self centrering 4jaw chuck

[Kenchony]

Hello. I am working on a lathe chuck that is a 4 jaw, but self-centering. I need help on how to time the jaws and also how to make them. if anyone has any info on this please provide me with the solutions.

[ctwo]

Gotteswinter on youtube has a video on making chuck jaws. While it was for a 3-jaw, the technique might apply to your application just the same.

[BadDog]

The "timing" should be no different than a 3 jaw, just reference to the back (scroll) side of the 4-jaw adjusters. And jaw pattern is most likely one of the American Standard top-jaw standards, a few measurements should confirm.

[pete]

Yep Stephans video is really good and I learned a great deal from it ctwo. Making a set of jaws? Myself I doubt unhardened material would stand up for long or maybe at all. Due to the high point loading on the jaw teeth as the chuck gets tightened up then proper material selection will be pretty critical as well.Timing them is calculated starting with the internal scrolls dimensions and since the jaws go into the chuck in order, the jaws rear teeth are positioned to account for that every 90 degree position so the jaws will meet all at the same time as there closed completely. Nothings ever perfect in the real world so the finished jaw tips are preloaded and ground after assembly. Depends on just what shop equipment you have and your skills. But as I said hardened material probably isn't optional. Due to the tight but still sliding fit in the chuck bodys jaw slots having a surface grinder at the minimum would be a good start. Or at least make the project multiple times easier. Stephan used some jaws he already had to copy those jaw teeth with a very good pantograph engraver. Starting from scratch without anything to copy would make it far tougher.

4 jaw scroll chucks can be real handy sometimes, but you could do one hell of a lot of dialing in work with an independant 4 jaw for the time invested in making a set of jaws. It's beyond my shops equipment and skills I do know that.

[BadDog]

When he talked about making jaws, I assumed he was talking about top jaws. All the 4 jaw scroll chucks I've seen have 2 piece jaws, and I was looking at one recently (pondering buying on ebay) that was missing top jaws. Which should just be an American Pattern. And I considered "timing" as simply getting the back jaws in the right positions, perhaps the offset tops confusing things. If he's really missing the bottom jaws, then yes, I think that's a very tall order for any home shop...

[pete]

You could be right Russ, maybe I read what he was meaning incorrectly and it's only the top bolt on jaws he's needing. My small Emco 3" diameter 4 jaw scroll chuck has the one piece jaws so two sets of jaws came with it. It's possible whatever chuck he has doesn't have anything properly stamped for location, but it's still pretty easy to figure out which jaw is 1-4 by looking at the jaw teeth.