How do you calculate this...

[gms1]

We are taking some GD&T training and I asked the instructor how do you calculate this feature with 3 MMC in this feature control frame. He said he would look into it but the gist of his answer was "its non linear, let pc dmis do the calculation". I told him I want to know how its done even if it takes massive amounts of calculus or something. So, anyone have a simple answer to this?

[Del.]

Not sure what you are asking but in this case the true position must be held as ONE pattern about the datums  AEF. It cannot shift in different directions as the datums depart from MMC. In other words they cannot shift independently. 

[BenK]

At a diameter of 33.98 (MMC for the hole) you have a position of .2 to datum A, E (when at MMC) and F (when at MMC). Without knowing what E and F are you really can't answer the question.

[mkd]

MMC's add to your total tolerance. the more the merrier, with respect to holes.

 True position is calc'd with the Pythagorean formula and arithmetic for the MMC bonus.

[gms1]

Yeah E and F are holes (A is bottom of part, E is a long hole in Y and F is a hole for X). I just make that counter bore to nominal and its all good but I wanted to know what my total tolerance was with all 3 of those mmc calculated together.

[jeff]

What the heck does MMC mean?

[specv]

Yeah E and F are holes (A is bottom of part, E is a long hole in Y and F is a hole for X). I just make that counter bore to nominal and its all good but I wanted to know what my total tolerance was with all 3 of those mmc calculated together.

 

So when those datum features are at their smallest(mmc) that is the tolerance, if they are all at their largest you gain your bonus position tolerance. So you need to factor in the size of each datum hole called out to figure the bonus tolerance.

[BFleeger]

What the heck does MMC mean?

Maximum Material Condition

[crazy^millman]

What the heck does MMC mean?

 

Here is a great site to check out.

 

http://www.tec-ease.com/

[gms1]

So when those datum features are at their smallest(mmc) that is the tolerance, if they are all at their largest you gain your bonus position tolerance. So you need to factor in the size of each datum hole called out to figure the bonus tolerance.

 

Yeah I can do the calculations for mmc in the main box and mmc on 1 datum. I cannot however get that "factor in" math to add in the 3rd mmc tolerance to figure out what the actual min and max are. Like what is the maximum deviation from nominal if my hole is made at the smallest and BOTH of my datum holes are made to the smallest size?

 

Everyone keeps telling me to let the software do the calculations. Well someone wrote that software what math did they use to program pc dmis I was just curious as to how exactly its calculated.

[specv]

in order to calculate them we would need to know the size of each datum hole and the tolerance for each. an example would be if you had a +.1 size tolerance for each datum and they were at largest diameter you would gain .1 position tolerance for each feature. So in that case you would have .1 (datum E bonus) + .1 (datum F bonus) + .15 (34mm hole bonus) so you would have .55 position tolerance.

You don't get any bonus if your holes are all at the smallest size(mmc) so your deviation would be .2.

[absolute technologies]

also take note of the diameter symbol on the .2 position requirement. This means that your tolerance zone is a .2 diameter, not a .2 linear distance in either direction. For better clarification get yourself a copy of ASME Y14.5 Dimensioning and Tolerancing standard. The book has examples for just about everything

[mike93]

just make it to cad

[THEE THAINZ™]

I'd just about kill to have true position tolerances of 0.00787 MMC.