Sunday, May 21, 2006


Simon & Vik's Bumper Fun Weekend Issue

Simon has been beavering away in his lair, producing a number of interesting bits of code. He's added a "homing" function, to get all the axes to find their minimum location using the sensors. He's also written a better algorithm for setting the heater temperature to reduce overshoot. It's a bit enthusiastic, but we're working on it.

I found a suspect inter-board cable and replaced it. That seemed to improve things a little. It appears that USB serial ports are still causing us trouble. I'll need another serial lead to attach the RepRap onto the PC with for the moment.

The electric screwdriver is now mounted and squirting happily. There is even an anti-backlash diode, which is needed now I'm using a TIP120 transistor to drive the extruder motor rather than a 754410. We discovered those don't have enough oomph. I also discovered they need an anti-backlash diode. Oh, and all the PC boards have sprouted smoothing capacitors.

The upshot: I can now print 2 layers repeatably. Why only two? Run out of 3mm filament again, haven't I? I've found plastic chopping boards are good for rolling it out between.

A fruitful weekend, and just as well as I'm off to Wellington next week for a couple of busy days. I can fit in a beer at the airport at 9pm Wednesday, Simon. My shout!

Vik :v)

Sounds like you guys are really getting into the nitty gritty. :-)
Yup. I've also got something that is getting more repeatable. If we are going to make sense of our results, we need that repeatability.

The extrusion speed variesnon-linearly with the diameter of the CAPA, and as a join goes through things can slow down or speed up.

Also, there is a lower limit to the speed at whcih you can run the extruder before it binds up and stalls. Speed variation is more apparent at lower extrusion rates.

Better control of the extruder speed will help, but I'm not yet sure how much of a problem that'll be. Fitting the anti-backlash diode and smoothing cap on the screwdriver seemed to help a lot.

Vik :v)
The extrusion speed varies non-linearly with the diameter of the CAPA, and as a join goes through things can slow down or speed up.

I am sorry to hear that. I noticed something very similar when I was working with the auger filament extruder a while back.

What I did notice that may be of more use to you is that when I started the experiments with the piston extruder I found I had much better control over the diameter and quality of the filament because, apparently, I was able to operate at much cooler temperatures, viz, 95-100 deg C rather than the 125-130 that the auger extruder required. It required more thrust with the piston extruder than I was able to generate with the auger, but the benefits were obvious.

Now that you have a heftier motor pushing your filament you might want to see if you get better results running the extruder head a bit cooler.
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