Basic Dimensions and How to Record on an Inspection Report

[@baptistpope]

I agree with your explanation, however, I think it inadvertently exposes a gap in GD&T for true position and diameters. If only the deviation is reported, then I can't tell which direction relative to the datums the hole has drifted. This has been a problem for me when trying to determine if a part can still be used. For this reason, I would prefer the distance from the datums be reported. It tends to be the same as the basic dimensions. So, why not put on basics that would guide the inspector on how to report the deviation and the direction from the datums?

[@Gdandtbasics]

This is a great question Thomas. We created another video recently that highlights the issues with reporting basic dimensions. We completely agree with you that simply reporting the total diametric deviation leaves the shop floor lost as far as error mitigation. Reporting a simple 2D coordinate measurement leaves a lot of assumptions to be made on how to get closer to a "perfect" part. So we highly encourage more information to be included when reporting the total diametric deviation. Many software will allow you to report visuals or give additional 3D information that supports the total diametric deviation and its extreme locations or orientations to help define the "direction" of error.

[@jon-williammurphy9780]

One way is to have the part laser scanned and compared to the CAD, that'll show exactly what's going on

[@johns5213]

Thanks you for clear explanation.

[@Gdandtbasics]

You are welcome!

[@surajghogale]

Excellent explanation

[@bobprazak]

9:25 it does matter a lot whether it is 3rd or 1st angle projection; if it was 3rd angle, all the depiction would be pointless; I have commented on this issue in your previous videos

[@tomgeiss5777]

Yes this is a first angle projection.

[@jerryyang2202]

One question on the median plane, how can we measure the median plane ? since it's an virtual plane, the only way to determine the median plane is by using CMM?

[@Gdandtbasics]

Using a CMM is not necessary but it is a solution. If we don't have a CMM we can simply place a best fit gage block inside this width feature and measure to one side of the block, and subtract/add half the size of the gage block. This would be the location of the midplane.

[@jerryyang2202]

thanks for the great answer @@Gdandtbasics

[@Shannon_Robbie]

How do you read depth or hidden lines on these prints for drilling depths?

[@Gdandtbasics]

When a depth is shown on a drawing for a blind hole, the measured depth must only include the full usable diameter.

[@tommywiseguy]

What if the source inspector insists that actual dims be reported? I had one SI say having these values allows him to confirm the position calculation. Ultimately, if he doesn’t sign off, everything comes to a grinding halt.

[@richp5060]

We have the same issue. I's a basic dimension people.

[@kitkitpig]

Hi guys, so it means the tolerance should be 0.05mm for dimension 30?

[@Gdandtbasics]

The 30mm basic dimension does not have a tolerance, it only helps us identify where the hole NEEDS to be and the 0.1 mm position tolerance tells us the diametric zone that it needs to be within. So each hole can deviate in position, from its ideal spot, radially 0.05mm. This would essentially mean that the maximum distance that 30mm could ever be would be 30.1mm and the minimum would be 29.9mm

[@davidnguyen2246]

Hi Can you make an assembly and show me how to come up with the tolerances and where to put the symbols? Thanks

[@Gdandtbasics]

Hello David, Thank you for your comment. If you are seeking some more detailed explanations and detailed reviews of specific drawings and situations, please consider joining our online courses. We review many of these items in our courses - but included with online access, as a student you will also gain access to our weekly webinars where you can interact directly with our instructors, ask questions, and provide suggestions for future webinar discussions. Check out our online course information on our website: www.gdandtbasics.com/gdt-training/ Thanks, Your GD&T Basics Team

[@lastwisdom984]

Hi , Thanks For the clear explanation can you make a video on the datum reference

[@srinivasanvivekanandhan8366]

😢Ii😮iui😢😢i

[@johnvmachado]

You did not demonstrate how to calculate the deviation from the true position.