Fixed the rotary table rotating backwards

Jan 27, 2011 2 Replies
I

I mentioned yesterday that the RT was rotating "backwards". Say, if the pointer arrow was at 20 degrees and I told it to go to 30 degrees by saying



G0 A30



it would actually go backwards and stop at 10 degrees instead.



Well, I fixed it by reversing DC leads and by changing the sign of INPUT_SCALE.



I am also sure that I have some kind of a tuning or mechanical issue with the RT and will try to open it up on the weekend. It takes a lot of torque to move (about 3-5 amps) and moves in a slightly jerky fashion. It may also be a servo loop tuning issue too, purely a software problem or a wrong setting of the onboard pots on the DC servo drive.



i
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P

You've checked that the RT turns smoothly and without excessive drag by turning the motor shaft manually with everything unpowered? No table locks / clamps / brakes applied and dragging? CNC RTs often have pneumatic operated table clamps that need to be released before movement.

Next you need to work up a design and G-code to machine a mounting bracket for your home switch and the ramp to trigger it.

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I

I will look tonight. I think that I need to open it.

It IS hard to turn by hand. I tried this months ago.

Yesterday, I opened an end cover of the place where bevel gears turn rotation by 90 degrees, and found some strange brown grease, which seems like it is clean. I will try to remove the turntable tonight to see how the worm system looks like.

I have not found pneumatic anything on it. I think that it is a VERY early model of CNC rotary tables, basically the same as the U12 rotary table, but with a servo motor and 90 degree direction changer, instead of a manual handle. This suite me just fine.

There is a lock nut on it, but I thought that I loosened it.

I will take some pictures if I open it up.

i

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