To get a really accurate placement, the next thing to do is indicate in the rotary table. Here you can see my rather old Starett Last Word indicator. I put it in a collett and preload it a bit. In the photo it looks like the tip of the indicator is hanging in space, but it is actually touchng the back of the hole in the rotary table. I then run the table through 360 degrees of rotation watching for the maximum deflection on the indicator. If there's more than a thou or so of deflection, then there's probably some debris on the insidie of the hole which needs to be removed. I'll then rotate the spindle 90 degrees to the left and 90 degrees to the right. The true center will be half way between the two readings.

I like to make sure that when I do the final adjusting for centering that I'm on the same side of the backlash as I'll be using when I'm cutting. So if the cutter moves from the center to the right side, then I want the cutter moving in the same direction when I'm doing the center adjustment. If I'm on the wrong side of the backlash, then I'll over compensate and start over now coming from the correct side. Bigger...

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