I’m looking for some recommendations for heat treating a 5.3 inch diameter gear out of 4140 steel. Ok…without going into too much detail, the basic problem this. I want to repair a large PTO spur gear from a farm tractor. The original gear had some broken teeth, which then lost contact ratio. The gear moves on a spline shaft and mates with a stationary pinion.
I machined off all the teeth from the original gear and saved the hub, which still has the interior spline cut out in it. My plan is to machine a new gear and press fit it over the original hub so not to have to re-machine a whole new interior spline for it. My main question is should I heat treat the gear overlay before I cut the gear teeth into it, or should I do it afterwards?
If I heat treat the blank for the gear overlay first it will be difficult to machine, since I will be using a HSS cutter (the gear cutter is only in HSS). However, I am certainly going to get a correct tooth profile, since any distortion from the heat treatment will be machined out.
If I heat treat after I machine the gear overlay I’m now restricted to using only two methods: induction hardening of the teeth, or flame hardening of the teeth. I really don’t know the original composition of the gear, so I don’t want to touch the hub. I cannot use my furnace, since I will have to heat treat the entire gear including the hub, which I do not want to do.
If I flame harden the teeth I have no means of measuring or controlling the actual temperature. Even if I could, I am now left with some distortion in the teeth, which I would have to grind back to the correct tooth profile, which I really don’t want to deal with either.
My original thought is to rough machine most of the material, heat treat, and then finish machining.
Any thoughts or suggestions?
I machined off all the teeth from the original gear and saved the hub, which still has the interior spline cut out in it. My plan is to machine a new gear and press fit it over the original hub so not to have to re-machine a whole new interior spline for it. My main question is should I heat treat the gear overlay before I cut the gear teeth into it, or should I do it afterwards?
If I heat treat the blank for the gear overlay first it will be difficult to machine, since I will be using a HSS cutter (the gear cutter is only in HSS). However, I am certainly going to get a correct tooth profile, since any distortion from the heat treatment will be machined out.
If I heat treat after I machine the gear overlay I’m now restricted to using only two methods: induction hardening of the teeth, or flame hardening of the teeth. I really don’t know the original composition of the gear, so I don’t want to touch the hub. I cannot use my furnace, since I will have to heat treat the entire gear including the hub, which I do not want to do.
If I flame harden the teeth I have no means of measuring or controlling the actual temperature. Even if I could, I am now left with some distortion in the teeth, which I would have to grind back to the correct tooth profile, which I really don’t want to deal with either.
My original thought is to rough machine most of the material, heat treat, and then finish machining.
Any thoughts or suggestions?