4specs.com    4specs.com Home Page

ASTM C 1036 Log Out | Topics | Search
Moderators | Register | Edit Profile

4specs Discussion Forum » Archive - Specifications Discussions #4 » ASTM C 1036 « Previous Next »

Author Message
Lynn Javoroski CSI CCS LEEDŽ AP SCIP Affiliate
Senior Member
Username: lynn_javoroski

Post Number: 931
Registered: 07-2002
Posted on Friday, September 25, 2009 - 02:13 pm:   Edit PostDelete PostPrint Post

The other day, I sent the following to ASTM:

Re: Table 2 Dimensional Tolerance for Rectangular Shapes of Type 1 Transparent, Flat Glass.

For SI designation, 6mm, 1/4 inch, the thickness range in inches has as its minimum 0.219 and as its maximum 0.244.
The maximum is therefore less than 0.25, which is equal to 1/4 inch (at least in the math and number system I learned in school).
I understand the need for a range of thickness, and the tolerances to govern that range.
I don't understand how the maximum can be less than the traditional designation nominal measurement. (even allowing for the
differences between 6mm and 1/4 inch)

Can someone please explain this?

Thank you for your attention to this question.


Here's the response I received:

Sorry to say there is no good answer; this has been this way for many years.
The fractions are called Traditional or nominal dimensions (i.e., not true valuates).
It is similar to why a 2" x 4" lumbar piece is not really 2" by 4"; it is less.


To which I responded:

For every other thickness of glass, the minimum is below (or less than) the nominal measurement and the maximum is above (or greater than) the nominal. 1/4 inch is the ONLY one where the maximum is LESS THAN the nominal. [Therefore, were I to put 4 panes of 1/4 inch glass together, using the maximum allowable thickness, I would get a piece of glass with a thickness of 0.976, which is dangerously close to the minimum for 1 inch glass (0.969). You'd think that it ought to come out closer to the nominal.]

To use your analogy, it's like saying that the maximum width of a 2x4 is 3...when we all know that the nominal width is 3-1/2.
If this has been this way for many years, perhaps it has been wrong for many years?


And the answer:

A 2 x 4 piece of wood is less than 2" thick and less than 4" wide, but it is called a two by four.
A 1/4" piece of float glass is less than 1/4", but it is called one quarter inch..
To me, that analogy makes sense.

But WE are not going to change this industry accepted nomenclature by talking about it.
And I honestly do not think the industry will ever change, but I could be wrong.

You may want to join ASTM C14.08 and submit your comments on the next ballot of C1036.


Typos not withstanding, anybody have additional insight into this?
John Bunzick, CCS, CCCA, LEED AP
Senior Member
Username: bunzick

Post Number: 1112
Registered: 03-2002
Posted on Friday, September 25, 2009 - 04:16 pm:   Edit PostDelete PostPrint Post

I always specify glass by metric dimensions. If they call in 1/4 inch in the field, so be it.

Topics | Last Day | Last Week | Tree View | Search | Help/Instructions | Program Credits Administration