I know how to centre the rotary table on the spindle using a dti and/or wiggler/edgefinder on the central hole. But what is the best way to accurately align a work piece on the table. I need to locate
a) a circular piece to be drilled out at 120degree intervals at a radius
b) a rectangular piece to be similarly drilled as well as bored out...
Having centralised the rotary table on the spindle I don't really want to move the underlying mill table else I'll lose that registration....
I'm sure the answer is a DTI set up on the underlying mill table but I cant quite see how...
It's a while since I've done this but as far as I remember, for the circular piece the process is the same as centering in a four jaw chuck - treating the rotating table as a chuck. I suppose it depends on your clamping mechanism as to how easy this is. A hinged DTI holder so you can lift the DTI out of the way and then drop it back in precisely the same position helps.
Another method is to turn a plug to go into the central hole of the table which then locates in in a hole bored in the workpiece but it's not always possible to do this and you need to get a good fit for accuracy.
If you can mark the centre of rotation on the workpiece with at least a good centre punch, you could use a dead centre between the point in the punch hole and and another centre or similar in the mill chuck and put the DTI on that.
Another way, would be to make the same spindle register (fitted to and centred on your rotary table) as is used on your lathe.
This way, you turn something on the lathe, remove the chuck with workpiece still chucked and move the chuck to the rotary table for the second op.
If necessary you can still take it back to the lathe for further turning.
This is easier with spindles that permit easy chuck removal ie short taper noses, rather than the usual threaded spindle nose.
I know that this doesn't solve your immediate problem, but perhaps for the next time?
Exactly so... so once I got the rotary table centred under the spindle i'd lock the gibs on the main table. Then I clamp the workpiece to the rotary table roughly centred, turn the table so that the dti was set up against one edge of the workpiece, then rotate table 180 and indicate offset on opposite side, then tap workpiece with mallet to correct. Repeat til centred... the repeat for other 2 sides....
wheres the catch...there has to be one!
Instead of using the rotary table why not just pitch the holes using good old fashioned Trigonometry
of course I could Peter, and indeed on the first one I did... but now I've got the rotary table I can bore the central hole and the surrounding holes completely concentric and I only need to move the table once - to offset the spindle, after boring the central hole, by 1/2 the PCD of the surrounding holes. Thats got to be more accurate.
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