JAY IN KY --Most small rotary tables have some sort of center hole, sometimes with a cylindrical bore but often with a Morse taper. If the part you're wanting to center has its own center hole, you might be able to make a plug that fits the rotary table center hole and the part center hole. The more common way of centering a workpiece on a rotary table requires that you measure the difference between workpiece radii that are 180 degrees apart, and then adjust the workpiece location on the rotary table to split the difference. The most common tool used to make the measurements is a dial gage or dial indicator that must be held stationary; most often the dial gage is anchored to the machine spindle while the rotary table base is clamped to the table. After you center the work on the rotary table by eye, set a dial indicator up to probe the reference surface. Adjust the indicator holder or move the table so that the dial gage plunger is pressed about half way into its range of travel before zeroing the indicator. Now turn the rotary table top and workpiece (as an assembly) a half turn before reading the dial gage. Now you want to move the workpiece relative to the rotary table surface until the dial gage reads one-half of the second value. Let's say your two dial gage readings are A. 0.000 inch, and B. 0.138 inch . . . you want to move the workpiece until the dial gage reads 0.069 inch at BOTH positions A and B. Next, you need to repeat the measure-rotate 1/2 turn-measure-split the difference process at positions C and D, which must be on a line perpendicular to that connecting A and B. Since it's about impossible to move the part on the table exactly the right amount in the right direction, it's vital that you recheck and readjust A and B after you adjust along C and D . . . and then you'll need to check and readjust C and D again, and so on and so on. While you're learning, it'll seem like you're chasing your tail, but it is a skill you'll learn. To reiterate, the important part is that when adjusting the part on the table you need to rotate the part and table together when you make your measurements, NOT the machine table. Then later, if you need to center the table under the spindle, you rotate the spindle to measure and move the machine table, which has the rotary table and part bolted to it, to make the adjustment. John
| 
