Rotary Table Work Holding - Threaded Insert

by Tim Krause

I've found setting up the rotary table on the Legacy Ornamental Mills to be time consuming and work holding for small pieces to be problematic. I've lost one too many pieces due to the grip of carpet tape failing. Part of the problem is the small parts that I make, there is not enough surface for the tape to hold onto the piece. One catch of the router bit, and the piece flies across the room. Finding the absolute center of the rotary table takes too long in my opinion, and is error prone.

My solution is simple in theory. Add a threaded insert to the middle of the table. In practice, it's much more complicated. The insert is best located in the dead center of the rotary table. This is a little tricky to find. I could have just drilled a hole in the center of the mdf waste table and installed a brass threaded insert. Instead, I decided to make a multi-purpose threaded insert that does triple duty. The insert holds small work, large work, and allows easy setup.

It started by modifying the center Delrin plastic portion of the rotary table. Not knowing if the concept would be practical, I decided to start by making a new center piece instead of modifying the original center. I machined a new rotary center from UHMW plastic and added a 1/2 - 13 NC thread to the center. A 1/2" diameter by 1/8" deep bore was added to the side that is next to the rotary table large gear. The part is similar to this drawing.

I made the threaded insert using a piece of 1/2-13 NC by 2-3/4" long brass all-thread. I drilled and tapped one end for a 1/4-20 NC internal threads. The other end was clearance drilled all the way through. This should prevent sawdust from fouling the threads. An oversized 1/2" (+.001) hole was drilled into the mdf waste board to allow the insert to pass through. The threaded insert goes through the center.

This pictures shows the bottom of the rotary table. A 1/2" nut is used to prevent the insert from pulling through the center and stops the insert from turning while installing the 1/4" bolt.

Now a 1/4" bolt or screw and washer can be used to hold the work.

With the insert raised, you can use a 1/2" nut and washer to hold larger work.

Here's the added bonus, a quick setup trick. The insert can be lowered and a 1/2" dia steel rod can be inserted into the router.

The router can then be plunged into the mdf, through the rotary table gear center and into the bore in the center plastic piece (not shown for clarity). The rotary table is now centered to the router. The table and either the x or y axis can now be locked down and the table is ready for use.

Any question of comments, feel free to contact me