Problem- Chuck is too big!

[Russ Kaiser]

OK, I have somewhat shot myself in the foot here with my new lathe purchase and I am hoping some of you experienced guys can help me find a solution.

The new lathe has a 6 inch chuck and one of the smallest round items that I normally turn (and turn a lot of) I used to hold with the outside jaws of my old lathe's 3 inch chuck.

The minimum diameter of the first step of my new outside jaws is larger than the OD of my piece. If I mounted it between the base of the outside jaws (next to the chuck face), the part would not touch the chuck body at all (through hole too big), so truing and support would be an issue.

I can certainly hold that piece now with the inside jaws of the new chuck, but again, with the through hole of the new chuck larger than the part, there is no support and I can't use the chuck face to help true it.

Also, because of the depth of the new chuck's jaws, I need to get this part as far forward as possible to complete the turning operation.

Any ideas? The chuck jaws do not screw on, it is an inexpensive, Chinese item. I would like to avoid mounting a smaller chuck since changing chucks is a pain and there are other operations where I need to use the larger chuck.

The part in question is a wooden mouthpiece for a brass instrument. This isn't a great photo, because the operation that is problematic requires the part to be flipped so the shank can be tapered and the backbore turned. For those ops the cup will be facing the chuck. As you can imagine, the farther out it is in the jaws, the better.



Would it be possible to drill and tap the new chuck's face to mount three removable "fingers" to provide a support platform for my work between the jaws? That is one idea I have been batting around.

Thanks,

Russ

[M250cnc]

Russ

A PITA to make but the solution is soft jaws these obviously can be made to fit the profile over a wider area which makes using them safer as well.

Just google "soft jaws" and you should get some ideas

Phil

[Russ Kaiser]

Phil,

Maybe I am missing something, but I have two sets of jaws for the new 6 inch chuck and they slide into the keyed slots of the chuck body and have the scroll machined on their back sides.

This isn't a more expensive chuck that has screw on, replaceable jaws. Can I find soft jaws for what I have?

Thanks,

Russ

[M250cnc]

Russ, even cheap chucks should have soft jaws available.

Sadly the soft jaws are not cheap.

Phil

Sent from my HTC Desire using Tapatalk

[Russ Kaiser]

While I appreciate the input on soft jaws, I would like to point out that I have cut the back taper on dozens of these without them. I am really looking for an inexpensive solution using items easily acquired.

I was thinking about chucking up something in my inside jaws as near to 1 inch in diameter and circular as I can find (a socket perhaps) and boring a small section out of the tips of the inside jaws, creating a shelf to hold the rim of the mouthpiece. I should be able to order another set of factory inside jaws so I would have a stock set as well.

What do you think about that approach?

[metlshpr]

Quick fix.....Clamp the small chuck in the large chuck....done.

[Russ Kaiser]

Is placing a small chuck in a big chuck a viable option? I have considered buying another small chuck and doing just this, but is it safe?

Russ

[metlshpr]

I have done it many times. Just be shure that large chuck has a good bite of the small chuck.

[Russ Kaiser]

Anyone mounted a 4 inch chuck on a threaded spindle lathe with 2-1/4, 8 TPI? It looks like most of the bolt circles for 4 inch chucks are around 3.3 inches. I am wondering if there is enough there "there" to make it strong enough and still have clearance for nuts.

I have found several 4 inch chucks mounted on 3MT shafts. Would anyone trust a 5MT to 3MT adapter to mount a chuck?

Also, I could buy a 4 inch back plate for 1" 10 TPI or 1" 8 TPI and mount the 4 inch on a straight shaft to chuck up in the 6 inch. I am thinking that the compounded run-out would be pretty severe.

OR... I could bit the bullet and buy a new 6 inch chuck with removable jaws and then make custom jaws for my mouthpieces. I hate doing what makes sense, especially when it costs the most.

Any other ideas out there?

[JimBoyce]

Does this lathe have a collet spindle (as opposed to a collet adaptor that goes in the spindle)? If so stops (short bars) that are held in a collet and project thru the chuck can be used. This is done frequently on Hardinge lathes, that is using a collet along with a chuck.

[Russ Kaiser]

Jim,

The lathe is brand new so to be honest I am not quite sure. It is obvious that the current back plate is screwed on. I am going to put on the 4-jaw independent chuck today and I will check at that time, but it is my understanding that it is a single piece spindle with a 2-1/4 8 TPI external thread with a 5MT taper machined into the end - one solid piece of tubular steel.

I can purchase a 4 inch chuck mounted directly to a 3MT shaft and my lathe came with a 5MT to 3MT adapter so a live center could be mounted in the spindle. I just have reservations about having two Morse taper connections holding anything as important and heavy as the lathe chuck itself without some positive way to secure it. If it had been a 5C spindle, I would have been home free since I could have secured the smaller chuck with a draw bar.


Thanks,

Russ

[Fastest1]

Take a piece of tubing or round stock, bore it to the OD of the mouthpiece, leave a ledge or some form of stop so the piece sticks out the desired amount (in fact a ring left on the OD of this piece would limit how far the holder would insert into the chuck), then slit it so it acts like a collet. When you tighten the jaws it should tighten on the piece enough to machine.