Which aluminum alloy for chassis plate?

[adamct]

I'm thinking of getting/making a custom chassis plate. I had a few questions when preparing to place my order:

1. What aluminum alloy is used for the stock Bottlehead kits?
2. Is there any reason to prefer 5052 over 6061 aluminum (or vice versa)?
3. Would another metal be preferable (e.g. copper or bronze)? I'm leaning toward aluminum, but if there are real benefits to others, I'd like to know before making a decision.
4. The stock Bottlehead chassis plates (Crack/S.E.X./Smack, etc.) are 0.08" thick, is that right?

Thanks!

Best regards,
Adam

[caffeinator]

Hi adamct,

I think the main reason to choose an aluminum alloy would be cost.  6061 is very common and should be less expensive.  5052, iirc, has enhanced corrosion resistance, but only for certain environments relative to other alloys - not worth a price premium, but if it's cheaper, no reason not to use it. 

There's a good summary on Wikipedia (http://en.wikipedia.org/wiki/Aluminium_alloy) of alloy series and their uses.  Generally speaking, if you can choose a temper, an 'O' condition will be soft and might tend to scratch more easily - not a consideration if it will be painted, of course.  The 6xxx series is a good general purpose material.

Having worked with steel and aluminum chassis plates, I can say aluminum is usually a lot easier to work with and thus preferable from that perspective.  Some bronzes can be hard and thus hard to machine.  Copper can be expensive, but, of course, it looks nice.

[adamct]

Thanks. I read the Wikipedia article before, but didn't know if there were any hidden "gotchas" with 5052. For whatever reason, it seems I can actually get 5052 cheaper than 6061, so I will probably go with that. But I note that 5052 is supposedly harder to "machine" than 6061. I'm not quite sure what falls under the mantra of machining. I would want to drill a couple of holes. I might want to do some very, very minor engraving, too. Those seem like fairly simple tasks, so I'm guessing 5052 is OK, but let me know if you think I'm on the safer side going for 6061.

Do you know if I am correct about the thickness of the stock Bottlehead chassis plates? And do you see any downside to using something thicker (e.g., 0.125")? Would 0.125" thick plate be significantly harder to work with in terms of drilling holes, etc?

Thanks for your assistance!

Best regards,
Adam

[Paul Birkeland]

6061 will work really well.  It has a good balance of strenght, scratch resistance, and price.  5052 will just bend a little more easily.

If you can get a steel plate, it will be heavier, stronger, and more scratch resistant, but it really must have a finish applied to it.  You cna also get away with a little less thickness, but this seems pretty unimportant for something as small as the Crack.

Going to 0.125" thickness will probably cause some issues with screw lengths.

-PB

[adamct]

Thanks. I just found another source for 6061 that is quite reasonable, so I'll stick with that. Thanks!

[Kris]

Just want to add my two cents as far as finish... If you want to have the plate anodized then 5000 series alloy is the way to go. If you plan to paint it though, then alloy doesn't matter.

[galyons]

...If you want to have the plate anodized then 5000 series alloy is the way to go...

Why?  I have anodized both and have seen no difference in process or finish.

Cheers,
Geary

[Kris]

I work for metal fabricator and we always have problem with anodizing shops when using alloys other than 5000 series.
Is not that it can't be done, but 5000 series is the easiest alloy to work with for anodizing shops.
Form my experience when I tried to get a quote on anodizing aluminum made out of 3000 or 6000 alloys, then the shop guys always complained and either raised the price or just simply didn't want to do the job.

[caffeinator]

Do you know if I am correct about the thickness of the stock Bottlehead chassis plates? And do you see any downside to using something thicker (e.g., 0.125")? Would 0.125" thick plate be significantly harder to work with in terms of drilling holes, etc?

I think stock is either 0.080" or 0.10".  I wouldn't recommend 0.125" for a small plate like the Crack, or even the larger BH kits, for that matter - way overkill in terms of stiffness.  As PB points out, you'll have some problems with fastener grip lengths, but more than that, it adds some unnecessary difficulty to all the chassis prep operations - maybe not a consideration if you're having it machined, but it will add cost.

I've used thicker material, like 0.125", when the chassis plate had heavy iron sitting on top and broad unsupported expanses.  Even then, it is sometimes easier (and cheaper) to add stiffeners locally as opposed to increasing thickness overall.

[adamct]

Thanks for the advice on choice of thickness. FYI, I plan on keeping the plate natural, although I might change my mind once I see the surface when I get the plate...

Best regards,
Adam

[Paul Birkeland]

I work for metal fabricator and we always have problem with anodizing shops when using alloys other than 5000 series.
Is not that it can't be done, but 5000 series is the easiest alloy to work with for anodizing shops.
Form my experience when I tried to get a quote on anodizing aluminum made out of 3000 or 6000 alloys, then the shop guys always complained and either raised the price or just simply didn't want to do the job.

Odd, I did a few runs of anodizing at another company I worked for, and we had incredible issues with getting good quality anodizing out of 5005.  Nearly every shop I spoke with said their process was optimized for 6061, with the most highly regarded local company (who is a popular subcontractor of Boeing) actually not being able to anodize 5005 (we requested black and it came back light gray, with the piece of 6061 looking pretty good).

That experience prompted me to figure out how to powder coat; I have no motivation to send out anything for anodizing, though there is one solid company in Arizona who does a good job.

-PB