Align keyway to tooth

[EngJW]

How do you center a keyway with a gear tooth, for example with cam and crankshaft timing gears? Do you put the keyway in the blank, or cut the keyway after the teeth are hobbed?

The next question would be how to do this with helical teeth. Do you have to pick some point along the length of the tooth, or can you just use the ends? (I think it should not matter as long as both gears are done the same way.)

Thanks. With some of our parts it does not matter if the keyway is aligned, while on other parts we call it out but don't specify how to do it. Most of our gears are helical.

 

[CouplingKing]

When we have to align a gear tooth form to a keyway, we usually cut the teeth first, then scribe the centreline of the tooth/gap down to the bore. From this we align for slotting/broaching.

Whilst simply "scribing" a line is not the most accurate method, it is good enought for our purposes.

If more accuracy is required and you have a long gear train then why not make one of the gears adjustable by using a Ringfeder or Tollok locking assembly.

CK

 

[gearman1234]

Hello,

I have experience with spur gears. We cut the teeth first. We have designed a broaching fixture whicvh takes the location of the teeth gap by using a spring loaded ball. ball. The location of the broaching will be at a calculated angle to the ball centerline. We achived an accuracy of 0.003" between the tooth centerline and the keyway centerline.

Same concept can be use for helical gear too but in this case the axial position of the gear should also be controlled. Hope this helps.

 

[EngJW]

Thanks Mr. Gearman. Our checkers like to make the gear tooth a datum and then give a true position tolerance to the keyway. I had no idea how it was done.

We have helical gears in an engine and they have to be timed. I would think that you could locate the keyway with respect to any position along the tooth (such as ends or middle) as long as you do it the same way for each gear. Is this true?

 

[magnograil]

True, but if you are including a visual mark on the gears for the correct mesh then aligning at the marked face facilitates this on a helical gear. Much easier to align the mark and keyway together at a valley or tip.