## Formula to calculate actual positional tolerance error

## Formula to calculate actual positional tolerance error

(OP)

Hello all.

I have a question regarding ASME GD& T and I will be thankful to all who respond.

The question is

Mathematically, in Cartesian Co-ordinate system, the formula to calculate the actual positional error is given is 2 sqrt delta x^2 + dlta y^. We find actual values of x and y, then find the difference from relative basic dimensions and calculate positional error.

Does any formula exists when we talk about polar coordinates having basic PCD and angle for locating a perfect position of a pattern of holes wrt appropriate datum feature references.

Thank you all

Best regards

I have a question regarding ASME GD& T and I will be thankful to all who respond.

The question is

Mathematically, in Cartesian Co-ordinate system, the formula to calculate the actual positional error is given is 2 sqrt delta x^2 + dlta y^. We find actual values of x and y, then find the difference from relative basic dimensions and calculate positional error.

Does any formula exists when we talk about polar coordinates having basic PCD and angle for locating a perfect position of a pattern of holes wrt appropriate datum feature references.

Thank you all

Best regards

## RE: Formula to calculate actual positional tolerance error

"Wildfires are dangerous, hard to control, and economically catastrophic."

Ben Loosli

## RE: Formula to calculate actual positional tolerance error

## RE: Formula to calculate actual positional tolerance error

Am i right in my understanding?

## RE: Formula to calculate actual positional tolerance error

## RE: Formula to calculate actual positional tolerance error

Evan Janeshewski

Axymetrix Quality Engineering Inc.

www.axymetrix.ca

## RE: Formula to calculate actual positional tolerance error

Still have no idea what they want and suddenly no longer care.

## RE: Formula to calculate actual positional tolerance error

I would suggest providing a figure or example which displays what you're inquiring about, otherwise I'm not sure what more help can be provided. Though perhaps someone better than I can decipher your question.

## RE: Formula to calculate actual positional tolerance error

Assuming alpha is the angle between Y axis and the line passing through the true position of particular hole and the datum axis, and R is the radius of the "pitch" circle, then:

x = R*sin(alpha)

y = R*cos(alpha)

## RE: Formula to calculate actual positional tolerance error

You may be right, the way I initially read it I thought the question was how to convert rectangular to polar - now that I re-read it may be the other way around.

Beyond that I'm with 3DDave I'm not really clear on whats being asked.

## RE: Formula to calculate actual positional tolerance error

I have worked it out.

http://home.eol.ca/~hgibson/tolerances/#x1-160003....

Note how the tolerances gets more accurate as your pitch circle gets bigger.

--

JHG

## RE: Formula to calculate actual positional tolerance error

My question was does the formula to calculate the actual positional error of the considered holes in Cartesian coordinates is also applicable to cylindrical flange having a pattern of holes at basic Bolt circle and basic angle wrt to DRF. If yes then how to find actual x and actual y?

## RE: Formula to calculate actual positional tolerance error

## RE: Formula to calculate actual positional tolerance error

In regards to cartesian vs. polar they are just methods of referencing coordinates in two different systems - they are interchangeable and can be converted from one to another. Their use usually depends on what is most useful/intuitive to utilize for the referenced shape, pattern, or mathematical function.

You have referred to basic dimensions - this is just a means of defining true position (or true profile), it does not somehow fix the coordinate system to be utilized. If these dimensions have been specified as a pitch circle and angle they can be easily converted to (x,y) rectangular coordinates and back again using the standard equations previously provided. A formula for calculating position tolerance in either coordinate system can then be used.

## RE: Formula to calculate actual positional tolerance error

## RE: Formula to calculate actual positional tolerance error

The position tolerance is exactly as specified - 8x cylinders of size 0.14@MMC (and of size 0.14+0.2=0.34@LMC due to bonus tolerance).

This suggests a measured feature or pattern of features, which your referenced figure 3-29 does not have (not sure than any do - perhaps you'd have to draw from an external reference/textbook example or create your own). Unless the DRF is fully constrained, this will require some sort of fitting method, this was discussed not too long ago in a thread https://www.eng-tips.com/viewthread.cfm?qid=445857 perhaps that would be an interesting read.