Hole position measurement on FRTZF

[SeasonLee]

I have a simple question on the lower segment hole position measurement, pls see the attached fig for details, pls let me know am I right on my assumption?
Thanks for your help

Season

 

[Belanger]

That is a composite FCF, rather than two-single-segments, so there is no 6.4 dimension from datum B (for your "true position" of the lower callout). That lower callout is only interested in orientation of the 3 holes relative to datum B.

 

[SeasonLee]

Thanks for your comments, Belanger.
Yes, you are right. Then, my question is how to measure those 3 holes position on the lower segment.

Season

 

[greenimi]

Then, my question is how to measure those 3 holes position on the lower segment.

Easiest way, with a functional gage. Three gage pins 5-0.25 = 4.75 placed on a gage plate / base and perpectly perpendicular to it. Then a mobile gage wall ("perfectly" perpendicular = within gage manufacturing tolerances- to datum A) comes and get in contact RMB (maximum contact) with the part.

 

[3DDave]

See

http://www.ttc-cogorno.com/Newsletters/130418CompositePositionalTal.pdf

 

[SeasonLee]

Thanks for all the help.
I found an example on the draft of Y14.45 "Measurement Data Reporting" section 11.5, a nice reference for me.

Season

 

[SeasonLee]

Even if I found this example, I still don't know how to get this data(0.384) as shown below, can someone tell me how it is calculated.
This example come from page 88 and 89 of Y14.45 "Measurement Data Reporting", 2 pages attached.

Thanks again for the help

Season

 

[3DDave]

Pick 3 colinear points, [20] apart (for this example)such that they are located to minimize the position error for the three features. This is complicated in the diagram "Measured Part" because they show both ends of each axis projected onto the view.
There is no method given to calculate the zone diameter for each of those three holes in the draft version of the standard.

To calculate this, start off with an assumed deltaX, deltaY and theta each equal to zero and apply that transformation to the three points. Then make an epsilon change to each in turn and see which position errors decrease, apply the one that makes the largest decrease and repeat until a minimum within desired limits results. As long as the initial epsilon is not too small the process should converge rapidly enough.

Note that in this process it is likely that only one end of each axis will be the greater driver of the zone diameter comparison, so take the MAX() of the radius from the transformed points to each end of the axis (for this example) as the value to be minimized and that it may be that, as the solution converges, the driving end may switch.

 

[SeasonLee]

Wow, that's not an easy work, I thought it will be a way just like we calculate the tolerance zone on the 1st segment PLTZF.

There is no method given to calculate the zone diameter for each of those three holes in the draft version of the standard.

Expect to see calculated process on the final version of the standard.

I think this calculation process far exceeds the work ability of an inspector, will the CMM automatically calculate this result for us?

Season

 

[Belanger]

A similar discussion in the thread below which might help with your latest question:

[URL unfurl="true"]https://www.eng-tips.com/viewthread.cfm?qid=350412[/url]

 

[SeasonLee]

Belanger, Thanks for you dig out my thread about 8 years ago, I have re-read it again and I know that a good CMM software must have experienced GD&T expert involved. I think CMM can calculate actual measured position tolerance automatically for us, but I don't have this experience before. Anyone willing to share your experience.

Season

 

[Belanger]

Sorry -- I didn't notice that you were the one who started that earlier thread! I've had that bookmarked for a while to show others because that is a somewhat common question.

 

[SeasonLee]

Belanger
Actually I will thank you since I really forgot that we had some discussion earlier regarding this topic.

Well, I like to see others opinions on:
1. The actual measured position tolerance zone calculation on the lower segment FRTZF.
2. Can CMM handle this calculation? Expect to see your experience sharing on CMM measurement.

Thanks

Season