To get a really accurate, to dial  indicate in the rotary table. In the photo it looks like the tip of the indicator is hanging in space, but it is actually touching 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. 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.

6. With a soft metal bar, tap the workpiece(away from the indicator movement) until no movement is registered on the indicator in a complete revolution of the rotary table.

You dial in a rotary  table by placing a dial test indicator in a chuck or collet in the spindle, which is then rotated by hand with the indicator tip in contact with the hole of the rotary table. If your machine can be taken out of gear, it helps to do so, so the spindle swings freely. It’s obviously easier to use a drill chuck than a collet, too, so you have something that you can turn easily. Make your adjustments using the saddle and table hand wheels.

You could center the table under the spindle first, by indicating off the hole in the center of the table. Then you could mount the workpiece on the table and indicate off the workpiece. There are two problems with this approach. First, you are assuming that the hole in the table is true and centered. That may or may not be true. Second, this approach risks a sort of accumulation of errors, as you’re measuring from two different features (the rotary table’s hole and some feature on the workpiece). First center the workpiece on the rotary table, and then center the rotary table under the spindle.

5. With the dial indicator just clearing the top of the test plug, rotate the machine spindle by hand and approximately align the plug with the spindle.

9. Engage worm feed on Mill. Bring quill to material.  Pull handle out to engage power feed.  When at desired depth push hand back to disengage feed and then turn off Mill.  Remove boring  head from hole.

Be sure all set screws are tight before operation. Be sure offset boring head has a clearance to fit into hole when boring.  Remove Allen wrench before turning the mill one.  Double check mill speed before operation.

7. Recheck the work alignment, as well as the alignment of the spindle with the reference point, to make sure it has not shifted.  If any error is evident, it will necessary to repeat procedure  6 before processing.

To perform a visual position. Your eye is pretty good and judging when the two circles are centered.  Normally within 0.010″ Sometimes.

To mill the end on the workpiece to a certain radius or to machine circular slots having a definite radius, following  procedure  below should be followed.

After the workpiece is centered on the rotary table, you now turn the spindle by hand, so the indicator  tip sweeps the inside of the hole. Adjust the position of the mill table as required until no needle deflection is noted.

For the final adjusting for centering that on the same side of the backlash as will be using when cutting. So if the cutter moves from the center to the right side, then want the cutter moving in the same direction when  doing the center adjustment. If on the wrong side of the backlash, then well be overcompensate and start over now coming from the correct side.

Once you have center located (the indicator will read the same as you rotate the spindle, it’s a very good idea to set both of your dials at “0”, instead of marking some random location. Make sure you have backlash set properly, too.  Set the dial is reading in a positive direction so it’s easy to count off any changes, and you never have to remember which way you had chosen to set backlash. I also always mark the table and saddle with a wax pencil so I know where center is located. That tells you when to stop turning the handle when “0” comes around if you want to get the table back to center to load another part.

With the table mounted on a secondary table, the workpiece is accurately centered on the rotary table’s axis, which in turn is centered on the cutting tool’s axis. All three axes are thus coaxial. From this point, the secondary table can be offset in either the X or Y direction to set the cutter the desired distance from the workpiece’s center. This allows concentric machining operations on the workpiece. Placing the workpiece eccentrically a set distance from the center permits more complex curves to be cut. As with other setups on a vertical mill, the milling operation can be either drilling a series of concentric, and possibly equidistant holes, or face or end milling either circular or semicircular shapes and contours.

When using a rotary table on a Milling Machine, whether to mill an arc or drill holes in some circular pattern, there are two things that must be done to set up the workpiece. First, the workpiece must be centered on the rotary table. Second, the rotary table must be centered under the spindle. Then the mill table can be moved some appropriate distance and you can start cutting.

The offset boring is an attachment that fits the milling machine spindle and permits most drilled holes to have a better finish and greater diameter accuracy.  Offset boring  head are used to create large hole when tolerance do not allow for a drill bit or do not have a large enough drill or reamer.  A offset boring head can be used to enlarge hole, or adjust hole centerline in certain instances.

If there are only a few pieces, which would not justify the manufacture of a special plug, or if the workpiece does not have a hole through it center, the following method can be used to center the workpiece on the rotary table.

6.  Mount the workpiece on the rotary table, aligning the center of the radial cuts with the center of the table. A special arbor may be used for this.  Another method is to align the center of the radial cut with a wiggler mounted in the machine spindle.

A rotary table can be used to make arcs and circles. For example, the circular T-slot in the swivel base for a vise can be made using a rotary table. Rotary tables can also be used for indexing, where a workpiece must be rotated an exact amount between operations. You can make gears on a milling machine using a rotary table. Dividing plates make indexing with a rotary table easier.

The boring head body has a black oxide finish for rust prevention. The bar holder or insert holder (#1) has been satin chromed for wear resistance. The dial screw (#3) has been precision ground to give accurate movement of the bar holder/insert holder in the dove tail slide. The gib tension has been preset at the factory. The two gib screws (#5) should not be loosened to make size adjustments. These screws are for adjusting the gib pressure only and are filled with red wax to prevent accidental adjustment. The locking screw (#6) is the only screw used for making size changes to the boring head.

7. Adjust the machine table by the longitudinal(X) and crossfeed(Y) handles until the dial indicator registers no movement.

Figure 1.  shows an offset boring head. Note that the boring bar can be adjusted at a right angle axis. This feature makes it possible to position the boring cutter accurately to bore holes of varying diameters.

Often it is necessary to perform a rotary table operation on several identical workpieces,  each having a machined hole in the center.  To quickly align each workpiece, a special plug can be made to fit the center hole of the workpiece and the hole in the rotary table.  Once the machine spindle has been aligned with the rotary table, each succeeding piece can be aligned quickly and accurately by placing it over the plug.

Rotary tables are most commonly mounted “flat”, with the table rotating around a vertical axis, in the same plane as the cutter of a vertical milling machine. An alternate setup is to mount the rotary table on its end (or mount it “flat” on a 90° angle plate), so that it rotates about a horizontal axis. In this configuration a tailstock can also be used, thus holding the workpiece “between centers.”

To center the workpiece on the rotary table, spin the rotary table and watch for deflection of the indicator pointer. Adjust the position of the mill table(X and Y) as required, until the needle no longer deflects.

2. Lightly clamp the workpiece on the rotary table in the center.  Do not move the longitudinal(X) or crossfeed(Y) feed handles.

7. Move either the crossfeed or the longitudinal feed(whichever is more convenient) an amount equal to the radius required.

Centering the jig or workpiece over the center of the rotary table. To do this,  rotate the rotary table and adjust the work piece until I get consistent run out all the way around.

Made a 3/8″ piece of brass and put a 60 degree point on it. It Should fit in the endmill holders. This method it to be quite useful for various setup operations.

Manufacturing Processes 4-5 Copyright © by LamNgeun Virasak is licensed under a Creative Commons Attribution 4.0 International License, except where otherwise noted.

This adjustment is more convenient than adjusting the cutter in the boring bar holder or changing the boring bar. Another advantage of the offset boring head is the fact that graduated micrometer collar allows the tool to be moved accurately a specified amount usually in increments of (0.001) without the use of dial indicator or other measuring device.

Once you have located center of the table and have set dials and locked the table and saddle, you usually have some feature on your part that you desire to be centered. In some cases it may be a hole, in others it may be the outside edge of the circular part. In a case like either of these, it’s common practice to use the same indicator and swing it inside the hole or the perimeter of the part. The perimeter may require you to get around clamps, which can usually be accomplished by using the quill to move the indicator up far enough to clear them. When you dial in parts to a table that has already been located, you tap the part around, you do not make adjustments with the saddle or table handles. Tap the part after you’ve snugged up the clamps slightly, so it doesn’t move about wildly. You can achieve virtually perfect location that way, certainly as close as the machine is capable of working.