[Ro...] Posted September 10, 2020 Share Posted September 10, 2020 Good Morning Guys, I want to calculate the true position for the image below, I've circled it. The way I go about it is I get datum A as Z axis ,B as Y axis and C X axis using them as a plane. Now for the true position I use X as 13.705 and Y as 67 and Z as 0 and use the 6 dia circle on the slot as the feature on which it has to calculate it for Is there something I am missing here or can there be another way to to it. We are having issues with our dimensional reports. Thank You in advanceCapture.JPG Link to comment Share on other sites More sharing options...
[Jo...] Posted September 10, 2020 Share Posted September 10, 2020 IMO that's a terrible Datum precedence, I would rather have A-C-B , to be more stable. I suspect Datum B could have projected error when using it to stop rotation. Make another Position Characteristic using A-C-B and see how it correlates. If Datum B is not square , using it as tertiary will effectively be the ot point, or maximum Link to comment Share on other sites More sharing options...
[Am...] Posted September 10, 2020 Share Posted September 10, 2020 Also just want to point out the drawing does have Datum targets if you aren't already considering those when creating your Datums. Link to comment Share on other sites More sharing options...
[Ro...] Posted September 10, 2020 Author Share Posted September 10, 2020 Please sign in to view this quote. Hello John, Thank you for the suggestion, I will change and how it would effects the dimensional layout. Link to comment Share on other sites More sharing options...
[Ro...] Posted September 10, 2020 Author Share Posted September 10, 2020 Please sign in to view this quote. Amel, If I am not wrong you are talking about Datum A correct?? If so, I haven't and thank you for pointing that out. Link to comment Share on other sites More sharing options...
[Am...] Posted September 10, 2020 Share Posted September 10, 2020 Please sign in to view this quote. Yeah Datum a is the only one. Link to comment Share on other sites More sharing options...
[Br...] Posted September 11, 2020 Share Posted September 11, 2020 Whats Odd is you have Datum C applied to two separate datum features. I guess you could make a center line that passes through both widths and call that datum feature C. Hard to say what the designer meant. It's not right though. The other thing is that the position tolerance is not applied to a diameter so I'm unsure why you would be using that. It's applied to the 6mm width of the slot. It's a non cylindrical feature of size. Thats why you don't see a diameter symbol in the feature control frame. The True Position is just a basic zero centered on Datum C and oriented to datums A and B. Link to comment Share on other sites More sharing options...
[Jo...] Posted September 11, 2020 Share Posted September 11, 2020 Please sign in to view this quote. I took Datum C to be a symmetry plane of those two features, because of its location. Inline with dimension is between, and it would be one surface if denoted on one leader line... Link to comment Share on other sites More sharing options...
[Ro...] Posted September 14, 2020 Author Share Posted September 14, 2020 Please sign in to view this quote. Hi Brett, Thank you for the input and I was thinking the same thing that it's not a true pos of the circle but the width itself, but wouldn't the center point of the circle be the basic zero for the slot as well? And about Datum C that's kinda confusing I will what you and John suggested and see what I get. Link to comment Share on other sites More sharing options...
[Da...] Posted September 14, 2020 Share Posted September 14, 2020 Please sign in to view this quote. I think he is using the dia. because there is a linear of 67 to datum -B-. I agree this is an odd call out but that linear has to be included, so I interpret this as perp. to -A-, linear from -B- and centered on -C-. It should have the dia symbol on it. Link to comment Share on other sites More sharing options...
[Br...] Posted September 14, 2020 Share Posted September 14, 2020 Please sign in to view this quote. It would in one direction. But the tolerance zones have different shapes and the features that are being controlled by the tolerance are different. On one hand you would have a width feature where a centerplane is produced by an unrelated actual mating envelope(UAME). This centerplane must not violate a the MMC boundary that exists at the True position. The boundary is the same shape as the flats of the slot and is 5.7mm wide. On the other had you have a diameter where the axis must lie within a 0.3 boundary. If you assume the diameter symbol was intended, now you have cylindrical boundary that is 5.7mm in diameter. Because the diameter is open ended, it could be displaced in one direction into infinity and never violate the boundary. This is why you never apply a position tolerance to a radius. It's also prohibited by Y14.5. Position tolerances must be applied to features of size. a radius is not by definition a feature of size. trying to get the CMM to measure a radius and project the missing portion into a full diameter, then find the position of that can be problematic. This might be your issue. Just looking at this drawing the way its drawn though explicitly applies a position tolerance to a width feature, not the end radii of the slot. Theres no reason to assume thats what should be measured here regardless if you find an extra basic dimension floating around in there. I would stick with the width feature. It will be a more reproducible measurement and it is literally what the print is defining. Link to comment Share on other sites More sharing options...
Recommended Posts
Please sign in to comment
You will be able to leave a comment after signing in