MMC mod on countersunk hole position
MMC mod on countersunk hole position
(OP)
I recently reviewed a drawing that used the MMC modifier on the position of several countersunk holes.
It seems to me that the corresponding fastner will tend to self-center in the countersink, thus rendering the MMC modifier usless. It just creates more clearance around the fastener shank, but the assembly can't take advantage of the increased hole size because of the centering effect.
Am I missing something?
It seems to me that the corresponding fastner will tend to self-center in the countersink, thus rendering the MMC modifier usless. It just creates more clearance around the fastener shank, but the assembly can't take advantage of the increased hole size because of the centering effect.
Am I missing something?





RE: MMC mod on countersunk hole position
The point being that the designer probably does care about clearance and fit for the fastener and thru-bore. Depending on how flexible the fastener is, & how many other fasteners are being tightened "simultaneously", the head may or may not "center" on the csink, it may (and usually will) only contact along one side.
RE: MMC mod on countersunk hole position
As an aside, unless separated out at the hole callout, both the hole and countersink (or counterbore) default to the same geometric control block.
RE: MMC mod on countersunk hole position
While I agree that contact will not be uniform, I still don't see that MMC gains anything. At some point there will be thru hole clearance that is not usable by the fastener.
Seems like the countersunk holes should be RFS, and the holes in the mating part MMC.
RE: MMC mod on countersunk hole position
RE: MMC mod on countersunk hole position
No need for an appology. It's been a long time since I actually designed parts for a living, and when I did the companies I worked for didn't make use of GD&T principles, so I'm not as up-to-speed with the concepts as I would like to be.
I hope this forum becomes an active one, seems like a lot to learn here.
RE: MMC mod on countersunk hole position
RE: MMC mod on countersunk hole position
Good explanation. That deserves a star!
RE: MMC mod on countersunk hole position
Tunalover