Rotary table

I have a un-named 8" horizontal rotary table. The centre of the table has an M12 screw thread, and it also has what looks like a very big screwdriver slot running across the centre (either side of the threaded hole). I'm just trying to work out how I centre the table to my mill. Is the part I can see in the centre likely to be a screwed in plug of some kind? Is there a chance that there is a morse taper in the centre of the table. Any suggestions would be helpful.

Martin

Had a look around for images but havent seen any with what appears to be a small M12 hole. Usually a lot larger to accept MT2 or more likely MT3 with an internal M12 thread in the collets.

Certainly the slots are for tensioning end float but usually on underside.

There should be numerous T slots to use as fixings. Using MT as a means of centring isnt accurate in the slightest, its just the easy way out.
More substantial to bolt either direct to table with long screws or via an adaptor like this.

Table here is like mine with 4 T slots, makes adding a chuck on harder. Drilled through chuck and into RT and tapped, its solid and gain extra height.

Generally you centre the job to the machine. To centre table assuming it runs true (it may not) just take a reading on outside dead centre (i prefer these cheapies to any other ) and split the difference, job done. Wont work with a chuck on you take measurement from protruding round held by the jaws.

Hi Martin,

Criterion rotary tables had a removable centre that had a slot cut through the centre to make removal easier. They were screwed in. Unfortunately on removal there was no morse taper cut in the bore.

Steve.

Thanks for the replies. I think my table sounds like the Criterion that you describe. I have a cheap 4 jaw chuck (quite a flat one) that I can fit to it (just need to drill 4 holes in it and make some spacers to hold the chuck high enough to clear the threaded boss on the back). I should then be able to centre the table to the mill using a large ball bearing sat in the centre of the chuck and lined up with the MT3 vertical head in the mill (or use a wiggler ). Then I can centre the chuck to the table using a DTI.

Martin

If it is a 4 jaw independent chuck there is no need to centre it precisly on the rotary table.

Les.