1. ## true position formula

i do quality control at the factory i work at and my question is when reading a blue print, sometimes there's a callout for a true position for a hole or slot, coming from datum points A/B/C

does anyone know the formula in finding the true position

say you have a hole that is 3.0mm on your X axis
and 5.0mm on your Y axis
and you have a tolerance of say .3mm for your true postion

what would be the formula to find this ?  Reply With Quote

2. There is always a hard point to pull off of for any master set of prints, If your looking at a detailed view it more then likely wont have the measurements you want, but will have a line some where that says  detail sheet M1(or whatever)  If this is the case go to sheet M1 to find the measurements to the area you are working in then go back to the detail sheet for final verification of sizes, location and direction.
Good luck... Brian
"edit" I R not to brite, sorry you want the formula.... sorry me bad
but will look.  Reply With Quote

3. Originally Posted by Hawk
i do quality control at the factory i work at and my question is when reading a blue print, sometimes there's a callout for a true position for a hole or slot, coming from datum points A/B/C

does anyone know the formula in finding the true position

say you have a hole that is 3.0mm on your X axis
and 5.0mm on your Y axis
and you have a tolerance of say .3mm for your true postion

what would be the formula to find this ?
Assuming the X and Y are basic dimensions, using the amount X and Y are out the formula as is follows. 2 * SGRT( X to the 2 + Y to the 2)  Reply With Quote

4. The measured location must fall within a circle with a radius of .3 mm centered at x = 3 and y = 5.

If Ym and Xm are the measured data, the formula is:

error = Sqrt((Ym - 5)**2 + (Xm - 3)**2), must be < .3  Reply With Quote

5. I am not sure of Kip's formula (**2?) I do understand Kip is using actual vs nominal, below is finding vs finding.
This is the actual formula:
2*sqrt(x^2 + Y^2)
"^2" is the term squared
Example; 2*sqrt(.0084^2 + .0020^2) = .0173 (.01727)

This can be confirmed via this online calculator:
http://www.engineersedge.com/calcula...sition_pop.htm

HTH   Reply With Quote

6. whoah, old school geeks   Reply With Quote

7. I was just passing by and caught this old post and thought I could help.   Reply With Quote

8. lol I didn't even notice the date. just thought it was kinda cool

And Welcome, pull up a stool and stick around   Reply With Quote

9. ## True Position CMM

well, this thread is old and probably retired, but maybe someone out here will catch it. I am having almost the same issue as the opening thread, but with a twist. I have a true position call out to a slot to A-B-C. Slot length is 7.6mm and width is 6.6mm. Now the twisty part, I actually have 2 TP call outs on the print, 1 to each of the dimensions to .5mm A-B-C. How do I TP a dimension on a CMM.
thx much.  Reply With Quote  Reply With Quote

11. ## not looking for the formula to calculate True position, i got that. I just want to know if its possible to call out TP on a "dimension". How do i tell my cmm to go to a number?  Reply With Quote

12. Originally Posted by GeekyEasyRider not looking for the formula to calculate True position, i got that. I just want to know if its possible to call out TP on a "dimension". How do i tell my cmm to go to a number?
Passing by again. Yes this is a legal callout, the TP is measured from the centroid of the width (a dimension) and again centroid of the length (a dimension).
The centroid of each may or may not fall within the same exact number but by perfect nominals it does share the same centroid.  Reply With Quote

13.   Reply With Quote

14. Originally Posted by QC Rick I am not sure of Kip's formula (**2?) I do understand Kip is using actual vs nominal, below is finding vs finding.
This is the actual formula:
2*sqrt(x^2 + Y^2)
"^2" is the term squared
Example; 2*sqrt(.0084^2 + .0020^2) = .0173 (.01727)

This can be confirmed via this online calculator:
http://www.engineersedge.com/calcula...sition_pop.htm

HTH Hello QC Rick, I understand how to calculate the true position as you explained above, but how does MMC factor in to that? Is there an additional calculation you have to make to get true position @ MMC? Thanks.  Reply With Quote

15.   Reply With Quote

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