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Filling Mainshaft speedo splines?

OT

NAXJA Forum User
Location
Jensen, UT
I have been considering filling in the gear on the mainshaft of my 242 (They are the spiral cut gears). I would be filling them with TIG and turning it all down smooth.

All the breaks that I have seen have been on this spiral geared section. The base of the splines is a smaller diameter than the rest of the shaft and this seems to be the weak point in it.

Will the heat from the TIG weaken the hardened shaft, or will the change be negligible due to the filling? Is there much chance of crystallization? Of course the shaft would be pre-heated and post heated to 550 degrees in the oven.

It should go without saying, but this is not my DD and I don't need the speedo. So save the "You won't have a speedo anymore" comments.
 
any idea what alloy the shaft is made of? my guess, from drilling the end out, is that it's some whitches brew of an alloy. Its strong, but not like a drive gear or the like. 550F is not even close to the recrystallization temp for such an alloy. However, the TIG will be melting the metal. the surface of the shaft, where most of the stress is concentrated, is not a good place to have uncontrolled recrystallization. you will be introducing a heat effected zone at the edge of the weld where the metal may become extremely brittle and varry greatly in hardness. not good. BUT, by adding an additional .25" of radius to the shaft, the strength increase may overcome any changes in the metal itself.

the shaft could also warp.

Someone may know more, just some considerations.

one thing that you might try is to cold grind the worm gear off this section so that its almost smooth. this would get rid of the stress concentrations inherent in the geometry of the gear teeth and you could/may gain some strength as a result. not sure how much of a gain, or if the gain would overcome the loss of material in this area of the shaft. try it!
 
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