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Sand casting a robot chassis
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chunkulator



Joined: 27 Jul 2016
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Sand casting a robot chassis

Anybody seen a robot successfully sandcast in aluminium before? I'm wondering whether this is a feasible idea.

One concept I have in mind is a ring spinner with a hardox ring spinning around a cast aluminium body.

Post Fri Jan 06, 2017 9:21 am 
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maddox



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Sand mould casted aluminium is very weak compared to the other kinds.

But it should be possible.

Post Fri Jan 06, 2017 10:19 am 
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Nick
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As some UK builders discovered, a Hardox or Bisalloy ring is very expensive. Like Mario said, cast aluminium is low strength and you will need to add lots of ribbing and it will end up heavier than if you built it from ali plate.
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Post Fri Jan 06, 2017 10:35 am 
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chunkulator



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Good to know. Is the expense in laser cutting the hardox or in the material itself? Should I be considering a mild steel ring with hardox or tool steel inserts or something of that nature?

Post Fri Jan 06, 2017 11:47 am 
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Nick
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Hard to say without getting quotes. Using thinner steel will lower the cutting costs, so a wider & flatter ring with be cheaper than a taller ring of the same weight. The ring is expensive because you are paying for the middle; the ring is cut from a square of steel and most of it is scrap.
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Post Fri Jan 06, 2017 12:01 pm 
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chunkulator



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So let's say I cut the ring from, say, 12.7mm mild steel and bolted hardox teeth to it. Does intuition say that should be strong enough or should I be looking at something more like 20mm mild steel?

I am thinking I can probably make a custom jig to cut circles in steel by mounting my die grinder (holding an end mill) on a compass arm type arrangement.

Post Fri Jan 06, 2017 12:15 pm 
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Nick
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Mild steel is going to be MUCH cheaper but also much weaker; I don't know if 1/2" plate will stand up to other spinners. The Bisalloy disk in Decimator was 6 or 8mm thick and was bent after just one fight. The replacement 16mm bar took on local and UK bots with zero problems, so I'd go at least that thick - more if you use mild steel.

Using a jig and die grinder might work but will probably snap a few end mills along the way. It might be cheaper & give a better result to use waterjet cutting VS laser; waterjet will avoid the heat affected zone along the cut.
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Post Fri Jan 06, 2017 12:26 pm 
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chunkulator



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Am i right in thinking that the size of the heat affected zone is only important for hardened materials, though. Not an issue for mild steel, right?

Post Fri Jan 06, 2017 12:34 pm 
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Nick
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Correct
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Post Fri Jan 06, 2017 1:00 pm 
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chunkulator



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Is there some material in between (in cost) mild steel and hardox that I should consider for the ring. Eg 4140 plate. Is that a thing?

Post Fri Jan 06, 2017 2:06 pm 
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Nick
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4140 and similar alloy steel mostly comes in bar shape, I haven't seen it as thick plate. Most steel is supplied annealed; the handy thing with Bisalloy and Hardox is that it is already hardened.
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Post Fri Jan 06, 2017 2:23 pm 
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Philip
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Would it be any good to cut a ring from mild and run hardening rods over the tooth area?
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Post Fri Jan 06, 2017 3:10 pm 
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chunkulator



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Ooo. Sounds interesting. What kind of welding gear do I need for that. Tig? Oxy?

At the moment my welding tech is pretty low - gasless MIG only. But at some point I probably need to upgrade to Tig.

Post Fri Jan 06, 2017 6:32 pm 
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Nick
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The hard-facing rods are extra low tech - they are for stick welders. I think some of the Rotwang bots used that technique and it worked OK.
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Post Fri Jan 06, 2017 6:46 pm 
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chunkulator



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Should be able to handle that. I think I've also read about MIG hard facing wire at some point.

Post Fri Jan 06, 2017 6:56 pm 
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