Profile Doubling?

[Peter Warcholyk]

Good Morning,

Normally speaking, when I have profile callouts, they are a bilateral tolerance and usually referenced to a datum.

I typically use vector points, snap on, and then report out dimension location with the "t" values.

I have been informed that some of our suppliers are applying a doubling to their results. I don't understand at all how this would work.

Can anyone explain?? Preferably with diagrams. Where and why would you use this?

Thanks in advance!

ZydecoPete

[Matthew D. Hoedeman]

Good Morning,

Normally speaking, when I have profile callouts, they are a bilateral tolerance and usually referenced to a datum.

I typically use vector points, snap on, and then report out dimension location with the "t" values.

I have been informed that some of our suppliers are applying a doubling to their results. I don't understand at all how this would work.

Can anyone explain?? Preferably with diagrams. Where and why would you use this?

Thanks in advance!

ZydecoPete

OKAY, by doubling the worst reading, you are telling them WHAT the minimum profile tolerance NEEDS to be in order for the part to be in tolerance. Think of it as TP for a vector point, TP is reported as a diameter, which is DOUBLE the radial amount the hole is off while "T" it the radial amount the vector point os off. It is NOT telling them WHAT the profile is, only what the MINIMUM REQUIRED tolerance would be (used as an equal +/- of 1/2 the total).

[Sean Harris]

What you report when you give a T value is deviation from nominal. A bilateral Profile is a zone that is equally distributed from nominal on both the + and - side. By taking the worst T value and doubling it you establish the size of the zone.

[JamesMannes]

OKAY, by doubling the worst reading, you are telling them WHAT the minimum profile tolerance NEEDS to be in order for the part to be in tolerance. Think of it as TP for a vector point, TP is reported as a diameter, which is DOUBLE the radial amount the hole is off while "T" it the radial amount the vector point os off. It is NOT telling them WHAT the profile is, only what the MINIMUM REQUIRED tolerance would be (used as an equal +/- of 1/2 the total).

I really liked your explanantion of this Matt. I saw it in another post and thought it was a very clear way of describing what is being shown. Thank you Forum Hoe.

[JoeRZ]

Doubling the profile or worst deviation from nominal does not tell you how to fix the discrepant area whether it's on the plus or minus side of target. I don't get that neither, some people will argue though.

[craiger_ny]

It is because the folks that make the parts are not the only ones you report the condition to. No it does not make sense to tell the guy who made the part his VME if he needs to make an adjustment. However, when you report double the deviation to an engineer that has to disposition a part you are reporting the tolerance zone the part occupies which is exactly what s/he needs to know, that is why profile was specified in the first place. Let's not forget there are many people that get reports on the condition of parts. You need to report in a maner that is helpful to the individual it is being reported to. It might not make sense to you but that does not mean it does not make sense at all. Anyone who has had to remeasure a part so it gets reported in a manner that is understandable to the one who receives the information knows what I am talking about. The best inspectors are the helpful ones, they are the ones that anticipate what info the machinists needs and what info the engineer needs. That comes from experience. Inspectors are underappreciated as it is. Tell the guy you are giving info to that what he is asking for does not make sense to you therefore it does not make sense at all and see how much less you are appreciated.

Craig

[Sean Harris]

Joe, you are correct. Thats why you have to report the T value OR a Graphical analysis. The Profile number in itself is basically useless for manufacturing. Just like the True Position value, by itself, will not tell you what you need to move to fix a part. The measurement needs to be evaluated in a little more depth to be of value to the machinists.

[Jan d.]

Not much to add.

Just that the XactMeasure GD&T for profile in V4.1 works VERY WELL (no need for T). Except, be very careful with the results, see the attached thread for that.

http://www.pcdmisforum.com/showthread.php?t=2210&highlight=profile

I report the MIN and the MAX, because this is useful to the machinists. Then I find the largest number of those 2 (do some variable manipulations), take the absolute value and double it. That is what I report into our formal SPC system (which is correct, but (in my humble opinion) useless information).


Jan.