Flatness Call Out confusing me - What they are wanting and how to check it?

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2

20110525R

#13
Here is how to check flatness without at CMM. This method has been used for years and years.
David, your flatness PDF file is incorrect, you are measuring Parallelism in this example. True Position is correct, you are measuring Parallelism if you measure the top of the piece. You would use the Height Gauge to measure the underside of the part with the part on the surface plate with 3 stands to measure Flatness.
The easiest method for measuring flatness is with a height gage positioned on a surface plate. Note that you must setup the part on three stands and find the minimum variation while adjusting them, just placing the part on the surface plate and using a dial indicator to find TIR on the opposite side of the part measures parallelism.
Mike
 
M

Mr.Happy

#14
David, your flatness PDF file is incorrect, you are measuring Parallelism in this example. True Position is correct, you are measuring Parallelism if you measure the top of the piece. You would use the Height Gauge to measure the underside of the part with the part on the surface plate with 3 stands to measure Flatness.
The easiest method for measuring flatness is with a height gage positioned on a surface plate. Note that you must setup the part on three stands and find the minimum variation while adjusting them, just placing the part on the surface plate and using a dial indicator to find TIR on the opposite side of the part measures parallelism.
Mike
I disagree with Mike, I think David is right !
:argue:
 
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D

David DeLong

#15
David, your flatness PDF file is incorrect, you are measuring Parallelism in this example. True Position is correct, you are measuring Parallelism if you measure the top of the piece. You would use the Height Gauge to measure the underside of the part with the part on the surface plate with 3 stands to measure Flatness.
The easiest method for measuring flatness is with a height gage positioned on a surface plate. Note that you must setup the part on three stands and find the minimum variation while adjusting them, just placing the part on the surface plate and using a dial indicator to find TIR on the opposite side of the part measures parallelism.
Mike
I am not measuring parallelism if I am zeroing on the top surface above the adjustable jacks at the 3 points. I have created a plane on the top surface and then I would sweep that surface and report the TIR or FIM. That is the actual flatness.
 

Jim Wynne

Staff member
Admin
#18
Sorry David, but you and Mr. Happy are incorrect.
David's method, which has been used forever, effectively isolates the target plane. One of the problems with it is getting the jacks properly adjusted, which can be very tedious. Another problem can be the size and shape of the part.
 
M

Mr.Happy

#19
When the object is very big you need to put the jacks on the "Bessel's points" just like you do under an measuring plate.:caution:
 
2

20110525R

#20
This is the same argument I have had many times before, but what all of you are measuring is Paralellism not Flatness. Flatness is measured from the underside of the piece (The Surface to be Measured) on the 3 points from the surface plate up to the part and swept across the bottom of the part with a dial indicator attached to the height gauge.
 
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