My 4 jaw chuck is too big??

[SteveG]

On the weekend I had the 4 jaw chuck mounted for the first time since getting my current lathe.
Its a Rohm brand - around 14" (350mm) diameter, and as I've found out its a "heavy duty" model. The gripping face of the jaws is about 12mm wide and it can't grip anything smaller than about 30mm across.
The 3-jaw (also Rohm) is  approx 10" and closes up pretty tightly so no such problem with that.


So I'm looking at options for smaller size 4-jaw work.

Firstly, I guess I've got the option of re-grinding the 45deg face on the jaws so they close tighter, but I'm wondering if I'll regret that down the track.
Next option would be to get a small 4 jaw (perhaps a 4 or 5"?) and just chuck it in the larger one.
Lastly, I could just buy another medium size 4-jaw ( 8 or 10") which would probably cover most of my work, and be lighter and easier to handle than the current one. Would mean sorting out a D1-6 backing plate to mount it which would be a bit of extra work/cost.
Pity I didn't realise about this chuck before I sold my old Hercus lathe, or I would have kept the 6" Bernerd chuck that went with that

Anyone care to throw other thoughts into the mix?

Steve

[Pete O]

I've seen smaller chucks gripped in the big chuck, seems like a reasonable solution to me- also the small chuck can be 3-jaw, make sure you get a chuck with your dividing head
My 4-jaw chuck will only close down to about 20mm, I use a straight-shank ER32 collet chuck for small work.
Another option might be to attach some soft jaws with a smaller face.

[SteveG]

Thanks Pete.
I guess its mainly the ability to be able to dial in an already round part that I'm after, so even though I was thinking small 4-jaw a 3-jaw would work - dialing it in using the outer 4-jaw as required.

I've already got a few ER32 collets for the mill and was planning to work out some form of collet chuck to mount on the backplate or or in the internal spindle taper, but I guess a collet block that I could chuck in the 4-jaw would be handy. Would cover that small size range up to 20mm.
Would still need something to handle between 20mm and ~30mm though...

Good thought about attaching some jaws with a smaller face - I'll think more along those lines too. If I could make some up that located over the main jaws well enough that they weren't a PITA to use it could work well. Even if it only handled that missing size range between ER32 collets and the main jaws.

Steve

[Dr Stan]

Get the smaller 8 to 10 inch 4 jaw so you can also use it with the dividing head and a rotary table. That's what I've done and also have a 6 or 8 inch 3 jaw used on the lathe, dividing head & RT. Making/machining the adapter plates should not be that big of a job.