Rotary Table or Spacer?

From the look of pictures in catalogs a "spacer" looks like a "rotary table" with a scroll chuck already installed.
What is the functional difference? What type of operations are best done on one rather then the other? How can you mount a chuck (3 screw from back) onto a rotary table (4 T slot covered by the chuck)?
Thanks
Mauro in Austin
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MG wrote:

Does the spacer use a worm gear, or just a set of indexing notches?
Cheers Trevor Jones
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The one I am referring use a worm gear. I have seen also collet holder with square or hex cross section. I understand those give basic 90 or 60 degree indexing.
Mauro
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    I think that it uses spacing plates with notches, so you can turn the chuck by hand until the detent snaps in again to stop it, and then you lock it down for that operation, unclamp, disengage the detent, and turn again.
    You have to replace the spacing plate to handle a different number of positions. It is nice for quick indexing, but no use for large numbers of positions, and especially uncommon ones.

    If the table is larger in diameter than the chuck, and if you     have a plain-back chuck, hers is how *I* would do it:
1)    Get a thick sheet of steel large enough to cover the table.
2)    Turn a plug to fit the center hole in the table, and attach     it to the center of the plate.
3)    Turn a registration step on the chuck side of the plate to     precisely center the chuck.
4)    Drill and countersink holes for appropriate flat-head screws to     hold the chuck to the plate.
5)    Drill holes in the outer (exposed) part of the plate to allow     screws into T-nuts in the slots in the table, so you can affix     it once you set it down centered by the plug in (2) above.
    Enjoy,         DoN.
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My lathe has a 1 1/2"-8 thread on the spindle nose, so what I did was make a copy of the spindle nose, turned it to fit the hole in the center of the table, slotted the back, made a bar to fit the T-slot in the table, drilled and tapped the bar and put an Allen through the hole I bored in the center of the threaded piece. I still have to center up the work piece, but with a 4-jaw, that's almost trivial. I seldom use a 3 jaw, so not a real problem.
Stan
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