January 29, 2019

What Is Your Glass Business Tolerance?

By Paul Bieber

Let’s talk about the tolerances you promise your customers on glass work that you do. Do you guarantee perfect dimensions? What does the contract between you and your customer say? And the big question, how reasonable and tolerant is your customer?

Computer-driven, automated cutting lines have certainly improved tolerances in the last 15 years. If you are ordering a hundred identical tempered insulating glass units (IGUs), the odds are they will come in as close to correct as possible. The problem comes in with small custom jobs, usually residential or interior work. A free standing ¾-inch conference table has no problem with size. But what if the bevel doesn’t meet perfectly in the corners? Know the tolerance that your vendor works with so you can be clear to your customer. On a $1,500 top, you don’t want a rejection.

What about hole size and location? You have a lite fitting into a bookcase that has columns in it. If you are off by a 1/16-inch, will the glass fit? Look at this when you do the quote. If you are fabricating a small lite like this, plan on making two and build this into your pricing. Buying it out? Again, know the tolerance that your vendor is promising. Another problem with exact holes comes from matching glass not fabricated in the U.S. It is impossible to match a metric-sized hole with a hole based on inches. You will always be an 1/8-inch off. Know your tolerances here.

What about thickness on IGUs? Different manufacturers will use different amounts of sealants, making the unit thicker or thinner, by up to 1/16-inch. This is especially true in units made with 1/8-inch glass as there really are different thicknesses of 1/8-inch glass. A temperer will have a heavier piece of 1/8-inch than an annealed window manufacturer. Ask your vendor what they sell when ordering 1/8-inch.

Fabricating these units yourself? Bring back a shard from the broken unit and place it next to a piece of 1/8-inch from your stock. If there is a difference, does the frame allow for a slightly thinner or thicker unit? Knowing this will save you time at the install.

Just about every glass contract has a back page printed with all sorts of rules, including tolerances. Most customers don’t read this. They go by what you or your office tell them. As a business person, one sure way to lose business is to go over 20 different points on the back of your order with every customer. So, what do you do? Know what tolerances your vendors work with. Work with the vendors that have tight tolerances and do accept the fact that you can’t please all of the people all of the time.