hardened gear on a mild shaft

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!!)
http://members.cox.net/rbelisle1/gear.JPG
bob in phx
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"Bob in Phx" wrote: (clip) any other ideas.... (clip) ^^^^^^^^^^^^^^^^^ Drill endwise into the interface between the shaft and the gear, so you have a round keyway, in effect. Then run a tapered reamer down this "keyway," and drive in a taper pin. Since it looks like the shaft sticks through the gear, you will have to place a collar over the shaft, so the drill can be positioned properly half way into the shaft and half way on the gear.
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I'd do something like that, but instead of a taped pin, I'd tap the hole and screw in a socket head "grub "screw with Loctite. It used to be a common fix and was called a Scotch key

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He said that the shaft was soft, the gear was hard. There is zero chancefor these options to work as the drill will invariably drift into the soft shaft and away from the hard gear.
CarlBoyd
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"Carl Boyd" wrote: He said that the shaft was soft, the gear was hard. There is zero chancefor

^^^^^^^^^^^^^^^^^^ I would use a collar, slipped over the shaft, up to the gear. Pre-drill the collar with a pilot hole. Use a carbice drill.
I like the set screw idea, except for the likelihood of breaking the tap. OTOH, a broken and stuck tap might be just as good for this purpose as a set screw. So, how about making the hole/"keyway" with a Dremel type tool and a diamond burr, and then deliberately running a tap in until it breaks? (Maybe "burrs," since you will probably wear out a couple.
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On Sun, 28 Sep 2008 16:38:15 GMT, "Leo Lichtman"
<snip>

The carbide burr sold by Dremel would cut it. I just recently used same to remove a hardened Easy Out that broke off. It was slow going, but the carbide burr held up much to my surprise. Still cut good when I finally got the Easy Out devoured and into the stuck bolt which is what I really wanted out :)
This is the cutter I had good luck with:
http://www.dremel.com/en-us/AttachmentsAndAccessories/Pages/AttachmentsDetail.aspx?pid 11
They have other carbide cutters too that may be a more suitable shape for your job.
--
Leon Fisk
Grand Rapids MI/Zone 5b
  Click to see the full signature.
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I have a feeling the gear is thru hardened. If he could locate someone with a mill that is big enough he could use a carbide em to punch a pin recess and just use a straight dowel.
Wes
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that was the thought, only on the top of the gear and the shaft... kind of like a "T" ... the insert would be hardened steel, glued in place..
bob in phx
wrote:

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snip
I've had good luck silver soldering in this situation - you can keep the teeth cool enough so they dont' loose temper because the "low temp" silver solder is around 1200 deg if I remember right. As soon as the solder wicks, cool the assembly do you don't detemper the teeth.
And I've also (when really annoyed) just zapped it with an arc welder....
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Bob in Phx writes:

Likely burrs on the gear and grooves on the shaft from spinning the gear are going to lock it on. It will take a properly fitted gear puller to get it off, and sometimes this means custom making such a puller. You can't pry or hammer against the motor bearings without ruining them.
JB Well-Duh is just epoxy glue with a stupid, lying name. If steel didn't hold up, glue with 1/20 the material strength certainly won't.
Perhaps this is a Chinese item? Improperly engineered for the actual instantaneous torque experienced in the assembly, which has nothing to do with the torque rating of the motor. Silk purse, sow's ear.
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I would love to pull the gear, but its just not looking possible. as you can see in the picture, the gear is right on top of bearing. I have not been able to find anything that would fit between the gear and bearing. The motor bearings are standard off the shelf parts, but the motor housing and shaft are not.
As for the country of origin,, well its not china, nor any asian country for that matter. The motor is a german Heinzman geared brushed hub motor. Max volts, 24, normal amps 20, max amps 30, max torque produced 35 nm.
The workmanship inside and out is very nice. I very nice casting followed with nice machine work. The motor is over 10 years old, but was not run much.
if any of you get the chance to test drive an electric bike... do it.... I promise you will be smiling when your done!!!
thanks for the tips... I am leaning towards welding.....
bob in phx

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I welded hardened steel once. Made bigger cracks than I was trying to fix.
Wes
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Bob,
It depends on how much time and effort you want to put into it. If it was important to fix then I would machine a cup that drops neatly over the gear. If you have a cnc then it can be made from a square chunk of aluminum about 1/2" bigger than the gear diameter. Then drill a hole where you the shaft and gear meet. Drop in a standard hardened drill bushing then use a carbide drill to carefully drill into the shaft and drill. Knock in a hardened dowel or a spring pin to take the drive.
I do similar to this on a production item which is not hardend but I have a steel pin into and aluminum body. I drill half the aluminum and half the stainless and the drill does not wander off at all into the softer aluminum.
Dave
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On Sat, 27 Sep 2008 21:52:43 -0700, Bob in Phx wrote:

There is no (well, extremely little) radial force on the root or crest of teeth. Place the pinhole from rott-to-root or crest-to-crest (or root-to crest if odd teeth); insert & loctite pin, file away any burr, done.
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wrote:

"_" is a paedophile by his own admission:
http://groups.google.com/group/uk.rec.cycling/browse_frm/thread/7bd06f1abd3f07fe #
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is
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You could also try warming the gear with a heat gun to expand it a bit and then wick some super glue into the crack. This may or may not work, but it would do no harm to try.
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Superglue gives up at 250F
Wes
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the motor has a 150 degree shutoff so, it shouldn't get that hot....
bob
wrote:

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I doubt you will get clearance to get glue in, shaft and gear both with expand.
The bearing looks like it is held in by 3 screws, if you take them out can you fully expose bearing? by pushing case backwards?
If you can cut the od of bearing off you can get purchase on gear to pull it.
Wes
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thats a good idea,,, I take a look and see how much play there is.... I hadn't thought about that... even 1/4 inch might give me a chance to pull the gear!!
If I can get the gear off, then machining it gets a whole lot simpler...
bob in phx.
wrote:

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