Using LMC on true position

[[Ky...]]

The customer has a call out of .001 MMC on key position and MMC on datum A. I know it should really be LMC but my question is how do I get calypso let me use LMC on the datum A shaft. The box is grayed out.

Ket true position.PNG

[[De...]]

This was in another thread but it applies..

"Calypso can only apply 'Datum Shift' in 2D with cylindrical features. Here are a few things to keep in mind:

1) Modifiers will only be activated when the datum feature(s) are cylindrical elements and reside in the same plane as the considered feature.

2) The shape of the tolerance zone must be cylindrical.

3) Using a "Point" as a datum feature does not work in the position characteristic. If you're getting a result, either a bestfit has occurred or the base alignment is being used for the evaluation."

I would also be curious to hear your explanation as to why it should be LMC and not MMC since the drawing clearly shows MMC and really LMC is usually only used to assure minimum wall thickness.

[[Ky...]]

I may be wrong in my understanding of MMC and LMC. I thouht MMC was for Holes, where you started at the smalest holes size then gained bonus tolerance as the hole was made bigger to the top of the tolerance.
Then in my thinking (and I could be wrong) the key .471 +0 -.004 you start at the top of tolerance .471 and as you made the key smaller you would gain bonus. If I am wrong please tell me.

[[De...]]

MMC is dependent on the type of feature.

I think of it as in what state will there be the most material.

On a hole then as you say the maximum material will be when the hole is smallest diameter.

On a shaft the opposite is true, the maximum material is when the shaft is the largest diameter.

So the same applies to a keyway (slot) vs a key in the case of a keyway the maximum material is when the keyway is smallest in the case of a key the maximum material is when the key is at its high limit.

So the MMC modifier is able to be used on both male and female features alike. The 'bonus' tolerance is applied as you move away from the maximum material condition. So If this is a key then maximum material condition is at 0.471 and as it gets smaller you gain bonus tolerance because it is moving away from maximum material condition.

It helps to think of why you get MMC, it is to allow more tolerance as the components gain more clearance between them. So considering that imagine the key is at high limit - you get the least tolerance - as you make the key smaller the tolerance is increased due to the fact that the key would now be able to be more out of position and still fit in the mating keyway.


Least material condition would mean that you had .001 true position allowed when the key was smallest and you would gain tolerance as the key got bigger.This is usually only used when the intent is to control the position of something in order to maintain a minimum wall thickness.

[[Ky...]]

Well I think I am wrong but it didn't seem to make a difference. I in put MMC instead of LMC and came up with the same number. so I will use MMC like the print shows. I need to learn more about GD&T !!!

[[Ky...]]

Thank you so much for your help. I was posting my reply while you were posting your answer. So I am wrong not I think I am wrong

Again think you so much

But I still cant get the MMC to work on the Datum A cylinder.

[[Na...]]

Kyle,

Like Derek S. said " Modifiers will only be activated when the datum feature(s) are cylindrical elements and reside in the same plane as the considered feature." Is Datum A coaxial to the cylinder?

[[Ky...]]

Called Zeiss yesterday while trying to figure this out. My problem is I am still using Calypso 2016. The nice person at Zeiss told me that this problem I was having could not be done in Calypso 2016. It was fixed in Calypso 2018. Have to get IT to upgrade my software.
Thanks everyone for your help.