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fastasleep (Mechanical) (OP)
23 Nov 04 0:32
I was taught a while back that when dimensioning to a virtual sharp to label the dimension as T.S.C. ("theoretical sharp corner", although I've heard some people call it "to sharp corner.")  However, I have been unable to find this method documented anywhere.  I've seen this done with just witness marks or no indication at all, which seems to cause confusion in print interpretation on some drawings.

What is the correct or, alternatively, preferred method for this?
ctopher (Mechanical)
23 Nov 04 10:08
For past 20 years, I have always heard it as T.S.C. That is how I have always dimensioned it and the dwgs were never questioned. All machine shops I deal with understand it and prefer it over drawing the marks.
drawoh (Mechanical)
23 Nov 04 10:41

   This is the first time I have ever hear the acronum TSC.  I must admit I was rattled about twenty five years ago when I first saw the acronum BCD (Bolt Circle Diamter).

   I have, on occasion, placed notes on drawings wtating that dimnensions were to sharp corners.

   There is no substitute for clear English on your drawings.

TheTick (Mechanical)
23 Nov 04 11:21
I believe this is a case of many conventions but no sandard.  I would love to see an actual reference to a real standard regarding this point.

As far as the marks, technically the intersection mark is just a pair of extension lines, which are valid drafting entities in most standards.

Intersections for non-90° corners with fillets are a perennial problem, as there is no good definitive way to physically measur such an animal without aid of digital devices.
TheTick (Mechanical)
23 Nov 04 11:22
and another thing...

Abbreviations are asking for trouble in an age where one can not assume the person making your part speaks the same language as you.
MintJulep (Mechanical)
23 Nov 04 12:20
Paraphrasing Jensen and Helsel's "Engineering Drawing and Design".

Extension lines are used to indcate the point or line on the part to which the dimension applies. ...  When extension lines refer to a point which is not a physical feature of the part, the extension lines should be drawn through the point.

No mention of TSC or similar.
fastasleep (Mechanical) (OP)
23 Nov 04 14:46
Thanks to all for the feedback.  The Tick's and Drawoh's points are well received.  I will spell out this type of dimension on future drawings and use extension lines to boot.  It would be nice to have a handy universal symbol to represent TSC though.
btrueblood (Mechanical)
23 Nov 04 17:47
Yup, even the "gospel" according to ANSI (Y14.1, Y14.5) shows dimensions to extension lines for sharp corners, no abbreviation given for "TSC" or other "sharp corner" reference.
ctopher (Mechanical)
23 Nov 04 18:40
I should have been clearer. I don't use the abbreviation, I meant I use "theoretical sharp corner" or similar notes. sorry
Helpful Member!  MadMango (Mechanical)
23 Nov 04 19:35
We use a block that is placed on drawings that have any dimension to a theoretical sharp corner.  It is used along with extension lines to indicate the sharp corners.

The block illustrates a bend with extension lines to the corner, with the words "dimensions are taken from true corner."

"But what... is it good for?"
Engineer at the Advanced Computing Systems Division of IBM, 1968, commenting on the microchip.
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fastasleep (Mechanical) (OP)
23 Nov 04 21:11
MadMango: I like that idea.  The idea of using just extension lines with no coresponding notation seems too vague to me, especially on washed out/faxed prints.  The use of a block to illustrate the meaning of the extension lines on the drawings seems to be a great solution.  Thanks.
ctopher (Mechanical)
24 Nov 04 10:42
Don't want to change the subject, but no one should be faxing drawings anymore, should be using PDF ... IMO. Reduces errors reading them.
fastasleep (Mechanical) (OP)
28 Nov 04 11:32
ctopher: agreed.  But, as hard as it is to believe, there are still some people out there running their small companies without e-mail. Some of those mom and pop shops do the best work, so I continue to use them for machining.  
ctopher (Mechanical)
28 Nov 04 22:03
I agree, they do the best work. In their case I will mail the dwgs to them. If they are close, I will hand deliver.

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