Gotteswinter's Method

[old mart]

All but one of the three jaw scroll ckucks at the museum have loose registers between the chuck and backplate. They also have 6 bolts/ SHCS holding the parts together, and none have ever been knocked out of place. The exception is the largest, a 6 3/4" serrated jaw which is 95% used with soft jaws, and would be pointless modifying. They generally run about 0.002" tir, but can be dialled in to zero for those rare high accuracy jobs.
The manufacturers make a huge profit selling the set tru style of chucks, and certainly don't want to advertise the free method.

[DennisCA]

Been using this method for two years now.

[Noitoen]

I have the same type of lathe Chinese from Spain and the chuck registers on a slight cone. I also have a Tripan quick change toolpost he has. The Swiss made tool holders cost more than the lathe is worth

[JoeLee]

It's actually a quite common practice for those that don't have a set true chuck.
I do it occasionally with the three jaw on my tool and cutter grinder.

JL......

[tom_d]

Buck Ajust-Tru Chuck is the name brand I grew up with. Advantage over what's shown in the video is the Buck is moved, and held in position with set screws. Easier to adjust, and less likely to get accidentally knocked out of place.

[mattthemuppet]

I did the bump Tru chuck thing on my previous lathe and found it to be quite a pain in the backside. A man or steak would knock it out and then I'd have to spend an age knocking out around with a rubber mallet trying to dial it in. Nothing like dialing it in with 4 screws at all.

[BCRider]

That was interesting.

So tell me this: is tearing chucks apart and re-building them part of being a machinist?

As the other two above said it sure is.

For me that's about every 3 years since it's just one of about 5 other hobbies. If I were doing machining for a living I think I'd be cleaning the chuck out about every 3 to 4 months.... or after about 4 heavy duty boring jobs that seem to feed the swarf straight to the scroll.....

[Doc Nickel]

So tell me this: is tearing chucks apart and re-building them part of being a machinist?

-Er, yes. The chuck, if used to any reasonable degree, will get chips and gunk in the scroll. For best accuracy and longevity, it's best to clean and re-lube it periodically.

Personally, the chuck on my most-used lathe, I tear down and clean about once a year, and it's always worth it.

Doc.

[Randy]

So tell me this: is tearing chucks apart and re-building them part of being a machinist?

Absolutely. I think that modifying your tools to suit your needs is part of being a machinist. And even without modification (not everything needs mods) a chuck still needs a thorough cleaning occasionally.

[Jammer Six]

That was interesting.

So tell me this: is tearing chucks apart and re-building them part of being a machinist?

[BCRider]

Ah!

So this procedure isn't going to work if I just waddle down to the basement and try it without modifying my chuck!

Now, that was important information!

There IS a few thousandths of how the scroll tightens between the scroll and the body of the chuck and how the jaws seat against the scroll. So there's a slight amount of wiggle room. For that you need to tap on the jaws or part as you tighten it. And it may or may not be enough.

If you want to try the partial or whole "Set-Tru" modification here's the full meal deal.

He starts out with the idea of easing the step on the back plate to allow .02 or so of wiggle room and tap it into true like Stefan did. Then he goes on to describe and show how to drill and tap for four set screws so you can worth that wiggle room in a much more predictable manner similar to an independent four jaw.

(51) HOW TO MAKE YOUR CHUCK SUPER PRECISE BY ADAPTING IT INTO SET-TRU - YouTube

[Jammer Six]

Ah!

So this procedure isn't going to work if I just waddle down to the basement and try it without modifying my chuck!

Now, that was important information!

[BCRider]

That's "Set-Tru" not "through". A 3 or 6 jaw scroll chuck where the body has screws that ride against a backing plate to permit zeroing the work.

The poor man's version is to make the body alignment step on the backplate about .02 to .03 smaller than the internal step size on the rear of the plain back chuck. Then loosen the chuck bolts and bump it like Stefan did or drill and tap for four set screws in from the outside so you can use those to move the slightly loosened chuck body with a little more finess. Just don't forget to re-tighten the chuck bolts.....

[Jammer Six]

Leads us directly to the next stupid question, what the hell is a "set-through chuck"?

[Doc Nickel]

I didn't watch the video, but I get the gist. I suspect somebody has either "made" a "set tru" chuck by turning down the backplate register a bit, or it's a plain-back chuck on a plain backplate with NO register.

On any of my chucks, the backplate is pretty firmly keyed to the chuck body by a step register. Loosening the bolts and tapping would do nothing at all. (My six jaw, however, IS a "set tru", and I'll commonly use it 4-jaw style at times.)

Doc.