Comments on RepRap: Blog: RP Pinch-wheel Extruder

you could reduce the gear ratio on the brass thing...

2009-02-20T23:45:50.664Z

you could reduce the gear ratio on the brass thingy by turning down a small section on the end and knurling it: (excuse the ascii art)

----\____
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this would probably put too much force/wear on the stepper bearing because of the increased leverage, but you could easily machine a standard 8mm ball bearing seat on the end of the brass thingy after the knurled section, which is a good idea anyway.

While microstepping would make it smoother, gearin...

2009-02-17T16:44:41.272Z

While microstepping would make it smoother, gearing would allow a smaller motor, which would be cheaper and lighter.

There is a lot to be said for simplicity though and without gearing you can back up very quickly to halt the flow and then step forward very quickly to take up the slack when you start again.

And gears would be something else to wear out.

Sorry Forrest - there's an "After" picture that is...

2009-02-17T14:49:26.498Z

Sorry Forrest - there's an "After" picture that is merely implied: the one where the gaps round the PTFE have had PU resin poured into them and it's set...

Microstepping would be good, though it doesn't seem essential. See the next blog, which also has a smaller diameter drive - the stepper shaft itself...

wouldn't microstepping dramatically decrease the t...

2009-02-16T20:05:09.459Z

wouldn't microstepping dramatically decrease the torque of the stepper motor? would it be possible to avoid gearing by using a smaller pinch wheel?

I've been looking hard at the pics and now I'm rea...

2009-02-16T17:18:46.563Z

I've been looking hard at the pics and now I'm really puzzled. How is that PTFE thermal break kept from being pushed out of that nice green base block by the filament being pushed into it by the pinch wheel?

I'm sure it is, because you're extruding with it. I just can't see how, though. :-s

Presently designing a 32:1 gear train for the GM-1...

2009-02-16T16:55:30.301Z

Presently designing a 32:1 gear train for the GM-17. It has three levels, plus an power sprocket. It looks like it should fit in a 75 mm x 100 mm x 25 mm box. I'm pretty sure that Chris could reduce those dimensions with that 0.3 mm extrusion nozzle of his.

Of course. I think the ideal would be to make one...

2009-02-16T15:45:53.764Z

Of course. I think the ideal would be to make one that either a stepper or a DC motor could be fitted to.

Holes are free!

cool design.i still think DC motors are the way to...

2009-02-16T15:10:44.231Z

cool design.

i still think DC motors are the way to go... extremely simple to drive, high torque, low complexity of drive circuit, low complexity of software (no timer interrupts!) low cost, etc.

would you be interested in helping design a dc motor compatible one? my 3d design skills are pretty bad compared to my 2d design skills.

weighs -> weights...

2009-02-16T11:18:31.663Z

weighs -> weights...

Dunno what the torque is. If I get the chance I'l...

2009-02-16T11:17:22.205Z

Dunno what the torque is. If I get the chance I'll set it to lifting some weighs and see when it stalls.

The whole thing has only four separate parts plus screws (RP clamp and nozzle, RP pinch thang, stepper motor, ball race).

Nophead suggests gearing down the motor so it can step faster and hence drive more smoothly. I'd rather microstep and avoid the gearing - I want it as mechanically simple as possible.

Yeah, you're right. A NEMA 17 is about 40x40 mm o...

2009-02-16T07:10:27.501Z

Yeah, you're right. A NEMA 17 is about 40x40 mm on the mounting plate. That thing is sitting on a centimeter grid and does that. It looks thicker along the axis than an ordinary NEMA 17, though.

it looks like a nema 17

2009-02-16T01:56:21.272Z

it looks like a nema 17

So you're driving it with a bipolar NEMA 23? What...

2009-02-15T21:00:27.929Z

So you're driving it with a bipolar NEMA 23? What sort of torque is that thing producing?