setting up to bore bevel gears

[JEM]

need info on how to set up to machine the bore of cast bevel gears. Gears have no machined surfaces. How do I set them up so I can machine bore ture to the gear?

 

[kf2qd]

How many teeth? If you can cover several teeth with the jaws of your 4 jaw it is just like centerring any other job in a 4 jaw. You might want to use some brass pieces between the jaws and the gear. If you can't cover several teeth witht he chuck jaws its a bit harder. The OD should be concentric with the Pitch Diameter. Eyeball it close before you get the dial indicator involved and when you do use the indicator make sure not to use very much of the travel of the indicator so it doesn't catch and move knock the indicator out of place. First time or two it will be a slow process, but after you do a couple it will be like old hat...

 

[JEM]

I can get the gear in the chuck, but I'm having a problem figuring what to surface to dial from.

 

[gbritnell]

If I follow this correctly the gears were cast with the teeth already on them and they have some type of hub. You need to bore a through hole perpendicular to the face of the teeth. If the gears aren't really large, over 2" dia., then I would take a piece of round stock and machine a hole into it matching the angle of the face of the gear. I would then drill and tap two holes around the outside of the bored hole to use as clamp holes. Just use a bolt with a washer to clamp the gear into the counterbore. Now you can drill and ream or bore the center hole and it will be perpendicular to and concentric to the teeth on the gear. You can also take a skim cut off of the hub to clean it up. It's just one of those fixture items that you have to make for special jobs.
gbritnell

 

[rake60]

At work we had a few jobs that required finish machining of
"Precision Cast Bevel Gears". The "precision" of those gears comes from
a ridiculous amount of free running backlash in the cast teeth of those gears.
None the less, that is what you need to set up to.

Common scene tells you to grip on the big end with the smaller end inward to the chuck.
It looks safer, but you are still just chucking on points no matter which way it's chucked up.
We would set it up the opposite way at the edge of the chuck, narrow point out.
Indicate the teeth round as close to the chuck as possible then move out to the narrow end.
Bump the gear in or out to get that end running round. Now the back side is out again so you
move the indicator back and re-indicate it using the jaws. Move back up to the narrow end and
bump it round again. Back to the jaws... It's going to take some time and patience to get it right.
You might go back and forth 20 times before it's close enough.

As kf2qd said, in a perfect world you would to indicate to the pitch diameter of the gear and everything
will be perfect. Unfortunately that is an imaginary line that you can't put an indicator tip on.
The best you can do is indicate to the OD of the cast teeth and hope they are accurately cast to
that imaginary pitch diameter line.

Rick

 

[toolsrul]

I visit places that machine various areas of gears & what they do is get pins to mount in the gear teeth & hold on the pins. This depends on how many teeth & how your going to hold it, but the pins have to be the same size & are higher then the teeth. If you use a collet or a 3 jaw chuck you need 3 pins spaced 120 degrees apart, 4 jaw 4 pins, etc. For concentricity everything is off the pitch diameter & that's what you'll be locating off of.
Good luck.