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Unread 11-05-2010, 15:32
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Re: pic: 3 Hour Chassis + 2 Hours

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Originally Posted by 548swimmer View Post

The tubes should have material underneath them. There's no constraint tool in real life, so spacers have a hard time just hanging there. Think about the assembly process when you're designing robots, that helps me the most. You can usually just pound them through with a gentle persuasion tool if the hole is a tad small.
I intend to weld the cross beams to the inner plates. Our team has a CNC mill, but it doesn't have a coolant system built in, thus milling operations can be quite cumbersome. By designing it this way, the only CNC operation necessary is the drilling of the holes so everything lines up square. The rest of the dimensions are more or less non-critical and can be cut with some careful band sawing.
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Unread 11-05-2010, 16:12
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Re: pic: 3 Hour Chassis + 2 Hours

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Originally Posted by Ty Tremblay View Post
I intend to weld the cross beams to the inner plates. Our team has a CNC mill, but it doesn't have a coolant system built in, thus milling operations can be quite cumbersome. By designing it this way, the only CNC operation necessary is the drilling of the holes so everything lines up square. The rest of the dimensions are more or less non-critical and can be cut with some careful band sawing.
I do a fair amount of aluminum machining dry without too much argument... what sort of tooling are you using? Are you making nice aggressive cuts to keep heat in the chip?

I've had good luck with carbide tooling and heavy feeds on 6, 2, and 7 series alloys.

I assume because you're planning on welding it you're going to use a 5 series alloy, which has a "poor" machinability rating, which may well be your problem.
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Unread 11-05-2010, 16:34
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Re: pic: 3 Hour Chassis + 2 Hours

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Originally Posted by JamesCH95 View Post
I do a fair amount of aluminum machining dry without too much argument... what sort of tooling are you using? Are you making nice aggressive cuts to keep heat in the chip?

I've had good luck with carbide tooling and heavy feeds on 6, 2, and 7 series alloys.

I assume because you're planning on welding it you're going to use a 5 series alloy, which has a "poor" machinability rating, which may well be your problem.
I'm also on 190, which has plenty of Haas CNC mills for me to do my worst with. My alma mater team, 319, has the CNC I've mentioned, but I've never seen it run. I was intending to use 6061, but should I choose something else due to my intention to weld? Also, is it difficult to weld two different alloys together?
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Unread 11-05-2010, 17:16
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Re: pic: 3 Hour Chassis + 2 Hours

6061 loses its temper when it's welded, so your 6061T6 becomes 6061T0, which according to wikipedia is an 80% loss in strength, which is what I've noticed/experienced with the welding and mechanical testing I've done.

Welding two aluminum alloy's together hasn't been an issue for me. Most, if not all, aluminum alloys will weld fine with the same filler material, so there shouldn't be much of an issue welding different alloys.

Haas CNCs are pretty good machines, I used one in college. Tooling, though, shouldn't be confused with the mill itself. You could have the best CNC on the planet, but if a low-quality HSS endmill is chucked up it'll run like crap. Look into solid carbide tooling, if you're CNC'ing plates you could easily get away with a 1/4" end mill, or maybe smaller. McMaster: 8829A19 about $24 for an end mill that will make you many a robot frame. If you have good compressed air for chip clearing you could get a 4-flute which is even less expensive.

IMHO, if you want to weld the chassis together (which I heartily approve of) you should CNC your side plates from 5052 (which has no temper and won't lose strength when welded) and then use AndyMark/KOP extrusions for your cross-bracing. It'll be a little less expensive, and you'll get tons of 1/4" mounting holes. My team's most recent chassis was made from CNC'ed and bent 5052 TIG welded to the KOP frame. I did the welding and found the 1/8" 5052 to be a very forgiving material to TIG. We dropped 3-4lbs in fasteners IIRC.
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Unread 11-05-2010, 17:03
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Re: pic: 3 Hour Chassis + 2 Hours

Quote:
Originally Posted by Ty Tremblay View Post
I intend to weld the cross beams to the inner plates. Our team has a CNC mill, but it doesn't have a coolant system built in, thus milling operations can be quite cumbersome. By designing it this way, the only CNC operation necessary is the drilling of the holes so everything lines up square. The rest of the dimensions are more or less non-critical and can be cut with some careful band sawing.
Could you use a smallish size end mill and cut like this:

______
|xxxxxx|
|xxxxxx|
|_____|

so the center piece falls out.

If you can use a 1/16 or 1/4 bit you can cut past the needed length/width just enough so that you end up with squared corners.
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