Mounting a Chuck on a Rotary Table ???

[Bob La Londe]

I am currently making an adaptor plate to mount a 3" 3 jaw chuck on a 4" rotary table. It seems straight forward if it works.

1. I am CNC milling the back of the plate to be close to an exact fit to the surface of the table. That job is running right now. Because of backlash in the Taig I machined exact size to the t-slot grooves. After its done I will measure and remove additional material as needed. This should put the rough form very close to center on the table.

Here is the rest of the plan.

2. After the form fits I'll go back and center spot to drill holes to mount the adaptor to the table.

3. I'll drill mounting bolt holes for the adaptor, and mount it on the table. If there is any slop, I'll try to rough adjust it to the center of the slop when I tighten the bolts into the t-nuts.

4. Then I will mount the table on one of the manual mills. Its slightly too big for either of the CNC mini mills without a base adaptor mount. (That is the next project) Then I will rotate the table while cutting to create a register for mounting the chuck. This should give me exact size and center. (pretty close anyway). I will also cut an outside surface reference on the plate. It should be concentric with the register, and centered the same. This will make later steps easier.

5. Dismount plate from table.

6. Coat back of chuck with grease and slide onto register.

7. Drill chuck mounting bolt holes in the gaps in the grease.

8. De-Grease and mount chuck.

9. Mount plate back on table.

10. Indicate reference surface on adapter and final tighten plate mounting bolts.

(All bolt holes are to be counter sunk for the bolt heads. I am sure there must be a flaw in my plan, but it will have to do for now.)

HERE IS THE QUESTION.

How would I approach the problem if I wanted to mount a 4" chuck on the 4" table? With the 3" there is just enough room to tighten socket head bolts to mount the plate to the table, but no clue how I would approach it except maybe with 2 adaptor plates or with a spool shaped adaptor plate. I can already see projects where I would like to have a 4" chuck on this table or a similar one. There is no central taper in the table. If there was I would have just bought a chuck with a taper on it already for the current job.

(I am also working on a stepper mount design for this rotary table, but that can come later. Right now I just need it to index a 3D part that needs to be cut on 4 sides to remove all voids.)

[Bob La Londe]

Well as it turns out... the slots in the table are not machined accurately. Not only are they slightly off center, but it looks like they were machines in four seperate passes instead of two, and one is not even straight from its mate on the other side of the table. Teach me not to buy a $49 rotary table. LOL.

Tha'ts good and bad I guess. I had to do some hand work on the slot keys on the adapter plate with a file. Now its a very snug fit. No play in any direction. I can drill, countersink, and bolt/t-nut it in place. I should be able to remove it a dozen times or more without losing position. I did mark 0 on the adapter relative to the zero on the table so I can put it back the same every time... I'll need to do it again when I finish it, but for now its marked.

[Bob La Londe]

Well, I rough finished the adaptor on the lathe and bolted it to the table. Now to do the machine to fit part for the chuck.

[Bob La Londe]

This is a lot of work. Next time I think I'll just buy one. It is pretty satisfying to have made this assembly myself, but I can buy a chuck and adaptor plate for $100. Certainly not worth the time I spent.

I'm still not sure how I would mount a 4" chuck on a 4" table.

Also, for anybody looking at doing this themeselves. A 4 jaw chuck with 4 bolt holes for mounting would have been a lot easier than the 3 jaw chuck with 3 bolt holes for mounting. The chuck mount holes just missed the alignment keys on the back of the plate, but the countersink for the bolt heads overlapped onto them. A 4 bolt mount could have just been rotated 45 degrees and all the bolt holes would have been equal distances between the alignement keys.

I haven't put a dial indicator on it (and given how cheap the rotary table is its going to be sloppy mattter how I did), but its visibley better than the lathe the chuck came off of. Of course that doesn't take much. LOL.

It was originally part of my long term plan to put a stepper on this unit and set it up so I could throw it on whichever machine I needed it on, but there is way to much backlash in the screw for that. I'll just use it as a manual indexer, and set up a direct drive with pulleys when I am ready to setup a CNC 4th axis.