How would you do it chuck back plate.

[DPittman]

Hey guys,
I want to turn a back plate for a new 6.25" four jaw chuck for use on my 10x22 lathe.
The only way I have of holding such a big piece is my 8" faceplate. I'm thinking I will mount the blank in the faceplate and turn the backside to the required lathe spindle dimension. I will also make the necessary oddball bolt mounting studs on that side at the same time. I then will be able to take the blank off and mount directory to lathe spindle to finish the other side to accept the new chuck. Does this make sense? Any suggestions?

I attached a picture of existing 5" chuck back plate and the new bare 6.25" chuck.

Don

 

[JohnW]

That is what I would do. By doing the second bit of machining while it is mounted on the spindle you guarantee that it will be concentric with the spindle. It is much better to mount it directly on the spindle than to mount it in another chuck, since there will errors in mounting it in any chuck.

The big thing to watch for is that your spindle probably has some surfaces on it that are used to position the chuck accurately and repeatably on the spindle. Make sure the corresponding surface or taper or whatever it is on your new chuck adapter is a really good fit on that part of the spindle. The combination of the back surface of the mounting plate and the taper that probably fits into the hole in your original chuck is what positions your chuck.

Having said that, you are making a mount for an independent 4-jaw chuck, so concentricity is not really that important since you will be adjusting any work piece in the chuck to be concentric with the spindle axis whenever you use it anyway. What remains important is that the chuck cannot shift during use, and it must be straight in relation to the spindle axis. Machining it on the spindle is the best way to do that.

You may wish to mark both the spindle and the new chuck adapter so that you always mount them in the same orientation that the adapter was machined in for the best concentricity. If there is any error on the spindle face, it would then be compensated for by the adapter.

Finally, watch the speed when machining the outside diameter of the adapter. It will not take much RPM for the surface speed to get pretty high. At 60 RPM on a 6" piece you will be near 100 feet per minute, which is getting near the limit for an HSS bit on soft steel. If your lathe's slowest speed is 100 RPM, you will need to use carbide to survive the 150-ish feet per minute surface speed you will have, or deal with any harder metal.

Light cuts will be a necessity since a 10x22 lathe will not have a lot of extra torque for cutting a 6" diameter piece.

 

[PeterT]

Maybe some similar operations to how I made my chuck adapter plate?
https://canadianhobbymetalworkers.com/threads/chuck-adapter-plate-for-rotary-table.427/#post-4211

The thing to pay attention to IMO is how you mount the rough slug to the faceplate to get that first machined surface. I've seen clamps that mount to faceplate but grip the stock edge. Useful but another tool departure. You could make a (threaded) hole pattern in the plate stock beforehand & secure it to faceplate with bolts from behind. That should be sufficiently rigid to face it. You likely would need standoffs like I used to make the donut hole & allow boring bar to extend through slightly. Maybe, depending on your faceplate slot pattern (6 vs 4 vs 8) & your backplate bolt pattern (3 or 4) theses mounting holes could serve double duty & be one of the same?

Just be careful doing edge turning on the faceplate like that though. It would almost be better if you could just face one side, that becomes the side facing headstock, complete the assembly to mount to spindle & then finish the 2nd face & OD in one shot so its all square & concentric. Your backplate mounting system looks different than mine though (mine is D1-4) which I've learned its a bit fiddly getting the nose taper 'just so'. What is yours? Does the center hole have to mate to a nose or is it just clearance?

 

[DPittman]

Thanks John and Peter. Always insightful and helpful information from you guys, and I appreciate it.

Peter, I attached a picture of my spindle mount to help answer your question of whether there is a nose. I would call it a nose but it is straight sided and not tapered. It's an oddball mount as far as I can tell.

Don

 

[Earl Wong]

Thanks John and Peter. Always insightful and helpful information from you guys, and I appreciate it.

Peter, I attached a picture of my spindle mount to help answer your question of whether there is a nose. I would call it a nose but it is straight sided and not tapered. It's an oddball mount as far as I can tell.

Don

Don, that's the same spindle mount on my Craftex CX706 10x22 lathe. I made a chuck back plate for my 5c collet chuck, the centre hole is just clearance, your chuck plate will register on the outer surface of the clearance hole, I believe it's 1.965 in diameter, not sure what your lathe is, but I think it's a Craftex as well. Not to get off topic, but If you need ideas on how to improve the lathe's rigidity as well, I'd be happy to share them with you. I think they are a good lathe as a base kit and then you can improve on them easily.

 

[DPittman]

Don, that's the same spindle mount on my Craftex CX706 10x22 lathe. I made a chuck back plate for my 5c collet chuck, the centre hole is just clearance, your chuck plate will register on the outer surface of the clearance hole, I believe it's 1.965 in diameter, not sure what your lathe is, but I think it's a Craftex as well. Not to get off topic, but If you need ideas on how to improve the lathe's rigidity as well, I'd be happy to share them with you. I think they are a good lathe as a base kit and then you can improve on them easily.

Hi Earl,

Yes my lathe is also a Craftex but the 10x22 version. The outer dimension of my spindle nose is 52mm.
I would love to hear of improvements I could make to my lathe!

Thanks!
Don

 

[Janger]

Harold Hall the author posted an article on making a rotary table which also required turning a large piece similar to your large back plate. You can find the article on projects in metal web site google: "harold hall simple rotary table" - you'll have to sign up to see the article but it's painless. He drilled and tapped some, two?, holes in the back of the stock and mounted a piece of fibre board between stock and faceplate. He could then turn the entire edge in on go and face the the front of the stock. the front then become the back later...