Model A & B

Ford Garage

Safety Glass and Tempered Glass Considerations

Craig Lewis, from Parksville, British Colombia, recently posted on Ford Barn some very good information and considerations about the topic of safety glass versus tempered glass, and the relative merits of each. Thanks to Craig for allowing his comments to be presented here on Ford Garage also.

In Craig's own words:

In 1992 I quit the body & paint trade and opened an auto glass shop. Here's a few of the basics I've learned for anybody who may be interested.

Laminated safety glass has been used in windshields since Model A times. A modern laminated windshield consists of a core of 0.030" clear vinyl, sandwiched between 2 sheets of plate glass. We all know how easily it breaks, with flying stones and any hard object...even a fist will break it. It has very little flexibility (until broken), thus requiring a framework to add rigidity and support around the edges.

Where laminated glass excels, is it's ability to keep folks IN THE CAR during a front-on collision. If you've ever tried to remove a windshield by kicking it out you'll know how strong and elastic that vinyl core is. If you DID punch through the glass and vinyl, the adhered glass fragments around the hole would likely cut you up REAL bad.

It seems though, in cases of car accidents, the laminated design holds together quite well, keeping the passengers "at the scene of the accident" as opposed to "on the road again".

Since about the early sixties, vehicles have utilized Tempered safety glass in the doors and backglass. Up until the late fifties or there abouts it was common to find laminated safety glass in the side windows of most American cars. It was relatively fragile and cracked easily if hit by a ball or even slamming the door too hard, especially if the glass was "floppin around" within loose runs and cat-whisker strips. You may recall many of these cars having a rigid chrome cap surrounding the door glass edges for strength. I liked that look!

Since about the early sixties, cars have utilized Tempered safety glass. Tempering is a process where the glass is heated red hot, then super cooled to trap high energy within the glass. The result provides up to a four-fold strength increase compared to untempered glass of the same thickness and, if broken, breaks into thousands of small cubic shaped fragments.

In the event of an accident, tempered glass can be shattered with a hard object, falling into a relatively harmless pile of bits, leaving an exit, while LAMINATED glass holds together (as it was designed to do) with considerable strength and elasticity!

For the record, I would NEVER install laminated safety glass in the side windows of my customer's car as it could potentially become a death-trap in the event of an accident.

Here's an example of how you can obtain tempered glass from your local glass shop by simply providing a cardboard pattern, pre-fitted to fit your window opening. I had the windows for my 1931 coupe made with 6 millimeter clear glass and tempered. I specified "no logo" on the order so they arrived without the manufacture's bug stamp etched in.

I had three sides of each door glass ground with a pencil polish. This displays a partially rounded, clear polished edge just like the original Model A plate glass and dramatically improves how the glass slides within the channel runs.

I'm confident these will pass in the event that my car ever sees judging, because they look exactly like the original plate glass. I can have a logo etched onto the glass if I choose at a later date.

On the subject of glass thickness, some research has found Model A door glasses measuring 0.204, 0.209, 0.217 and 0.266 inches.

Whenever I order tempered glass, I've found that most glass people don't seem to measure in thousands of an inch. Instead everything is done with a tape measure and there's definitely variation in each order. For example, to get what Americans call 1/4", I order 6 mm in Canada (yah that silly metric system).

My 6 mm coupe windows came 0.219" thick while two other 6 mm orders came in at 0.226" & 0.230", all from the SAME outfit! It seems these figures are close enough to 1/4" and everything seems to work out good.

I believe most glass shops will continue to make side windows from laminated glass with little regard for people's safety. They can turn out the job fast, without wasting a lot of time trying to educate the customer & fabricating patterns & waiting for the tempered order to show up.

I've touched on this subject before, but how can you argue with something they recommend in the judging standards?
Regards

Craig Lewis
December 2008



Related web pages on Ford Garage:

  1. Model A & B Original Body Glass Details & Specifications