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Driveshaft modification

Driveshaft modification

Driveshaft modification

Hello There

I hope that you can help.
A good friend of mine has a VW split screen van that he has shoehorned a 3.0L V6 renault engine into.  He is having problems with the driveshafts which he is making up from 2 existing shafts to suit.  Essentially, he is trying to join one half of a renault 25 shaft to the other half of a VW shaft.  He is planning to join the shafts by machining both to a common ID with a leading taper and then plug welding them into a machined sleeve.
His concern is ensuring that the welded joint is strong enough to withstand the applied torque and that the shaft balance is ok.   
 Has anyone out there got any advice?
Our plan was to evaluate the plug welds in shear and add a safety factor.  What sort of factor would be appropriate?
Should we consider fatigue? if so, how?
Should we treat the weld as mild steel for its yeild stress?
What about hardening?
I hope you can help.  If we can sort this out he will have a crazy van.



RE: Driveshaft modification

For your weld strength in shear Shigley and Mishke recommends using 0.40Sy for the max stress with a design factor of 1.44.

For your shaft balance, you are welding two shafts together?  How long will the shaft be?  Will they be one long driveshaft?  If the driveshaft gets too long, at speed you could hit the critical speed and destroy the driveshaft.  Basic formulas for this is available in the Machinery's Handbook.

RE: Driveshaft modification

Assuming that these are driveshafts and not prop-shafts I dont see a problem in principle.
Lots of trike builders in the UK have mated bike prop-shafts to 'car' (Reliant 3-wheeler) prop-shafts this way (much less meaty than car mechanicals). However, I suggest you make sure the sleeve is positioned right at one end of the shaft (preferably the one that moves least). This should simplify your balancing problems.


RE: Driveshaft modification

He could machine the larger socket of a driveshaft slightly too small and heat it to get the ends to slip together.  This would give you a considerable amount of friction between the 2 driveshafts and reducing the shear on the weld.  How is the yolk welded onto the end of the driveshaft?  Why don't you do it that way?

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