Finished cartesian bot using bike chain

Re: Finished cartesian bot using bike chain

JohnWasser — Wed, 27 Aug 2008 19:10:39 -0400

Kyle Corbitt Wrote:
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> I'm a bit confused - why all the effort to cast
> roller chain?

I agree. My best guess is that somehow the Ladder Chain discussion in another topic spilled over into this Bicycle Chain discussion.

Re: Finished cartesian bot using bike chain

Kyle Corbitt — Wed, 27 Aug 2008 12:01:54 -0400

I'm a bit confused - why all the effort to cast roller chain? It's available worldwide and is much cheaper/more accessible than most of the other "vitamins" that RepRap depends on. Not to mention that in my opinion Darwin doesn't have anywhere near the resolution necessary to make an acceptably toleranced but also low-friction chain. Even commercial bike chains, manufactured with tolerances orders of magnitude higher than Darwin's capability, need to be lubricated to ensure that they work well.

Re: Finished cartesian bot using bike chain

Ru — Wed, 27 Aug 2008 09:01:26 -0400

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I think we can design a time-efficient process, though. Don't forget that casting is used for mass manufacturing.

Things like little bits of plastic would presumably be injection molded. This is a pretty speedy task, once you've created the molds... but this sort of manufacturing is probably a little out of our league ;)

Resin casting of the sort that's desribed in the reprap wiki would appear to be a slightly more sedate process.

Quote

Well, if you design it just right, cutting a part away from the tree could be as quick and simple as making one snip with scizzors/wire cutters/whatnot

It depends what your part needs to look like. When I think about casting small parts, what I mostly envisage are lots of small parts ruined by air bubbles. So things will need to be liberally decorated with risers to let the air escape.

This also implies that the time required to make the mold in the first place will have to increase.

As always, I'm open to being corrected here. I'm happy to spend, say, an hour casting a one-off part. But spending a day manufacturing, cleaning and assembling chain links isn't something I'm likely to greet with enthusiasm. If it turns out all this can be done with a minimum of effort, that's great... otherwise I'll just go buy a length of chain. Perhaps I'm not in your target demographic though :)

Re: Finished cartesian bot using bike chain

Joshua Merchant — Wed, 27 Aug 2008 08:25:34 -0400

Ru Wrote:
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> Now I think about it a bit more, I guess a
> no-overhang version might be okay. You might have
> to make a few compromises which might limit the
> strength of the link, but I guess you can heavily
> over-engineer the whole thing and not worry too
> much about its strength.

> From what I've seen so far, casting is also a
> tedious and time-consuming process ;)
Sure, if you do it for the first time, experimentally and hobby-styled. I think we can design a time-efficient process, though. Don't forget that casting is used for mass manufacturing. Since we can rapidly prototype the patterns or molds...

> The word that springs to mind is 'sprue', which I
> associate with a set of airfix parts or little
> plastic soldiers all joined together.
>
> When you're removing parts from a sprue, you tend
> to need to tidy them up a little by trimming
> various little bits of the support framework that
> linked them together and bits of plastic webbing
> and so on. This might be a little quicker than
> excavating scaffolds from a printed link, however.
Well, if you design it just right, cutting a part away from the tree could be as quick and simple as making one snip with scizzors/wire cutters/whatnot. You just have to make the area where you're going to snip easy to snip (so you can quickly make a near-flush cut), like by making it flat or convex (just as long as it's not too concave it should be fine), and designing the tree mold such that the line to snip is in a spot on the object where surface shape is not too important and doesn't have to be so precise (so you can just snip once and possibly leave a small bit of the tree on the cast object).

Re: Finished cartesian bot using bike chain

Ru — Wed, 27 Aug 2008 07:52:36 -0400

Quote

Well I was imagining a modified design which requires no overhangs (or limit it to overhangs which could be created by gap-spanning as Nophead has displayed)

Now I think about it a bit more, I guess a no-overhang version might be okay. You might have to make a few compromises which might limit the strength of the link, but I guess you can heavily over-engineer the whole thing and not worry too much about its strength.

Quote

As to the bit about removing support struts from a hundred little chain links, I did suggest casting them

From what I've seen so far, casting is also a tedious and time-consuming process ;)

Quote

If you cast a few of em, you can use those to make a tree mold

The word that springs to mind is 'sprue', which I associate with a set of airfix parts or little plastic soldiers all joined together.

When you're removing parts from a sprue, you tend to need to tidy them up a little by trimming various little bits of the support framework that linked them together and bits of plastic webbing and so on. This might be a little quicker than excavating scaffolds from a printed link, however.

Re: Finished cartesian bot using bike chain

VDX — Wed, 27 Aug 2008 07:29:35 -0400

... for moulding chains - look here: [www.rc-panzerketten-forum.com] - it's from a german forum, but the images shows the complete path ...

And for gears or sprockets - here the moulding of a tire, but similar for gears: [www.rc-panzerketten-forum.com]

Viktor

Re: Finished cartesian bot using bike chain

Joshua Merchant — Wed, 27 Aug 2008 07:21:34 -0400

Ru Wrote:
-------------------------------------------------------
> I know there are also lego counterparts. IGUS
> 'enerygy chain' also springs to mind, though that
> is for a slightly different purpose it has the
> same structure.
>
> The overhangs are the difficult bit... you could
> perhaps use some scaffold supports to hold them
> up, but I for one do not fancy removing support
> struts from each one of a hundred little chain
> links.
Well I was imagining a modified design which requires no overhangs (or limit it to overhangs which could be created by gap-spanning as Nophead has displayed).

As to the bit about removing support struts from a hundred little chain links, I did suggest casting them (as far as I know, you can cast plastics too). You could just print one and cast the rest. If you cast a few of em, you can use those to make a tree mold (I think that's what it's called) which you could then use to cast multiple units at a time. Or perhaps just print the tree mold itself (perhaps in two parts, which could allow overhangs).

Though, getting the support material working is one of the first things I plan to do once I get my RepRap up and running, so it may not be necessary to have struts and whatnot. See the bit about the possibility of using PVOH (polyvinyl alcohol) in my post here [forums.reprap.org]. It's near the bottom.

> I woudln't have thought that soft metals would do
> the job here. Even if they aren't warped by their
> own weight or stretched by tension, they're going
> to be comparitively delicate and easily mangled.
> I'd have to get some bits and fiddle with them to
> see, though.
Well, plastic should work. Though, if we thicken the chain links, couldn't that make them stronger and allow the use of softer metals? Alternately, there are many other castable materials that we could use. If all else fails, I'll do steel (actually, I'll probably do steel eventually anyway if the chain turns out to be a good idea, as steel is just plain cool).

Re: Finished cartesian bot using bike chain

Ru — Wed, 27 Aug 2008 05:01:45 -0400

Quote

I seem to remember having a K'NEX toy with similarly shaped plastic chain link

I know there are also lego counterparts. IGUS 'enerygy chain' also springs to mind, though that is for a slightly different purpose it has the same structure.

The overhangs are the difficult bit... you could perhaps use some scaffold supports to hold them up, but I for one do not fancy removing support struts from each one of a hundred little chain links.

Quote

possibly cast them out of metal in the future, maybe tin or one of the low melting point solder alloys

I woudln't have thought that soft metals would do the job here. Even if they aren't warped by their own weight or stretched by tension, they're going to be comparitively delicate and easily mangled. I'd have to get some bits and fiddle with them to see, though.

Re: Finished cartesian bot using bike chain

VDX — Wed, 27 Aug 2008 04:37:25 -0400

... with salvaging old copiers and printers i found an interesting 'evolutionary' development:

In the old copiers (before 1985) i found big DC-motors with chain-sprockets and chain-transmissions. In the printers from this age i found direct driven linear drives or stepper-motors (Nema17 or Nema23) and many nested gears as power-transmission.

In the copiers and printers from 1985 to 1995 i found Nema23-steppers and tooth-belts and/or nested gears as power-transmission. All the scanners had Nema17-stepers and tooth-belts too.

In the 'modern' printers and scanners i find mostly tin-can-steppers or small DC-motors (sometimes Nema17-steppers in bigger scanners) and mostly tooth-belts, sometimes nested gears.

So tooth-belts seem to be much cheaper and easier in use than chains and you can find them easily in outweared/broken printers and scanners.

When i'll have to build transmissions, i would prefer tooth-belts ...

Viktor

Re: Finished cartesian bot using bike chain

Joshua Merchant — Wed, 27 Aug 2008 03:47:12 -0400

Quite interesting. I seem to remember having a K'NEX toy with similarly shaped plastic chain links [www.knex.com].

We can probably print similar chain links with a simpler design (to reduce overhangs) and thicker walls (to reduce the risk of breaking the chain). It would probably be interesting to use a mold with a tree so that you can cast a bunch of them at once (possibly cast them out of metal in the future, maybe tin or one of the low melting point solder alloys [which are mostly tin]; iron or steel would be cool, but the high temperatures make it not worth doing unless you are casting other stuff as well).

We wouldn't, of course, simply copy their design - I think that might be illegal; more importantly, though, is that it probably isn't fit for our use anyway (yes, that's more important than the law :D).

Re: Finished cartesian bot using bike chain

brucew — Tue, 26 Aug 2008 15:52:55 -0400

It looks great James Good luck and I hope to see a cup from you soon.

The chains are a great idea...

Bruce Wattendorf

Re: Finished cartesian bot using bike chain

Enrique — Tue, 26 Aug 2008 14:46:34 -0400

Great idea! It is certainly better than using belt for the z axis.

For the x and y axis, is the sproket wider than the original Darwin gear? If so, how do you get the necessary resolution and torque?

Re: Finished cartesian bot using bike chain

JohnWasser — Tue, 26 Aug 2008 12:43:15 -0400

Looks great! Bicycle chain is certainly widely available around the world. It will be interesting to see how nice a roller chain sprocket one can print on a RepRap. It has got to be easier than printing molds and casting timing belt sprockets.

Finished cartesian bot using bike chain

james glanville — Mon, 25 Aug 2008 18:41:31 -0400

Hi, I'm waiting for the electronics to arrive so I can start printing, but I've mostly finished the cartesian bot:

[www.flickr.com]

As you can see, I used bike chain instead of toothed belt. I did this because it was cheaper (chain + sprockets <