I want to ask if we can get run out in shaft D280x3500 mm araund 30 micron in cnc machine . While the shaft inside the machine we have the value with in 30 micron but when we take the shaft in CMM room we have different value around 80 micron
if any one can help me??

Are you supporting the shaft in the CMM exactly as it is supported in the CNC? It's own weight may be changing the measurement, provided your measuring devices are accurate and precise. Same thing goes for identical temperature.

In machine the shaft supported by chuck, steady rest and tailstock but in CMM the shaft support in V-block , how we can make same clamping in cmm

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Originally Posted by sultan60

how we can make same clamping in cmm

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I think it unlikely that you'll be able to. The act of moving it from CNC to CMM could introduce variance as well. I don't have enough experience machining items that large to give you a concrete process to follow to achieve the tolerance you need. There may be a AMHD member here with such talent who may see your post and offer a suggestion, but you probably have a time constraint for resolving the issue. Why don't you seek out and retain a consultant with such experience? If the shaft needs <30 micron runout installed in its application, the whole process from machining, shipping, and installation needs a coordinated effort to maintain the tolerance.

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Originally Posted by sultan60

in machine the shaft supported by chuck, steady rest and tailstock but in CMM the shaft support in V-block , how we can make same clamping in cmm

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I know this response is probably too late but I just joined today!

What Scleros is totally correct.

When you measure the run out in the machine you must do so with out any steadies. The shaft must be only held at the chuck and center. You will only then get a true run out reading.

I suspect you are resting on a steady, which will never give the true run out vale.

Also mic your shaft diameter in 4 position and check it is not oval

Sorry for a late response - just joined.

Be sure to look at your tail stock pressure in the machine and part flexing or sagging while chucked up. When it is in a relaxed state you might see a difference.

Is the raw material out of round? Finished product?
Is the Spindle Chuck free of excessive T.I.R.
Is the Tail Stock exhibiting excessive T.I.R.

In the machine you are likely clamped at the ends of the shaft. At the CMM are the V Blocks spaced accordingly to best replicate the turning condition?

Next try to evaluate if the runout is in a consistent orientation to the part. If you can identify a trend or pattern you will be able to narrow down the possibilities.
You could load a part and mark the chuck and part in a line. When you measure runout at the CMM note which direction your high point is in relation to the marks on the part. If this repeats from part to part you can take a more focused approach to resolving your problem.

You need to be between centers for run outs. Chucking can give false readings, Have you considered inspection in place? Portable CMM's are available. I work 50 to 120 ton propulsion shafting for the navy and slightly smaller shafting for the coastguard. We hold inspections between centers.. It's required..

You need to be between centers for run outs. Chucking can give false readings, Have you considered inspection in place? Portable CMM's are available. I work 50 to 120 ton propulsion shafting for the navy and slightly smaller shafting for the coastguard. We hold inspections between centers.. It's required..