Usefulness of cross slide rotary tables?

Have you seen the one that was published in Home Shop Machinist a year or two back?

I was pretty interested in programming the CNC mill at work to cut a base for the R/T portion, and it turned into a nightmare really fast, when the dimensions started adding up wrong.

The reply from the editor was not promising either.

It still looked like a decent project, just not one that could be done relying upon the dimensions given as being accurate.

The PITA part of the equation is that the really small mills don't have the headroom for the stacked pile o bits, while the ones that do have the room, want a little larger R/T and slides.

Hell, I'd be pretty interested in a decent, low profile, smooth turning rotary table, suitable for my Centec or on the slide of my Myford. The small, nice ones that I have seen go by were huge money, and the small affordable ones were not worth buying for being so rough.

Best of luck getting this going. An article written and submitted to one of the Model Engineering magazines would very likely rouse some interest in kits, if one were to go that way.

Cheers Trevor Jones

Greetings Trevor, Thanks for the reply. One of the reasons I'm making the cross slide is because I want as low a profile as possible. With the small table on a Bridgeport it doesn't make that much difference. But the low profile also has the advantage of being more rigid. Nevertheless it still will use up about 1 1/2 inches of spindle to table clearance. I guess what I'll do is finish the thing and if I like it correct my drawings and post them to the dropbox. If people like them I'll consider writing an article. The cross slide would need to be adapted to an existing R/T. I have seen plans for low profile ones. The little 4 incher I have is a Taiwanese one that I bought considering it a semi-finished kit. It wasn't real accurate when I got it but I went through the whole thing and now it's a fine tool. Cheers, Eric

Well that right there is a pretty good subject for a written article.

Some of the asian import R/T's I have looked at in person were, well, nasty.

If you can massage one into a decent running rotary table with only a little work, then that in it's own right is an accomplishment.

I have a Myford lathe, an Aamco shaper, and a Centec 2A mill.

The Centec is REALLY challenged for height, really needing a riser to do anything much larger than small model stuff with small cutters.

It has about the same work envelope as a Sherline mill, except it has several hundred pounds of cast iron in it, rather than 15 pounds of aluminum.

Got any sketches? I'd be interested in seeing the design.

Cheers Trevor Jones

Greetings Trevor, Sketches of the cross slide or of the rotary table fixes? I have drawings of the cross slide but am correcting them as I make the parts. When they are complete I'll post them to the dropbox. Eric

Sketches of the cross slide general layout and such.

Sketches or a rundown on the rebuild of the R/T would be nice too! :-)

I can wait.

If I have too. :-)

Cheers Trevor Jones

Well Trevor, I can describe the R/T changes to you pretty easily. First thing I did was to take the whole thing apart. This left me with the table separated from the spindle. After cleaning everything I machined a groove in the underside of the table about 3/8" wide and

1/8' deep. I then filled this groove with silicon bronze by tig brazing. After brazing the bottom of the table was faced flat and a groove cut into the silicon bronze 1/8" wide and .094 deep. The bottom of the worm gear was also faced flat. The spindle was then reattached to the table, turned so that it was square with the table, the thread on the end chased so that it was square, and then tapped for a threaded insert. The body of the R/T was then machined inside: it was bored for a bronze bushing to accept the spindle, grooved for a bronze insert that the bottom of the worm gear bears on, and a register turned on top that fits into the groove machined into the bottom of the table. This register and groove makes a labyrinth seal as well as a radial register. I lapped, with Timesaver compound for soft metals, the bronze areas and checked with bluing to make sure that there was proper contact of the bronze and cast iron areas. This is actually running a little longer than I thought so I'll need to come back and finish up. Eric

Thanks Eric!

Looking forward to it!

Souns like quite the kit build!

Cheers Trevor Jones

Well, here's some more. I have to back up a little. The first work was done on the body was to surface grind the bottom and the right angle surface to make them flat and square. After the inside work on top was done I turned the body over to bore and face the bottom of said bore for a thrust bearing. I used a needle type thrust bearing along with two washer type races made for the bearing. I made a new nut that clamps onto the spindle threads so that the preload could be kept where I wanted it. The spindle was threaded in the lower part to recieve an insert. This insert is threaded .532-24 on the OD , 3/8-16 and 10-32 on the ID. It's an inch long and the 10-32 thread is about

5/16 long with the remainder the 3/8 thread. The spindle is bored from the other end for a morse taper center. The 10-32 thread in the insert is for using a screw to push the morse taper center out of the table and the 3/8 thread is for a clamping stud to be threaded in. The original table clamp was a screw that threaded through the R/T body and pressed against the worm gear. That threaded hole was threaded 1/4-28 and a zerk fitting installed. I machined an annular groove in the table on center 1/8 wide and deep. Two 3/8 wide slots were machined tn the body opposite each other and tapped 10-32 in the bottom. These slots hold clamps that fit into the annular table groove. After all the work so far done it was time to address the worm assembly. Because the table position had shifted slightly I though the worm might not contact the warm gear properly. As it turns out it was so far out it wouldn't have contacted the worm gear properly before any mods. So I bored the body to correct the worm center location and bushed the bore back to size to accept the worm assembly. I made a new split cotter to clamp the worm assembly and a new handle to turn the screw which toghtens the cotter. Lastly I tapped another hole in the handwheel opposite the existing hole so that an arm could be attached to the handwheel effectively increasing the diameter of the handwheel. This makes milling with the R/T much easier because of the increased leverage. I did this to my 10 inch table and the 12 inch Troyke too. I think that covers all the work I did to the thing. Now I'll never be able to justify the time except that it was fun and the R/T is now a fine tool and I know just how accurate it really is. The next mod is to add an encoder to the worm assembly. I have the encoder and readout. The encoder is a 900 line device. The R/T has a 72:1 gear ratio. This means that with the encoder mounted to the worm and read in quadrature the resolution will be 5 seconds. Probably not the accuracy though. Hope you found this enlightening. When I get a new digital camera I will take some pics and post 'em. Eric