Tolerance of Implied 90 Degree Angle

[PeterStock]

Per ASME Y14.5M-1994, when a 90 degree angle is shown and the features are defined by non-basic dimensions, the 90 degree angle has a tolerance as defined in the title block or in general notes. Our major client does not use default tolerances in the title block, all dimensions are toleranced directly or by GD&T. What would determine the tolerance on the implied 90 degree angles in this case? I don't think the standard gives a good indication for this case.

Peter Stockhausen
Senior Design Analyst (Checker)
Infotech Aerospace Services

 

[ctopher]

It's either from the tol block or tol added to the dim. Without either, there is no tolerance assumed, therefore the machinists' can make it whatever they want.

Chris
SolidWorks/PDMWorks 08 3.1
AutoCAD 08; CATIA V5
ctopher's home (updated Aug 5, 2008)
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[PeterStock]

That is what I am thinking, I may need to see if we need to add something to the format or to notes.

Peter Stockhausen
Senior Design Analyst (Checker)
Infotech Aerospace Services

 

[fcsuper]

Ok, maybe I'm misunderstanding the question, but this does not seem like a possible interpretation to me.

If, on the drawing, no angle is stated on a particular square feature (this is what I'm guessing you mean by "implied"), then the control is the dim associated with that feature. The entire surface must full within that dim.

If the 90deg is stated, but no tolerance is provided, then Chris' comment is correct.

However, for any of this to matter, ASME Y14.5 needs to be invoked on the drawing. Yes, I also recommend adding the tol table to the title block.

Matt Lorono
CAD Engineer/ECN Analyst
Silicon Valley, CA
Lorono's SolidWorks Resources
Co-moderator of Solidworks Yahoo! Group
and Mechnical.Engineering Yahoo! Group

 

[PeterStock]

Matt the situation is this:
1. a surface is located with a toleranced dimension.
2. that surface is 90 deg from a different surface.
3. no angle dimension exists.
4. no default tolerances are called out in the title block or in general notes.

According to section 1.4 Fundamental Rules:
"(i) A 90" angle applies where center lines and
lines depicting features are shown on a drawing at
right angles and no angle is specified. See para.
2.1.1.2.
(j) A 90" basic angle applies where center lines
of features in a pattern or surfaces shown at right
angles on the drawing are located or defined by basic
dimensions and no angle is specified."

Paragraph 2.1.1.2 "Implied 90" Angle. By convention,
where center lines and surfaces of features of a part
are depicted on engineering drawings intersecting at
right angles, a 90" angle is not specified. Implied 90"
angles are understood to apply. The tolerance on
these implied 90" angles is the same as for all other
angular features shown on the field of the drawing
governed by general angular tolerance notes or general
tolerance block values. Where center lines and
surfaces of a part are depicted on engineering drawings
intersecting at right angles and basic dimensions
or geometric controls have been specified, implied
90" basic angles are understood to apply. The tolerance
on the feature associated with these implied 90"
basic angles is provided by feature control frames
by a basic size and tolerance symbol as in Fig. 2-
3. See ANSI B4.2 for complete information on this
system."

As there is not default tolerance given in the title block or in notes, there is no tolerance. A .99-1.01 x 2.99-3.01 block is only required to fit within the tolerances as a parallelogram, not a rectangle. Without an angular tolerance the angle of the parallelogram can be anything including 45 deg or bigger.

Peter Stockhausen
Senior Design Analyst (Checker)
Infotech Aerospace Services

 

[ringster]

PeterStock,

Any chance this drawing was generated by NASA?

 

[PeterStock]

No it was not NASA.

Peter Stockhausen
Senior Design Analyst (Checker)
Infotech Aerospace Services

 

[fcsuper]

" A .99-1.01 x 2.99-3.01 block is only required to fit within the tolerances as a parallelogram, not a rectangle."

It sounds like you answered your own question.

Matt Lorono
CAD Engineer/ECN Analyst
Silicon Valley, CA
Lorono's SolidWorks Resources
Co-moderator of Solidworks Yahoo! Group
and Mechnical.Engineering Yahoo! Group

 

[PeterStock]

I was hoping for a better answer. It turns out that a company spec called out with ASME Y14.5 does cover this situation and most of the time a control is required.

Peter Stockhausen
Senior Design Analyst (Checker)
Infotech Aerospace Services

 

[MechNorth]

That's one of the reasons that I prefer to use surface profile to locate surfaces rather than +/- tolerances if possible. The surface profile includes the orientation of that face to the related datums.

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

http://www.profileservices.ca

TecEase, Inc.

http://www.tec-ease.com