On machine probing

[mechie23]

Hi,

I have a doubt regarding on-machine probing, I mean using touch trigger probes on CNC machines. Considering that machine tools themselves are not that accurate and repeatable, how can we rely on results given by a probe mounted on the machine tool spindle? Isn't a CMM probe more accurate?

Thank you.

 

[mechie23]

I have seen another recent thread in this forum where the author was asking about using a CNC machine as CMM also. And someone suggested that 'statically' CNC machine would give ~5 micron accuracy. But is this not too high a variation? And if this concept is used on large milling machines where also probes are used, the error easily crosses 20 micron. Any idea how this error is taken care of with this on-machine probing concept ?

I am sure this might be properly addressed by probe manufacturers, but I am not clear with this.

 

[berkshire]

The trigger probes are accurate to +- .001" on average. They are most often used for an initial preset, followed by a test run and measurement.
At least that is the way I have used them.
B.E.

"A free people ought not only be armed and disciplined, but they should have sufficient arms and ammunition to maintain a status of independence from any who might attempt to abuse them, which would include their own government."
-George Washington, President of the United States----

 

[mechie23]

berkshire - Thank you. But 0.001" sounds pretty high. Are you really sure on this?

Secondly, in addition to initial preset people are using this to check final part dimensions after machining on the machine itself. It's here I've doubt that how well these values match with that of CMM measured values.

 

[berkshire]

That may have been the machine I was using. The type we had, used a spring loaded metal block attached to the bed of the machine. When you brought the tool down to the block, an electrical circuit was made. Sometimes the block would depress a little before the machine automatically reversed.
B.E.

"A free people ought not only be armed and disciplined, but they should have sufficient arms and ammunition to maintain a status of independence from any who might attempt to abuse them, which would include their own government."
-George Washington, President of the United States----