Profile using size dimensions

[powerhound]

Another question guys:

I am currently dealing with another spline type issue but it's a different part. The spline is the female part. The standard invoked is 1994.

The 9 spline center of the part has the minor diameter called out as a datum and it is a toleranced dimension. The minor diameter does not meet the definition of a feature of size as there are no opposed elements. There is a profile of a surface control applied to the minor diameter.

Here's the question: Since the minor diameter is toleranced and also has a profile control. Does the profile tolerance add to the +/- tolerance? If it were a feature of size, I would say no but since I don't think it really is, I'm not sure.

I'm sure the intent was to never violate the MMC boundary but we're trying to figure out if that what is legally being conveyed.

Thanks guys,

Powerhound, GDTP T-0419
Engineering Technician
Inventor 2010
Mastercam X5
Smartcam 11.1
SSG, U.S. Army
Taji, Iraq OIF II

 

[Belanger]

Ugh. Profile of a surface on a minor dia? No can do, I would say.
But even if so, profile must be applied to a true profile (read: basic dims, not +/-).

John-Paul Belanger
Certified Sr. GD&T Professional
Geometric Learning Systems

http://www.gdtseminars.com

 

[pmarc]

I would first ask following:
Why there is a size dimension (+/- toleranced diameter) on something that is not a feature of size per '94 edition of the standard?

 

[powerhound]

I'm with you pmarc, I'm just trying to get some support for my argument and make sure I'm not completely wrong about this.

Powerhound, GDTP T-0419
Engineering Technician
Inventor 2010
Mastercam X5
Smartcam 11.1
SSG, U.S. Army
Taji, Iraq OIF II

 

[powerhound]

You can have a +/- tolerance on a non FOS per the 94 standard (i.e., slot depth), you just can't apply rule #1 to it.

Powerhound, GDTP T-0419
Engineering Technician
Inventor 2010
Mastercam X5
Smartcam 11.1
SSG, U.S. Army
Taji, Iraq OIF II

 

[MechNorth]

First, I thought the spline was the female on the other post ... doh.

Now for this one; my thought is that the profile is an attempt at co-cylindricity of the minor diameter surfaces of the spline. Don't see an issue with that per-se; it will ensure uniform assembly which would/could be an issue if +/- alone were used. Opposed points (teeth) could be within the size tolerance but shifted to either side of the intended center axis. To me, +/- doesn't help here, it hinders the appropriate control. J-P, why the concern over the profile on the minor diameter of the female spline?

I've always told my students that you exclusively use (1)a FOS with a position control OR (2) a profile control (with datums) ... NEVER both because there is no indication of which has priority, and therefore they typically will fight each other in some way.

Jim Sykes, P.Eng, GDTP-S
Profile Services

http://www.profileservices.ca

TecEase, Inc.

http://www.tec-ease.com

 

[powerhound]

If the drawing as it is is clearly illegal, then my original question is moot. If someone believes the drawing to be legal, then my question is still "Does the profile tolerance get added to the size tolerance?"

Thanks again,

Powerhound, GDTP T-0419
Engineering Technician
Inventor 2010
Mastercam X5
Smartcam 11.1
SSG, U.S. Army
Taji, Iraq OIF II

 

[Belanger]

Jim, the concern is: what is the surface you're profiling? The high points only of each spline tooth? May be a place for the tangent plane modifier here.

John-Paul Belanger
Certified Sr. GD&T Professional
Geometric Learning Systems

http://www.gdtseminars.com

 

[powerhound]

Each spline has a land of about .125". The splines are not pointed on top and their collective radii form the minor diameter. They are kind of like a square spline with a concave shape at the tip.

Powerhound, GDTP T-0419
Engineering Technician
Inventor 2010
Mastercam X5
Smartcam 11.1
SSG, U.S. Army
Taji, Iraq OIF II

 

[MechNorth]

Did I miss somewhere that the spline was a sharp at the minor diameter? If that is the case, then you're right that profile isn't good there. If there's a flat (well, a cylindrical section) then there's no problem with a profile control there.

Powerhound, it's illegal.

Jim Sykes, P.Eng, GDTP-S
Profile Services

http://www.profileservices.ca

TecEase, Inc.

http://www.tec-ease.com

 

[Belanger]

Well, OK PH. I'll buy that (maybe to be a stickler add a note like "12 surfaces, interrupted")

Let me try the next tack -- ground that we've debated before. The standard says that profile is to be applied to a true profile. And by definition a true profile is one given with basic dimensions. The only except is for a cone, where there may be a size tolerance if neither end of the cone is a datum. So here, the +/- tol still bugs me.

John-Paul Belanger
Certified Sr. GD&T Professional
Geometric Learning Systems

http://www.gdtseminars.com

 

[powerhound]

It bugs me too J-P. My position is that if this is not illegal, (which I think it is) that it is at the very least, a bad way to do this. I just need more than my own opinion to reinforce my thoughts about it.

Jim, you didn't miss anything, I just further clarified the geometry a couple of posts back.

Powerhound, GDTP T-0419
Engineering Technician
Inventor 2010
Mastercam X5
Smartcam 11.1
SSG, U.S. Army
Taji, Iraq OIF II

 

[MechNorth]

Looks like I was composing my message when yours hit the system. Tks.
Agree with the "12 SURFACES", though not sure that "INTERRUPTED" adds value. Then again, if the radii essentially run together, you may want to put a "between" modifier on the profile control and call out "12 SURFACES"

Jim Sykes, P.Eng, GDTP-S
Profile Services

http://www.profileservices.ca

TecEase, Inc.

http://www.tec-ease.com

 

[Belanger]

Sure; nix the "interrupted." After posting, I also realized that my tangent plane modifier comment is totally useless, cuz it's not a plane (duh!).

But still, that ± thing...

John-Paul Belanger
Certified Sr. GD&T Professional
Geometric Learning Systems

http://www.gdtseminars.com

 

[MechNorth]

yup, kill the +/-

Jim Sykes, P.Eng, GDTP-S
Profile Services

http://www.profileservices.ca

TecEase, Inc.

http://www.tec-ease.com

 

[powerhound]

Thanks for all the help folks. I'm going to recommend the minor diameter be basic with a profile callout and "9 SURFACES" attached to the FCF. I'm also going to say that whether or not the profile tolerance adds to the +/- tolerance is irrelevant since the callout is illegal anyway. Is that a fair assessment?

Powerhound, GDTP T-0419
Engineering Technician
Inventor 2010
Mastercam X5
Smartcam 11.1
SSG, U.S. Army
Taji, Iraq OIF II

 

[MechNorth]

and have the +/- removed from the drawing otherwise the downstream users may still misinterpret.

Jim Sykes, P.Eng, GDTP-S
Profile Services

http://www.profileservices.ca

TecEase, Inc.

http://www.tec-ease.com