GD&T call out question

**Hi-Tech Redneck** · 11-04-2019, 01:19 PM

I don't know, but I want to say you are correct, based on this:

The number following the circle U designates how much tolerance is displaced to the outside of the basic profile that adds material. This new symbol was first introduced in the ASME Y14.41 standard and is now in effect in the ASME Y14.5-2009 standard. The standard still allows, as an option, the chain line to define an unequal tolerance, but the circle U symbol is certainly preferred.

**Paul Sarrach** · 11-04-2019, 01:21 PM

Do not look at it like a slot. It has the ALL AROUND SYMBOL on the leaderline. And you have all your Basics. I assume you have cad. Each line and radius can be +0.075 / -.0 Check it with points and create a set, and Profile using Form Only. In reality OAL can be plus .15 if both were exactly .075 outward.

**Matthew D. Hoedeman** · 11-04-2019, 01:32 PM

Actually, that callout is 'wrong' in that the leader-line & arrow are to be pointing at the side of stock (and ON the side of stock) that gets the value AFTER the (U). Since the arrow is pointing to the 'side' of stock that is inside the part, the meaning is flipped from what you might think. SO, based on a 100% strict interpretation, the size of that hole (and it isn't a size callout!) would be none bigger but 0.15 smaller than the called out size. That leader-line & arrow should be INSIDE the hole, pointing to the INSIDE of the hole, not pointing to the 'outside' of the hole (as in, going through the opening to point at the opposite side of the hole that it is pointing to right now).

Since it is a profile, if you MUST (and it's wrong) use it to check size, remember, that tolerance is for BOTH sides of the hole, not just one side, so it gets doubled.

TOL 1.0 (U) 0.0 means that the surface the arrow is pointing to (and the SIDE it is pointing to) gets 1.0 total tolerance, with 0 "added" stock. So, how do you add stock to the side of the hole that is inside the stock already? THIS is why that leader-line & arrow is wrong.

**DAN_M** · 11-04-2019, 02:08 PM

I can't see your picture.

All I know is... The number after the U is the amount of IN SPACE tolerance you have. 0.075 is the total.

So..Imagine you're measuring the OUTSIDE PROFILE of a square block and the nominal width was 1". You'd have to be 0.925-1.000 to comply.

**louisd** · 11-04-2019, 02:21 PM

According to ASMEY14.5, 2009, this tolerance zone would be +0.075, minus zero from the basic, all around. The width of the slot can technically be +0.150", but not minus 0.0001" from basic.

8.3.1.2 Unilateral and Unequally Disposed Profile Tolerance. A unilateral and unequally disposed profile tolerance is indicated with an unequally disposed profile symbol placed in the feature control frame. See Fig. 3-11. The unequally disposed symbol is placed in the feature control frame following the tolerance value. A second value is added following the unequally disposed symbol to indicate the tolerance in the direction that would allow additional material to be added to the true profile.

(a) Unilateral Tolerance in the Direction That Adds Material. Where a unilateral profile tolerance is 0.3 and applies from the true profile in the direction that adds material, the tolerance value would be 0.3 and the value following the unequally disposed symbol would be 0.3. See Fig. 8-1.

(b) Unilateral Tolerance in the Direction That Removes Material. Where a unilateral profile tolerance is 0.3 and applies from the true profile in the direction that removes material, the tolerance value would be 0.3, and the value following the unequally disposed symbol would be 0. See Fig. 8-2.

(c) Unequally Disposed Tolerance. Where an unequally disposed profile tolerance is 0.3, 0.1 applies from the true profile in the direction that adds material, and 0.2 applies from the true profile in the direction that removes material, the tolerance value would be 0.3, and the value following the unequally disposed symbol would be 0.1. See Fig. 8-3.

**Matthew D. Hoedeman** · 11-04-2019, 02:42 PM

Mike: My info is from the GM 'standard', when they implemented it (and I think they are the ones that got this rolling into the real standards). It's the GM ADDENDUM from 2004, all arrows to be pointing TO the side of stock that is effected, no arrows 'going through the part' to indicate, must be pointing TO the surface that gets the (U) from the side that gets the (U). The 'real' standard appears to be different, but who in their right mind would point THROUGH a part with a leader-line/arrow to indicate the SIDE of stock for the unilateral? This may be due to GM & sheetmetal. Think about it this way, very thin part (say, 0.012") on a 1-1 scale drawing, you'll never be able to tell what side of stock is indicated by the arrow, if ya follow what I am saying. Don't think only cubical parts, very thin stuff is out there as well, and if half the arrow go THROUGH the stock and half don't, you'll never figure out what they want. It would be 'obvious' (but stupid) on a block part, but thin sheet metal, there MUST be something to ensure you are 'adding' the stock to the right side. And in sheetmetal, it isn't really 'added stock', but more a direction in which the part can move. One side get 'added' while the other side 'loses', so, you have to know!

**aliptpatel** · 11-07-2019, 10:11 AM

I have similar callout on my drawing I am working on. Our former CMM guy still work with us as an engineer and said if we use .030 U 0 for profile without datum, PC-DMIS won't know where to show deviation arrows and may show wrong data. He is insisting to use datum structure. I am currently getting all the arrows pointing INWARDS which satisfies condition asked. Can someone comment on my former CMM GUY's note?

Attached Files

**Sora5** · 11-07-2019, 10:24 AM

Your former CMM guy is probably going by what he used to work with. That used to be the case with older versions of PCDMIS, specifically legacy dimension. Legacy demanded a Datum before it allowed you to specify unidirectional tolerance on a profile. With Xact measure, that's no longer the case.

**AndersI** · 11-07-2019, 10:31 AM

Do note that, at least in ISO, the "all around" still doesn't mean that everything should be evaluated as a single set - it would also need "CZ" for that.

**VinniUSMC** · 11-07-2019, 01:51 PM

Originally posted by Matthew D. Hoedeman View Post

Actually, that callout is 'wrong' in that the leader-line & arrow are to be pointing at the side of stock (and ON the side of stock) that gets the value AFTER the (U). Since the arrow is pointing to the 'side' of stock that is inside the part, the meaning is flipped from what you might think. SO, based on a 100% strict interpretation, the size of that hole (and it isn't a size callout!) would be none bigger but 0.15 smaller than the called out size. That leader-line & arrow should be INSIDE the hole, pointing to the INSIDE of the hole, not pointing to the 'outside' of the hole (as in, going through the opening to point at the opposite side of the hole that it is pointing to right now).

Since it is a profile, if you MUST (and it's wrong) use it to check size, remember, that tolerance is for BOTH sides of the hole, not just one side, so it gets doubled.

TOL 1.0 (U) 0.0 means that the surface the arrow is pointing to (and the SIDE it is pointing to) gets 1.0 total tolerance, with 0 "added" stock. So, how do you add stock to the side of the hole that is inside the stock already? THIS is why that leader-line & arrow is wrong.

I have GM Addendum 2004 and the new one for 2009. Matt, you've read the Addendum wrong.

See fig NEW 6-56 on page 55 of the 2004 addendum. It describes exactly this scenario, and the figure also points at the feature in exactly the same manner. The number after the U is still "Add material". And, on the previous page, fig NEW 6-55 shows that the number after the U is always "add material".

I didn't come back to the forum just to tell you that you're wrong, I promise!

**Matthew D. Hoedeman** · 11-08-2019, 07:17 AM

Originally posted by VinniUSMC View Post

I have GM Addendum 2004 and the new one for 2009. Matt, you've read the Addendum wrong.

See fig NEW 6-56 on page 55 of the 2004 addendum. It describes exactly this scenario, and the figure also points at the feature in exactly the same manner. The number after the U is still "Add material". And, on the previous page, fig NEW 6-55 shows that the number after the U is always "add material".

I didn't come back to the forum just to tell you that you're wrong, I promise!

The "only" problem with that is that there is NO 'added stock' possible in sheetmetal. You have a thickness tolerance (per a print I am looking at, 2.3 to 2.7, thinning not to exceed 25%), then you have a prof 3 (U) 0 ABC, and you can't add 3mm of stock to either side of the part as that is more than the maximum stock thickness. So you absolutely have to know which direction the entire part is allowed to move as one side can get 'heavy' by 3 while the other side can get 'lighter' by 3. If the arrow is just randomly pointing "here", which direction can it go? And keep in mind, you may or may not be able to check the part on the 'called out' side of stock, so you may have to use +3/-0 or +0/-3. The only way to ensure that you are tolerancing correctly is if the arrow IS pointing to the correct side of stock from the correct direction (as in, not through the part). It may have been a BMW 'clarification' of this addendum I am thinking of, but "added stock" is not a possibility in sheetmetal.

**Matthew D. Hoedeman** · 11-08-2019, 08:59 AM

BUT without a guidline, you can't know which direction is which. Like I said, it may have been a BMW (or Merc, or even GM) that gave out the 'clarification' on the arrow use for direction of movement.

**Matthew D. Hoedeman** · 11-08-2019, 09:26 AM

Actually, he IS trying to measure a sheet metal part.

GD&T call out question

GD&T call out question

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