|4" Rotary Table Worm Screw Assembly|
With Thrust Bearings and Preload Screw
A few weeks ago I posted a review of an inexpensive 4” rotary table, sold by Grizzly, Shop Fox and others. It didn't take long to realize that to hit the price point the manufacturer had to cut a corner or two. To make my table a bit more accurate (and easier to crank), I decided to modify it a bit. This mod is pretty inexpensive and easy to do, especially if you have access to a lathe. The basic idea is to add thrust bearings between the shaft and the sleeve and a preload screw. The only parts you'd need for this mod is a pair of thrust bearings, a 1/4-20 screw and a washer. For the side closest to the warm gear I used a smaller 10x18x5.5 bearing and 10x26x11 for the opposite side. Both are readily available on eBay and can be had for around $7-10 (including shipping).
|Collar Mounter on the Lathe|
I started by modifying the collar to make space for the larger bearing. This is probably much easier to do on the late, but a boring bar on the mill would do the just just fine. Since the bearing needs to protrude at least a few thousands, I ended up boring my collar to 10.5mm deep and 26mm in diameter. Once that was done, I turned a straight shoulder on worm gear (on the end facing the bearing). This removed about 3 mm of material, so I had to shorten the sleeve by about 3 more mm to keep the overall length close to the original. That's all there is to adding the thrust bearings, so you can stop here. On the other hand, adding a nut (or screw) on the end of the shaft would reduce the stress on the tiny set screws and provide good control over the bearing preload.
|The Shaft Is Made of Two Pieces|
My initial plan was to turn down the end of the shaft and cut M8 thread. The first part went fine, but as I was cutting the thread the end of the shaft started spinning with the die. Turns out the shaft wasn't one solid piece. The main body had a hole cut into the end and another piece pressed in. There was still enough of the shaft left for secure handle attachment, so I decided to cut internal 1/4 – 20 thread instead.
Once the shaft was modified, all I had to do is cut an indentation in the handle to hide the preload screw. I did this on the mill, since those two handles spinning on the lathe made me a bit nervous. After locating the center, I simply plunged a 3/4” end mill into the handle deep enough to hide the screw head.
|Modified Rotary Table Parts Ready for Reassembly|
The whole process, start to end, took no more than 30-45 minutes. My total cost was under $4, since I already had a few of the larger bearing laying around (they are used on my Seig X2 mini mill). The smaller bearing might be available at your local hobby store, actually, since it's used in a few RC helicopters. Otherwise, it's readily available on eBay. I haven't had a chance to use the table for an extended period yet, but was able to make a few cuts on a scrap piece. Properly preloaded bearings almost eliminated the backlash and provided for much smoother turning.