Rotary Table Problem

[Jmccrack]

Hey guys.
I have an 8" rotary table. When I set it at zero and the micro handle to zero then rotate 360 deg back to zero on the handle the table is out 2 deg. Any thoughts?

 

[purpleknif]

Did you take out the slack ?

 

[Jmccrack]

Yes. Everything is tight and no back lash.

 

[Nick Hulme]

You have backlash which the adjustment doesn't eliminate!

Good practice is to always approach every stop point from the same direction, you don't need to go through 360 but you should go back to -10 degrees and then wind back to zero in the same direction in which you approach your machining points,

- Nick

 

[ninefinger]

2 degrees is alot of play, in fact its a half a turn of the crank on a typical table with 90:1 worm reduction - each full turn is 4 degrees.
Are you counting the turns and then saying you're out 2 degrees? Which measurement are you going by - the micro collar on the handle or the marks on the table?
Try putting a piece of tape on the micro collar - it may be slipping on you as you crank. Also, as mentioned - you need to approach the stop point from the same direction (i.e. clockwise or counterclockwise) in order to eliminate backlash.

Mike

 

[///]

Try putting a piece of tape on the micro collar - it may be slipping on you as you crank.

That was going to be my guess. I'd also be trying tape before anything else. (assuming you are cranking in only one direction)

 

[Jmccrack]

thanks for the info guys. So here goes. Say I turn the wheel counter clockwise to 0 on the main table. Being careful not to go clockwise. At zero I set the micro dial to 0. I then rotate the table counter clockwise a full 360 deg. When I reach 0 on the micro dial I still have 2 deg to go on the table. So I machined the fly wheel using the 1 deg marks on the main table. It worked but I can do better.Here is a pic to the flywheel I still need to clean it up.

 

[Blogwitch]

It all depends on which RT you have.

Some of the expensive ones have anti backlash built in so that you can turn both ways without having to reset for backlash, so it looks like yours is like the other 99% of RT's that have to have that allowed for and so to get that perfect setting, you can only turn one way.

I had a bit of an argument with a chappie a couple of months ago about this very same thing, where he had fitted a digital turner and stepper motor but hadn't allowed for the backlash. He wasn't happy that he had more work to do before he could use it digitally where you can turn and machine in both directions without allowing for backlash, even though my Division Master can automatically cater for it, I never use it as it can introduce more possible errors like having to retract the cutter before you end the cutting sequence, then allowing the cutter to go past the end and come back before dropping the cutter again for the reverse cut.
I have a digital driver and stepper on my 6" Vertex RT, and the first thing I had to do was to eradicate that backlash for the above reason, a thing that can't be done without a bit of machining work on the insides and introducing some thrust washers to the handle operating spindle.

John

 

[Nick Hulme]

Your investigation is incomplete, what happens if you rotate the table multiple turns?
Do you lose a further 2 degrees with each and every rotation?
If it loses more with each rotation it suggests something somewhere is slipping.

Whatever it is will be a basic engineering issue and should be fairly easy to identify given access to the RT.

- Nick

 

[Charles Lamont]

One answer would be that your table has a two-start worm and 181 teeth on the wheel!

 

[petertha]

Say I turn the wheel counter clockwise to 0 on the main table. Being careful not to go clockwise. At zero I set the micro dial to 0. I then rotate the table counter clockwise a full 360 deg. When I reach 0 on the micro dial I still have 2 deg to go on the table.

Another thing to check is how well (or not) your settable dial is actually setting. If its a friction style vs. a thumbscrew it might be slowly skidding out of position as you crank. I've seen this effect on another machine. The handle shaft assembly had a little bit of end play. If you pushed in ever so slightly while turning, the edge of the dial band would partially catch & go along for the ride a bit. If it was pure rotation, it stayed in place (which explained the apparent inconsistency). Similarly if there is grit in the gap to allow it to partially stick. The thumbscrew retention style should be a bit more stable but anyway but it doesn't have huge clamping force if it was a poorly machined or fitting band. You see what I'm getting at - check that the edges of the settable dial aren't riding up where they shouldn't be.

 

[Jmccrack]

Hey guys thanks for all the help. I solved the problem. Turns out I did not have a problem at all just me!! Heres the deal. I would rotate the handle thinking every time I would come to 5,10,15 deg on the main table the micro handle should read 0. Well of course it does not. It only will read 0 when the deg measurement on the table is divsable by 4 , the deg rotation on the micro handle. 90 deg = 22 1/2 rotations 180 deg = 45 rotations and so on. Thanks all for being so patient. Here is a pic of the finished product.

 

[BaronJ]

It always amazes me how often we miss the obvious.