FULL R vs R --- It's origins and how to use it properly

[ScottishRasta]

I came across a thread from 2018 called "FULL R vs R" where it appears that no one actually knew the correct answer... so I wanted to clear up a couple of misconceptions.
I can only assume that everyone on the thread was too young to have worked professionally as a draftsman on the board.
(This is where I realize that I'm getting really old )

BACKGROUND: Back before CAD was widely used as it is today, when the details where drawn manually (by hand), the FULL R annotation was intended for use on semi-circles (as one might see in a slot) in cases where calling out the diameter was not appropriate because the feature being dimensioned was not a full circle. The purpose of the notation was to assure suppliers that there wasn't a small indistinguishable flat between two radii instead of one continuous radius being shown (since everything was drawn by hand back then and you couldn't check the CAD file to see for yourself).

Although never stated on drawings, FULL R (as well as FULL RAD or FULL RADIUS) has always implied that both ends of the radius are tangent to the connecting lines/surfaces.

For product design, I believe that the more common usages for FULL R decades ago was in sheet metal forming to show that there were no minor flat sections in a 180° bend, for slots/mounting holes, or in seal/elastomeric applications like the one shown in the image below:

I hope this helps!

 

[greenimi]

Thank you very much for the info.

2009 version of ASME Y14.5 states:

1.8.4 Rounded Ends and Slotted Holes
Features having rounded ends, including slotted holes, are dimensioned using one of the methods shown in Fig. 1-29.
For fully rounded ends, the radii are indicated but not dimensioned.
For features with partially rounded ends, the radii are dimensioned. See Fig. 1-30.


I guess the standard verbiage is in alignment with what you just described above. Thank you again

 

[chez311]

Although never stated on drawings, FULL R (as well as FULL RAD or FULL RADIUS) has always implied that both ends of the radius are tangent to the connecting lines/surfaces.

Sounds pretty much in line with the current dimensioning principles in the latest editions of Y14.5 - instead of "FULL R" to denote tangency, one now simply utilizes "R".

The purpose of the notation was to assure suppliers that there wasn't a small indistinguishable flat between two radii instead of one continuous radius being shown (since everything was drawn by hand back then and you couldn't check the CAD file to see for yourself).

I don't want to say your wrong, you clearly have the benefit of many more years of experience - however I'm a little more skeptical of this use. In opposition to the other use, noting essentially that it is tangent to both sides, this would suggest it is essentially only tangent to one side. If one wants to denote this, would it not be easier to simply add center lines to your radius showing that the center point is coincident with the one side?

Concidentally, depending on the tolerances involved a small flat would actually be possible and still be within tolerance.

 

[drawoh]

ScottishRasta,

Is this based on your experience, or is terminology based on an official standard?

With standards such as ASME Y14.5, the GD&T is incidental. The standard provides a precise interpretation of everything you write on your drawings.

--
JHG