true position of a distance?

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Ortega H
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true position of a distance?

Post by Ortega H » Fri May 10, 2019 8:53 am

i have been coming across this alot more as of late,, engineers asking for true position of a distance? wth man? what are these guys thinking?

i have been creating the feature as an open slot and doing positional tolerance from that.

is this becoming common place and is this the best way to do it.
tp disr.JPG
also i have been seeing them using true position on its the only thing i can think is they are using it like concentricity
i usually use true position with no datums but i am having trouble with that working

whats the best way to do these in cmm manager?
tp on its self.JPG
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Ryan Christopher
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Re: true position of a distance?

Post by Ryan Christopher » Fri May 10, 2019 11:49 am

Like most things in Y14.5, these situations are confusing at first.

Paragraph 7.4.5 begins the topic of "Noncircular Features of Size". Long story short, the way to evaluate the position of a 'slot' (in this case) is to find its center plane and calculate the position of that. (Fig. 7-31, and 7-33 in the standard illustrates the point)

Your second image is showing a 'composite position' feature control frame. It is used for patterns of features.

The top section answers the question: "where is the pattern with respect to the datums (generally outside of the pattern)"
The bottom section answers the question: "where are the holes in the pattern with respect to themselves."

You can get some outstanding on-line gd&t training from these folks for a very reasonable price.

https://gdandt.com/
Ryan Tackes
Applications Manager, VMS Inc.
http://www.vantagemeasure.com/

Ortega H
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Re: true position of a distance?

Post by Ortega H » Fri May 10, 2019 1:52 pm

I USE THAT SITE ALOT ,,
LIKE I SAID I KNOW THE IDEA BEHIND WHAT THEY ARE ASKING FOR BUT CMM MANAGER HAS ISSUES WITH BOTH TYPES OF FEATURE REPORTING.
TRUE POSITION TO AN OPEN SLOT IS JUST NOT A VERY ACCURATE READING THAT I HAVE SEEN SO FAR AND TP TO ITS SELF IS EVEN WORSE, I GET A BETTER RESPONSE FROM CONCENTRICITY WHICH ESSENTIALLY IS WHAT THEY ARE ASKING FOR

Ortega H
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Re: true position of a distance?

Post by Ortega H » Fri May 10, 2019 1:55 pm

GD&T BASICS IS ANOTHER GOOD GENERAL INFO AND TRAINING SITE BTW

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CrashN8
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Re: true position of a distance?

Post by CrashN8 » Mon May 13, 2019 5:42 pm

Ortega H wrote:
Fri May 10, 2019 1:52 pm
I USE THAT SITE ALOT ,,
LIKE I SAID I KNOW THE IDEA BEHIND WHAT THEY ARE ASKING FOR BUT CMM MANAGER HAS ISSUES WITH BOTH TYPES OF FEATURE REPORTING.
TRUE POSITION TO AN OPEN SLOT IS JUST NOT A VERY ACCURATE READING THAT I HAVE SEEN SO FAR AND TP TO ITS SELF IS EVEN WORSE, I GET A BETTER RESPONSE FROM CONCENTRICITY WHICH ESSENTIALLY IS WHAT THEY ARE ASKING FOR
TP of Open Slot will account for TILT of feature, so remember your manual calculation that you're probably doing to double check the software should involve some trig in order to account for tilt angle in regard to nominal tilt. If you do not want to include tilt for your TP then construct a point and use bi-lateral TP of the constructed point.

Ortega H
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Re: true position of a distance?

Post by Ortega H » Tue May 14, 2019 8:16 am

constructed point of the center of the open slot?
or center line of the distance.. (or plane)

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medupriest
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Re: true position of a distance?

Post by medupriest » Mon May 20, 2019 3:42 pm

If you would like to eliminate the tilt form the calculation, construct a centroid point of the slot. Bi-lateral position will then only show the single axis deviation with no tilt.

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