Dimension to Intersecting Corner 9

[ImnotfromMars]

Hello,

Question about ASME Y14.5.

When a drawing is dimensioned to a sharp point of two intersecting surfaces or planes and there is a note on the drawing requiring break edges, how does the inspector know (from the ASME Y14.5) to inspect to the broken corner or the point in space where the surfaces or planes would have intersected prior to the deburring or breaking the corner?

 

[drawoh]

ImnotfromMars,

Good question. I run into this problem sometimes.

If you prepare a straight plus/minus drawing without datums, I would measure from the physical edge of the point, i.e. tangent to the radius.

You need to prepare your drawings carefully.

If your two angled surfaces are datums_A and_B, or datums_B and_C, anything positioned from these datums comes from the theoretical sharp point.

Sometimes, I have the problem of dimensioning to the sharp point. Make the dimension basic. Apply a profile tolerance to the angled face. Think your datums out carefully. Typically, I am primarily concerned with the position of the flat face, rather than of the sharp point.

JHG

 

[dgallup]

I've seen TSC (to sharp corner) or TSP (to sharp point) added to dimensions to indicate the design intent.

The Help for this program was created in Windows Help format, which depends on a feature that isn't included in this version of Windows.

 

[KENAT]

Or line extensions of the corner.

Posting guidelines faq731-376

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

(probably not aimed specifically at you)
What is Engineering anyway: faq1088-1484​

 

[fcsuper]

Both ISO and ASME have a rule about the point location from to intersecting lines that never meet (a sad love story is in there somewhere). Anyway, they both call for the use of extension lines that cross and extend a little bit beyond the intersection.

Should you dimension to it? Both standard demonstrate yes, but never explain what that means in terms of tolerancing. There is no need to label the dimension if you do so, however.

WWMD? (what would matt do?) I dimension to the point location when it was obvious what was meant or use a reference dim.

Matt Lorono, CSWP
Product Definition Specialist, DS SolidWorks Corp
Personal sites:
Lorono's SolidWorks Resources & SolidWorks Legion

 

[dgallup]

The problem with those lovely intersecting lines is sometimes there is not enough room on the print for that level of detail to be visibly shown. That's when adding the TSC notation comes into play.

The Help for this program was created in Windows Help format, which depends on a feature that isn't included in this version of Windows.

 

[prdave00]

Is there support for these acronyms (e.g. TSC, TSP, etc.) on any ASME Y14 standards? I had a coworker that would dimension from a virtual sharp and after the dimension put TPI (to point of intersection). Without knowing what the acronym it wasn't clear. Threads per inch? ASME Y14.5-2009 has an example of using crossing extension lines and the intersection as the origin for two converging surfaces (that don't form a physical edge) but I think that's different from what the OP is asking. I read the question as "if I have 2 intersecting surfaces that form a corner, but then that corner is broken, from where do I measure the part". I think you have to find the theoretical intersection of the 2 surfaces to establish an "origin". The edge break shouldn't come into play. At my company we use an optical comparator and DRO with metrology software to construct a point of intersection - the limitation being this boils this down into a 2D measurement using edges and not the entires surfaces.

 

[MadMango]

I've seen a general note to the effect of "ALL DIMENSIONS TO SHARP OR TRUE CORNERS UNLESS SPECIFIED."

"Art without engineering is dreaming; Engineering without art is calculating."


Have you read faq731-376 to make the best use of these Forums?

 

[drawoh]

Is there support for these acronyms (e.g. TSC, TSP, etc.) on any ASME Y14 standards?

I hate TLAs.

I strongly recommend not using them. If you are using ASME Y14.5, you can use datums, basic dimensions and feature control frames, and make your requirements clear to everyone. There is no reason to resort to obscure terminology.

JHG

 

[drawoh]

A TLA is, of course, a Three Letter Acronym.

JHG

 

[weavedreamer]

We are glad that you distinguished it from the Two, Ten, Twelve, Thirteen, Twenty and Thirty Letter Acronyms.

Obscurity is a pet peeve here as well.

(No offence intended to the Two-hundred, Thousands, Trillions or any other T-number not specifically enumerated here.)

 

[fsincox]

The purpose of the datum reference section of the tolerance block is to specify the instructions of how to set up the measurment, this was refined in 2009 to give more options.
From a recient topic of discussion in the yahoo group GD&T forum it appears like we know less and less about how to set-up measurement without formal GD&T.
When I was taught the 1982 standard the line was that there is no legal definition without referencing the standard. It seems now with the 1994 & 2009 there is less certainty of definition of the intent of plus and minus dimensions than I was led to believe then.
Frank

 

[drawoh]

fsincox,

I don't think we have lost the knowledge of how to set up the measurements. We have stopped believing that we can set up the measurements. We have never actually been able to do this.

Far more important than GD&T, standards like ASME Y14.5 tell us exactly what the drawing means.

JHG

 

[SeasonLee]

Here is an example I met few years ago on my work, the part surfaces were defined with angles and intersection point, and there is a note to describe it’s an intersection of two surfaces.

What you can do if the tool maker and inspector in factory is not very understanding about profile tolerance, the intersection point gives me a good idea, after the calculation its easy to get max point (the outer profile boundary intersection point) and the min point ((the inner profile boundary intersection point), just tell them it’s a good part as long as the intersection points lies between the max and min point on each respective points.

SeasonLee

 

[MechNorth]

I've always labeled "INT PT", "TAN PT" for Intersection point & Tangent point respectively. Someone showed me two legitimate alternatives for TSC (can't remember them anymore), so we avoided the TLAs where possible. I have no problem using intersection points or tangent points for construction geometry; I have MAJOR issues with using them as control points. Projecting surfaces to the intersection point is not supported in the standards, so just don't do it. The reality is that even the slightest angular difference on either of the faces will move the intersection point significantly. Profile is the better way to go. As for what to use +/- tolerances on; I try to limit it to FOS (features of size) almost exclusively. Beyond that, on junk features like c'bore depths, clearance depths ... but I tend to use profile for s'faces because that gives me better location and orientation of the surface ... usually important aspects of the s'face.

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

http://www.profileservices.ca

TecEase, Inc.

http://www.tec-ease.com