View Full Version : older Jet lathe question

Angus in Wyoming
02-08-2009, 10:11 PM
Hello all. This is my first post here. I have been lurking for some time and have enjoyed much reading. I have one question, for now, about my lathe and probably will have more about adding a mill or mill/drill to my toy box later this year.
I have a Jet 12 x 40 lathe made in 1983. It is the old green one. I inherited it from my dad. I love the lathe, but would rather have my dad back. The question involves getting a 4 jaw chuck. My dad never had one for it. It has a threaded spindle. It is 2 3/8 by 8tpi (the book lists it as 60mm by 8tpi) I can not find a back plate for it. I found a guy who had an extra back plate for his Jet 12 x36, made in the late 70's. It threaded on just fine, but was not right. The collar on the back of the back plate bottomed out before it bumped up against the part of the spindle where it is supposed to.
Now I have looked for rough back plates with no luck either. The collar on the back has to be 2" long. That is if you set the back plate on the bench, with the face of it down, the collar has to be 2" from the back of the back plate.
Hope this makes sense. Thanks in advance, and what should I do next??? Angus

02-09-2009, 04:43 AM
Welcome to the forum!!

Can you machine an accurate spacer to take the place of the collar?

The back plate for my (late '70s, I think) Jet 1024 has a collar that's only about 1" long. The internal threads start about 3/8" from the end. Fortunately, mine came with every available accessory.

It might help if you posted a picture of the spindle and the back of your chuck.


02-09-2009, 04:56 AM
Can you undercut some of the thread of the Jet 12 x36 back plate so that it can seat up to the spindle register?

This may assist you. http://www.green-trust.org/junkyardprojects/FreeHomeWorkshopPlans/FittingALatheChuck.pdf

02-09-2009, 07:45 AM
I had a jet 10x24 of the same vintage with the same spindle. When I bought a 5c collet chuck I ordered a backplate from enco that threaded right on. A new backplate (cheap) would probably cure all.

Angus in Wyoming
02-09-2009, 01:01 PM
Sparky--Nobody makes a 2 3/8 by 8tpi any more--wish they did

I have thought about making a collar for the back plate.

Now, what would be the problem of making an adapter plate that would use the back plate off the three jaw to fit the 4 jaw? I would have to switch the back plate everytime I switch chucks. I don't think that is too big of a deal. Thanks Angus

02-09-2009, 03:58 PM
Do you have a face plate? My 1236P came with one so there may be one around somewhere. You could bolt a 4 jaw to the face plate.

Next choice turn that backing plat you found to make it fit, then make an intermediate plate if you have to.

Maybe someone on this list would like to make up a couple of back plate blanks for us old jet owners out here. Just a disk with the 2.38 X 8 thread in the center.

Group buy?


Charlie W.
02-09-2009, 08:48 PM
I had this 1981, Jet 1236 for about 10 years. The 2-3/8 x 8 is slightly large. It really does have a 60mm x 8 thread on it.

I sold the lathe about a month ago and upgraded to a 1440 gearhead. I liked the lathe very much and had a somewhat difficult time parting with it. The guy I sold it to was starting out and couldn't buy all the accessories. I have an extra chuck, milling attahment and a hardinge collet closer and some collets for it still.

The backing plate for the 3-jaw chuck was made from a barbel weight.

To get the thread fit right, I made a spindle thread gage to fit it to.

The collet closer had a 2-1/4 x 8 thread and I bored it out to fit the plug gage.


I think backing plates with a 2-1/4 x 8 thread are an excellent choice to convert to the 60mm x 8 thread. I sold all my excess backing plates last November except for 1 that I still have. I'll have to check but I think it could be bored out and used as a backing plate for a chuck.

By the way, I am a new member here and this is my first post.

02-09-2009, 09:40 PM
Welcome Charlie W. - Great first post if you asked me.


Charlie W.
02-10-2009, 12:45 AM
Thanks Dwayne. If there is interest in some sort of a group buy, I would be interested in threading them.

Angus in Wyoming
02-10-2009, 11:25 AM
I would be interested. Angus--- I don't have the gears to cut metric threads

Charlie W.
02-10-2009, 01:32 PM
There is a little confusion here. You don't need gears to cut metric threads. The 60mm is the diameter (slightly under 2-3/8") the thread pitch is 8 tpi. I made the plug gage and did all the threading on the Jet.

This is how I did it.

I started out by making the plug gace the same size as the spindle. This is used to determine when the thread fit in the backing plate is correct. I didn't have thread mics. or thread wires at the time so I improvised. I used three gage pins. I placed them in the spindle threads and used a micrometer to come up with a number. I then threaded the plug and kept taking small cuts once I got close until I got the same measurement as I did when I measured the spindle.

Once the gage is made, the backing plate is bored and threaded to fit the plug gage.

The backing plate is threaded on to the spindle and machined to fit the chuck to be mounted on it.

I still have the plug gage I made for threading the backing plates.

The barbel weight worked quite well but if I had to do it again, I would buy a blank or a 2-1/4 x 8 backing plate and open it up to the 60mm x 8 thread. Making it from the weight took waaay too much time.