Thank you for the video. I think for the last example "deviated .018" should be "deviated .020" according to formula that resulted .030 total deviation.
Jason, this is one of the most common questions I encounter in GD&T. Thank you for discussing it. I have a request though, by any chance could you follow up by explaining WHY The formula you mentioned is used to report unequally disposed profile. I assume it is to provide an absolute, positive result. Also, could you explain why the result is ultimately not doubled, since the 2X is canceled out by the /2, whereas you suggest the result for bilateral profile is doubled? The reporting and computation of position and profile is an area that I feel the Y14.5 standard could be more clear about, and I field a ton of questions on both.
That's a great idea for a follow up video. For those wondering, we use this equation because we need a singular value that we can compare to the allowed tolerance value from the FCF. If we simply reported "high to low" or the most deviated point and its absolute value from nominal, we would not be taking into account WHERE our allowed tolerance is at and might accidently report a value that is less than our allowed tolerance but clearly outside the tolerance zone. As you mentioned, when we consider normal profile measurements, we find the most deviated point from nominal and double it (as mentioned at the beginning of this video in the first example) This doubling still occurs in the unequal equation but its taken with respect to the center of the tolerance zone and not necessarily the "nominal". The 2x does not cancel out the /2 but rather the /2 redistributes the tolerance to be centered on offset the zone. This is a tricky topic, hope this helps!
For the unequal example, if you had a measured high of +.001 over nominal and a measured low of -.001 under nominal, you end up reporting a higher deviation than if the measured values were +.010 and -.000. It seems like this reporting method is favoring the middle of the tolerance zone over favoring the nominal. Also, when the "uneven" modifier is applied, how do you decide which direction to apply the uneven tolerance zone? Is it driven by the basic dimension applied to the feature?
You are absolutely correct when you say that the reporting method is favoring the middle of the tolerance zone. And that's exactly how it should work. Lets imagine a part that is .030 unequally disposed .030 instead of our example that is disposed .020. In this new example our "nominal" is at the very edge of allowed tolerance, any deviation in one direction immediately results in a failed part. So if the machinist targets the center of the zone, rather than nominal, they have a much higher chance of producing a passing part. For the uneven modifier the value that follows the symbol is the amount of tolerance that exists outside the part. Check out this article. www.gdandtbasics.com/unequally-disposed-profile/
Thank you for the video.
I think for the last example "deviated .018" should be "deviated .020" according to formula that resulted .030 total deviation.
Jason, this is one of the most common questions I encounter in GD&T. Thank you for discussing it.
I have a request though, by any chance could you follow up by explaining WHY The formula you mentioned is used to report unequally disposed profile. I assume it is to provide an absolute, positive result. Also, could you explain why the result is ultimately not doubled, since the 2X is canceled out by the /2, whereas you suggest the result for bilateral profile is doubled?
The reporting and computation of position and profile is an area that I feel the Y14.5 standard could be more clear about, and I field a ton of questions on both.
That's a great idea for a follow up video. For those wondering, we use this equation because we need a singular value that we can compare to the allowed tolerance value from the FCF. If we simply reported "high to low" or the most deviated point and its absolute value from nominal, we would not be taking into account WHERE our allowed tolerance is at and might accidently report a value that is less than our allowed tolerance but clearly outside the tolerance zone.
As you mentioned, when we consider normal profile measurements, we find the most deviated point from nominal and double it (as mentioned at the beginning of this video in the first example) This doubling still occurs in the unequal equation but its taken with respect to the center of the tolerance zone and not necessarily the "nominal". The 2x does not cancel out the /2 but rather the /2 redistributes the tolerance to be centered on offset the zone. This is a tricky topic, hope this helps!
@@Gdandtbasics That is a terrific and clear explanation. Thank you.
For the unequal example, if you had a measured high of +.001 over nominal and a measured low of -.001 under nominal, you end up reporting a higher deviation than if the measured values were +.010 and -.000. It seems like this reporting method is favoring the middle of the tolerance zone over favoring the nominal.
Also, when the "uneven" modifier is applied, how do you decide which direction to apply the uneven tolerance zone? Is it driven by the basic dimension applied to the feature?
You are absolutely correct when you say that the reporting method is favoring the middle of the tolerance zone. And that's exactly how it should work. Lets imagine a part that is .030 unequally disposed .030 instead of our example that is disposed .020. In this new example our "nominal" is at the very edge of allowed tolerance, any deviation in one direction immediately results in a failed part. So if the machinist targets the center of the zone, rather than nominal, they have a much higher chance of producing a passing part.
For the uneven modifier the value that follows the symbol is the amount of tolerance that exists outside the part. Check out this article. www.gdandtbasics.com/unequally-disposed-profile/