Finished cartesian bot using bike chain
Posted by james glanville
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Re: Finished cartesian bot using bike chain August 27, 2008 03:47AM |
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
).
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
).
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Re: Finished cartesian bot using bike chain August 27, 2008 07:52AM |
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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.
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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
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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.
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Re: Finished cartesian bot using bike chain August 27, 2008 08:25AM |
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).
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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).
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Re: Finished cartesian bot using bike chain August 27, 2008 09:01AM |
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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.
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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
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