Material spec for custom driveshafts

[Simon_Longley]

Good morning :-)

I'm building a Tiger Avon based kit car at home and have deviated somewhat from the usual spec. I have changed the old Sierra diff to an RX8 torsen lsd and plan to use mazda engine box.

The kit is based on a Sierra / cortina running gear and therefore I need to machine custom driveshafts to accept a ford CV one end and RX8 the other.

At work I regularly machine halfshafts for vintage racers using EN24T and they have never failed however the diff gears and hubs are driven through a taper not splines as in my own car.

The RX8 shafts are hard so my questions is will EN24T in its toughened state be good enough for the splines or will they likely wear after a while?

My other option is to use something like EN36b and have the shafts case hardened but I'm concerned about warpage unless I grind them and machine the splines after heat treatment but I'm reluctant to do that.

Any help appreciated
Simon

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[MartinS]

Hi Simon

Heck, this takes me back a few years.....when I was working we made many, many halfshafts. As you say, En24 is a common material used for halfshfts and, depending on the section, can be taken above "T" condition (V or W). Though this may need an intermediate stress relieving operation.

Also En24 is often induction hardened. Either the whole length or just the splines. Whether you do the whole length or not depends on the torque and likelyhood of breakage. As above, if you induction harden the whole, a stress relieve op may be necessary to reduce the amount of bending.

In my opinion case hardening is unusual on halfshafts, I can't see it's benefit.

My other option is to use something like EN36b and have the shafts case hardened but I'm concerned about warpage unless I grind them and machine the splines after heat treatment but I'm reluctant to do that.

I don't follow the logic here.....surely you are worried about the splines resistance to wear. If you are removing the case to enable the splines to be milled/hobbed, then you have a spline surface no better than En24 for wear resistance. (not to mention bend and grinding through the case.)



It comes back to what you want:

a)Will En24T (or "V") carry the torque? (unless there are any sharp changes in section, the shaft will fail at the point where the spline leaves the hub)

b)Will the spline wear excessively?

If you are worried about a) then push the En24 to "V" or above or/and add induction hardening

If you are worried about b) then induction harden the splines (En24 will take nitriding. Not as good as En40B. Worth thinking about)

Hope this helps

Martin

PS, it might be cheaper to machine two sets of shafts and depending on how long the first ones last, the spares can be used "as is", or hardened.