Adding shims under key when keyway broached too tall

[kyleShropshire]

I have two gears that have been keyed incorrectly.
The widths on gears and shafts are correct.
The depth of the keyway in the shafts are correct.

One gear has been broached too tall by 0.02" and tapered 0.006".
The other gear has been broached at an angle and leaves a keyway height of 0.502 on one end of the gear and 0.520 on the other end.

What do you think about broaching both keyways parallel to the bore axis and adding ≈0.025" thick of shim stock under the keys?
The shims should prevent the keys from rolling in the keyway and we can still use standard keystock.

 

[kyleShropshire]

Going up to the next size key does not leave enough material between the keyway corners and the gear hub diameter and I would be afraid of it cracking.

 

[dvd]

Step keys

 

[kyleShropshire]

Does the sharp corner on the step-key shear plane reduce shear capacity?
Also I would have to cut a larger keyway in the gear and I don't want to do that.

 

[GregLocock]

People have been using custom keys since 1880 if not before. I'd be inclined not to remove any more metal and get keys ground to fit.

Cheers

Greg Locock


New here? Try reading these, they might help FAQ731-376

http://eng-tips.com/market.cfm?

 

[dvd]

How much time and effort are you going to put into these to save them? Is it worth it? What do the gears look like - is it possible to install a shrink disc on the hub (if it has such). If not a shrink disc, then possibly a shaft locking device. Shrink discs or locking devices can most likely span a keyway on the shaft.

Shrink Disc

Shaft locking device

 

[kyleShropshire]

Since these are custom 4140 gears I ended up having them put on a shaper and the keyways cut parallel to the bores.

Made steel spacer-shims to bring the vertical clearance to 0.002in and standard keystock.

I referenced an old Koike power drive design manual where it talked about toque of snug fit keys and went with the spacer idea.