Measurement of a part with position control refinement

[Jieve]

Hello,

Question about measurement of a part with a refined position control frame. Assume I have the part whose top view is shown in the picture. The circles on the inside of the part represent exaggerated tolerance zones of 4 hole axes to be drilled into the part. Datum A is the flat face perpendicular to the holes, and datums B & C are the side faces as shown. The following position control frame is used:

|Pos|Diam 0.15|A|B|C|
|Pos|Diam 0.05|A|

After receiving the machined part, I have four hole axes located at the centers of the smaller circles. The dimensions specified on the drawing between each hole and the next and from the datums to holes are all basic dimensions, horizontal and vertical. Now, how would this part be inspected without using CMM to ensure that the holes truly are within the tighter tolerance between each other when the pattern is rotated from the datums? Are the distances simply measured between the holes themselves (not the diagonal) and then checked to make sure all dimensions are within the basic dimension +/- 0.05 of each other, after initially verifying that all holes are within the larger tolerance zone?

I think I am being thrown off by the fact that the tolerance zones are rotated.

Thanks!

 

[powerhound]

I can only answer per the ASME standard. I don't know if ISO differs in it's view of composite or single segment position.

In this scenario, composite or two single segments have the exact same meaning. You should make a gage with the four pins located at the same basic dimensions as the hole spacing as well as perpendicular to the gage surface but the diameter of the pins needs to be the MMC size of the hole minus 0.05. I don't know if simply checking to make sure all the holes are within 0.05 of each other will give the full picture of the condition of the features.

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

 

[Belanger]

CH -- his callouts do not have the M modifier, so the functional gaging idea won't work.


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

http://www.gdtseminars.com

 

[pmarc]

Jieve,
You can even use your CAD system to verify this (yeah, I know it is not up to designer or drafter to do the inspector's job, but this is how it can be really quickly vierified or at least double-checked). Assuming that inspection report documents actual position of holes centers as 4 pairs of [x,y] coordinates (as it usually is), you can simply draw that 4 points in a sketch, independently of it draw a pattern of 4 circles of 0.05 diameter spaced at basic dimensions apart, but not tied in location and orientation to datums B, C and then try to play with the pattern (rotate and/or translate it) to find a configuration for which those 4 points reside inside the circles. If you are succesful to find such configuration, it means the holes meet positional requirement stated in bottom FCF. Otherwise part fails.

Each inspection software that is able to execute the same procedure will work fine too.

 

[powerhound]

Oops, sorry about that. I totally missed that. Forget what I said about the gaging Jieve. I need to brush up on my attention paying abilitites.

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

 

[Jieve]

Thanks for the responses.

Pmarc I understand what you are saying, assuming that the part is inspected by some method and XY coordinates are given, very interesting. But On a more Basic level, without CMM how would the XY measurements most likely be Made with basic shop measuring tools? Many of the parts that are being made for a project of mine are being machined by machinist apprentices that are doing a 3 year apprenticeship. Sometimes I spec GDT tolerances that they dont know how to measure, so they claim they Cant. In many cases they actually have the equipment, they just dont know how. It helps when talking to them if I know how to do the measurements.

Thanks!