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Re: shaft materials question

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Posted By<" ">Bill Beam on June 03, 2002 at 11:05:24:

In Reply to: shaft materials question posted byBob on May 30, 2002 at 21:56:19:

: I need help in specifying the motor shaft material and heat treatment for my Battlebot (well that's my hobby). I already did have a shaft made out of unhardened 4140 steel and the electric motor twisted the shaft until it sheared.

: The electric DC motor (it's a DeWalt hammerdrill motor overvolted by 50%) is generating 68 ft-lbs of torque at stall and the electronics are built so that its ok to stall the motor. The shaft is 0.393" diameter and has 4 splines cut into the shaft, each cut is an arc of depth .070 and length of .182. So the x-sectional area of the shaft would have been .121 square inches without the splines and the x-sectional area with the splines is .083 square inches.

: Of course the shaft needs to be made of something conventional, our budget for the whole Battlebot is around $5K.

: If anyone has a suggestion for the shaft material and heat treatment, well that would be really helpfull,

The 4140 is a pretty good steel but with that much torque I don't think any soft steel will hold up. I think you stand you best chance with 4140 if you heat treat it. The proceedure for 4140 is preheat to 1250 deg F then bring it up to 1550 deg F. Let it soak at temp for probably 15-20 min and oil quench. Max hardness on 4140 is around 55 Rc I don't think you would want it that hard my sugestion would be to draw it back to about 46-48 Rc. There is another steel that is recommended for splined shafts and that is 6150. It is not as common but it might work. The heat treatment for it is the same as 4140

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