I'm looking to build a bike carrier for the ducati - I bought one and hate it, and think I can improve on it's design. I would like to make the tray from aluminum.

The piece I would like to use is 8" wide x .250"thick x 3.75" tall rails by approx 75" long and weighs about 5.79 pounds per foot. It is 6061 T-6 with the following standards (ASTM B308, AMS 4113) - I have no idea what they are or what they mean, but figured some of our smart engineering-type people may.

Is there any way for me to figure out what the capability is of such a piece?


Thanks in advance!
-sean

http://www.matweb.com/search/SpecificMater...assnum=MA6061T6

Yeah, how will it be loaded and supported? Design it such that the stress never exceeds 1/2-1/4 of the yield strength and I doubt you will have to worry about it failing. I generally design with steel so you may want to wait until someone with more AL experience chimes in, but if you give me approximate support points and loading, I could take a first look at it. From your description it sounds like a C-channel, right?

yeah, it'd be a c channel...I could draw something up and post it for you to critique.

Sounds good

A channel at .250 thick oughta be strong enough to run a semi across it.

Be aware, ifin ya weld it, the heat treat (T6) goes to T0 near the weld. T0 is dead soft and much lower in strength than the T6 heat treat.

Aircraft structural epoxy is your friend along with rivets when joining aluminum parts. Be careful that you don't mix steel and aluminum parts. That can make a galvanic couple that will accelerate rust in the steel parts.

Ken

Ken,
I was thinking of a total bolt-together solution, so I don't have to pay someone to tig for me, and was gonna powdercoat so the steel hitch mount wouldn't cause the galvanic reaction.

sound like it'll work?

"Aircraft structural epoxy is your friend along with rivets when joining aluminum parts. Be careful that you don't mix steel and aluminum parts. That can make a galvanic couple that will accelerate rust in the steel parts"

You can use stainless steel where fasteners are required. I sell aluminum / glass railing systems, and the stainless is pretty inert. The problem comes to finishing the aluminum. You can use alodine as a pretreatment for the finish. The best is a full chromate conversion. You can buy a 2 stage system from PPG that is an acid bath, then chrome iodine treatment. This is important as without pretreatment, the finish really will not bond with the aluminum. The powder can peel after the surface is breached

My materials
diyrailing.com

By the way you can retreat the aluminum back to T6 after welding. You just need a oven large enough to fit your project in.

Sean, prolly work OK. Zinc or cad coated bolts would be good to provide extra insurance. Mebbe a little dab of grease in the hole too.

Yes, you can get the T6 treat back by reheating it but you would be surprised at how few people realize that welding kills the precipetation hardening in aluminum

Gee, wonder if that is why Len puts the welded heads back into the oven????

Ken

Someone please correct me if I'm wrong, but -T6 heat treating is done in a special oven where the aluminum is immersed in a media (like a part tumbler). Its referred to as an "artificial" heat treating that cannot be done with conventional methods.

I don't have my Machiners Handbook with me, but as a general rule of thumb, aluminum is 1/3 the strenght of steel... but 1/3 the weight too. I understand its a "bike rack", but what are the weights we're talking here? How much of this weight is going to be hanging off and how far? (I'm curious for load torque and twisting that will be applied to this tray). Do you have a picture of one that will show us exactly what the final objective (bike mounted on a motorcycle) will be?

Finally, what model Italian Diva do you have? I'm looking to get a 998 in a year or so (if I can't find a 1098 for a good deal)... NOTHING purrs like a V-twin!

Cheers, Don

PS: GOOOOOOO Rossi!!!!

I bought a 907...here are pics of an R1100S on a similar, but steel, rack...and a pic of my bike.

This is going to sound really bad... but for some reason I thought you wanted a bicycle rack for your Ducati... HAHA wow, that was dumb.

Anyways, I will talk to some engineers and look up some numbers tomorrow and get back to you.

Cheers, Don.

How does that rack tie back into the car frame? Through a hitch? I would be inclined to make that portion of the rack out of steel, maybe even make a small frame out of steel to support the aluminum C-channel and to better distribute the load. How heavy is the bike? Distance between wheel centers?

-Chris

The hitch to receiver connection will definitely be steel. The bike weighs about 470lbs. Wheelbase (center to center) is 59.4". My durango is rated at 10,000 tow capacity which is roughly 1000 lbs tongue weight, so no problem there.

Ok... so lets just assume your 907 is 450lbs so each tire will have a load of 225lbs. The main safety factor we're designing this for is the acceleration load of this rig when you hit a sharp bump like pothole or steeps speed bump. That is the main force you need to be concerned with. The aluminum channel you listed above will work, but your going to want to make the receiver section as well as a gusseted base out of steel. Here is an example I just wiped up...

Don, that is very similar to what I had in mind....thanks for making a visual for it.

woohoo solidworks!

I'd make it out of stainless, and brush finish it. It would look sweet and you wouldn't have to finish it. Just make sure to acid treat the welds.