistors

It turns out that the 220 Ω resistors set the DIM current, with the 100 Ω resistors in parallel to set the BRIGHT current. Weirdly, the display operates in two halves: one resistor for the lower and middle segments, the other for the top segments. The resistor numbers give a hint of what the schematic might look like:

RCA clock – LED current-set resistors

The current control isn’t all that good, because the brightness varies with the number of active segments. With 470 Ω resistors (yes, from that assortment) in place, the variation became much more obvious; the LEDs are operating far down on their exponential I-vs-V curve. We defined the result to be Good Enough for the purpose.

Four short screws hold the circuit board in place, but one of them arrived loosely held in a pre-stripped hole. I cut eight lengths of black Skirt filament, anointed them with solvent adhesive, dropped two apiece into each screw hole, and ran the screws back in place. I likely won’t be back in there, so it should be a lifetime fix:

RCA clock – ABS filament in screw hole

Done!

As with all the trade names you remember from back in the Old Days, the present incarnation of “RCA” has nothing whatosever to do with the original Radio Corporation of America:

RCA clock – data plate

2011-12-13
Mindless Entertainment

Sometimes I need a task that doesn’t require a lot of thinking, like reducing the entropy of a bag of mixed SMD resistors…

Sorting SMD Resistors

I’ve heard tell of a TV-thing that serves the same purpose. Dunno when you’d have time to sort your resistors, though.

Resistors being marked, I didn’t need those SMD tweezers.

(Yes, this makes no sense. It’s mindless. Sometimes, ya just gotta do this stuff. OK?)

2011-12-10
SMD Measurement Tweezers

While fiddling around with those SMD capacitors, it occurred to me that I really needed some SMD tweezers: small forceps with isolated jaws, connected to the capacitance meter’s terminals. In the nature of a proof-of-concept, I sacrificed a (surplus) Tektronix banana plug cable and an old plain-steel tweezer (stamped Made in Japan back in the day when that had the same quality connotations as does Made in Pakistan right about now) and lashed them together:

SMD tweezers – overview

I chopped off the tweezer joint with a bolt cutter, scuffed up the steel with a file, soldered the cable wires, cut a small wood block to fit, and epoxied the whole mess together:

SMD tweezers – epoxy joint

When the epoxy cured, a generous wrap of silicone tape hid most of the hackage. Two lengths of clear heatstink tubing insulate the handles from my sweaty fingers:

SMD tweezers – joint detail

Part of the reason for picking this victim was its cheap-and-bendy steel: more easily soldered than stainless, no regrets about filing the jaws to suit. They’re flattened on the bottom and filed to grip SMD chips along their length:

SMD tweezers – tip shape

That’s on the top panel of my indispensable AADE LC meter. The stray capacitance of that cable is around 50 pF, but the meter can null it to a fraction of a pF. At least as long as I don’t change my grip, that is, which isn’t too severe a restriction. [Update: got the link right this time.]

That gorgeous Tek cable turned out to be entirely too stiff and the natural curve doesn’t lie in the correct direction. The next version will probably use a length of RG-174 mini coax and a dual banana plug. I think I’d like angled jaws, too, so as to attack the chips from the top down.

But even this version works wonderfully well, as I sorted out a few hundred random SMD caps in two half-hour sessions that I’d been putting off for far too long. This is the last batch; I’ve learned the hard way that it pays to transfer batches of chips to their storage bins long before I think I should:

Sorting SMD caps

Yeah, it’s false economy, but it keeps me off the streets at night. OK?

2011-12-08
Canon SX230HS Close-up Adapter: Up-amped LED Ring

Paralleling a 510 Ω resistor with each of the 180 Ω resistors on the LED ring light around the macro lens holder boosted the LED string current from 15 to 20 mA:

LED ring light – paralleled resistors

The complete botch job in the lower right is what you get when you don’t wipe the soldering iron tip first.

LED brightness being pretty nearly linearly proportional to current, the exposure gets another 0.4 EV that probably doesn’t matter in the least.

A hand-held picture of the pile of SMD resistors (which willingly produced four of the five resistors and required enhanced interrogation to extract the last one):

SX230HS – macro lens – 15 x 20 mA ring light

That’s pretty much overhead at f/8, so the depth of field is as good as it gets.

2011-12-06
Harbor Freight Digital Thickness Gauge: Lubrication Thereof

Picked up a Harbor Freight thickness gauge to measure Thing-O-Matic filaments and suchlike; it has a plastic piston and anvil, so it’s not well-suited to measure anything other than plastic parts. In fact, it’s all plastic and the various sliding surfaces produced a remarkable amount of friction.

Fortunately, the back cover pops off without too much of a struggle:

Harbor Freight Digital Thickness Gauge – cover removed

Dabs of silicone lube at all the contact points considerably improved its disposition.

The display offers 0.01 mm resolution, but I don’t believe that rightmost digit for an instant. The stated accuracy is ±0.1 mm, which is probably closer to the truth, and it agrees reasonably well with my considerably better quality digital caliper.

2011-12-04
Thing-O-Matic: Large Hole Calibration
Flushed with success on the small-hole front, I conjured up a large hole testpiece using the same HoleAdjust function that proved unnecessary with the little ones:

Circle Calibration – solid model

The first version didn’t have the cross bars, which turned out to be a mistake, because the individual rings distorted even under minimal pressure from the calipers:

Large circle cal – unlinked rings

However, measuring as delicately as I could, the holes seemed a scant 0.20 mm too small, more or less, kinda-sorta:

Nominal Nom+0.0

10 9.83

20 19.75

30 29.85

40 39.84

50 49.84

60 59.72

70 64.76

80 79.28

90 89.77

So I fed in HoleFinagle = 0.20 and the second iteration looks like it’d make a great, albeit leaky, coaster:

Large Circle Calibration object – HoleFinagle 0.20

Measuring those holes across the center with the calipers on facets (rather than vertices), produced somewhat more stable results:

Nominal Nom+0.20

10 10.08

20 20.17

30 30.08

40 40.08

50 50.00

60 60.02

70 70.05

80 79.98

90 90.07

Frankly, I don’t believe those two least-significant digits, either, because a different set of measurements across different facets looked like this:

Nominal Nom+0.20

10 10.13

20 20.11

30 29.84

40 39.90

50 49.88

60 59.90

70 69.84

80 79.82

90 89.66

I also printed a testpiece with HoleFinagle = 0.25 that averaged, by in-the-head computation, about 0.05 larger than that, so the hole diameter compensation does exactly what it should.

Applying the calipers to the 10.0 mm hole in the small-hole testpiece gives about the same result as in this one. The fact that HoleFinagle is different poses a bit of a mystery…

The only thing I can conclude is that the measurement variation and the printing variation match up pretty closely: the actual diameter depends more on where it’s measured than anything else. The holes are pretty nearly the intended size and, should the exact size matter, you (well, I) must print at least one to throw away.

All in all, a tenth of a millimeter is Good Enough. Selah.

Oh. The ODs are marginally too small, even using PolyCyl.

The OpenSCAD source, with both adjustments set to neutral:
```
// Large circle diameter calibration
// Ed Nisley KE4ZNU - Nov 2011

//-------
//- Extrusion parameters must match reality!
//  Print with +1 shells, 3 solid layers, 0.2 infill

ThreadThick = 0.33;
ThreadWidth = 2.0 * ThreadThick;

HoleFinagle = 0.00;
HoleFudge = 1.00;

function HoleAdjust(Diameter) = HoleFudge*Diameter + HoleFinagle;

Protrusion = 0.1;			// make holes end cleanly

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

//-------
// Dimensions

Width = 2.5;
Thickness = IntegerMultiple(2.0,ThreadThick);

DiaStep = 10.0;

NumCircles = 9;

echo(str("Width: ",Width));
echo(str("Thickness: ",Thickness));

BarLength = (NumCircles + 1)*DiaStep;

//-------

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=HoleAdjust(FixDia)/2,h=Height,$fn=Sides);
}

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

  Range = floor(50 / Space);

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

}

//------

module Ring(RingID,Width,Thick) {

  difference() {
	PolyCyl((RingID + 2*Width),Thick);
	translate([0,0,-Protrusion])
	  PolyCyl(RingID,(Thick + 2*Protrusion));
  }
}

//------

ShowPegGrid();

union () {
  for (Index = [1:NumCircles])
	Ring(Index*DiaStep,Width,Thickness);
  for (Index = [-1,1])
	rotate(Index*45)
	  translate([-BarLength/2,-Width/2,0])
		cube([BarLength,Width,Thickness]);
}
```
2011-11-26