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Yes, BUT, there are TWO Axis thare are reportable. The IMPLIED ZERO is the second Axis. Also, the SHAPE of the feature does NOT necessarily dictate the shape of the tolerance zone. You do NOT have to use a Diametric tolerance zone for a hole if you do not want to. You CAN use spherical for a point if you want to.
Sorry about the pic that I did not include. I will try to add it.
Yes, BUT, there are TWO Axis thare are reportable. The IMPLIED ZERO is the second Axis. Also, the SHAPE of the feature does NOT necessarily dictate the shape of the tolerance zone. You do NOT have to use a Diametric tolerance zone for a hole if you do not want to. You CAN use spherical for a point if you want to.
BTW, that is NOT a diametric True Position. That is an AXIAL true position called out Craig. If it were Diametric then the Diametric Symbol would be in front of the TP tolerance and it is not.
Sorry about the pic that I did not include. I will try to add it.
You are correct the callout is missing the diameter symbol, with the diameter symbol it would be an axis, the callout is bad without it. I'll edit it to make it legal. You are really reaching on the rest man lol. Your original position was what that you need three basic dimensions. That is what I am demonstrating, that you do not. Also the shape of the feature does in fact dictate the shape of the tolerance zone. you can only TP a FOS which a point is not so that would be illegal.
Also, please explain the criteria for reporting diametric TP when there are THREE basics controlling it's location. I am not asking because I know the answer and want to crack on you. I am asking because I know what I do and want to see what others do.
If the FCF calls out three datums and one is the surface that the hole is normal to, then the axis of the hole (cylinder) must be within the TP tolerance zone. Based on ANSI Y14.5 you CANNOT just verify a point projected into the plane.
Forget the CMM. Put a pin into the hole. As close as you can to where the pin enters the part indicate its position to the basic dimensions that control it's 2d location. Now, indicate the it's position on the opposite side as close to that surface (or move away from the surface the a distance equal to the depth of the hole.) You must maintain the TP tolerance at both those locations.
In other words, you have to evaluate the AXIS of the cylinder, not just the center of it at one surface. This is just another way of controlling perpendicularity.
I think I am agreeing with CMMGUY and VPT here.....
Just like John said. Three basic dimensions give the location for the axial feature, the first datum in the FCF is the feature to which the axis is to be normal. Then look at the pic I posted demonstrating this (it does not include the FCF sorry). As far as TP to a point it is illegal. It doesn't matter if GM does it or Ford or Boeing or whoever. You can't TP a point, per the standard it needs to be a FOS. Does this mean you can not make PCDMIS do it? No. Does it mean you are misinterpreting it and design intent is not being met? No. Is it a bad callout? Per the standard it is.
There are no exceptions that I know of in regards to the shape of the tolerance zone. The shape of the tolerance zone is dictated either by the shape of the feature or by basic dimensions (i.e. profile).
You do not necessarily HAVE to have the feature normal to the first datum in the FCF, do you? Say you have a BASIC angle into which a hole is bored. Why is it illegal to use the BASIC angle to control the orientation or the normailty of the hole?
I need to get the standard in my hand. See where it is called illegal. If all of this stuff is illegal then that is a mistake IMO and does not serve the community.
Wait a minute. Page 60 of my trusty GD&T handbook Y14.M-1994 shows TP as a bi-directional control (single Axis) on ROUND features. A round feature should dictate diametric IF what you are saying is correct. I think it's OK man. It's OK to use single axis tp with round features.
I will investigate the corner point further and may well conced it is illegal.
I don't believe it should be illegal to have an angle for the hole like you illustrated. Never said it was. Yes you can have a non-diametric tolerance zone for a FOS but you need to place the FCF in a manner that shows this. In other words the FCF can not be attached to the FOS but rather to the dimension lines. If it is attached to the FOS it is diametric. Your page 60 and mine are much different, I am in section 5.9 also demonstrated in illustration 5-42 (my page 60 is on datums). So yes you can do a non-diametric tolerance zone but where you place the FCF dictates the legallity of it.
Just curious as to why there would be two different ways to define that an FCF is diametric? There is the diametric symbol AND there is WHERE you attach the FCF? Why the redundancy? Just curious more than anything and since I realize you didn't actually write the spec I don't expect you to have all the answers here. Still, it doesn't make sense to have redundancy like that because it will inevitably lead to ambiguity and conflict.
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