Chuck in a Chuck

[skipd1]

I posted a this pic on my Instagram page and I got a comment that this is a very dangerous practice. I have see many times machinists use this method so I don't really know if it is true or if there is suppose to be a specific way to do this safely. I would appreciate any comments regarding this practice. The pic shows a 10 inch 4 jaw with a Buck 6 jaw inside. Although I wouldn't spin it this fast, the lathe is capable of 1000rpm and the 10 inch chuck is rated for a lot more.
Thanks

[Doozer]

Seems fine to me.
What exactly is dangerous about it ?
Smart really.
I see the Buck is a set-true, so maybe
just being lazy? No crime there either.
If you really want a death grip, machine
the backing plate with some ring grooves
to match the serrations of the 4 jaw jaws.
But nothing intrinsically unsafe about a
chuck in a chuck as I see it.

-D

[darryl]

Not chuck in a chuck, but I've used my Unimat chucks on the bigger lathe. Just machined up an mt3 adapter with Unimat threads on it. Looks funny though- tiny chuck almost disappears-

Chuck in chuck- you lose some length capability and you also put the point of cutting further out from the headstock. This might lose you some accuracy, and it probably will increase any wobble. A set-true could get you closer to centered, but won't affect wobble.

[BCRider]

Other than the RPM considerations if you grip it well I can't see the issue. Are they worried about the chuck flying free? Or the extension on the jaws? Could you use the outer steps instead? Or is the chuck mount sticking back and would foul the inner steps?

Not quite the same scale of things but I use this 4" four jaw in my 6" three jaw quite often. It's really handy when features can't be easily cut directly into the stock while held in the original grip.

[JRouche]

I posted a this pic on my Instagram page and I got a comment that this is a very dangerous practice. I have see many times machinists use this method so I don't really know if it is true or if there is suppose to be a specific way to do this safely. I would appreciate any comments regarding this practice. The pic shows a 10 inch 4 jaw with a Buck 6 jaw inside. Although I would spin it this fast the lathe is capable of 1000rpm and the 10 inch chuck is rated for a lot more.
Thanks

Looks good from here. Is that abrasive in between or just to keep the jaws from marring the small chuck? JR

[skipd1]

Looks good from here. Is that abrasive in between or just to keep the jaws from marring the small chuck? JR

Its brass shim stock. I thought it might help in the grip and keeps the chuck from getting marked up.

[Doozer]

Some people do not make declarations based on logic and reason.
They make declarations based on emotional feelings they get when
they look at something. If they get the feeling that something is new
and unconventional, then that means it goes against the tribal norms.
They have such a strong allegiance to the tribe that they categorically
object to anything that their tribal members might object to as well.
So if they feel something is bad, because they feel the other tribal
members will feel the same way, they put it into the category of bad
to appease the other members, and not to seem like an outcast for
breaking tradition. Just look at the tribal rules that most of the fellows
here abide by.
1) It must be cheap.
2) Functionality is secondary to cheap cost.
3) Appearance is secondary to cheap cost.
4) It can cost more, as long as it is complicated as possible.
5) They have to get permission from their wife, who has their balls in her purse.
6) It can't be too heavy to move.
7) It can't be an Industrial machine because
8) It can't be too productive because
9) This is home shop and things need to take as long as possible
10) Because this is a hobby, and they are in the shop to hide from their wives.
There are more rules, like buying only a new import machine, so when it breaks
you have someone to blame, and convenient to trash the country where it was
foreign made. Have to feel American pride by putting down someplace else.
Also folks in the tribe here are all legal eagles, they have an extreme allegiance
to the law and believe lawyers protect them from the actions of people outside
the tribe. And there is a huge evangelical safety movement among tribe members.
Everyone is a self deputized safety expert and enforcement officer. They use this
as an inroad to mind everyone else's business but their own, under the vail of
friendly and neighborly keeping the tribe safe. Heaven forbid the kids should see
something unsafe and traumatize them. They might catch fear of the world and
never move out of their parent's basement. Can't have that. They need to grow
up safe and drama free so they can get a service sector job, pushing paper
and being the boss, who is a youtube expert on everything.
So take that chuck out of the chuck. You are messing up the generations to come.

-D

[skipd1]

I kept the 6 jaw mounted on the inside of the 4 jaw to keep it inboard as much as possible to minimize stick out length.

[Tim The Grim]

The “danger” in the initial picture is the potential of the excessive jaw presentation grabbing something like a sleeve or arm and wrapping it up in the works.
We were not allowed at most shops to have more than 1/2” of jaw extend out from the OD of the chuck. In this instance it’s not that far but extends so much more forward that it creates a significant hazard.

[old mart]

Its safe enough if you don't take huge cuts or run too fast. Having to use the smaller chuck would normally be due to the work being too small to clamp in the larger chucks jaws.

[Tim The Grim]

Back when the oil refinery was privately owned and our brilliant management team put on Nomex and joined us for brainstorming sessions in the process units, People like me were allowed to petition to purchase scrap. I got a bunch of B7 and B16 threaded sections that spent a few years holding 900 degree F flanges together and some bull plugs that procedure required be replaced with new.
I took one of those hex drive bull plugs, single point threaded it to match the Craftsman Lathe spindle, reamed a through hole and made this Chuck in a Chuck mount for doing smaller work in the 13 inch lathe. The big laws only extend 7/16” so I feel “safe”.

[Doozer]

We were not allowed at most shops to have more than 1/2” of jaw extend out from the OD of the chuck. In this instance it’s not that far but extends so much more forward that it creates a significant hazard.

The big laws only extend 7/16” so I feel “safe”.

All about feelings. As I said. Brilliant.
Sounds like you were working for a bunch of fools.

-D

[Rich Carlstedt]

Doozer.......post 7 .......😃😃😃😃😃😃

Rich

[davidwdyer]

Now I'm inspired. I've been thinking about doing that very thing!

For me it would be a way to use a four jaw without taking off the big have three jaw.

[SVS]

I’m enormously humored by Doozer’s post and pretty well agree with it.

BUT, for myself, the chuck in a chuck just seems like a half-ass way to do things.

Brass strips to protect the little chuck ALSO increase the chance of throwing it out. I tend to pucker up around heavy things rotating fast, so I wouldn’t do it, but I couldn’t care less what anyone else does. I’m only commenting because comments were asked for.