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Glass shelf tolerance and quality-- your experience with glass suppliers?

Matt M

Good afternoon gents,

We are suddenly having great difficulty with obtaining tempered glass shelves, particularly those corner cabinet diamond-shaped shelves. Normally we don't need tempered but sometimes the job is spec'd out for it, and thus our problem.

In the past, we give them a template, they make it, and the shelves almost universally fit with reasonable fit. There have always been the occasional tight fit.

Both of our local suppliers are telling us that the margin of error on tempered stuff is as high as 1/8" (1/16" on each edge), which on a corner/diamond shaped shelf makes for an utter trainwreck for proper fit.

That's exactly what is happening now. Stuff is coming in consistently 1/8" heavy too big, but they are playing hardball on replacing them. This is the first time that we have ever had this issue.

We provide them with a template machined from 1/4" MDF, cut by a CNC router. The templates are dead-nuts accurate.

If I may ask a couple questions of you guys, I greatly appreciate your input.

1) Do you typically order your glass shelves the same size as you would with a plywood/melamine adjustable shelf, meaning, about 1/8" smaller than the cabinet opening?

2) Do you have difficulty with your local glass suppliers when you order tempered? Meaning, do you find tempered glass having a higher margin of error on size?

3) If so, how do you deal with the potential size discrepancies?

Thanks all-


4/11/16       #2: Glass shelf tolerance and quality-- ...

I don't really understand why any job would be spec'd out to have tempered shelves. There is no safety issue with shelving like you need where safety tempered glass is code in doors and windows.

Do the designers understand that tempered is a one shot deal? 3/16 or 1/4 plate is more than adequate and can be sized down or recut at your local glass shop.

That all being said, most, if not all tempered is not made in house as the process is very expensive. There is expansion and contraction during and after the tempering process, which is the reason for the low tolerances. I think that you'll find this is very common throughout the glass industry.

I've built many kitchens and my family owned a glass shop for 25 years. I've never put tempered glass in a cabinet for shelving and to my knowledge, we never had a request for it on the glass side either.

You should have plenty of room to allow 1/8" all around when ordering your glass.

4/11/16       #3: Glass shelf tolerance and quality-- ...

I should've added this...If you really need safety glass, have them cut you some laminated.
You get the same safety protection while still being able to resize if necessary. Should be cheaper as well as it can be cut in house.

4/11/16       #4: Glass shelf tolerance and quality-- ...
Matt M

Your points are well taken and I do agree. We seldom need tempered glass for shelving, and this is the first time out of those rare ones that we've had a problem.

These particular shelves were just large, which is why I'm assuming they were spec'd out as tempered. 1/4" thick. This was a decision made by the designer, not our shop.

The cabinet also had fairly tall glass doors also spec'd out tempered.

If I may ask, if the glass shelves were corner-cabinet diamond shapes, and 34" wide (side to side, not the longer corner-to-corner), would standard annealed/plate glass suffice at 1/4" thick?



4/11/16       #5: Glass shelf tolerance and quality-- ...

We only use tempered, much stronger than float. Yes there are more issues with size but much of that is also due to the manufacturer. We get ours directly from the manufacturer and they are pretty good. The previous mfgr wasn't so good. We send CAD files, not templates. The glass is CNC cut, then tempered. We make some allowance for the affects of the heat used in tempering. Ask the manufacturer what allowances you should make.

4/11/16       #6: Glass shelf tolerance and quality-- ...

Depends on what's put on them...a 36" square supported at the ends will support approximately 40 lbs.
Any of your suppliers should have a load calculator to let you know of potential problems.

4/12/16       #7: Glass shelf tolerance and quality-- ...
Matt M

That's a good point, thanks.

On this job, it was a smaller detail (or so we thought) put in by the designer, so we just priced accordingly and ran with it. And the times in the past we did this, we didn't have any troubles. Apparently we just got lucky.

4/13/16       #8: Glass shelf tolerance and quality-- ...
Kevin Jenness

I think you need to find a new glass supplier with better tolerances and fewer excuses. And good luck with that.

I haven't required tempered glass shelves, but I have numerous times ordered tempered insulated glass units from Green Mountain Glass including curved patterns and they always came through right on the money, so it can be done.

I have seen plenty of poorly dimensioned work come from various glass fabricators and have concluded that their customers settle for what they get often enough that they just keep on doing what they can get by on. Plus their prices must be high enough to absorb the numerous rejections. I don't spec glass often enough to invest a lot of time in finding a better source than the local guys, but there surely is an opportunity for some enterprising glassmeister who can hold tolerances close to what woodworkers achieve every day.

4/14/16       #9: Glass shelf tolerance and quality-- ...

Yes! I've found the same issue with our suppliers. However, we send the miscut shelves back.

In terms of size we actually have them cut 1/4" shorter than opening, and then use the "L" shaped shelf pins which add approx 1/16" each side. This may help a bit with variable sizes.

I agree with others about tempered shelves- we do not use them for shelving. Only in glass doors.

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