Tolerance zone from respective datums

[thecadman2]

Please help! I’m new to GD&T and very confused the resulting tolerance zone from the referenced datum planes.

Let me try and explain: When you set up your datum’s to immobilize your part I get. I also get the many examples shown of a rectangular block (or square sided objects) with front, side and hole used to set up your datum referencing system. What I don’t get is when your reference places are not parallel or perpendicular to the tolerance feature what effect does this have on the resulting tolerance zone. I have attached an example of what I mean. Do your datum’s produce directions??

I have a copy of ASME and spent hours on the internet to try and grasp the concept…I hope you understand my explanation. Thanks

 

[drawoh]

thecadman2,

In ASME Y14.5M-1994, check out Figure[ ]4-4.

JHG

 

[thecadman2]

I have looked at this and read 4.4.1.1 but still don't grasp it. Ok on Figure 4.4 if the position feature only referenced C would that mean the hole position zone at MMC would be 0.1 + and - (2 positions) in the direction perpendicular to datum face C? Please look at my new example.

I'm also looking at drawings with datum faces on compound angles to the respective feature and its confusing the hell out of me. Maybe I'm looking to deep into it or being stupid!

 

[axym]

thecadman2,

Don't worry, you're not looking too deep into it or being stupid. Inclined datum features are tricky for a lot of people. But it looks like there are a couple of basic GD&T concepts that you need to review before trying to deal with inclined datum features. This would include how Position tolerances work and what features they apply to, and how datum reference frames are created from datum feature simulators.

Do you have any GD&T books or resources other than the ASME Y14.5 standard? It's very difficult to figure out GD&T on your own with just the ASME Y14.5 standard and internet resources.

Evan Janeshewski

Axymetrix Quality Engineering Inc.

http://www.axymetrix.ca