Concentricity v/s coaxiality (yet again) on a CMM

[Reman101]

Greetings to the forum, new guy here.

I have read a few posts about the battle over concentricity, etc. and I do agree that yes it and it's spawn are pure evil.

Here is a little background of my situation. Our customer has a cylinder head that they want us to re-build for them and there is a concentricity (actually a DIN coaxiality) call out on the drawing. They recently opened up the tolerance but we are still having issues. At first we were having troubles machining it, but a quarter million dollars and a new machining center later we have the capability to cut to tight tolerances but our antique CMM isn't up to the task.

We have been sending our heads out to be measured on a scanning type CMM until we can convinve our management that we need one (as this is what our customer uses in their facility).

I guess my question is how do we know that we are measuring this correctly? At first we were doing the concentricity thing but then we were corrected and told to do the coaxiality on the cylinders that make up the valve guide and valve seat pocket.

Thanks,

Mike

 

[powerhound]

You mentioned the DIN coaxiality. Is the concentricity per ASME or ISO? I believe the definitions are different thus the inspection setup will be different.

Powerhound, GDTP S-0731
Engineering Technician
Inventor 2010
Mastercam X6
Smartcam 11.1
SSG, U.S. Army
Taji, Iraq OIF II

 

[fsincox]

Absolutely they are different, are the features actually coaxial?
Frank

 

[Belanger]

"I guess my question is how do we know that we are measuring this correctly? At first we were doing the concentricity thing but then we were corrected and told to do the coaxiality on the cylinders that make up the valve guide and valve seat pocket."

To know if you are doing it correctly, look for the standard imposed on the drawing (DIN, you say, which would be invoking the general "coaxial" control akin to position). Then get hold of that standard, show it to your inspection shop, and that's how you'll know.


John-Paul Belanger
Certified Sr. GD&T Professional
Geometric Learning Systems

http://www.gdtseminars.com

 

[fsincox]

JP,
I am just trying to find out if they actually used coaxiality as a replacement for position if the datum features referenced are not even coaxial?
Frank

 

[CheckerHater]

"coaxiality on the cylinders that make up the valve guide and valve seat pocket."

Looks more like runout :

[URL unfurl="true"]http://www.sweethaven02.com/Automotive01/fig0360.gif[/url]