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Is anybody else building an Acrylic RepRap? I've got a few questions. E.g. does the Ponoko X Idler Top Bracket use 25mm screws, not 20mm as the instructions imply?
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RussNelson
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General
FYI, I'm currently building a Ponoko lasercut RepStrap. Have bought all the M3 x25 screws that Evans & Whites has, and they were completely out of stock of 3' faus-M8 (5/16ths) rod.
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RussNelson
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New York, Potsdam RepRap User Group
If the board has already agreed to the text, why haven't the edits been made? On the one hand, it seems like a tempest in a teapot, but on the other hand, if you expect people to agree to something, then that thing should be something an honest person can agree with. Otherwise you're telling people "we don't take our agreement seriously and neither should you." in which case why have the agreem
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RussNelson
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General
There are too many forums. RSS doesn't work well because it loses the hierarchy. Reading new posts via the website is slow because you have to go in and out and in and out and mark read and ...
I liked Usenet. Whatever happened to Usenet? How come everything has to be done on the web now?
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RussNelson
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Administration, Announcements, Policy
I think Adrian and Ed have thought about a head swapping mechanism. I haven't seen their thoughts written down anywhere, so I thought I'd write down my thoughts and let y'all have at 'em. I have an International tractor with a "Fast Hitch". It uses implements that have two bars projecting from their front. The tractor has two hitch receivers into which the bars fit, and are held. I'd reverse
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RussNelson
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Plastic Extruder Working Group
I gather that the toothed belts are expensive. I grabbed 14 feet of Christmas bead garland at the dollar (plus tax) store. The beads are 8mm in diameter, and are spaced 2.3mm apart. That's big enough that the gear which drives them could be fabbed. In the meantime, we could use a technique like Vik's to create a gear.
The cord that holds the beads is quite inelastic. Over a 15cm section, a
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RussNelson
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Mechanics
Sean, you're ignoring the cost of capital. You're also ignoring the cost of organizing the labor. Even union organizers get paid a salary.
The thing that ends slave labor is prosperity, and prosperity comes from free markets and private property. Even Marx realized that socialism relies on capitalism to create wealth.
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RussNelson
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General
Anybody else in the area building? I have some parts, mostly for experimental purposes. But I'd love to get together with anybody else in the area who has even the least interest in a reprap.
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RussNelson
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New York, Potsdam RepRap User Group
James Hogan.
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RussNelson
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General
I suggest that there should be a Potsdam, NY group, because of the presence of Clarkson University, a technical school of technical schools. Oh, and I live here, too.
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RussNelson
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New York, Potsdam RepRap User Group
Herewith I expose my ignorance of stepping motors. I have some six-wire motors. I speculate that they could be used as either unipolar, by connecting the center-taps to ground, or as bipolar by ignoring the center-taps. True?
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RussNelson
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Controllers
Well, and, I guess in order to be a proper open sourcer, I should volunteer to do it myself. I just need the appropriate privileges.
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RussNelson
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General
The front page of reprap.org loads more slowly than it could, because it's resizing images in the browser. I made a local version of the page which loads images which are already the size specified in the HTML and it loads noticably faster. Does anybody have the editing privs to fix this and keep it fixed when the page changes?
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RussNelson
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General
Here's a link to the coverage of the RepRap at Pop!Tech:
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RussNelson
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General
So, I've been thinking about how support material would need to be deposited. Right now, it seems as if the build material needs a 50% overlap, allowing Vik's liquor glasses. What if you used a support material which wasn't necessarily hard enough to support itself, but hard enough to support the build material? So, instead of being able to work with a 50% overlap like the build material, the
by
RussNelson
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General
There's a lot of theorizing about post-scarcity societies. There's also a lot of theorizing about zero-point energy and perpetual motion machines. It's all fantasy. Scarcity exists because humans dream beyond their abilities. The only way to eliminate scarcity is to stop humans from dreaming (I think they call that "hell") or to give humans unlimited abilities. And yet we live in a society w
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RussNelson
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General
There is no such thing as a post-scarcity society (rich people want stuff they can't afford too). There is no such thing as a money-free world as long as you have trade (money is just that commodity which everybody takes in trade -- in the future HDPE maybe?). I appreciate enthusiasm for the reprap, but ignorance of economics is just a shame.
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RussNelson
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General
I'm trying to derive a general theory for extrusion so that I can predict what materials will extrude well and which will not. For example, water very close to freezing would probably extrude reasonably well into a supercooled surface.
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RussNelson
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General
The problem, in general, with extrusion is that you need to extrude a substance which undergoes a rapid decrease in viscosity between the inside of the extruder and the outside of the extruder, AND which adheres to the previous layer well, AND which does not gum up the extruder exit.
Actually, and I'm not sure I can think of how to say this concisely, there's a tradeoff between the pressure you'
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RussNelson
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General
Hmmmm..... I think that perhaps the best support material would be something which is soft when heated, sticky, cools quickly to a hard surface, AND is water soluble. Caramel! Or something else involving sugar.
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RussNelson
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General
Do the green parts on the front page still have their support material attached? It looks as if so.
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RussNelson
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General
RussNelson Wrote:
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> Hmmm..... Sparkfun has $15 1.8 degree steppers
> that appear appropriate from the specs.
DOH! NEMA-17, not NEMA-23. Sorry. But still, NEMA-17 motors might work, and they're a lot cheaper. It's just that they're not what is currently specified, so my suggestion was junk.
Oh, and they're out of stock of the moto
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RussNelson
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Mechanics
You'd still need three motors. Plus you'd have a hard time making a straight edge. You would have to coordinate the movement of three motors at different speeds to make a straight edge.
Not to prick your balloon -- because I also keep thinking of different things that might be done.
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RussNelson
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Mechanics
Yep, already thought about that. The problem is: what happens if you miss a step? Then your platform isn't level anymore, and because you're driving them in parallel, you can't resynch. You would have to have hard stops at the bottom of the travel, and then just bang the Z stage back into synch. The hard stop would have to be something that stops exactly at a certain place in the rotation. M
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RussNelson
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Mechanics
Yes, emf, that's the name of it! Thanks!
I've been thinking further about the support / filler material. It really only needs three properties: 1) it needs to support the construction material, 2) it needs to be removable using a solvent that doesn't dissolve the construction material, and 3) it needs to be accurately dispensable.
Note that I said nothing about slump, or hardening. It doesn
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RussNelson
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General
What if, rather than using a pressurized feed, and controlling the volume by measuring the deposition time, a thinwall tube is used along with a set of rollers which squish the tube against a semicircular path. Like this:
You can get a controlled flow as long as the tubing you're using holds its size well enough against the tube.
Hmmm.... but maybe that would work better using a pressurized
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RussNelson
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General
rubbing alcohol has water in it. But more to the point, plaster of paris is an exothermic reaction, so rubbing alcohol doesn't have much of an effect on it. It hardens even in lack of air, which is NOT what we want. Oh well.
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RussNelson
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General
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