There is no 1/10 rule of thumb for qualifying the datum features. The 1/10 rule of thumb is for the gages and fixtures (datum feature simulators) that are used at inspection.
Just like other features of the part, the datum features are controlled by tolerances to make sure they are useful for...
What about weighing and measuring the dimensions of the part and calculating the sag at the center based on that, then subtracting the deflection value from the measured total runout?
Hi Burunduk,
Thank you.
I would also expect any decent software to support all invariance classes, but I guess if GOM doesn't, it's already a red flag.
Looks like lack of correlation between software and standards... :confused:
Hi jassco,
The part is clamped against datum feature A and makes contact at either datum features D-E (with equal precedence) or B-C (also with equal precedence), because the design is symmetric. The 2 accurate holes are for pres-fitting the dowel pins that this part locates in the larger...
Hi jassco and 3DDave,
The assembly is like I described in the paragraph right beneath the image in my previous post. So it's not the entire periphery being in contact with the mating part but half of it, with the caveat that we never know which half because of the intentional symmetry and the...
Hi jassco,
I made a simplified example quick hand sketch on my phone. Sorry for the way it looks but I hope it's readable.
This rhombic part is an aluminium connector that locates two 3 mm dia. dowel pins near the acute angle corners. It mounts on the far-side flat face that was selected as...
I agree about the suggestion about datum targets. The datum targests that you define should be in the contact areas where your part mounts to immitate the mating conditions and immobilize the part relative to the origin of measurements. You can use points, lines, and areas as datum targets for...
Hi 3DDave,
That seems interesting. I visited the PC-DMIS website but I'm not sure where to look for that type of information. Could you maybe provide a link to that specific info, about fitting to a closed shape and then using datum "stand-ins" as part of establishing a datum reference frame for...
Hi, jassco,
Thank you for this info. It is helpful.
A follow up question: let's say the part's "all-around" periphery is some more complex and irregular shape that also includes some curves, and not a shape that has default best-fit alignment options in the software. According to your experience...
Hi greenimi,
Thanks, I'll check the forum you suggested and other CMM resources. But if it's OK, I'd also like to get some input from the GD&T experts here. I got an impression that many here are with strong ASME Y14.5 background and can understand the theoretical side of my question thoroughly...
Hi all.
I have what may be considered a metrology/inspection related question but since it's strongly GD&T related too I think that may be here is the best place to ask.
Consider interpretation per ASME Y14.5-2018. A part has a periphery that is some polygon. The bottom flat surface is used as...
Suppose that blind holes for location of dowel pins have a tolerance of position specified. The primary datum feature A is the functional mating surface the holes are perpendicular to (the one in which the holes were drilled).
For manual inspection without CMM, how is the primary datum being...
What is the logical or functional reason for the ASME Y14.5 rule that the datum order and material boundary conditions need to be preserved down all segments of a composite tolerance feature control frame?
