Mounting a 3" 3 jaw chuck in a 6" 3 jaw chuck to hold work by a small ID

[pcortes]

Hi,

I'm a hobbyist. I just sold my 8x12 lathe because I purchased a 13x40 lathe which is a lot nicer. Yesterday I needed to hold a flange shaped like an isosceles triangle by the ID of the hole to cut a groove in the face and realized that the hole was too small to fit over the jaws of my chuck. I then kicked myself for selling the smaller lathe.

I've seen people hold a small 3 jaw chuck on an arbor in a larger chuck. Is this done by making a custom arbor and back plate? Can a chuck that mounts on a 5C arbor be held in a 3 jaw? Could I just use the external jaws to grab a bare 4 jaw chuck by the OD? Anyway, I'd like to know the methods the pros use. In the meantime, I'll make an arbor to mount the flange to this project, but I'd like to come up with a solution for the future.

Thanks for your time.

Thank you everyone for your answers!

Three people responded that a 3-jaw / 4-jaw setup would be easier to dial in. I think I'll get a small 4-jaw chuck since I have the 3-jaw on the machine most of the time. I'll make an arbor and check into Sherline chucks.

One person suggested soft jaws, which I've never used before, but it seems like it would be a great solution, so I'll look into it.

One person recommended expanding arbors. I actually have some, but the hole is too large for my largest size. I'll see about getting a larger set.

 

[dalmatiangirl61]

A 3 jaw in a 3 jaw is going to be a pia because of the combined runout. A 3 jaw in a 4 jaw is easier to dial in.

 

[richard newman]

If your 6" chuck has 2 pc jaws, you can use soft jaws and hold that part very accurately.

 

[howieranger]

I hold a 4" 3jaw in a 8" 4jaw when I need to hold under 3/16". Very easy to dial in and safe if you use some common sense.

 

[Terry Keeley]

5C emergency collet?

 

[implmex]

Hi pcortes:
I do this quite often, but I made a stub arbor to hold a Sherline 3 jaw or 4 jaw chuck in a bigger 3 or 4 jaw chuck on my Monarch 10EE.
The stub arbor is easy to make, and as dalmatiangirl points out, the 4 jaw for one of the chucks (it doesn't matter which one) is a better choice because it lets you dial in the part.

I've done it both ways, but I prefer the small chuck to be the 4 jaw for most things.

Sherlines are good because of three things:
1) They're good quality (at least mine are but they're decades old)
2) They're cheap (by chuck standards)
3) They'll let you grip really tiny things.

Cheers

Marcus
Implant Mechanix • Design & Innovation > HOME
Vancouver Wire EDM -- Wire EDM Machining

 

[L Vanice]

You can get cheap expanding arbors in sets or individual sizes. Mount one in a chuck or collet and turn a step on the end to fit your work. As long as you leave the arbor in the chuck, the arbor step will have no runout, so the chuck can be any that suits you. The arbors can be turned smaller for future jobs.

Ampg Z9125 $65.63 Expanding Arbor 8Pc Set, 1/4" to 1-1/4" | Zoro.com

Larry

 

[pcortes]

It does have 2-piece jaws. Thanks for the suggestion!

 

[mike44]

Cut PVC pipe that will fit over the step on the jaws. Then mill a flat on each jaw. Place the pipe on the jaws with the flat turned so all 3 come together. These are soft jaws and will hold small parts.
I think I used 3/4" PVC about 1/2" long . You only have to mill a flat 1/16" deep .
Any pipe the correct ID will work. I used PVC pipe because I had it.

 

[fciron]

Is thereA reason you can’t just turn up a little stepped arbor to hold the work by the ID?

Make a washer a bit larger that the ID to clamp other work on the arbor.

 

[Ben]

I made and arbor with the threads of my chuck and just mount it in my larger 4 jaw on my big lathe. I have a 3" and 6" 4 jaw chuck I interchange. I never liked the idea of trying to clamp the backplate in the jaws of the larger chuck. My arbor is whatever piece of round stock I found. It doesn't need to be hardened or an exotic steel, CRS works fine for the last 20 years.
Ben

 

[AlfaGTA]

Have made ID collets for a job like this....
Turn a stub close to the ID.
Tap drill the stub for the appropriate sized NPT ID thread....
Remove stub form the lathe and cut slits along the long axis from the end ...6 or 8 pie shaped on the band saw.
Return the stub to the lathe ,thread for pipe .
Finish OD for a slip fit to your part.
Fit part and install pipe plug with anti seize...
Tightening the pipe plug will expand the stub and grip your part.....
Takes less time to make than it takes me to type this...works fine and can be quite accurate...

Cheers Ross

 

[EPAIII]

Instead of holding the small, three jaw chuck in a larger one, why not just remove the larger chuck and mount the smaller three jaw directly to the spindle? Am I missing something here.

I have made a mount for my SB-9 which allows any of my smaller, Unimat chucks to be mounted on it. I just remove the six inch chuck and screw on the mount. Then screw on the Unimat chuck. Works like a charm.

 

[implmex]

Hi EPAIII:
Short form...I do it because I'm lazy.
Humping a bigger chuck off and on from a lathe spindle can be a bit of a challenge for an old fart like me, so I avoid it when I can.

That's it...not very edifying, is it?

Cheers

Marcus
Implant Mechanix • Design & Innovation > HOME
Vancouver Wire EDM -- Wire EDM Machining

 

[doug925]

Hi,


I've seen people hold a small 3 jaw chuck on an arbor in a larger chuck. Is this done by making a custom arbor and back plate? Can a chuck that mounts on a 5C arbor be held in a 3 jaw? Could I just use the external jaws to grab a bare 4 jaw chuck by the OD? Anyway, I'd like to know the methods the pros use. In the meantime, I'll make an arbor to mount the flange to this project, but I'd like to come up with a solution for the future.

Yes to both questions. I use 3" & 4" 5C mounted chucks, held in 8 & 10" 3 jaw chucks all the time. (using the OD, NOT the 5C shank)
I have a 6" Kitagawa holding an 8" 4 jaw, in my Okuma as I type this.

If you need real concentricity, the OD of a chuck isn't always super concentric. Especially on the Chinese ,5C chucks. This is where a 4 jaw will help out.
If the OD of the smaller chuck IS concentric withing your parameters, then using/boring a set of soft jaws will help keep concentricity.

Doug.

 

[dalmatiangirl61]

Instead of holding the small, three jaw chuck in a larger one, why not just remove the larger chuck and mount the smaller three jaw directly to the spindle? Am I missing something here.

I have made a mount for my SB-9 which allows any of my smaller, Unimat chucks to be mounted on it. I just remove the six inch chuck and screw on the mount. Then screw on the Unimat chuck. Works like a charm.

Because a 3" chuck won't fit a A1-5 or L0 spindle, and the time to make custom adapters is greater than just picking up the 3" chuck and sticking it in the larger chuck.

 

[dian]

Cut PVC pipe that will fit over the step on the jaws. Then mill a flat on each jaw. Place the pipe on the jaws with the flat turned so all 3 come together. These are soft jaws and will hold small parts.
I think I used 3/4" PVC about 1/2" long . You only have to mill a flat 1/16" deep .
Any pipe the correct ID will work. I used PVC pipe because I had it.

i didnt get how that works. can you explain, please?

 

[EPAIII]

Well, they are a bit pricey and start at a 5" size, but I see no reason why a 3" chuck can not be attached to one.

https://www.mscdirect.com/browse/tn/?searchterm=backplate A1-5&hdrsrh=true&rd=k

If you object to the larger size, you can probably turn off some of the 5" diameter the first time you use it. Perhaps get it down to 4" or less.

The OP says he is a hobbyist so I would assume that he does have time, probably more time than money. And he doesn't state what kind of spindle he has so perhaps it is a threaded one. Some of the other ideas being discussed here also will take time. Soft jaws need to be mounted and turned to size. I am not familiar with the Sherline chucks and weather they use back plates or not. I have two 3" Unimat chucks: one with a back plate and the other with a built in mount. The one with a back plate uses one of reduced size. The one without a separate back plate has a similar, reduced size at the rear so holding either one in a larger chuck may be a bit of a gamble. I did take the time to make an adopter for my SB-9 so I can use either of them on it.

On the other hand, if his existing three jaw is an 8" or a 10", then the weight may be a very good argument against removing it. And if he gets a four jaw for his 3" chuck, then anything he uses if for will be dialed in so the errors of a scroll chuck will not matter. But, depending on just how the chuck he buys is configured, he still may need to make some kind of back plate or adapter. He should look into that before buying it.

Because a 3" chuck won't fit a A1-5 or L0 spindle, and the time to make custom adapters is greater than just picking up the 3" chuck and sticking it in the larger chuck.

 

[dalmatiangirl61]

Well, they are a bit pricey and start at a 5" size, but I see no reason why a 3" chuck can not be attached to one.

https://www.mscdirect.com/browse/tn/?searchterm=backplate A1-5&hdrsrh=true&rd=k

None of those backing plates would work with a 3" chuck, at least not without enough modification to make purchasing one mote. With A series spindles direct mount chucks are the only way to go, with backing plates the backing plate has to be mounted first, then mount chuck to backing plate, this is not how other spindles styles work where backing plate stays with the chuck.

Pictured below is an L0 adapter and a 5" chuck, that whole bottom piece is the adapter, LOL, and no thru hole

I can pick up 3" chuck with one hand, the larger chuck IS the adapter!

 

[jims]

Holding on the inside of a part.

Hi,

I'm a hobbyist. I just sold my 8x12 lathe because I purchased a 13x40 lathe which is a lot nicer. Yesterday I needed to hold a flange shaped like an isosceles triangle by the ID of the hole to cut a groove in the face and realized that the hole was too small to fit over the jaws of my chuck. I then kicked myself for selling the smaller lathe.

I've seen people hold a small 3 jaw chuck on an arbor in a larger chuck. Is this done by making a custom arbor and back plate? Can a chuck that mounts on a 5C arbor be held in a 3 jaw? Could I just use the external jaws to grab a bare 4 jaw chuck by the OD? Anyway, I'd like to know the methods the pros use. In the meantime, I'll make an arbor to mount the flange to this project, but I'd like to come up with a solution for the future.

Thanks for your
Thank you everyone for your answers!

Three people responded that a 3-jaw / 4-jaw setup would be easier to dial in. I think I'll get a small 4-jaw chuck since I have the 3-jaw on the machine most of the time. I'll make an arbor and check into Sherline chucks.

One person suggested soft jaws, which I've never used before, but it seems like it would be a great solution, so I'll look into it.

One person recommended expanding arbors. I actually have some, but the hole is too large for my largest size. I'll see about getting a larger set.

Easy to do with an 5c Id collet. I have made my own for over 50 years. Hardinge makes them but they are pricey. Other brands like Rovi work good and can go up to 6 inch dia
Bores. You turn them in place on lathe and can load and unload parts in seconds with a lever collet set up. About 70 to 80 percent of parts made have holes or bores that can be used to hold the part. Plus they hold parts dead length.Rovi collets can be seen on you tube.
Next I would go with soft jaws .
Jim
Jimsehr