Saturday, November 20, 2010

GJ trip for extruder parts

I'm going to junction today to buy the hot end parts (I'll be getting several bolts and acorn nuts, and enough washers & jam nuts to make two hot ends)

Fastenal 243-5754, pn 75170: brass ¼20 acorn, ea. ¼20 no more than an inch. 5/16 3" 10 in the ¼20 4", $17.90, 5/15 3" $40.25 for 25 of them.

Peachtree hardware on north has the acorn nuts but not the stainless steel bolt. 970-245-1736

Classic computer in delta has heatsink compound, little syringe full for 8.95. I'd prefer something cheaper (in both senses of the word) but that's available today, so I'm going to go for it.

I found a tool that would work for putting a taper on the inside of the extruder. It's 1/4" per foot taper, called a "taper pin reamer" designed for making tapered holes for a tapered pin.

More info on taper pin reamers: has a pdf which lists gauge sizes, with tip and end sizes in decimal inch for each end of each reamer. According to that I want a '5/16" (2/0)' size, which has a tip of .1137 (<.125) and a large end size of 0.1638. It's flute length is only 1-9/16", but the overall length is 1" longer, so I should be able to get it deep enough in the barrel to taper the melt zone! Found a 2/0 for 7.25+shipping which was the best price I found. But their order page didn't load after giving them my CC#. I guess I'll have to wait till Monday to see if they received my order... The taper isn't essential to extruder operation, but would help especially with some types of plastic. (PLA?)

Things I got done:

Peachtree TrueValue lied to me, they had a few of the smaller sized acorn nuts that where solid brass, but the rest are brass plated. So I got the two that looked most likely to be solid brass and called it good. I got enough jam nuts (half nuts) and big fender washers to make two extruder hot ends.

I went ahead and got 25 Stainless carriage bolts, for ~$44. Way more than I need, but maybe I'll sell a few? I can hope.

Fairly major accomplishment, I got the end-stops rewired using 18/2 shielded, it's white tempurature control cable I had left over from working on St. Mary's in junction. The grounds now go to the breadboard, and the ground topology should be more favorable to noise suppression now.

Next up on the Todo list:

re-secure X and Y axis guides to eliminate twisting of the bed.

Test endstops, and endstop code. See if debounce is adequate.

Drill a couple bolts for the extruder.

Friday, November 19, 2010

Ditch our firmware, run EMC2's RT code on our micros instead.

I've been reading about EMC2 lately, and running it in simulation mode as well. I'm becoming convinced that the smart thing to do is to throw all our firmware efforts away, and rewrite the RT portions of EMC2 to run on a microprocessor instead.

EMC2's understanding of acceleration and path following is MUCH, MUCH more sophisticated that what we have, or likely will have in the next 5 years unless we use their code. They even have implemented auto-calibration routines for stepper-based machines to find the maximum speed and acceleration on a per-axis basis.

I think it would wring considerably more performance out of our existing hardware, getting faster and more accurate prints than any other method. The only serious question I have is if it's even possible to reimplement it in that way, (does it require a floating-point hardware to get adequate performance?) and how beefy a micro it would need.

I know that we can use EMC2 right now with a parallel port, but adding more extruders or controlling the heaters requires dodgey workarounds, and heaven help you if you don't have a parallel port, or if your computer's hardware is a bit quirky, and can't do the low-latency stuff that EMC2 requires to function.

Current EMC2-type solutions to this require expensive dedicated IO cards, or older computers in the case of latency issues. EMC2 can't use the USB port approach because of latency issues. But the USB port with an external micro to run the RT code could get around this, and result in significant cost reductions for all users of EMC2, as well as nifty things like analog inputs, high-frequency PWM, and higher frequency stepping than is possible with current EMC2 implementations.

Wednesday, November 17, 2010

New Blog, Missing stuff at the hardware store.

I deleted my old blog, and started a new one, My old blog was "swearing at Java" and was started mainly because I couldn't find a way to do reprap without dealing with "reprap host" and "the arduino IDE" both of which are Java. I really hate Java, but since I found better way - skienforge and a simple "make" file - I can ignore them and focus on getting things done. So I don't need to feel that way about Java anymore.

I've pretty much settled on 5/16" hardware for the extruder. I want to ream it out for a tapered melt zone, and I think that 1/4" will leave much too little actual thread down at the bottom where the nozzle and heater block go.

I visited the hardware store in Delta today, and they didn't even have brass cap nuts. Their cap nuts where merely "brass plated" which looks about the same (it's shinier) but won't drill nearly as well. And of course it wouldn't conduct heat as well either. They also didn't have the brass jam nuts that I was wanting to use between the fender washers to make the heatsink. I suppose that I don't really know how much difference it would make, steel isn't as good a heat conductor as brass, but it's still *much* better than stainless steel. But they also didn't have a stainless steel bolt that was threaded for the ~3" that I need.

The whole point of using SAE was that I can get it locally for cheap. If I can't get it locally for cheap and have to order off the internet *anyway* I might as well go with metric, right?

But I'd still have to figure the correct size, allowing for reaming.

I think that eventually molten zone volume will be a significant factor as well. I think it'll correspond fairly linearly to "how far do I have to back off the extruder to relieve pressure?" For now a short melt zone is far more important.