Understanding True position - Drawing Feature Control Frames - ANSI Y14.5

[kcmomde]

Need help understanding true position. Earlier this year my company laid off the majority of our workforce, so now the rest of us are trying to help out other areas the best we can when the need arises. Just so happens that we no longer have an inspector, so I have been asked to help fill in. I have done a little bit of inspection in the past (20 years ago), but I just can't seem to understand what I'm supposed to do measurement wise when there is a true position called out in a feature control frame on a drawing. I've read ANSI Y14.5 and I know the definitions, but applying what I've read for some reason is not sinking in. For example, just a basic feature control frame that shows the true position symbol, then a number, let's say .002 and then has a datum feature "A". What am I going to be measuring?

 

[Vicman]

kcmomde

There is a need of a formal training for you, or the individual that's going to make the inspections.
There are several sources in the US, search and you will find one, I teach GD&T in Tijuana Mexico.
What you are talking in your post is basic for someone with this proper knowledge but not so, for someone without it.
There is always the need to see the drawing in order to give you an advice.
I hope this helps.

 

[Umang Vidyarthi]

Need help understanding true position. Earlier this year my company laid off the majority of our workforce, so now the rest of us are trying to help out other areas the best we can when the need arises. Just so happens that we no longer have an inspector, so I have been asked to help fill in. I have done a little bit of inspection in the past (20 years ago), but I just can't seem to understand what I'm supposed to do measurement wise when there is a true position called out in a feature control frame on a drawing. I've read ANSI Y14.5 and I know the definitions, but applying what I've read for some reason is not sinking in. For example, just a basic feature control frame that shows the true position symbol, then a number, let's say .002 and then has a datum feature "A". What am I going to be measuring?

Here is a good article "Exposing the myth of True Position" by Richard Clark. This will give you a fair idea on your querry.

Here is a Free 'True position calculator'

Google 'GD&T free tutorials' and you will find many to choose from. Good luck.

Umang

 

[Kales Veggie]

Need help understanding true position. Earlier this year my company laid off the majority of our workforce, so now the rest of us are trying to help out other areas the best we can when the need arises. Just so happens that we no longer have an inspector, so I have been asked to help fill in. I have done a little bit of inspection in the past (20 years ago), but I just can't seem to understand what I'm supposed to do measurement wise when there is a true position called out in a feature control frame on a drawing. I've read ANSI Y14.5 and I know the definitions, but applying what I've read for some reason is not sinking in. For example, just a basic feature control frame that shows the true position symbol, then a number, let's say .002 and then has a datum feature "A". What am I going to be measuring?

Some one did this before at your company, so there should be a gage somewhere, I would think.

Two ways:

1) attribute gauge (usually a gauge that has been designed using the datum feature and the characteristic you try to measure (an example is a bold hole pattern on a bearing outer ring using the ring OD as the datum)

2) variable gauge (usually a CMM style piece of equipment)

Measuring true position by hand accurately is difficult and time consuming nope

 

[kcmomde]

Thanks for the help. Of course there's no time or money for formal training. I'm just going to have to get one of these engineer's to give me a quick run down on what I need to do. From what you provided, plus some of the other tutorials I've found and then getting one of those engineer's to help, well I should be able to tackle most of the inspections.

 

[Stijloor]

Thanks for the help. Of course there's no time or money for formal training. I'm just going to have to get one of these engineer's to give me a quick run down on what I need to do. From what you provided, plus some of the other tutorials I've found and then getting one of those engineer's to help, well I should be able to tackle most of the inspections.

Please come back if you need more help.

I don't know if you've been on this site?

Good luck!

Stijloor.