Boiling water for finishing PLA

April 7, 2014

You all probably know this already, but if you don’t or had forgotten, read on. I was making a bunch of screwable containers because they’re really good for convincing people about stuff that can’t be made easily by conventional methods, but the tops and bottoms kept jamming together. I print the tops about 2% bigger for clearance, and it’s still not good enough.

In fact, a bunch of them got stuck in the almost-closed position, which is pretty much worthless. Since they were pretty much a writeoff, I figured it might be worth experimenting with water from our tea/coffee tap (about 90 C) to at least see if I could expand the outsides enough to unjam and then go after them with sandpaper and a swiss army knife. A few splashes got each one unstuck, and then I figured what the hell, while I was standing in front of the sink. I put the outside (“top”) on the bottom of the sink and splashed it full of hot water, then as quickly as I could started the bottom threading into it, then picked the pair up and screwed them open and closed a bunch of times until the water had cooled.

I don’t know if the tops were just being expanded a bit, or if enough of the surface roughness was being smoothed down to make things work, but darned if I don’t have three working containers that were formerly useless in a kind of embarrassing way.

People keep talking about all these weird chemicals as possible smoothing agents for PLA, but it seems as if a little boiling water (either applied fast or with cooling of the bulk PLA) may be just the thing for me.



October 25, 2013

that's almost right



What’s worse than this dog’s breakfast is the fact that I thought I had blown out the stepper motor in the previous extruder after weeks of running it way too hot, but after I’d gone too far with this version to unwind my hot-end modifications, I found I hadn’t.  It’s a really bad design, but it was what I could do without being able to print up any new parts. Probably my most serious mistake  is the idler, which is a skate bearing in a bent-aluminum frame being pushed against the old makerbot drive pulley by those three torsion springs, which were the strongest things I could find at the local hardware store. All the pivoting designs have a serious mechanical advantage, but this has none. The springs acquire a permanent bend and stop working after a few hours, so I am ordering some stamping-machine compression springs from McMaster-Carr…

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Bodgestruder lives!

April 11, 2013

Ugliest extruder ever?This winter, when I finally ditched the DC motor on my cupcake’s extruder and switched to a stepper, I ran into the same problem pretty much every 3D printer owner has faced. To upgrade your printer, you have to print new parts.

My first try — just unbolting the old motor from the plastruder and swapping a stepper  — was a miserable failure. First, I wasted a month getting the 4.5mm toothed stepper shaft to fit the 6mm filament drive gear, and then when I did, nada. Couldn’t push filament out of a paper bag. Then I got a “high-torque” stepper. More fun drilling out the bushing inside the drive gear to fit a 5mm shaft, tiny dribble of filament, lots of knocking sounds as the stepper skipped steps.

That’s when I decided to bring the stupid. I had some blocks of UMHW plastic from the wood shop, some extruded aluminum bar and angle and a random collection of bearings. First try was with the toothed-shaft stepper and a teeny little 12mm bearing that coincidentally has a 4-40 (aka M3 diameter) tapped hole through the middle. Almost worked, but lining the bearing up with the shaft and getting the pressure right was too much trouble. Oh, and you would think drill bits couldn’t wander way off course going through 3/4″ of plastic, but you’d be wrong.

Then what you see here: a block of UMHW with a couple holes to anchor it to the extruder platform, a couple more holes to bolt on the stepper, and a big chunk of aluminum angle to hold a skate bearing for an idler. At first I ran a couple of springs across the top, but that didn’t work, so I settled on the little piece of bent and twisted aluminum bar stock you see here. It has enough flex to put good pressure on the filament, and the leftover m3 bolts offer adjustment.

And it prints. It still skips steps every now and then, but it can pretty reliably spit out about 35mm/sec for an hour at a time. ABS or PLA. I have a couple test gears and some fan ducts.

Next step is a geared extruder. I might try to print something eventually, but for now my plan is to fake Greg/Wade  starting with a chunk of aluminum box extrusion and some hobby gears. And a 5mm bolt carrying that same damn 6-now-5mm bore drive gear.

Si muove

December 1, 2011

OK, I was wrong about the noise. Or at least wrong about where it was coming from. Once I had an oscilloscope to look at the signals it became clear I had the pinout wrong. I was misreading the Sanguino breakout board, and once I moved the wires over one space everything started working wonderfully. (What does it say, by the way, when signal leakage across an air gap or a few megohms of resistance is sufficient to make the stepper driver respond…)

So as a test I clamped a stepper to the end of a piece of plywood hanging out in the general direction of the y axis, coupled the shaft to one of the surplus nylon lead screws, and ran it. It ran the platform back and forth  fine up to about 1600 steps/s, which is about 120 rpm, or about 50 mm/s.  I can probably tune that up some with lubricant and a little more voltage and current.

Quiltrap here we come. I’m not sure what I’m going to be extruding, but I’ve got a maximum build volume of 300x225x280mm.

For one brief shining moment…

November 20, 2011

It seemed possible that my solution could be reduced to “solder the bleeping pin, you moron!”. Of all the pins on the three stepper boards I assembled way back when, which solder joint had been omitted? The one connecting the direction line to the stepper-controller socket. So I soldered it. (And thank you, Adafruit Industries, for selling me a real soldering iron. So much easier with a real tip than with the Radio Shack version.)

Nothing doing. Didn’t make any change for the board I fixed. The other two boards worked exactly the same way. Looks like I’m going to have to get a scope. Grr.

Noise, Noise, Noise, Noise.

November 17, 2011

I am the Grinch, and my old reprap boards are WhoVille. This is nothing the rest of you don’t know already, but gosh the old connection system is a mess. I’m trying to get the old electronics working so that a) maybe I can actually make the original quiltrap with its huge build space and b) I can check out some surplus stepper motors without letting any more magic smoke out of the boards on my cupcake.

Anyway, the first time I tried this a bunch of lights flashed, but only when I was probing the breakout-shield contacts with my multimeter to see if anything was happening. This time the same thing, only I discovered I don’t have to have the other probe on the ground terminal, I just have to be holding a probe in my hand and touching the step contact. If I press hard the sound of the stepper goes from an ugly rattling noise to a smooth whine, and it turns much faster. Hmm.

Wikipedia says the human body has a capacitance of about 22 picofarads, so I guess that’s about the amount of decoupling I’m going to have to throw on to get rid of all the electrical noise. I’m also going to shorten the cables between the sanguino and the stepper boards something fierce. And maybe even consider — since I’m working in a basement — attaching an honest-to-goodness ground wire to the whole thing.

After that, it will be time to see if I can get the Sanguino to run something other than the stepper-test program I uploaded last year, which still seems to be running whenever it starts up.

My First Thing

August 26, 2011

It’s even potentially useful. Limited application to be sure, but if you want something like that, that’s what you want.  I have a few ideas about working around the skeinforge no-fill issue, but none of them are pretty.

I also learned a certain amount about designing simple stuff for cupcake. You need parameters to adjust anything that’s supposed to be an exact fit to outside stuff. And where a “normal” design would align things to the center of the main block, a design for extruder is much easier with alignment to one edge so you don’t need support. Also, I keep making stuff too big.

Associativity in Openscad

August 13, 2011

I’m probably missing something, and it’s probably about creating modules. Unions and differences are kicking my butt.

I was trying to create an annulus (the difference between two cylinders, like a donut or a tire) and then take only a section of that, so that I’d have a piece that was curved along one axis and straight along the other. Then I wanted to use that piece to take a bite out of a rectangle (so, for instance, C’s head thingy could have a smiling mouth).

No can do. Try to take a difference where one of the nodes is itself a difference and (as far as I could tell) nothing happens. I had to make a union and move one of the cylinders out of the difference and slice its edges off all over again. I’m sure there’s a rule for how you decompose and recompose stuff like this, but oy. If it’s by making modules somebody tell me (I’ve already sketched out the math for annular sections made by differencing cones and then cutting off rectangles to clip the parts you don’t want), or if I have to go learn CSG properly I think I might try and build a set of openscad bindings that will do the ugly stuff automagically.

On the other hand, the last couple hours of noodling show that it is possible to get the shape I want, just annoying.


(Oh, yeah, and I’ve been printing some calibration cubes and gosh. Not even close.)

This is what happens when you let a 6-year-old drive openscad

August 11, 2011

not porous Yes, I know, my skeinforge settings need work. I think I’m extruding too much plastic way too hot (the thermocouple never gets below 210C), and probably with too small a layer height. The raft also sticks to the back of the object (as it has with a bunch of other prints) and my “tower” setting is way optimistic. Any other obvious mistakes I’m missing?


On the other hand, a 6-year-old knows none of these things, only that he helped sketch something and then 20 minutes later was dropping it in a cup of water to see whether it floats. And that the original design can be tweaked and improved pretty much endlessly until it looks like what’s in his head.

I think this is potentially(!) as big a deal for teaching kids as Logo was — C got the idea that you could make things out of “cubes” and spheres and “cylinders” pretty quickly, and he was even the one who suggested cutting a rectangle out of the big block to make the mouth. And of course we put things in the wrong places to start with, so the “translate” function was pretty obvious as well.

And he gets something to keep and play with that he can enjoy even when he’s away from the computer.

Okay, now it works

July 28, 2011

I have a mug. I have a couple of really bad lego blocks, I have a mostly acceptable half-cube and small tower.

The tweaking will be endless. Hurrah!


Oh, yeah, and I have to install sun java so the whole thing doesn’t crash every 20 minutes or so.