GDT Position Tolerancing
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Re: GDT Position Tolerancing
Re: GDT Position Tolerancing -- kds	Post Reply	Top of thread	Forum

Posted by: kds ® 11/08/2005, 17:52:45 Author Profile Mail author Edit

We are using an older version of the Z535 Meteorology computer, by RSF Corporation. It works well, which makes doing first item inspections a lot easier. I have never done position tolerances before and am not sure if I am doing it right or not. I went to Engineers Edge web page (/true_position.htm) on position tolerance and also used their true position calculator(/calculators/true_position_pop.htm)but I am not too confident with my results. For instance how does my X & Y offset dimension, relate to what my drawing is calling out? Or once I have found out what my true position is with the true position calculator how does that relate to what I have on my drawing. Does any of this make sence?

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Re: GDT Position Tolerancing
Re: Re: GDT Position Tolerancing -- kds	Post Reply	Top of thread	Forum

Posted by: traingdt ® 11/09/2005, 19:12:05 Author Profile Mail author Edit

First, I presume you are talking about a hole (or a pin; usually we talk about position of a diameter). The GD&T system gives position tolerance as the imaginary "zone" within which the hole's axis must lie. Most likely, the position tolerance you are dealing with includes the diameter symbol before the number. This indicates a cylindrical zone, centered at the true (perfect) position. Keep this in mind, because it means we can really only deviate half of that amount from the true position. (It might help to sketch this concept.) Now, your gage reading gives the X and Y offset, but the position tolerance is shaped like a circle. So we have to convert the X-Y numbers into a single number representing the radial deviation, regardless of direction. That's where the position calculator comes in. It simply uses the Pythagorean theorem to find the radius; it then doubles that number because the geometric tolerance speaks in terms of diameter. So, you input the X deviation and the Y deviation, and it calculates the size of a cirlce swept by that point. It then compares that to the allowable diameter of the position zone. Feel free to post a follow-up question...

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Re: GDT Position Tolerancing
Re: GDT Position Tolerancing -- kds	Post Reply	Top of thread	Forum

Posted by: traingdt ® 11/02/2005, 17:42:07 Author Profile Mail author Edit

Sure, you may post a question here (even if it's a general explanation you seek). Or you can contact me offline if you prefer at surritter@aol.com. John-Paul Belanger Certified Senior GD&T Professional

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