Bi-Directional TOP

[SeasonLee]

Normally, bi-directional TOP allow a hole to have more location tolerance in one direction than in another direction, if both direction has same tolerance, can we add the diameter symbol Ø before the tolerance as shown on the attached print.

I know the difference between them is tolerance zone, but I am wondering is it the right way to call out the TOP for this case.

Thanks for your inputs

SeasonLee

 

[dingy2]

Diametrical tolerance zone should be placed on features of size that are round and since your hole is not round, do not place a diametrical tolerance zone in this feature control frame. With DTZ, the tolerance is applied in both axis.

I would further suggest that you place the term BOUNDARY below the feature control frame. This boundary is the virtual condition boundary which will control not only the location or position of the hole but its orientation. This information is shown in the ASME Y14.5M-94 standard on page 143 fig. 5-47

Dave D.

http://www.qmsi.ca

 

[KENAT]

Agree with Dingy, drop the dia symbol.

KENAT,

Have you reminded yourself of faq731-376 recently, or taken a look at posting policies:

http://eng-tips.com/market.cfm?

 

[axym]

SeasonLee,

I agree that the diameter symbol should not be used here. I don't agree with Dave's reason why though. The diameter symbol should not be used because the tolerance zone isn't cylindrical (because a bidirectional position tolerance was specified) - not because the hole isn't round. A bidirectional tolerance (with a square or rectangular tolerance zone) can be used with round holes - the shape of the tolerance zone isn't necessarily tied to the shape of the feature.

I think you're right to wonder if this is the right way to call out the TOP in this case. An equal bidirectional position tolerance at MMC on an elongated hole is a bit of a mess, and I'm wondering what the function of the elongated hole (it's really a round-end slot) actually is. The fact that MMC modifiers were used implies that a mating feature (elongated pin or round-end block) will be inserted with clearance on the sides and clearance on the ends. The mating feature will be oriented and located to features that mate with datum features A, B, and C. Is this correct? If not, then we'll need to encode the position tolerance differently.

Evan Janeshewski

Axymetrix Quality Engineering Inc.

http://www.axymetrix.ca

 

[dingy2]

Evan:

Using your concept, could you please let us know when one might use a diametrical tolerance zone on a feature of size that is not round?


Dave D.

http://www.qmsi.ca

 

[SeasonLee]

Evan

Thanks for your input, the mating part should be a round block in the elongated hole and I guess the elongated hole caused by the 8° slant, for a casting part supplier we are not quite sure its application.

As I know something wrong on the callout, so we measure it with a rectangle tolerance zone even there is a diameter symbol.

Thanks for all inputs again

SeasonLee

 

[ctopher]

Looking at Sect D-D, is the hole a counter-bore? If so, you may need another tol for the bottom. The section view looks like it may have a thread also (not clear).
Personally, I would remove the two dims and call out a positional tol. Otherwise I agree with the others.

Chris
SolidWorks/PDMWorks 08 3.1
AutoCAD 08
ctopher's home (updated Aug 5, 2008)
ctopher's blog
SolidWorks Legion

 

[SeasonLee]

Chris

You are right, its a counterbore hole with .040 depth on a slant.

SeasonLee

 

[ctopher]

Counterbore on a slant? That would mean the hole is no longer circular but elongated, possibly changing how your dim/tol callouts are used?

Chris
SolidWorks/PDMWorks 08 3.1
AutoCAD 08
ctopher's home (updated Aug 5, 2008)
ctopher's blog
SolidWorks Legion

 

[axym]

Dave,

Here's one instance where I've seen a cylindrical zone used on a non-round feature. The feature in question was a square hole, and the mating part was the square shank of a carriage bolt. The client wanted location control that was equal in all directions, and was willing to live with the uncertainty involved in finding the "axis" of a square hole. The form of the square was close enough to perfect to make the axis quite reproducible. So we used a position tolerance with the diameter symbol on a square hole. Possibly not quite Y14.5 compliant, I'll admit.


Evan Janeshewski

Axymetrix Quality Engineering Inc.

http://www.axymetrix.ca

 

[dingy2]

Evan:

Would be most interesting if the positional tolerance was at MMC. Wonder what the shape of the virtual condition boundary??? Round? Square? I do agree that it is "Possibly not quite Y14.5 compliant".

Dave D.

http://www.qmsi.ca

 

[wallyd999]

If I were to inspect this from a customer with this drawing, I would break it up into 4 seperate enities and divide up the positional tolerances equally. But there I go editing the print to solve my problem and who would tell me that I'm correct.

So I would have to say the boundary would be the correct choice on this.

Good questions & replies all around.

Thanks

 

[CheckerRon]

We use a circular position tolerance zone on the square end of a ball valve shaft (where it connects to its' actuator)for circular alignment. The tertiary datum clocks the square to the valve below.

An extension piece for a socket set, or the hex in a socket head screw also comes to mind.

 

[SeasonLee]

Dave

Here is another example of TOP with diameter symbol, but it's not a bi-directional TOP, it's an elongated C'bore not a round feature, according to what you said “Diametrical tolerance zone should be placed on features of size that are round”, can we add diameter symbol for TOP here ? It seems a lot of designer makes this mistake.

SeasonLee

 

[ringster]

Seasonlee,

I fail to see where the C'bore is elongated. It appears to be dimensioned as a dia. Where are you getting the elongation of the C'bore?

 

[PeterStock]

I see the C'bore as a diameter and the slot inside it as elongated.

Peter Stockhausen
Senior Design Analyst (Checker)
Infotech Aerospace Services

 

[CheckerRon]

I see what Peter and ringster see. Moreover, maybe some dimensions were purposely left off, but your slot is not dimensioned or toleranced.

 

[SeasonLee]

Here are more information about the elongated C'bore.

SeasonLee

 

[SeasonLee]

Sorry for I can only upload one file each time, here is another one.

SeasonLee

 

[CheckerRon]

The best slot dimensioning I've seen is per Figure 5-47 of Y14.5M-1994. I use it all the time.