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Author Topic: 4th axis rotary table control  (Read 3309 times)

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4th axis rotary table control
« on: March 15, 2008, 11:26:45 AM »
What all do people consider when choosing their motors and encoders?  Is the idea to match your resolution and max feed rate at the max diameter of the rotary table with that of the rest of the mill?

I'm setting up my 1st cnc mill ( show n tell thread here: http://www.machsupport.com/forum/index.php/topic,3990.0.html ) and immediately after getting it's current goodies running I'm adding a rotary table to it.  I already have a large, brand new camco rotary table for the job.  Right this second I don't remember how large since I've had it and the mill sitting while I've been busy finishing a couple masters degrees which I just finished (sitting somewhere else or yes I would go look, lol).  I've been collecting up the parts the last couple weeks to go ahead with this project and now that I have the parts for the x,y, and z  I'm starting to think about the rotary table.

What I'm looking for here is advice from people who have rotary tables or are very familiar with their set up.  Hopefully someone can put me on the right track and tell me what I need to know to do it to full advantage.  Precision and finish quality requirements on the parts I'll maching on the rotary table will be very high.  The camco rotary table is set up to be able to be used in a gang set up so it has both a servo motor mount and an output shaft  so I have plenty of places to mount encoders if they aren't integral to the servo motor.  I am using servo motors by the way.  I have a galil 2160 controller and am using 110V 5.9A 1800RPM DC servo motors with a 60V power supply, 1000 line encoders with indexes, and 5 tpi precision ground ball screws.  The gears in the camco rotary table are 30 to 1.  I'm going to guess my rotary table is 12" if not it's 10.  What all do people consider when choosing their motors and encoders?  Is the idea to match your resolution and max feed rate at the max diameter of the rotary table with that of the rest of the mill?

I know on the galil control I can set the home routine to look only for the index and not worry about a home switch.  Is this how homing a rotary table is normally accomplished?

Offline jimpinder

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Re: 4th axis rotary table control
« Reply #1 on: March 16, 2008, 06:11:18 AM »
I would have thought the speed at which the table should move would be dependent on what material you are wanting to cut, and the depth you are wanting to cut at. You are not giving any idea of the size of your machine - but from the pictures, I get the idea - and it looks like a metal working machine.

You are saying you want a good finish, so, regardless of the maximum speed of the table, you must ensure that the table(s) are geared so that if you are wanting to take a good cut, you have the power to do it. Have you fitted the main axis yet - what speed of travel are you thinking of trying for - I found a physical limitation on my machine - although I am ripping out the leadscrew and putting in ball screws with a hope of getting a bit more speed. Cutting is fine at 4 ipm - but waiting for the thing to traverse takes ages.

There must clearly be an advantage to standardising all you drives, so if the motors you are quoting would fit the table why not use one of them. It would give, however, a 90 ipm rotation at full speed - about 1 turn per sec - will it physically do that - is the motor powerful enough. I think I would gear that down by a factor of two.

This is equivalent to 7.5 - 9 ipm on the diameter, which I would have thought quite reasonable. It would home in 1/2 sec - I don't think your main axis would home that fast. You could even gear it down further.

I must admit I use steppers, so gearing down also adds to the accuracy I can get.

As far as homing is concerned - I think it would be more convenient if the rotary could home in both directions - you might only be a few degrees away - and certainly you would if using it manually - the only thing to bother about then is backlash (if any)
Not me driving the engine - I'm better looking.
Re: 4th axis rotary table control
« Reply #2 on: March 17, 2008, 08:57:35 PM »
Yes it's a large, heavy duty, precise metal working machine.  60V power supply, 110V 5.9A 1800 rpm permament magnet servo motors, 5 tpi precision ground impressively smooth no backlash ballscrews all around, large tubular ways that the table slides very easily on despite having no slop, NMTB 40 tool holders in a massive spindle,  2hp spindle motor, I'm very impressed with the machine.  Ex-Cell-O and Spindle Wizard were both obviously top notch.

I want to be able to machine any material that might ever light my fancy to.

I doubt I'll find another of the same motors I have for the xyz axiis as they are indiana general motors and the gearing of the table is already set because I already have it.  It's 30 to 1.  How fast can I cut with this machine?  I have absolutely no idea yet.




I would have thought the speed at which the table should move would be dependent on what material you are wanting to cut, and the depth you are wanting to cut at. You are not giving any idea of the size of your machine - but from the pictures, I get the idea - and it looks like a metal working machine.

You are saying you want a good finish, so, regardless of the maximum speed of the table, you must ensure that the table(s) are geared so that if you are wanting to take a good cut, you have the power to do it. Have you fitted the main axis yet - what speed of travel are you thinking of trying for - I found a physical limitation on my machine - although I am ripping out the leadscrew and putting in ball screws with a hope of getting a bit more speed. Cutting is fine at 4 ipm - but waiting for the thing to traverse takes ages.

There must clearly be an advantage to standardising all you drives, so if the motors you are quoting would fit the table why not use one of them. It would give, however, a 90 ipm rotation at full speed - about 1 turn per sec - will it physically do that - is the motor powerful enough. I think I would gear that down by a factor of two.

This is equivalent to 7.5 - 9 ipm on the diameter, which I would have thought quite reasonable. It would home in 1/2 sec - I don't think your main axis would home that fast. You could even gear it down further.

I must admit I use steppers, so gearing down also adds to the accuracy I can get.

As far as homing is concerned - I think it would be more convenient if the rotary could home in both directions - you might only be a few degrees away - and certainly you would if using it manually - the only thing to bother about then is backlash (if any)