Expectations of 4 inch Rotary Table?

[epanzella]

I bought a 4 inch rotary table some years ago to try and use with my lathe milling attacment. Now that I have a mill I realized that a 4 inch table is just too small for my needs. I made some Teeny Teenutz and attached a 6 x 3/4" inch round plate to my RT. When trying to machine the OD of the plate using the rotary table itself I get chatter and the endplay keeps increasing. Adjusting the end play back to spec only lasts a few seconds until the end play increases again. I tried climb and conventional milling. It seems there's only some setscrews to hold the end play. I'm posting a pic of my setup. Part of the OD was turned in the lathe but I'm trying to do the rest with the mill. Is this table a piece of junk or am I just asking too much of it ?

 

[francist]

I’m thinking a little bit of both. I recently bought an even smaller RT at 3” diameter and the first thing I did was take it completely apart right down to the casting. Then, piece by piece, reassembled it taking pains to get as good a fit as I could manage in each component. For some pieces I made new parts to get the fit I wanted. When I did get it all back together my lash was maybe one or two increments on the dial compared to almost a quarter of a rotation when I first got it.

The second question, are you asking too much of it? Maybe so. It’s all fine and well to add a larger clamping table (I did for a recent project) but keep in mind that the size of that new table is going to load all the inner workings much more than the original table. So milling around the perimeter of a six inch disc using a four inch table as the driving foundation is putting a lot more load on the gears, locking devices, etc than what it was designed for. Kind of like putting a three foot cheater on a 3/8” drive ratchet, something will give.

My rotary table didn’t start out great and it still isn’t the best, but it is an order of magnitude better than when I bought it because of the rebuild. You may find similar success if you have the time in your project to do that. I suspect you are correct in the long run though, a 4” is just a shade too small for what you’re wanting to do with it.

Good luck!

-frank

 

[Bob Korves]

Make sure that the rotary table is locked down for any cuts that do not require turning the table. Even then, it will help to have the table lock tight enough that it gives some drag against the table bouncing back and forth in the backlash. The rule for all machining is to have everything locked down except for what needs to move to make the cut. Especially with lighter machines and tooling, this is an important technique to have engraved in your brain, and a habit in your hands.

 

[homebrewed]

It looks like your particular RT also can tilt. I see a scale in the lower left quadrant of your second photo which suggests that. Like swivel-base vises, that scheme probably isn't as rigid as a fixed-base setup. Not sure if you can remove that part of the RT and still clamp it to your mill table though.

 

[epanzella]

I had my x,y, and z axis' all locked. I had the RT table lock dragging. I had the tilt locked. I can remove the tilt base and put the RT in my mill vice. All the movement I saw was in the table turning back and forth with the cutter with the back lash continually getting bigger. I'll finish this disc off in the lathe and hopefully smaller parts will mill OK when they're more into the design envelope of this table. Thx for the responses.
Ed P

 

[Bob Korves]

It may be possible to adjust the gear attached to the handle shaft in and out to adjust the backlash, usually using shims.

 

[epanzella]

It may be possible to adjust the gear attached to the handle shaft in and out to adjust the backlash, usually using shims.

I did adjust it but the adjustment won't hold when trying to mill the perimeter of that disc.

 

[macardoso]

4 inch might just be too light duty for your needs. Perhaps a gentle cut with a roughing endmill would help, otherwise buy or borrow a larger rotary.

Edit: Using the smallest endmill possible will go a long way in reducing cutting forces.

 

[pontiac428]

I did adjust it but the adjustment won't hold when trying to mill the perimeter of that disc.

Probably because the spur gear is out of concentricity, causing the backlash to vary with table position. On my Kamakura RT, I can adjust the centering of the spur gear with the extra play in the bolt circle. I support taking the RT apart and squaring it away.

 

[francist]

I believe there are two places where the lash adjustments can occur, at least on these small tables. The first is the interface between the gear and the worm, and this (at least on my table) is adjusted by rotating the entire dial assembly in the casting. The dial wheels are keyed to the worm shaft, but the shaft itself passes through a collar that is eccentric. To adjust the gear-worm clearance you rotate this collar within the casting to bring the mesh either closer together or further apart. You need to re-position your ‘zero’ hash mark plate slightly after doing this.

The second place is a small dog pin that (again, on my table) came in from the bottom of the casting. It is shaped like a small tab on the end, and this tab is supposed to engage a groove cut into the eccentric collar thereby holding it and the dials into the casting. When I took a look at this pin in mine it was all goofy and shaped with a taper that caused the fit in the groove to be very loose.

After some thought, I concluded that the design feature here was to make it loose fit in the groove and to incorporate a set screw so that you could turn the pin so two corners of its tab engage opposite sides of the groove thereby “reducing” clearance. Um, I didn’t see that lasting for too long so I completely rebuilt that pin with a precisely fitted tab to match the groove. It took some fiddling, yes, but there is no more monkeying with trying to twist a tab to fit the groove and try to lock it in place with a dinky little set screw. Plus, how long would you expect a zero clearance to be maintained if the only bearing points are two corners of an unhardened pin! If the fit of the tab in the groove is loose, the collar can slip in and out of the casting and regardless of how close you have the gear and worm the backlash is still there.

-frank