INSPECTING RUNOUT HAVING AS DATUM A PATTERN OF HOLES

[roberto1brazil]

Hello everybody.
Please, I need your help. I have attached the main features of a part and its hard gauge to inspect the runout of internal diameter and having as datum a pattern of holes. I know that is possible to inspect it making use of a CMM machine, but we are interested on developing a hard gauge to this issue. I have design the basic dimensions and geometrics features of the hard gauge based on part dimensional and geometric features. Would it be possible to tell me if the hard gauge would meet the inspection of the runout of the part? Should it be better to include the symbol of MMC (M) in the frame of position on the gauge? Please, feel free for any comments or criticism. Thanks a lot for any help.
NOTES
- The internal diameter “E” of the gauge was introduced in order to make easier the setup (center) of gauge in the rotary table.
- Dimensions in millimeters.
Regards
Roberto

 

[CheckerHater]

By definition

"Runout is a tolerance used to control the functional relationship of one or more features to a datum axis established from a datum feature specifies at RMB"

Hence runout cannot be established wrt feature(s) at MMB and cannot be checked by "hard gage".


"For every expert there is an equal and opposite expert"
Arthur C. Clarke Profiles of the future

 

[roberto1brazil]

Hello CheckerHater!
Thanks for the information. Sorry for asking one more doubt: It means that after correcting the simbols from the drawing part 1 (see new sketch attached), we only will be able to inspect the runout by a CMM machine? In fact the original drawing had no "M" simbols in the frames. When I introduced the "M" simbols I had in mind to relax the manufacturing requirements.
Your comments are important to me.
Regards.
Roberto

 

[CheckerHater]

I understand.

If from functional standpoint it is possible to "relax" the requirements, you may not have to call it "runout" anymore.

By "functional" I mean that GD&T represents how your part works in real machine. For example, how the mounting holes are used? If they are placed over studs / bolts in "loose" manner, than you can use Position control at MMC.

The same way Position can be used for big central hole instead of Runout. If you are concerned with form of the central hole you may use Roundness or restrict it by tighter diameter tolerance.

Once again, you are the boss and only you know how the part works.


"For every expert there is an equal and opposite expert"
Arthur C. Clarke Profiles of the future

 

[roberto1brazil]

Thanks for the explanation.
I would like to complement my doubts saying that my site is located in Brazil and has received drawings from our matrix (abroad) of parts like the last one attached. Being more accurate in my descriptions, I can say that the holes in the flange are to be assembled in another part with bushes (interference) and so keeping the required concentricity between parts. I have understood that the use of MMC is not adequate to that condition. I became confused because I had received a tooling drawing from then showing pins of diameter 7,000 – 6,980 located at true position of ø 0,01 to inspect the runout. Probably the clearance generated between part and gage would result in false indication. According to what I have understood from you, it is not a good practice to indicate runout in the internal diameter having as reference the three holes (pattern). The correct way would be to check the center of internal diameter making use of position to control concentricity plus the roundness. Isn’t it? If I have insisting on this point is because the correct understanding of using GD&T is significant to me.
Thanks and regards.
Roberto

 

[CheckerHater]

Well, the most important part about runout is that it is measured about an axis. Yes, deriving axis from multiple holes is difficult, but not entirely impossible.
Now, about using RMB. It assumes some form of self-centering device.
Imagine car wheel being held by nuts with conical surfaces on them. When you tighten them, your wheel becomes oriented about an axis. Now you can check runout of the wheel.
Now, imagine the wheel hanging loosely on the studs. This is your MMB condition. Can you spin the wheel and measure runout?
This is the rough explanation, but it gives you idea why pattern of holes at MMB and runout control do not belong together.


"For every expert there is an equal and opposite expert"
Arthur C. Clarke Profiles of the future