Rotary Table Setup - two at same time

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BobsModels

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Just wanted to thank all those who shared setting up a rotary table in the thread that got resurrected in late January - https://www.homemodelenginemachinist.com/threads/rotary-table-alignment.31500/

It came at an opportune time as I had a part that needed an accurately setup rotary table. You can see the part in the first photo. One of them has some long screws in it just to show the angles needed for the holes. My goal was to do all the machining on the end of a .750 diameter stock. After the part was machined I took the .750 piece to the lathe and parted off the piece.

The part is .586 long x .146 wide x .190 thick and is centered on the end of the .750 stock. There are 3 different radius edges and one straight edge. One edge has a .073R with a 180 degree arc, the next has a .024R with a 215 degree 12.5 minute arc. and the last has a 1.387R with a 166 degree 54 minute arc. There is a .078 hole positioned .230 off the center of the stock. A 2-56 hole needs to be tapped at a 30 degree angle to the flat surface into the center .078 hole ( ie a set screw). Another hole, 0-80 needs to be tapped at 90 degrees (second set screw) to the first one into the center of the .078 hole. It is sort of at a 60 degree angle (if you lay out a tangent on the curved surface) to the 1.387R surface. Again the tapped holes are best visualized by looking at the photo with the long screws sticking out to show the angles.

The problem is multiple radius centers, steep angle holes, and having the tapped holes all concentric to the .078 hole. I thought it best to do all in one setup on the mill. I am sure there are other ways but here is my approach and why the thread on the rotary table setup really helped.

The multiple radius issue I have dealt with before. I have a rotary table with a mini x –y table mounted on it. In the simplest use I center the rotary table, mount the x – y table so it is parallel to the X – Y of the mill table. I then mount my part on the x-y mini table and move the parts’ first center under the spindle center using the mini x-y, then using the Mill X or Y I offset the spindle and make the cut through whatever arc is needed. Keep moving the mini x-y around to the next center and repeat. If I did not have the mini x-y I would have moved the part around on the rotary table and would have achieved the same result. However, with a little thought and the mini x-y table much can be accomplished in forming a part with multiple centers and connecting surfaces.

Given the above the multiple radius and the offset hole were simple. The issue became how to tap those holes at the angles needed and hit the center of that .078 hole. If you can visualize the part needed to be held at a 90 degree angle and then rotated. I thought of all kinds of ways to flip the rotary table to the horizontal position, refind centers and tap the holes. I needed to make 4 of these parts. Flipping the table up and down each time did not seem reasonable and I was not sure I could reposition everything. I thought about using a square collet holder thus being able to reposition with a reference surface.

Finally, after a bit, I concluded I could do the least amount of steps and introduce the least amount of error by putting my adjustable angle plate and a second rotary table on the mini x-y table. Now this was going to really require everything be set up concentric under the spindle and aligned with the Mill X-Y and the mini x-y.

The procedure used was the method from the thread showing an indicator mounted on the rotary table surface running around the mill spindle as opposed to my Blake centering the hole in the rotary table (I did both as an experiment and using the centering hole did give a different reading off by .004 in the X axis and .006 in the Y axis). Clearly my tables’ centers are not true, which I knew for the little one and was surprised how much off the larger on was.

Here is how I set it up:
  1. Main Rotary table centered, mills X and Y set to 0 – 0.
  2. Mini x-y table mounted on rotary table and indicated parallel to the Mills X Axis.
  3. The angle plate with the second rotary table mounted square on the mini x-y table so when flipped up the second rotary table was parallel to the Y axis.
  4. The second rotary table was then indicated under the spindle by the above method. The mini x-y dials set to 0 – 0 after positioning to center.
At this point with the indicator on the second rotary tables’ surface I could rotate the main rotary table through 360 degrees with no needle movement and the small rotary table through 360 degrees no needle movement (it was .0001 indicator and it jiggled a little but no movement).

Not going to go into all the machining sequence but the setup was clearly on the mark, as those tapped holes dropped right dead center on the .078 holes’ center axis as you can see in the photo. Yes light cuts were necessary but not that bad. I took .050 off at a pass to get the outline done in four passes on each side.

You can see the part in the photo and the set screws that will be used.

Thanks again for the help

Bob

Cam-Part-1.jpg
Cam Part

Cam-mill-setup-1.jpg
Cam Milling Setup 1

Cam-mill-setup-2.jpg
Cam Milling Setup 2

Cam-2-56-Thread.jpg

Tapping the 2-56 Hole
 

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