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draikani
08-06-2011, 12:53 AM
I was looking through some of the mech warfare threads trying to find out what type of aluminum you guys were using and where you got it, but just couldn't find the right bits of info. I'm wondering what thickness and which alloy you're all using. I was looking at mcmaster and the 1/32 looked pretty good, but I'm worried it might be too thin. I haven't really done too much with aluminum before though so I wouldn't really know. Any insight is appreciated, thanks guys!

tician
08-06-2011, 02:09 AM
Not sure what the others use, but the DARwIn-OP fabrication manual states (http://ncu.dl.sourceforge.net/project/darwinop/Hardware/Mechanics/Physical%20Information/DARwIn%20OP%20Fabrication%20Manual.pdf) on page 10:

"The majority of the DARwIn OP parts should be fabricated from 5052 aluminum.
This alloy was selected for its formability and strength. The parts were originally
designed to be fabricated with aluminum sheets with thicknesses of 1.5 mm and 2 mm.
However, if stock sold in metric units is hard to find, 0.0625” and 0.08” sheets may be
substituted instead. In some cases, difficult to bend parts can be made out of 3003 series
aluminum sheets. This type of alloy has better formability than the 5052 aluminum, but it
is considerably weaker."

So a minimum of 1/16" would probably be wise, especially since even I can bend that thickness with my bare hands (I really don't have that much hand/grip/upper body strength).

McMaster has a very wide selection and appears to be the primary/recommended source in the manual. The only major downside (other than somewhat higher prices versus other online sellers) is they never estimate shipping costs (still, I'm close enough to a distribution center/warehouse I mostly wind up with same day UPS delivery for ~$20 :D).

Onlinemetals has a pretty wide selection, and a 12"x12" 5052 sheet is ~$6 and ~$7 for 0.063" and 0.08" thicknesses, respectively. McMaster runs $3~4 more expensive for 0.08" and I did not find 0.063".


Another possible choice is 6061 which is slightly more expensive at OM and much more expensive at McMaster (~$18). It is a bit stronger and harder than 5052, so it will not be the easiest to form by hand. You should be fine if you have access to a shop with decent quality sheet metal tools like a bender and cutters (not just tin snips). I'm lucky. There are several drill presses, a corner cutter/press, and a really nice configurable sheet metal bender in the engineering department's shop (built protective housings/mounts out of some scrap for the HaViMo2 camera modules we got a few weeks back, and my only wound was a small gouge in my thumb when the sheet got snagged and spun by the drill press).

Gertlex
08-06-2011, 08:42 AM
I don't know about sheet aluminum, but in the past I've almost exclusively used 6061 or 6063 aluminum for projects, typically in the form of 1/8" or 1/16" thick extruded angle, channel, and square tubing. It's what you'll typically find at a hardware store.

Regarding thickness, which tician mentioned, I'd say 1/16" might be your upper limit of thickness rather than minimum, at least for mech warfare sized bots. Cire's Immortal was done with .04" thick material, and was designed for .025" thickness.

Wiki's page is actually pretty good: http://en.wikipedia.org/wiki/Aluminum_alloys

cire
08-06-2011, 09:24 AM
There is no one size fits all, it depends on your design and the loads associated with it. Bipeds tend to have much higher stress area's, especially in the legs, although its not to say that you cant make a really high stress part in a quad too.

Anyways, you should be able to get away with 1/16" for just about anything, minus maybe a ankle/foot bracket for a biped.

If you decide to use 6061, make sure you leave a generous bend radius (like 1/8" at least), otherwise the material will crack because it is more brittle.

billyzelsnack
08-06-2011, 09:36 AM
http://www.use-enco.com/CGI/INLMPI?PMPANO=0599951&PMKBNO=2535&PMPAGE=59&PMCTLG=01

FSCAUG promo code for $25 free shipping that expires Sept 30.

I think it's best to order a selection of thicknesses and be willing to redo parts until you find the thickness that feels right. I start out as thin as reasonable to make prototyping as easy as possible and often am amazed at how thin I can get away with once the metal has some structure to it.

tician
08-06-2011, 10:47 AM
There is no one size fits all, it depends on your design and the loads associated with it.
Indeed ...although I have to say that I very often tend towards overkill.

If you decide to use 6061, make sure you leave a generous bend radius (like 1/8" at least), otherwise the material will crack because it is more brittle.
I guess the scrap I picked off the pile was 5052 or similar (or maybe it just was not the T6 temper of 6061?), because at 1/16" thick it had absolutely no problem with zero internal fillets on 90 degree bends.

cire
08-06-2011, 11:38 AM
Indeed ...although I have to say that I very often tend towards overkill.

I guess the scrap I picked off the pile was 5052 or similar (or maybe it just was not the T6 temper of 6061?), because at 1/16" thick it had absolutely no problem with zero internal fillets on 90 degree bends.
1/8" is probably generous for 1/16". The best way to find out if your bending too tight is to bend a small scrap piece before you bend everything else. If you see any cracks, or if the metal changes color on the outside of the bend you compromise the material.

draikani
08-06-2011, 12:04 PM
Thanks for all the insight, exactly the types of info I was hoping for! I guess I could have told you guys what I was doing. It's just for a small rover, probably not more than 2kg and I would be surprised if it got even that heavy. So I won't be twisting the frame like a leg would. It's currently built with 1/16" plywood, which was great at first but I'm not a fan of wood for robots, they need something shinier.

draikani
08-06-2011, 12:06 PM
Oh, and where are you getting your scrap aluminum? I'm just making some smallish things so it's not like I actually need to buy a fresh sheet.

tician
08-06-2011, 04:12 PM
If the pieces you intend to make are sufficiently small (no more than 1.5~2" in width), you may be able to find flat bar/plate (or angle that you can cut into flat bar) in a local BigBox home improvement store. I know mine has 1/8" x 1-1/2" x 4' (and 8') pieces, and supposedly has 1/16" x 2" x 8' angle that could be cut into 2" bars. Of course those are likely to be 6063 (or maybe 6061). Mine also sells ~20 gauge plain steel which would be a bit heavy and I think it also sells very thin aluminum sheet (too thin to make frames/brackets but might work for skin/shell). If you cannot find any in a store, there is likely to be some sort of scrap yard or recycling center near you. Or you could just order from somewhere online, eat the shipping cost, and end up with more material than you need for this project (so that you won't have to scrounge for future projects).


Careening off topic again...
Some clarification on the sheet metal tools in the shop that I referenced earlier:
'Box and Pan Brake' or 'Finger Brake' for making clean bends with near zero interior fillet (have not measured but it is likely less than 1/32")
'Sheet Metal Notcher' for cutting out the 90 degree corners to be able to easily form a very nice box with the brake

Unfortunately, I am not finding many brakes online that are comparable to the 20+ year old one in the shop. The 'finger dies' that hold the sheet metal on the old one are not slivers of plate metal, but large triangular blocks of steel capable of bending 24~30" wide pieces of 12~14 gauge mild steel. I suppose a vise, a block or two of wood, and a plastic or rubber mallet might make a suitable (and far less expensive) substitute for some situations.

jwatte
08-04-2012, 02:37 PM
You can buy 1/16" sheets in 12x12 or 12x24 at the Home Depot. You can also get extruded angles in 1/16" and 1/8" there. I like the 1"x1" 1/16" thick extruded L angle bars; they have enough clearance from the bend to put screw holes for PCBs and what not, and are easy to glue with J-B Weld.
I also use a local metal supplier (Alan Steel and Supply) for things like 3/16" thick 3" wide aluminum bar, but their opening times are highly inconvenient (8am to 4:30, Monday to Friday, that's it.)