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Author Topic: Ballscrew pitch comp  (Read 2282 times)

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Ballscrew pitch comp
« on: June 27, 2014, 08:49:10 AM »
Are there any current plans or have there been any plugins for ballscrew pitch comp? I would like to build a very very large machine but need ballscrew pitch compensation for the machine. How it works is we shoot a laser and comp the ballscrew in .0001" increments every inch. I plan on a 200" travel X and a 100" Y travel bridge mill. This works in conjuction with backlash.
Re: Ballscrew pitch comp
« Reply #1 on: June 27, 2014, 09:15:21 AM »
You do realize that, especially on a machine that size, unless you have closed-loop control with linear scales for feedback, the effects thermal expansion of the screw and machine will completely swamp any error in the ballscrews?  And if you have linear scales, you really don't need to map the screws.  In other words, mapping the screws is very unlikely to make the machine as a whole any more accurate....

Regards,
Ray L.
Regards,
Ray L.
Re: Ballscrew pitch comp
« Reply #2 on: June 27, 2014, 09:44:25 AM »
Thank for your input Ray! Thermal expansion can be greatly reduced with the properly materials. We could use a scale but to use a scale for positioning is one thing and to use a scale for contouring is a completely different system. We can get feedback from a scale to mach but I do not believe mach has the speed to react with fast 3d moves or even 2d moves with comp using an outside ethernet board like a smooth stepper. Without paying 90K to Fanuc for their control (3 axis) we are looking for an alternative. Our longest machine currently is a 150" Haas which has no thermal comp or scales. Every CNC mill and lathe we have are comping the screw without scale feedback. I would love to use scale feedback but I have not seen it for motion on any machine using mach 3. Maybe they are out there. The one machine we have that uses scales needed the backlash to be very accurately calculated as well as pitch comp or you will see the result in the finish of your part. As far as I know it is absolutely needed with scales for any kind of milling.

Our shop stays 15 degrees on the floor with in floor heat and AC. It stays within 3 degrees at chest height.
« Last Edit: June 27, 2014, 09:47:43 AM by BTA CNC »

Offline ger21

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Re: Ballscrew pitch comp
« Reply #3 on: June 27, 2014, 10:07:49 AM »
Mach3 already has screw mapping.
Gerry

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