hardened gear on a mild shaft

Bob in Phx · 2008-09-28T04:52:43+00:00

Ok, I need some suggestions here. I have an electric bike motor that has "spun" a gear. The shaft is mild steel and the gear is hardened. the gear is about 3/4 of an inch across and the shaft is about 3/8's or so. The gear and shaft are press fit. The max torque that this gear and shaft see is around 35 foot pounds. When the motor gets hot, the gear slips, but I can not pry the gear off. The gear is attached to the rotor of the motor with the comutator on the other side of the housing. A couple of folks have had this same issue. They have been able to remove the gear by hand and then use bearing retainer and JB weld to mate the shaft and gear again. The motor never gets above 150 degrees.my options as I see them.Keep using the motor until the gear is so loose that I can pry it off and then "glue" it back on. I don't want to do this, as I am scared that the shaft damage and may not be symmetrical, thus the glued on gear could be out of wack.I could try and just jb weld the top of the gear to the shaft. The shaft sits down inside the gear by a couple of 10ths. The problem here is that I don't know the amount of torque that jb weld can stand in this configuration,I could have a pin machined through the gear and shaft, but I am worried that the hole in the gear face could cause a wear on the driven gear.I could cut a key slot in the top of the gear and the shaft and glue in hardened steel. but my brothers mill is down so I would have to take it to a machine shop. I don't know any good ones and I think this is to much of a pain in the back side for most machine shops here in Phoenix.I could have it EDM's lengthwise down the shaft and the gear and then put in a standard key, but again pain in the back side and hassle of the machine shop come into play....any other ideas....Here is a picture of the shaft, gear and my suggested milled key way... (yes it was done in ms paint!!) in phx

Sep 28, 2008 20 Replies

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hardened gear on a mild shaft

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