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hwingo
07-20-2013, 01:59 PM
Hey Guys:

I have a personal project ongoing that requires either an 8 tooth or 9 tooth gear. The 8 or 9 tooth requirement is no longer an issue; I have one. I purchased a starter bendix? (is “bendix” the correct word) that replaces a worn our gear on a 1990 Chevy starter motor. To get this gear I completely disassembled (and destroyed) the housing in which the gear was contained. There was no damage done to teeth or gear hub. The gear was basically held in place by, and ran inside of, a set of roller bearings.

1. Problem #1: I need to drill and tap a hole in the hub of the gear so it can be installed and retained on the ½” shaft of a gear-reduction motor. I am nearly certain the gear is a casting. The hub is seemingly “glass hard” because a file simply slides on the surface without leaving a mark. Can the hub be annealed and if so how would I go about annealing the hub without affecting the teeth on the gear?

2. Problem #2: The gear, as it comes from the factory, has a pressed brass sleeve inside the gear which the shaft of the starter motor slips into. As is, with the brass sleeve in place, the ID of the gear is too small for the ½” shaft of the gear reduction motor. Having pressed the brass sleeve out, the ID of the gear is too large for the 1/2” gear-reduction motor’s shaft.

The ID of the brass sleeve measures 0.478”
The OD of the brass sleeve measures 0.517”
The ID of the gear w/o the sleeve measures 0.518

Mathematically, the brass sleeve’s wall thickness is 0.039”
Physically, the brass sleeve’s wall thickness runs the range between 0.020” and 0.023”.

Provided I’ve done my math correctly, I would need to bore the inside just a little more than 0.0085” to accommodate the reduction motor’s shaft.
.517
-.500
.017” / 2 = 0.0085”

That would leave a brass wall thickness of 0.022”. At that wall thickness, am I running the risk of the brass wall collapsing? How would you approach this issue to realize the required ID?

Harold

hwingo
07-20-2013, 03:02 PM
I forgot to include images.

Harold

http://i234.photobucket.com/albums/ee38/hwingo_2007/Gear1_zps93bfa863.jpg (http://s234.photobucket.com/user/hwingo_2007/media/Gear1_zps93bfa863.jpg.html)

http://i234.photobucket.com/albums/ee38/hwingo_2007/Gear2_zps25fda984.jpg (http://s234.photobucket.com/user/hwingo_2007/media/Gear2_zps25fda984.jpg.html)

CCWKen
07-20-2013, 03:48 PM
There's not enough meat there to just anneal the hub without getting to the gear. You'll need in the range of 1200 degrees. Besides, you should have chosen another gear. I think those are sintered from powdered alloy. They may not take an annealing and re-hardening cycle without fracturing. You might try using carbide tools. I bet that gear is at least RC-60.

A reduced ID bushing shouldn't be a problem. Use shim material. If you must use that gear, I'd use it captured to the shaft with a nut. You could grind a slot on the hub for a key or pin. You'd just need a method to back the gear up on the shaft like a welded flange.

rohart
07-20-2013, 05:03 PM
If you have access to a welder, try welding a dummy piece of rod onto the hub. Then hacksaw it off again. By the time you've finished, the spot where you welded it on will be annealed, and drillable for a set screw.

hwingo
07-20-2013, 05:57 PM
Thanks guys for your replies. I've about decided to attempt drilling/milling a hole with carbide and pin the thing.:rolleyes: To a degree, those of us living in Alaska are sometimes at a disadvantage. We don't have to our immediate avail sources where parts can be easily obtained. I, for one, will need to drive over 120 miles round trip to Anchorage where they *might* have such a part. For that matter, in comparison to others living in the bush, I have it very easy. I will attempt to make do with what I have and later see if I can find something on line. Shipping charges to Alaska are often horrendous but I suppose it couldn't be much worse than using \$75.00 (or more) in gas.

Much appreciate your responding to my post.

Harold

JCHannum
07-20-2013, 06:05 PM
The eccentric bushing makes me wonder if the bore of the gear is concentric to the gear itself. As Ken points out, these gears are MIM (molded in metal) and as such, might not be particularly precise. The bushing might be for the purpose of truing the bore.

You might want to do some checking with an indicator to check for runout of the bore.

Uncle O
07-20-2013, 06:06 PM
You may be able to do a spot anneal, as opposed to going for the whole hub....just concentrate the torch onto one small area of the hub....
As far as the bushing goes, I would press in a new one with more meat on it and then bring it into size.

hwingo
07-21-2013, 10:00 PM
The eccentric bushing makes me wonder if the bore of the gear is concentric to the gear itself. As Ken points out, these gears are MIM (molded in metal) and as such, might not be particularly precise. The bushing might be for the purpose of truing the bore.

You might want to do some checking with an indicator to check for runout of the bore.

Hi JC,

I had a little time on my hands and I indicated the bore. I held the gear by the ground & polished part (see previous image to identify "ground and polished") using a 5-C collet in a Bison adjustable collet chuck. It appears that the bore, without the bushing, is about 0.004" out of round. I would think that reinstalling the brass bushing and boring the bushing to enlarge for the 1/2" shaft would "fix" out-of-roundness. Good catch!

Harold