The week isn't complete without a lab fire

I made the last few connections on the 2nd printer last night, fired it up and did some test prints.

First discovery, those really tiny surface mount resistors can't handle a quarter watt. I didn't bother to calculate the power dissipation, after all it was just running a single LED. After it popped, smoked and caught fire (how exciting!) I ran the numbers:
18v, 2v drop on the LED, 1000 ohms resistor, that's 16ma. Perfect. 16ma @ 16v = 0.288 watts. OK, that's not so good on a resistor the size of a pinhead.

Anyway, I peeked underneath after becoming confident that the fire was out, determined it was just the LED resistor, and powered back up. I don't really need the LED, it's just pretty.

I did a test print, the nickel calibration piece. The first one was too small, I investigated and found that those are 10 tooth cogs I printed for the X and Y axis, not 12 tooth. Recalculated, fixed the firmware, printed again, it's fine.

Now my problem is that the filament is misfeeding. I think the problem is that my extruder is biting the filament far too hard and it's deforming the filament and dropping ABS shavings down into the hole and jamming things up. I'm going to get slightly longer screws to reduce the pressure on the extruder and see how that goes.

Fighting the printer

I've had a number of problems with the new printer, but in the end I tracked them all back to problems with the extruder. I'm using a Greg's accessible hinged extruder and a hobbed bolt that I made with a combination of the dremel cutoff wheel method (but on the flat part of the bolt) and an M8 tap to "sharpen" the teeth.

The hobbed bolt was sharp and extremely grabby but it has no tendency to center the filament, and the "accessible" extruder has no guide for the filament. What happened is that the filament drifted all over the place, getting kinked and jammed, and often falling right off the idler bearing, causing complete failure.

I made a new hobbed bolt today using a chainsaw sharpening file with a 5/16 bolt chucked in the drill press to make a groove, then using RotorIT's "hobbing thing" and an M4 tap to put teeth on the inside of the groove. This seems to be very grabby.

Funny thing - I went to the hardware store today to buy an M4 tap. Apparently they don't sell very many of them because the two that were on the peg were extremely faded, priced at $2.79 where most taps of the same size from VA are more like $4.50. It was so old that it didn't have a barcode on the package.

I'm having to print a new gearset since when I did the last one, the hex head was far too large and I had to J.B. Weld the old hobbed bolt to the gear.

I'm also going to print up kylikki's variant on Greg's extruder, with a filament guide. I was almost ready to go all the way back to an original Wade's extruder to get a filament guide.