Modifiers in GD&T
Modifiers in GD&T
(OP)
When we give MMC or LMC modifier in any position tolerance in GD&T, what will be the applicable tolerance of the feature when part is not made on MMC
INTELLIGENT WORK FORUMS
FOR ENGINEERING PROFESSIONALS Come Join Us!Are you an
Engineering professional? Join Eng-Tips Forums!
*Eng-Tips's functionality depends on members receiving e-mail. By joining you are opting in to receive e-mail. Posting GuidelinesJobs |
|
RE: Modifiers in GD&T
RE: Modifiers in GD&T
RE: Modifiers in GD&T
John Acosta, GDTP Senior Level
Manufacturing Engineering Tech
SSG, U.S. Army
Taji, Iraq OIF II
RE: Modifiers in GD&T
Can be “otherwise”?
Departure from MMC to where if it is not “LMC”?
If the feature departs from the MMC toward “the other boundary” (lets stay in the Y14.5 terms and call it virtual boundary) then the feature is non-conforming already, by violating its size requirements.
Am I right?
You might say, “ Yeehh, but you don’t know that!!” You will find it later if you are measuring the size (and you should).
RE: Modifiers in GD&T
If you call your feature up at MMC, the least material condition is allowed to have a significant positional error. Is this a valid LMC condition?
I like to user zero positional error at MMC. This means that the MMC outline must not be violated. The measurement below MMC is your positional tolerance.
--
JHG
RE: Modifiers in GD&T
I agree! But that would be valid if you can "afford" the size tolerance increase. (like if you assembly something with clearance).
RE: Modifiers in GD&T
Which is probably the main application for Position with MMC so reasonable initial stance.
What is Engineering anyway: FAQ1088-1484: In layman terms, what is "engineering"?
RE: Modifiers in GD&T
Yes it is, but also could be used to maintain the minimum clearance. Don’t you agree?
RE: Modifiers in GD&T
Main place I'll use LMC is in patterns of holes for mass reduction or air flow or similar.
What is Engineering anyway: FAQ1088-1484: In layman terms, what is "engineering"?
RE: Modifiers in GD&T
When people try to explain logic behind position tolerance specified at MMC (or LMC) something like this can be very often heard/read: "When the size of the feature departs from MMC (or LMC), additonal tolerance (bonus) is available..." so on and so forth.
But what size exactly are we talking about? Would someone like to clarify?
RE: Modifiers in GD&T
RE: Modifiers in GD&T
Imagine two external features that are adjacent to one another (two buttons on a keyboard) and the minimum edge distance between them must be maintained. MMC would be the correct modifier to use.
See page 229 (Bryan Fischer book)- Tolerance stackup
RE: Modifiers in GD&T
What about feature of size controlled by position tolerance at LMC? Size of what should be used to calculate bonus?
RE: Modifiers in GD&T
It's not the local size and it is not the actual mating envelope, it is the unrelated actual minimum material envelope. When that envelope departs from the LMC size, you have more material to work with and therefore can physically and by design permit more tolerance.
RE: Modifiers in GD&T
RE: Modifiers in GD&T
RE: Modifiers in GD&T
RE: Modifiers in GD&T
What is Engineering anyway: FAQ1088-1484: In layman terms, what is "engineering"?
RE: Modifiers in GD&T
John Acosta, GDTP Senior Level
Manufacturing Engineering Tech
SSG, U.S. Army
Taji, Iraq OIF II