Ballscrew pitch error compensation

[Scott_bob]

If there is a better way to ensure a CNC machines accuracy, I don't know it.

Do you?

I'm talking about using a laser to measure, and then compensate the CNC machines X, Y and Z axis pitch error comp table.
Please, Let us know if you do, or if you don't know about this process. Or, if you are aware of another method of maintaining CNC machine accuracy...

This service is not all that expensive when you consider the benefits of, or the consequences of NOT keeping your CNC calibrated.

Anyone else doing annual or semi annual calibration?

Sincerely,
Scott_bob

[sab]

laser interferometer is best solution .................i think there is no need to calibrate CNC machine annually but it should be verified properly.............you can use renishaw's BALL BAR for this purpose.

[Ron22]

In my option how often you need to calibrate depends on what the machine is and how often it is run.
If it is a ball screw machine with rotary encoders on the ball screw or motors I would say at least annauly check it. If the machine need the compensation table adjusted would depend on what you see and what accuracy you are looking for.
If the machine has linear encoders (glass scales) for positioning you can get away with less often. the linear scales will compensate for some ball screw wear.

As for how to calibrate your machine it all depends on what kind of tolerance you want and size of machine.
Laser interferometer is the best . Renishaw's ball bar is good but is limited to size. You can also cut a test piece with holes every 1" and have the part CMMed.

I do not think there is a standard answer allot depends on what you are trying to do with your machine.

[laserman]

Hi Scott bob,

I have a number of customers who annually calibrate their machines. Some of it depends on the way they have their iso program written. I always reccommend if you have more than 4 or 5 cnc's you should have a ballbar in house. This enables you to keep a record of your machines health and plan when it needs work, rather than have a breakdown at a critical time.
If you do have the calibration performed make sure that all of the geometries of the machine are checked and corrected first. We use a geometry laser to do this and an Renishaw interferometer system and ballbar to finish the calibration process.

laserman

[RICHARD ZASTROW]

Scott bob First make sure all mechanicals are operating properly. Calibrate on a schedule and if the schedule indicates longer intervals will suffice adjust schedule. We had one job that required geometric checks and recalibration between workpieces. They weighed 350 tons each of 3 required per assembly. When on floor plate they deflected floor .100"+ down,

[navyfalcon]

I worked many years in maintenance on NC, CNC, & DNC machines
We had a Hamer Geometric Laser, an HP Precision Laser and an Optodyne doppler laser.
The Optodyne laser was far superior to the others, the HP was next and the Hamer was last choise. The most important part was proper mounting for the setup, then the setup. We used two Optodynes for gantry checks and two to check axis, set for 90 degrees apart to check for play when positioning (ie. loose gibs or bearings - tycos). Mechanical correction is required if compensation is beyond a certain value(ie backlash compensator, etc.). Don't forget, you have 6 degrees of freedom (pitch, yaw and roll). After the mechanical checks are made, and corrected, then you can compensate for ballscrew wear.
Spot checks are made between calibrations, and after any major damage.
Some of the main problems we ran into was temperature compensation and drafts (they can bend the beam). Remember, you can measure less than .000001, but corrections change that. CMMs are set for less then .00005
(50 millionths).
Now, lasers can measure and make corrections on the fly.
see http://www.optodyne.com/opnew4/home.html
or
http://www.optodyne.com/opnew4/download/pdf/lds1000.pdf
with glass scales, we had the most problems cleaning oil from the glass scales (regular maintenance procedure). Some of the machines had Farand scales, which helped with temperature compensation. Also they had an Invar rod to compensate for spindle growth due to heat.
Most of the problems we had when calibrating was timing, we started very early so the temperature change was not as great, unless we were in a temperature controlled room.
Also when reloading, you had to make sure that you also loaded the compensation tape.
Because of the requirements from the customer, we had to calibrate annually.
-
hope this helps
falcon

[mangalmoorthy]

Originally Posted by Scott_bob If there is a better way to ensure a CNC machines accuracy, I don't know it. Do you? I'm talking about using a laser to measure, and then compensate the CNC machines X, Y and Z axis pitch error comp table. Please, Let us know if you do, or if you don't know about this process. Or, if you are aware of another method of maintaining CNC machine accuracy... This service is not all that expensive when you consider the benefits of, or the consequences of NOT keeping your CNC calibrated. Anyone else doing annual or semi annual calibration? Sincerely, Scott_bob

Hi Scott,
We are placed in India. Actually we have Renishaw equipment with us and we had calibrated more then 3000 machines in india. Also our speciality is we can Do laser calibration and we can compensate pitch error into the CNC paramters irrespective of CNC system. We not only calibrated but evolve the problematic areas for causing accuracy disturbances. We have Ballbar system with us which is a very handy instrument to diagnose the problems in few minutes.
Periodic calibration will definately give a higher performance of the machine. You will also have a check on the machine with all datas related.
Regards,
Mangalmoorthy.A
Head Calibration department.