Profile Applied to Slotted Hole

[rsm7400]

Attached is a quick drawing I have for a part we are working on. With a profile of .001 applied to the .071 feature and a MMC bonus on datum A what is the min and max of my .071 feature? My interpretation was that I get a ± .0005 band around the slot. Meaning the slot can be .070 to .072 in length and .039 to .041 in width. The vertical position of the band is set by the .500 which gets a ± based upon the MMC of datum A? Is this interpreted correctly per the print?

________________________________
Ryan M
Quality Engineer
3d Printer Hobbyist

 

[chez311]

rsm7400,

Please note that your callout is applied to the datum in your FCF so it is considered Maximum Material Boundary (MMB) - this is NEVER a bonus tolerance.

When you say "what is the min and max of my .071 feature" what exactly are you asking? If it is what is the min/max SIZE of your slotted feature it is exactly as you have noted: .039/.041 wide by .070/.072 long - the MMB callout will not affect this in any way.

If it is in relation to the location of this feature - this is a slightly more nuanced question. The MMB callout allows the datum feature A to float around its Maximum Material Boundary (virtual condition of the datum feature) and effectively gets closer or further away from the slotted feature in question. Note that the slotted feature never moves in relation to the theoretical datum, only the datum feature can shift. Its a fine distinction, but an important one.

 

[Sem_D220]

I think that for your interpretation to be correct the profile FCF needs a leader to the outline of the slot and an all around symbol placed on the leader.
As it is now it looks like the FCF is related to the .071 length dimension only, which is an incorrect use of profile.

The MMB callout allows the datum feature A to float around its Maximum Material Boundary (virtual condition of the datum feature) and effectively gets closer or further away from the slotted feature in question. Note that the slotted feature never moves in relation to the theoretical datum, only the datum feature can shift. Its a fine distinction, but an important one.

'If the mountain will not come to Muhammad, then Muhammad must go to the mountain'
In this particular case, I don't think it's much different from an MMC bonus. Only that the "bonus" here is dependent on the produced size of the datum feature. This shouldn't be generalized for other cases with M modifier on the datum, though. MMB applied to datums concept needs to be treated with caution.

 

[chez311]

semiond,

You are correct, it is not much different in this particular case but the distinction is important and I'm careful to point it out every time someone brings up a question like this. Personally its just as easy to think of it in terms of only the datum feature being allowed to shift and not the controlled feature(s) and it prevents thinking of it as a bonus tolerance in those instances when the distinction is very important.

 

[Sem_D220]

chez311, I agree.

 

[rsm7400]

Thank you for your input. I realize it wasnt quite drawn correctly - that was my quick Microsoft Paint drawing of the features. It is correct on the actual print with different dimensions and tolerances.

The reason I asked these questions was for the inspection of these features. My Optical CMM takes an image of the hole and I call out the width, length, radii, position of arcs, position of center of mass etc. When all of those things are good I call the profile good. I do not apply the MMC in anyway and have not needed to use it so far - it was just a point of clarification. Typically on slotted holes I see a tight true position left to right and a looser true position top to bottom (which I think all makes sense on the how and why). I am not that used to profiles - except on dome shaped items.

Thanks again!

________________________________
Ryan M
Quality Engineer
3d Printer Hobbyist