Inexpensive 4” Rotary Table From eBay - A Quick Review

I've been eyeballing a small rotary table for my mill for some time. Unfortunately my toy budget has some firm limits, so I could not justify getting one. Until recently, that is, until I came across a 4” rotary table for under $60 on eBay. This exact rotary table is also sold by Grizzly (H5685), Shop Fox and others. Surprisingly, there is very little information on this table. I've found several forum posts, but that's about it. One thing that was clear is that this is by no means a precision table. Never the less, I though it should be good for making rounded corners etc. After having spent some time using the table, I'll try to do a short review/teardown.

To be honest, having purchased a number of cheap import tools for Harbor Freight and eBay, I was prepared for some “finishing work”. At the very least I was expecting a thorough scrubbing to remove the shipping grease. Surprisingly the table came in bone-dry, without any signs of lubrication. Since that was a bit unusual, I decided to take it apart and make sure that the mechanism was lubricated. Well, it wasn't – the inside was covered in swarf and abrasive grit from the grinding. After a compete disassembly and lubrication the table was ready to use. As a side-effect, I now knew exactly how it's built.

Construction

Rotary Table Work Surface

Bottom Sub-Assembly

The construction is pretty basic, or even to some degree crude. The round work surface rests on the top of the casting and is attached to the base through a ball bearing via M7 screw. Unlike the more expensive precision tables that have gear teeth cut along the perimeter, this model has a small brass gear pressed onto the “spindle”.

Worm Shaft Assembly

The worm shaft is inserted directly into the sleeve, which is attached to the casting via 4 screws. Higher end tables use an eccentric sleeve to remove the backlash. This table, though, uses a different mechanism: the hole in the casting is a bit larger than sleeve's OD and the holes on the flange are a bit oversized as well. To remove the backlash one has to loosen the four screws so the sleeve can move freely, tighten the little set screw on the side of the casting and retighten the flange screws. Even though this is a bit of a trial-and-error process, the backlash caused by the gear mesh can be almost completely removed (at least while the gears are not worn out). 

The bad news is that the work shaft has a major design flaw – the collar and the handle are attached to the shaft using two set screws (one each). Most rotary tables I've seen before had a nut at the end of the shaft, used to preload trust bearing or bushings. This table, though, has no such provision (neither does it have any trust bearings or bushings). While I was able to take out most of the backlash by pressing the collar in and tightening the set screw, but literally a few seconds into a cut the collar started slipping, resulting in a lot of chatter.

On the opposite side of the casting there is a knurled brass screw that is used as a gib of sorts, pressing against a shoulder cut on the underside of the table. Mine, unfortunately, tends to bind, since the shoulder isn't cut concentric. Since I'm on the subject of concentricity, I should probably mention that the table itself isn't concentric either. This makes locating the table on the mill a bit challenging.

Finally, another drawback is that the table doesn't have the usual morse taper in the center. Instead, the M7 thread used by the screw at the bottom is cut all the way through. This means that attaching a chuck requires a backplate. This isn't a big deal, though.

Potential Improvements

This table can't be made into a precision rotary table, but there are a few things that can be made a bit more usable. There are a few small improvements that I am planning to make:

• Replace the stock sleeve with a concentric one. This shouldn't be difficult to make and should improve the gear mech adjustment.
• Drill and thread a hole at the end of the worm shaft and add a preload screw. This should keep backlash in check.
• Add trust bushings and/or bearings to the worm shaft. In conjunction with the preload screw this should reduce the backlash and hopefully remove the chatter.
• Add a brass bushing between the table and the top of the casting. I don't know how useful this will end up being, but I get a bit nervous when I see cast iron on cast iron friction.

Conclusion

This little table is by no means a “precision instrument”. It has some shortcomings that can't be overcome even with the mods I suggested above:

• The resolution is fairly low, at 10 degrees per handle rotation and 1/6 of a degree marks on the collar.
• There is no morse taper in the center, making chuck attachment more tedious
• There is no way to attach a standard dividing plate
• The collar does not rotate on the shaft

Newer the less, I still think this table was a good buy for under $60. Granted, as is this table is barely usable, but a few simple improvements should make it useful for a lot of projects. After all, if all you want to do is to make rounded corners of cut a retaining ring grove, spending over $200 for a ultra-high precision Phase II table makes little sense.