How to measure positional tolerance without CMM? 2

[AutoMeterman34]

What is the best way to measure/inspect a positional tolerance of a circular magnet? For instance... Position Tolerance .002 |A|B|.... Datum A is outer diameter (ø0.512), Datum B is flat surface.. Thickness of magnet is .130 and Thru hole at the center of the magnet is ø0.033 this is where the Position tolerance is called out. Please Help I hope I have included all the necessary information.

 

[dgallup]

If the tolerance is constructed properly with MMC it is possible to make a functional gauge. This is frequently the preferred way to measure production as it is fast, cheap and simple. However, it does not give you any quantifiable data, just attribute data. It is not practical for very small tolerances either.

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The Help for this program was created in Windows Help format, which depends on a feature that isn't included in this version of Windows.

 

[AutoMeterman34]

dgallup thanks for the advise I will take that into consideration. But I really need quantifiable data as this is a 1st piece sample that needs dimensional approval.

 

[dingy2]

No CMM? Need data for ISIR? I know that what I say will be tough but you can do it with a height gauge, indicator and great math to figure out the diametrical tolerance zone but it would be at best, provide a 60 - 70% confidence level in the result. Today, there aren't too many people skilled in using older measuring tools. Good Luck!!!!

Dave D.

http://www.qmsi.ca

 

[MechNorth]

First, a terminology correction. You are given the positional tolerance on the drawing. You want to find your positional error.

Assuming basic abilities & equipment in benchtop / open setup metrology:
1) Put magnet into a collet, holding on the datum feature diameter. Put collet in holder on a stand or lathe chuck. The axis of the collet simulates the datum axis of the datum feature (diameter)
2) Find the largest gage pin that will fit into the hole; put it through the hole
3) Using a deflection probe, master your indicator vertically at the axis of the collet
4) Probe the top of the pin and subtract half of the pin diameter. Record this as your delta-Y
5) master your indicator horizontally at the axis of the collet
6) probe the right side of the pin and subtract half the pin diameter. Record this as your delta-X
7) Use the pythagorean theorem to establish the radial error of the position of the hole.
8) Double the radial error to get the diametral error, which is your positional error.

Hope that helps.

Jim Sykes, P.Eng, GDTP-S
Profile Services

http://www.profileservices.ca

TecEase, Inc.

http://www.tec-ease.com

 

[btrueblood]

Jim's method works as long as there is no significant off-axis error of the hole relative to the datum axis. If there is an off-axis error, then the apparent positional error is magnified by how far out along the gage pin you place the gage pin (the indicator is effectively measuring a projected positional tolerance). You can back into that non-axial error by measing in two places along the pin and extrapolating back to the hole.

 

[AutoMeterman34]

NMechNorth thanks for the information this worked!

 

[MechNorth]

Gave you a star for that, BTB. I figured for a thin magnet the projection would be minimal, but it is good to point it out.

Jim Sykes, P.Eng, GDTP-S
Profile Services

http://www.profileservices.ca

TecEase, Inc.

http://www.tec-ease.com