Machine Tool Calibration - Machine Capability Studies on CNC Machine Tools

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mlthompson

Anybody have any resources/experiences regarding machine capability studies on CNC machine tools? I've done machine studies measuring parts, but I recently read some information regarding using a ballbar and laser systems.

Is doing a machine capability study valid if the machine isn't under load?

Any help will be appreciated.
 
B

Boscoeee

Re: Machine Tool Calibration

Anybody have any resources/experiences regarding machine capability studies on CNC machine tools? I've done machine studies measuring parts, but I recently read some information regarding using a ballbar and laser systems.

Is doing a machine capability study valid if the machine isn't under load?

Any help will be appreciated.

Check out this article, just thought it was interesting!:D
http://www.moldmakingtechnology.com/articles/040306.html

I have always had the same question regarding running a machine under load, hope someone will weigh in here that has more experience in this area.

I use Ball Bar Testing as part of preventive and predictive maintenance program.

Our CNC Machine tool capabilities are determined by using either parts or test pieces designed to test the capability.

Have no experience with calibrating CNC Tools with lasers!:cool:
 

AndyN

Moved On
Re: Machine Tool Calibration

I'm not sure what the benefit of using a calibration technique is going to be to determine the capability of a cnc machine tool.

It's inappropriate to use the term 'calibration' - but since the OP uses the words 'capability' I think that's really what we're talking about. A part study has always been the most applicable, since it's more than simple geometry of the machine slides, like the interactions of head/spindle/bed etc. that contributes to the result - the capability.

Unless there's been some dramatic or revolutionary difference in the past 50 years machine capability practices, then I think you're going to be running parts.......:lol:
 
M

mlthompson

AndyN

So, what you are saying is that there is a difference between machine tool calibration and machine capability studies?

When you google "machine tool calibration" you get a long list of websites discussing linear calibration, volumetric calibration using ballbar/laser systems, etc. All this is intended to verify that accuracy of the machine.

I am looking for the most applicable method to verify that my CNC machine tools are accurate and have good repeatability. Is it your experience that to check accuracy and repeatability is like the difference between gage calibration and Gage R&R studies?
 

AndyN

Moved On
Mike:

The real problem lays in the way people use the term 'calibration'. Even in this small and (well) educated community on the Cove, it means different things to different people. Often folks are convinced they 'know' calibration and then they describe something else.......

You can perform alignment checks at install/commissioning etc with lasers and other precision equipment. You can do this periodically as part of a pm program, but the proof, the machine capability is determined from measurement of output. In some ways it's like checking a car's front end alignment - will it affect the performance if it's out? Yes, but ultimately it's how it's driven, what tires it has, type of gasoline etc, etc. which defines 'performance'.
 
A

AggieRob02

In my experience Calibration and Certification go hand-in-hand. As far as process capability goes, It is determined by Cp or Cpk, as far as I understand. SPC should help this along with control charts.
 
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