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I bought a sliding glass door set for self assembly. Below is a picture of the clamps for the glass. There are some additional plastic inlays that come between the aluminum clamp and the glass. Then each clamp has these 4 visible screws which tighten both sides of the clamp together to hold the glass.

How do I know the right tightening of the screws such that the glass is held safely but is not under too high pressure?

I have a newton-meter wrench for my car, but the range there is 28NM - 210NM. Not sure if 28NM might be already too much for glass? Glass is 10mm hardened glass. No other specs available, no manufacturer visible.

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    – isherwood
    Commented May 11, 2022 at 13:20

2 Answers 2

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I agree with Ecnerwal's general mounting advice. For a ballpark, a similar unit calls for 10 ft-lbs (14 Nm) of torque on the hex screws for "monolithic glass", or 4 ft-lbs [5 Nm] for "tempered, laminated glass".

More general advice for a 4mm socket cap screw is ~5 Nm.

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  • Did some more searching and found many glass ginges with torque specifications like this one: Screws M 6: 10 Nm, Screws M 6: 15 Nm, Screws M 8: 20 Nm., or this one - stainless steel screws M6 (torque setting 12 Nm), or this one - 20Nm for monolithic glass. So your suggested 14Nm is a good value in my opinion, thanks.
    – AndyZ
    Commented May 6, 2022 at 9:21
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I agree that a newly purchased product with no instructions and no manufacturer inormation should probably be returned (as much because things with "no manufacturer information" are usually that way because they are poorly made and trying to avoid liability etc. When it turns out that the glass panels are (say) not actually tempered and slice you to bits when they break, who are you going to seek redress from? For that matter, do you even want to risk the potential injury?)

However, to the question asked, if the plastic bits prevent point contact of the metal to the glass, glass in compression will take a huge load. These folks (no affiliation) claim 10 tonnes for a 1cm cube. So you probably won't break it by cranking on the screws.

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    I can imagine the asker is trying to find a ballpark amount of pressure - too little and it'll drop on its own some day, and too much and it might eventually shatter after a while. But yeah, liability wise I'd definitely want some clear information from the manufacturer.
    – MiG
    Commented May 5, 2022 at 12:27
  • @MiG, in terms of raw strength, glass is one of the strongest materials around -- if you over-tighten the screws, it's the clamps that are going to break, not the glass. Its reputation for being easily breakable is because that strength is paired with a low toughness, but toughness doesn't come into play when dealing with gradually-applied loads.
    – Mark
    Commented May 6, 2022 at 0:44
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    I'm aware of the material science. That raw strength goes down orders of magnitude in real life though, through scratches etc. And in this case we're not talking about a stationary framed window, but a moving object. You know what happens when you drop a glass, for one.
    – MiG
    Commented May 6, 2022 at 5:25

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