Tweaking a Rotary table... suggestions?

[Cedge]

I managed to score a small chinese made 4 inch rotary table from the old fellow I recently bought tools from. Like most chinese iron, it needed a bit of tweaking before it was ready to go to work. There seemed to be quite a bit of lash in the system, so after cleaning the red grease off the little fellow, I proceeded to attempt making adjustments.

The thing needed a bit of attention. The key way had some slop in it, but a few stout taps of the hammer on the square key had it fitting nice and snug. Then I had to loosen the two retainer nuts behind the dial and tease them into a position where the end play in the shaft disappeared. So far so good.

The shaft assembly is housed in an eccentric which allows the worm gear to be adjusted to the pinion gear. this assembly is locked by two setscrews. If the eccentric is moved too far, the work will disengage from the pinion. Moving it the other way engages the two gears. I've got them meshed as well as itappears they can be mated, but I'm still seeing a bit of travel in the dial before the table moves.

I have a pretty sure feeling that the remaining lash is due to loose tolerances between the gears. I have not torn the table all the way down, yet but I'm wondering if anyone has any suggestions on how I can chase that last bit of slop out of the gears.

The factory "zero" mark is one of those riveted tags and it appears that the operator missed his mark by about 3.5 degrees, but That one is easy to solve. I'll make up a new zero mark and correct that with no problems. I know... its not a high dollar tool, but its mine.... for $25.00 ...LOL

I'm excited about the new toy and want to get it working at its best potential. It might not replace the fun of using my homemade indexer, but it will surely add a new level off accuracy, with or without a bit of annoying lash.

Steve

 

[wareagle]

Steve, I pulled an RT apart about a year or so ago, and there wasn't anyway that I saw that one could effectively take the backlash out. Fortunately that wasn't the problem of the one I speak of. It was taken apart due to waste oil being put into it, so we took it apart and cleaned it up. :

The RT that I have has a slight amount of backlash, but I have been able to live with it to this point. You will certainly enjoy yours!

 

[malcolmt]

Hi Steve
I think the person who may be able to answer any question regarding rotary tables would be John Stevenson i would recommend a pm to him, mind you seeing how prolific he is and generous with his help he may well get on to you with answers before you get a chance.

Kind regards

Malcolm

 

[John S]

Some point son these tables that can give problems.
You have found out about the adjusting screws in the worm shaft, these are very hard to get right especially if the nuts haven't been taped square which is very common.
I make a one piece nut and hold it in the correct position with a brass pad and grubscrew in the side to get away from this fiddle of adjusting.

The work also need both ends of the thread filing to remove burs and a polish with some scotchbright as the finish is straight off the machine.

The wheel needs removing and deburring, a rotary wire brush is good for this.

Then it needs a good clean prior to reassembly.

The main point to check is where the screws bear on the eccentric housing, usually one is turned parallel and fits into a groove to prevent the housing coming out. the other is usually a pointed screw and fits into a dimple in the housing.

This is a mistake because the Chinese dimple the housing without taking a lot of care in the cleanup and once dimpled the screw will always go back to it's preset place.
The answer to this is to turn the dimple out and make a groove and alter the second screw to suit.

This way you have control over the mesh of the gears.

On the ones I do I also bore the eccentric housing out and fit needle roller bearings plus two sets of needle roller thrusts, not a hard job but requires a couple of jigs and setups.

.

 

[Cedge]

John
Thank you!! Your input was invaluable. I took the table apart and saw what you were talking about. That dimple is truly bad engineering. It effectively eliminated all the good any adjustment would have done.

A thorough cleaning was definitely called for and a bit of fine grit sandpaper had things much smoother in short order. After cutting a new groove, things improved rapidly and the lash was reduced by about 80%. The table also operates MUCH more smoothly now that all the metal trash and old red grease are gone. A fresh load of lithium grease on the newly smoothed surfaces was just what the doctor ordered. It feels much more like a precision tool when the handle is turned.

Now, I'm really getting excited to find a project to try it out.

Many thanks
Steve