Adapter for Chuck

Hi,

I have a second hand lathe (no company markings, I think it was a home made tool), which I am trying to add an xact 4” jaw chuck to. I’m having trouble though as the screw on my head is 7/8” x 8 tpi. The new chuck has an adapter, to fit 3/4” x 16tpi, or I can connect directly to the chuck at 1” x 8 tpi. Problem is that I can’t find anything online that references the measurements on my lathe.

I don’t suppose anyone has any ideas that could help?

Thank you in advance

Andy

The info so far is you have a 7/8 thread on your lathe,removing the chuck adapter it fits then at 1 inch 8tpi which you do not have and no adapter will enable you to reduce 1/8 of an inch. Start from scratch did you just buy the chuck?

Peter,

Unfortunately 7/8" x 8tpi is not a standard lathe thread so there is no-one who makes a off the shelf adapter to convert from that size to either 1" x 8tpi or 3/4" x 16tpi.

The only option is to find an engineering firm or someone with a metalworking lathe to make you an adaptor. As Peter says, no insert will reduce by 1/8" so this will need to be a spindle extender type adaptor which will also move the chuck further from the headstock increasing the strain on the bearings and reducing the capacity between centres.

No new chuck I know of is available with a 7/8" x 8tpi thread so you are pretty much stuck with the spindle extender option.

Sorry if this is no help at all, but such are the problems encountered when trying to use modern accessories on old machinery, especially non standard machinery.

agowinuk said:

I don’t suppose anyone has any ideas that could help?

Thank you in advance

Andy

Click to expand...

The only way around this is as Walter has said, have an engineering company drill and tap one for you.

What I would do is buy one of these to suit the 100mm chuck

Unmachined Chuck Backplates

To suit a chuck like this that is supplied without a backplate again 100mm chuck.

Chinese Imported Lathe Chucks

I would then speak to an engineering company to get the backplate drilled and tapped to suit your lathe and turned down and drilled to accept the chuck and bingo you should have a chuck that will fit and suit your lathe.

The other way would be to look at the MT option, see if buying an MT to suit your lathe with a threaded end to suit the chuck you want to buy. They do adaptors for rotary tables which may be of use for you.

Chronos Ltd Engineering Tools

Remember if you go down the mt option then make sure you use a threaded bar to hold the mt in place.

I think Walter is right engineering firm will be your best option,to get an extension made.

Hi Andy, all the advice you need has been given and I can't add to it, but welcome to the forum

A long time ago I bought a ready made adapter had a workshop retap for 1 inch 10 thread to a small Hercus Metal Lathe three jaw chuck, used it for many years for pen mandrel holding.

Peter.

Just had an adaptor mad for my lathe, unfortunately my metal lathe is out of action at the moment.