[ptxman]

<Not getting any replies on 'work fixture hold-down' forum, so at the risk of double posting, Ill try here...>

I have a Bison 5C collet chuck with an integral D1-4 backplate mount that I use on my lathe. I was thinking it would beneficial for me to also mount this on my 8” rotary table. That way I can accurately hold anything with the collets for radial/indexing operations on the mill. Better yet if I could maintain the workpiece in the chuck & move it back & forth from the RT to lathe for certain operations. I haven’t come across any commercial fixtures like this, any backplate accessories seem to be the same diameter as the chuck & not really mountable like with a flange. I considered:

- machining a dedicated ‘disc’ with holes that mate chuck’s D1-4 pins extending off the back & with integral mounting holes on an extending flange to clamp the chuck/plate assembly to the RT tee-slots (seems like somewhat of a project, at least for my skills).

- removing the pins from the back of the chuck (they appear to be held in position with allen head cap screws, kind of indexed into the pin side) which exposes what I suspect is a pretty accurate rear face of the chuck, then mounting this to the RT with some simple type bar clamps once centered. (I’m doing this now with a conventional 3-jaw chuck, but it is already a plain back style so no pins to contend with). But is removing/replacing the pins advisable in terms of maintaining chuck accuracy?

If these options aren’t advisable for any reason, am I looking at buying a plain-back 5C collet chuck just for the use on the RT? I’ve seen less expensive 5C collet holder ‘blocks’ with variations of a lever activated clamping mechanism. They cost less than a 5C chuck & could be similarly mounted, although most appear to ground square & intended for mill vice setups etc. Any help/comments appreciated.

[Smrtman5]

Ive tried to do something very similar to your idea. I had a small 6" rotary table which i tried to machine an adapter plate to fit closely over the edges of the table. A separate plate mounted to a 6" chuck and both the plates were mounted together.

long story short it became a real hassle trying to indicate the chuck to run concentric with the table and the part to be concentric in the chuck.

Admittedly i had some problems holding tolerance, so if you made a plate on a cnc it would probably work out better.

Ive found that the 4 sided and 6 sided collet blocks have been way more useful than my rotary table in quickness and ease of set up and accuracy.