Adjusting backlash on 4" rotary table

[homebrewed]

I have a 4" rotary table I purchased from Little Machine Shop a number of years ago. They still carry it, part# 1810. I have run into a problem regarding adjusting the backlash. Till now I haven't found it necessary to adjust the backlash so that portion of the mechanism hasn't been touched.

According to the user's guide I found on their web site, it's done by loosening the two set screws on the side of the table nearest the hand wheel, then the vernier "color" (I assume they mean "collar") is rotated slightly counterclockwise to reduce the backlash. I assume there's an eccentric hole in there so the clearance between the gears can be adjusted.

The problem is that I can't move the vernier collar after I loosen the set screws. Is it usually in there pretty tight, or is something else going on? Hardened grease? Any suggestions on how to loosen it up? I don't want to damage it -- I also got the tail stock and dividing plates for a very good price by today's standards so it would be a real shame to screw it up....

 

[ChazzC]

Can’t directly answer your question, but drop them an email or give LMS a call: I’ve always found them responsive & helpful. They should be able to give you an idea of how much force may be required or if you need to drop it in a bucket of mineral spirits.

 

[homebrewed]

Can’t directly answer your question, but drop them an email or give LMS a call: I’ve always found them responsive & helpful. They should be able to give you an idea of how much force may be required or if you need to drop it in a bucket of mineral spirits.

I got just a bit more aggressive with the collar and it did rotate once the set screws were loosened. BUT it doesn't appear to make any difference. The user guide indicates you have to be careful & not turn it too far, else it will be too difficult to move -- also not the case.

One thing I noticed is that the set screw closest to the handwheel will force the collar to rotate back, unless the other one is locked down first. No mention of that in the user guide. The other thing is that if the collar is rotated it no longer lines up correctly with the mark on the body.

LMS has been pretty good at answering my questions, too. I guess it's time to contact them. Thanks for the suggestion!

 

[VicHobbyGuy]

I don't own that exact LMS table, but I have a similar 4" one. It was pretty much unusable when it arrived (via Amazon, so not a surprise) so I had to 'take it to pieces'. I don't remember all the details; it was a few months ago. That collar with the eccentric bore just controls the engagement of the worm and rack teeth, so a limited amount of adjustment, and as LMS says, too tight and nothing will move. If you get to work on the insides, all will be clear. BTW, mine had hardened grease 'from the factory', and there were a lot of rough edges and burrs inside. So a complete 'once over' de-burring and polishing will probably improve the performance overall.

 

[francist]

I will second the suggestion to tear it down completely if you feel up to it. I bought mine (also an 4” typical import style) about three or four years ago from a local tool supplier so it’s been long enough that I can’t remember exactly what the innards look like. But I do recall that there were a few adjustments that weren’t exactly intuitive until I opened the thing up. Once I had it back together the difference in performance was night and day.

 

[Larry$]

I have an 8" Vertex rotary table. I suspect they are all made similarly regardless of size. I agree with the others, take it apart. There's not much to them. Mine worked fine when I got it. But being me... I took it apart to see how it was made. It was clean with a few minor burrs. It's been a long time but I think there are very few adjustments that you can make. How tight the table is pulled onto the body and the clearance between the worm & worm gear. One of the set screws likely is a stop for when the worm is in the proper depth to the worm gear and the other set screw is likely what you can loosen to swing the worm away from the gear so you can freely rotate the table by hand.

 

[cathead]

Yes, TIA. That's newspeak for take it apart.

In old speak, it would be a transient ischemia attack.

 

[homebrewed]

Yes, TIA. That's newspeak for take it apart.

In old speak, it would be a transient ischemia attack

A little update.

Once I freed up the collar it wasn't too difficult to remove it -- just back out the set screws more and rotate until the worm gear is clear of the spur. Then you can just pull out the handwheel and worm gear assembly.

Once removed I found a divot in the collar that would force the collar back to a fixed location. Once I saw that I was able to reduce the backlash (by not tightening-down the front set screw). Comments regarding the adjustment being a bit fiddly were true, there's not much leeway between too tight and too loose.

I also found that it's very easy to over-tighten the nut that attaches the hand crank assembly to the shaft. There's no thrust bearing in there, it's a metal-on-metal thrust washer. So a bit too much torque and the hand crank locks up. As a result there's no way to eliminate a certain amount of backlash. There a mod lurking in there if I want to take it on. But at the moment it's better than as-received. The usual methods of handling backlash will be fine for a lot of uses so at present I don't see a reason to do any modifications to my RT.

 

[rabler]

I had to do something similar with mine about a year ago. Don't remember the exact details.