Is there an aluminum that can handle this project?

[SorryOciffer]

I have an Italian sportbike that I would like to have custom axles made for. OEM ones are steel, grade unknown. I can have custom machined Ti axles and swing arm pivot made for roughly $1400. They would come from a highly regarded company that makes many products for motorcycles in Ti. They use a grade of Ti rated at 190K psi and has some sort of coating on it when done.

I would like to know if there is an aluminum alloy that can also work, not only because the material is cheaper to buy and cheaper to machine but because it is even lighter than Ti. Lightness is the holy grail to sportbikes.

The axles are hollow so they would likely have to be gun-drilled and highly accurate.

Would a metal with these specs work?



Any suggestions?

Much appreciated,
Bryan

 

[Metalguy]

Are you size-limited? Even strong alum. alloys have to be bigger/thicker than Ti or high strength steel. Also, while Ti and steel have what is known as fatigue strength limits (a stress level below which fatigue cracking will not occur), alum. alloys do not.

That's why you might see alum. con rods in short-life racing engines, but not in endurance engines. Also, high elong. by itself doesn't buy you much. By the time you're in the elong. area, you're past the yield point and the axle is deformed.

"You see, wire telegraph is like a very long cat. You pull his tail in New York and his head is meowing in Los Angeles. Do you understand this? Radio operates the same way: You send signals here, they receive them there. The only difference is there is no cat." A. Einstein

 

[SorryOciffer]

I am limited in overall diameter but can go thicker as far as wall thickness. I don't want to go to thick though or I would lose the advantage of being light weight. Thankfully, the pieces are not very long and have little weight focused near the center, most all is at the ends. I will post pics of the stock parts.

I even had someone suggest a thick walled carbon fiber tube with press fit/epoxied metal end fittings with one end being threaded to accept the stock nut. I found a CF tube maker that will make custom tubes with extra thick walls. Could something like that work? What if it had a thinner metal rod running inside to add even more stiffness?

 

[israelkk]

Assuming the professional axles were carefully designed using stress and fatigue analysis, you need to recalculate each options you are considering to same criteria Therefore, there is no way to tell you without calculations which alloys can be used and what will be the weight gain. Even if you do not have the calculations used on the current axles you can study and calculate the current axles based on their dimensions and material properties. Then you will be able to re-engineer different axles to the same strength and fatigue life.

 

[SorryOciffer]

Israelkk, I wouldn't even know where to begin to do that as this is not my field of expertise. If the the Ti axles are appropriate, can one go off the various info from those for strength etc and then design a part using another material that matches the critical properties?

 

[israelkk]

If a qualified experienced engineer that have an experience in product development,reverse engineering, strength and fatigue analysis will have the axle and will know the exact material specification of the axle, he can measure it and analyse it based on its function in the bike. Then he can try to design a different axle from different material and technologies to match the same strength. There is also the issue of other engineering areas such bearings, lubrication, surface protection, etc., that should be taken into consideration.

 

[EdStainless]

No. I doubt that you could possibly make a high strength Al part thick enough to get the fatigue strength that you need.

I have worked on projects that go the other way, we used a high strength stainless steel to replace Ti, kept the weight the same and increased the strength and fatigue life.

= = = = = = = = = = = = = = = = = = = =
Plymouth Tube

 

[SorryOciffer]

A search came up with this company. Going to contact them to see if they have done anything with motorcycles.

Hopefully I hear back from them.

Would it make any difference if the axle itself was stationary? Unlike a car, a bike axle does not rotate and the assembly that does rotates on a bearing, it's not having to resist a twisting force. In my case the axle only has to support weight spread out almost over it's full length.

It would seem that the most stress it would endure is the weight sitting on it from above and the force/weight of the bike it is pushing forward against as it accelerates.

 

[MikeHalloran]

The axles are intimately involved in braking, too.
Make a Free Body Diagram to find out how.

... Don't know what that means, right?

No offense is intended, but this stuff seems to be _way_ above your head.

This is serious shit.

You will not ride away from an axle failure on a sportbike.

Leave the axles stock, and go on a diet. That will give you the most bang for the buck, and maybe save your life.



Mike Halloran
Pembroke Pines, FL, USA