4-jaw chuck dilema

[Illinoyance]

I like a part like that backed up, so with the jaws sticking up is my preference. What about using a DI on the carriage, move the carriage back to index the chuck?

Using the "outside" jaws definitely provides back up for the part. It also eliminates the dangers having the jaws sticking way out from the chuck body.

 

[TomWS]

Put a spacer in between the chuck face and the workpiece

Newbie question: do you leave the spacer in while turning? That would seem dangerous if the spacer ever came loose.

 

[markba633csi]

Not if the spacer has a large enough diameter- close to the workpiece itself
Machinists make little "crutches" like that often

 

[TomWS]

Not if the spacer has a large enough diameter- close to the workpiece itself

Ok, that makes sense as long as the spacer is trapped inside the jaws. But OP said he used a couple of parallels for spacing the workpiece. That got me wondering about this technique.

 

[markba633csi]

You could use parallels then slip them out

 

[NC Rick]

Hi all..... I will be making a backplate for a 4" chuck which will be used on a rotary table. I am having a little trouble deciding which way to hold the stock in the 4 jaw chuck. If I hold the workpiece with the jaws in the "normal" position the jaws stick out quite a bit. If I reverse the jaws the jaws do not stick out BUT because of how deep the workpiece sits into the jaws I am unable to put a dial indicator on it to center it.
So....I was wondering if I could get your opinions as to which way might be the best. I have attached photos to help show what I am talking about. Thanks for your help.View attachment 385756View attachment 385756View attachment 385757View attachment 385757

Looking at your setup again, I can’t see if you could grab the round in the uppermost step of your outside jaw? I did a similar project but used a 4 jaw with back stops. Doing it agin, I’d use a 3 jaw if it would fit. I don’t see why you couldn’t get in there with a test indicator? One thing I did was bore a through hole which was needed anyhow to provide maximum part depth in the chuck while mounted on the rotary table. assuming you can’t jump up a step of your jaws you can run the chuck in reverse and use a boring bar to cut the outside diameter. With the OD turned and a through hole bored concentrically you will have more options when spinning the part to work the opposite side.
i don’t like the extent of extension you have going on using the “normal jaw” position and I wouldn’t face that without a lot more backing support. You want the plate to have parallel surfaces when you are done.