Tag: radii

Controlled Radius

It’s been many years since ASME Y14.5M-1994 introduced the controlled radius symbol.  Yet, we will still frequent find individuals in the industry who have never seen the symbol, nor know what it is.  The symbol is CR. 

It’s been many years since ASME Y14.5M-1994 introduced the controlled radius symbol.  Yet, we will still frequent find individuals in the industry who have never seen the symbol, nor know what it is.  The symbol is CR.  Really, a controlled radius is actually just a radius that is a fair curve, with no reversals.  I’ve not read ASME Y14.5-1982 in a very long time, but I believe this is actually similar to the original definition of a plain ol’ radius from the older standard.

Since ASME Y14.5M-1994, a simple radius has no fair or reversal limitation.  As long as the arc of the radius feature’s profile falls within the tolerance zone, it is considered acceptable.  These are represented by R.

So much time has gone by since the introduction of CR, I am left wondering why so many people have never seen it.  The reason CR was created, as it seems, was to allow engineers to specify a radius without the need for it to be fair or non-reversed.  This is good for breaking edges or filling corners.  A CR would be more useful when fit and/or function is important, such as guiding features.  In this way, the added expense of a creating a fair and non-reversed curve would only be employed when it is necessary for function.

Controlled radius vs radius

Foreshortening Dimensions (Radial, not linear)

[Updated to address changes in SOLIDWORKS 2016]

SOLIDWORKS provides for the foreshortening of diameters and radii dimensions.  Older releases of SOLIDWORKS didn’t allow for the foreshortening of linear dimensions (or clipped dimensions), except in break views where both ends of the dimension are visible.  When I first encountered this limitation years ago, I was concerned that SOLIDWORKS developers just simply overlooked this functionality.  After all, if one can foreshorten a radius, then why not a linear dimension?  I was even sure I could find examples of this already being done on other drawings in detail views.  I was trying to use an open ended dimension line with double arrows on the open end.  I may have actually used this method a couple of times back in my AutoCAD days.

But what didn’t SOLIDWORKS support this for many years?  The lack of foreshortened linear dimensions can be understood by reading ASME Y14.5M-1994 paragraph 1.8.2.2.  This paragraph established the foreshortening of radii.  Its title Foreshortened Radii seems to preclude these methods for linear dimensions.  But why?

The clue is the intent.  1.8.2.2. states that if the center of a radius is outside the drawing or interferes with another view, the radius dimension may be foreshortened.  Strangely enough, paragraph 1.8.2.2 does not specifically describe the just how foreshortening is demonstrated, other than to say the dimension line is radial to the arc.  It does reference a figure that shows radii centers repositioned with zigzagged radial and coordinate dimension lines.  The key is that the center of the radius is still within view.  The dimensions have known termination at both ends.

Allowed foreshortening of radial dimensions

There is an issue with using this methodology on any dimensions where the termination of both ends is not clearly shown.  Without both ends of the dimension in view (or known through some other way), there is no established way to determine where the dimension’s open end terminates.  It is an incomplete specification.  In other words, if I have a detail view and attempt to dimension to a feature not in that detail, the fabricator does not know the location of the other end of that dimension.  SOLIDWORKS previous limitation was not really a limitation after all.  It follows the drafting standards in a very logical way.

Disallowed foreshortening and diameter forshortening

Another thing SOLIDWORKS allows is the foreshortening of diameters.  Although this is not directly supported by the standards, it is common practice.  Unlike the foreshortening of linear dimensions, foreshortened diameters make sense since the other end of the dimension is known, even if it is not shown.  I’ll address foreshortened diameters in more detail a future article.

As of SOLIDWORKS 2016, foreshorten of linear dimensions is supported without restriction.  This was added for customers who still need methods to clip dimensions regardless to the issues mentioned above.