Question About Workholding: Gear Blanks

markba633csi

markba633csi

Mark Silva
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When a gear blank is made on the lathe, how is it then mounted to the rotary table or indexer keeping it in perfect concentricity? Do people use a collet system on both machines? I don't see how it's done if the indexer has a 3-jaw chuck.
Mark S.
 
You generally make a mandrel/arbor to hold the gear blank. The arbor is then held generally in a 3-jaw chuck that is mounted on the rotary table dividing head. The mandrel/arbor is similar to that used on a mill for holding slitting saws and such.
 
Alternatively, (provided the mountings match), the lathe chuck can be removed from the lathe and fitted to the indexer with the gear blank in place.

Cheers Phil
 
Long answer second.
If you have an adjustable 3 jaw chuck dial it in. If not use a 4 jaw.

If a 4 jaw is not available use shims to knock the run out of the 3-jaw to where you require it, this often leads to madness however so be prepared.
Common notebook paper works well for this as a .001 shim under a jaw, making this work can be a frightful experience.

As a disclaimer, I have never once made a gear in the 25 years that I have been working in this business as they are mostly available off the shelf, this merely requires boring, broaching and possibly a setscrew. Companies that make such products produce 100's per day, you cannot compete with that on price.

Good Luck
 
I assume you are talking about a gear for a machine. Gears are best cut mounted on a mandrel between centers. They need to be mounted accurately, very accurately, and with very little run out, to not end up being scrap metal... There are lots of good tutorials on YouTube about how to make gears. Tubalcain has a tutorial series with a bunch of videos showing various ways to cut gears. Shortcuts and work arounds are usually a bad idea unless a crude gear will suffice for the job.

How about posting some more specific information on what you are making, what it will be used for, and what resources you have to make it with?
 
My first lathe I rebuilt over 30 years ago, I had to make two pinion gears and a double bevel gear for the apron of that old lathe. The two pinion gears were a no brainer to make and did a nice job on them. I wish I had taken pictures of them. The double bevel gear was a little more difficult. Luckily, I got the factory cutters to make it. They had been resharpen so many times there wasn't much left to the cutter teeth. Slowly but surely, I was able to cut the bevel gears. How I go ahold of the factory bevel gear cutters, that's another story for later. Since that time I have replaced a couple of pinion gears with modified stock gears from Boston Gear. So far they are still holding up on my lathes today. Now if I can find a 127 tooth gear!
 
There are various different methods. It really depends on what equipment one has, what kind of gear is to be made, how many you need to make - and so on. I made up about 25 change gears for my spiral milling unit (1507 teeth in all). I chose to mount the blanks on a shop build arbor (the dividing head has a 4MT taper). When I made the arbor, I cut the 4MT and the gear mounting position in a single set up on the lathe.

Scroll down to post #12 of the thread about my little die sinker mill.
http://www.hobby-machinist.com/thre...ling-drilling-and-boring-machine-mh600.30766/

DSCF4583.JPG
 
David,

Sorry for your unfortaunate accident you had unloading that once beautiful mill you had there. Everyone thinks those handy carts are cool and needed under every machine in the shop! If not designed correctly, they are nothing but an accident waiting to happen! They are dangerous, period! I don't recommend anyone to use them! No exceptions! Sorry to get off subject here.

Back to gear cutting!
 
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