Aluminium bars

Hi,

Now that the Mendel's design is very good at avoiding jammings, could it be possible to replace the stainless steel bars by cheaper aluminium bars? It would be cheaper and easier to cut.
Plus, aluminium has a relatively low melting point (~660 C) so the parts could be prepared in ceramic molds from recycled cans or foil and distributed cheaply by anyone who does a bit of pottery...

To get the same stiffness as steel the aluminium would need to be thicker, so the cost would increase.

I think steel is three times stiffer and I think stiffness of rod is proportional to the fourth power of diameter. So I think you would need 10mm rods and change all the bracketry. Are 10mm AL rods cheaper than 8mm steel ones?

AL would also wear more quickly than steel.

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[www.hydraraptor.blogspot.com]

Do you need to have such stiff bars? Maybe the top bar that supports the weight along its radius needs to be very stiff, but surely the side and base bars don't need to? Especially for Mendel, it does not seem to demanding in terms of rigidity, does it? Maybe it could be possible to combine aluminium and steel bars, depending on their use?
About pricing, the point is that Al could come from a recycled source, home-made (kind of). Steel can't.

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About pricing, the point is that Al could come from a recycled source, home-made (kind of). Steel can't.

It's quite a bit of work to cast Al rods, and then even more work make them smooth. I'd use the material and pouring time to make a figurine or gears or something, and just buy the rods.

It is true that it would take time and effort to cast Al rods. But it would also be one more step towards a completely self-replicating machine.
Maybe some people among the reprap community can organise some 'production centres'? Well, anyway, it does not look like it is going to happen in the near future.

I have also been thinking about Al rods for the same reason. Al foundries are simple to build out of scrap and can be fueled with almost anything. Al casting is very efficient relative to creating new Al and steel. Al scrap is freely available worldwide whereas steel rod is not.

I have thought that one of the first things I would like to put on Thingverse are the models for casting a Gingery Lathe. While the lathe is not a small project(1-3 years hobby time I'm told), it is a real machine tool and would allow you to make as many smooth rods as you liked. Besides 40 pounds of AL it requires a few feet of cold rolled steel, some shim stock, some V-belts, nuts, bolts and lathe tool bits, and a washing machine motor. The work is done with hand tools, although an electric drill is recommended. I don't know if one has ever been converted to CNC but I don't think it would be impossible.

Rod stock is probably the biggest and most critical non-printable part of RepRap (OK, maybe motors). While not for everybody, a series of shops that made that component for the price of scrap would be a big step forward towards universal access to manufacturing.

The basic question seems to be would anything more than straight scaling up of the rods and fittings be needed? Also is the hardness of the rods critical at any point? I don't know much about the Mendal design, but I am fairly sure the Darwin design could be converted over to Al, and I believe Mendal is supposed to be lighter and less stressed than that. Perhaps Adrian or some of the core crew would care to comment?

Very good link, i will try to get this book!

About the issues for replacing steel by Al, I also think there may be some problem with frictions. Al tends to give more friction and jams more easily than steel. but the mendel design uses a good system for bearings, so I don't think it shouldbe an issue. I don't see any other problem on top of my head with Al (apart from scaling, as you mentioned)

About the foundries, Al has a relatively low metling temperature, so I wonder if it would be feasable to melt some Al using solar power? I will have a look at that and let you guys know.

re: solar melted Al, there are commercial designs for solar power stations that store energy into the night in the phase change of molten salt at 800 celsius!

Al rod, and rod in general is one of the less expensive components of the project.
I think we'd get a bigger payoff from working on gear making, pick-and=place, designing a 5' x 10' CNC table you can make with a RepRap, a robot arm, or a construction kit similar to VEX, erector set, or Lego.

Edited 1 time(s). Last edit at 10/30/2009 09:31AM by SebastienBailard.