Volume 43, Issue 11 - November 2008

Buyers's Block

How's Your Tolerance?
If Seeking Perfection, First Check the Standards
by Paul Bieber

You order glass, it comes in and it looks great, yet when you deliver to your customer it is rejected. Did you make a mistake? Did your fabricator screw up? Maybe not, but you still have an angry customer because he expected perfection and you provided industry standard products. 

We know there is no such thing as perfect in our retail glass industry. You can buy perfect glass in the optical or military market, but at considerably more than our retail market would pay. How do we let our customers know that?

Standard Wiggle Room 
The standard that most fabricators work to is the American Society for Testing and Materials (ASTM) specification C1048-04, Standard Specification for Heat-Treated Flat Glass, which covers tempered and heat-strengthened glass. You fabricator should give you a copy of this spec, or you can download it for a fee from ASTM.org.

Let’s look at a basic shower door, 3⁄8-inch tempered, with notches, holes and polished edges. The size tolerance is plus or minus (+/-) 3⁄32 inches, or as much as single thick float. The bow and warp tolerance for lites up to 47 square feet is a little more than 1⁄6-inch. Hole and notch sizing is +/- 1⁄16-inch.

A door can be 3⁄32-inches too large, and a hole can be off by 1⁄16-inch making a final hole or notch location off by 5⁄32-inch. Yet, this is acceptable according to our industry standards. When you place your orders, do you specify standards on your purchase order? Most people don’t, so don’t feel bad. Even if you specified tighter measurements than your vendor’s standard, more often than not you will get a phone call stating they won’t accept the order as is. When you write “glass size must be perfect” and the fabricator doesn’t respond, it is up to you to know industry standards. If you ask for perfect, then you should be prepared to pay a huge extra, as your supplier will cut two or three pieces to get one.

There’s the Rub 
The other important spec is for scratches, rubs or inclusions in the glass. Here we go to ASTM C1036-06, the Standard Specification for Flat Glass. Basically, small marks are acceptable. The definition of this is that if you cannot see the mark when standing 11 feet away, under normal lighting conditions, then the mark doesn’t exist. Yes, 11 feet under normal light … but if Mr. Customer has a magnifying glass, forget about pleasing him. 

Therefore, the question is one of tolerance. You should go over these tolerances with your customer as you sign up the order. Putting this on the back of your invoice, in tiny print, will not protect you. Go over this with your customer so they know what to expect. If you get a lot of pushback, demanding “perfect,” or insisting that “everyone should be able to read a tape measure,” I would let this sale go to your competitor.

If you have a fussy customer after discussing industry standards, ask your fabricator for a quote with the required standards. Explain to your customer that near-perfect costs extra, and explain why. Remember if the customer is fussy about the glass, they will be equally fussy about your metal, caulking and cleanup. 

Clean-up your installation with glass cleaner and metal polish. Leave the installation better than you found it. If the customer sees one small problem, then they take out the fine-tooth-comb. If you leave a nice, neat job, you will avoid problems.

There is one other tolerance that I call “mother-in-law” tolerance. If you receive many doors that you wouldn’t be proud to put in your mother-in-law’s house, consider having a discussion with your fabricator about his quality control. 


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