Guides
Toughened glass cannot be cut, drilled or notched once it is made, so every size, hole and edge is fixed before the furnace. Here is why, and how to get your sizes right first.
By the SW Glass workshop team· Published · 5 min read
No. Toughened glass cannot be cut, drilled or notched once it has been toughened. Toughening locks the surface in compression, so every cut, hole, notch and polished edge has to be finished before the glass goes into the furnace. If a toughened panel turns out to be the wrong size, the fix is a new panel made to the right size. Laminated glass is different: it can be cut and drilled after manufacture, within limits.
Toughened glass starts life as annealed glass, the ordinary float glass that is not safety glass. The annealed sheet is cut, drilled and edge-finished, then heated close to its softening point and cooled rapidly. That locks the surface in compression, and the strength comes from there. Our toughened glass is made to BS EN 12150.
The same locked-in stress is why there is no going back. Any cut, hole, notch or edge work has to be done before toughening. Once toughened, the glass is finished as it is. If it ever breaks, it crumbles into small, blunt pieces across the whole pane rather than long shards, which is why it is used as safety glass.
For more on how the three types differ, read toughened, laminated and annealed glass.
Every piece we toughen goes through the same sequence, and nothing can be added at the end:
Before step 1, every order is confirmed with a dimensioned drawing. Check it carefully: it is the last point at which a number can be changed for free. Our help page on drawings and checks explains what to look for. The furnace runs in batches, so toughened pieces take longer than plain cut ones. For timings, read how long toughened glass takes or ask us.
Not after it is toughened. Holes, notches and cut-outs go in at step 2, before the furnace. In our configurator you place them on the drawing when you order, and we drill holes up to 100 mm across online. Above that, you give us the diameter and we price it by hand.
This matters most where hardware is involved. Our shower measuring guide puts it plainly: the cut-outs go in before toughening, so a hinge chosen after the glass is ordered means a new panel, not a new hole. Choose your fittings first. See holes, notches and cut-outs for how positions are measured.
Laminated glass is two or more sheets bonded with a plastic interlayer. Unlike toughened glass, it can be cut and drilled after manufacture, within limits. It is heavier and thicker than toughened glass for the same pane. If you think you need to alter glass on site, ask us which type suits the job before you order.
| Glass type | Cut or drill after it is made? | What that means for you |
|---|---|---|
| Toughened | No | Every size, hole, notch and edge is fixed before toughening |
| Laminated | Yes, within limits | Can be altered after manufacture; ask us first |
Give us the right kind of number, and say which kind it is. Glass going into a frame, a channel or a profile needs clearance. You can give us the opening and let us make the deduction, or give us the exact glass size if you have already allowed for it.
| What you give us | When to use it | What we do with it |
|---|---|---|
| Opening size | Glass that goes into a frame, channel, profile or clamps | We take off the deduction the fittings need |
| Exact glass size | You have already allowed for the fittings | We cut to it; mark it clearly as the glass size |
| Finished size | A free-standing table top | Our table top guide says this is the one place it is safe to give |
The common mistake is an unmarked glass size: we read it as an opening and the deduction gets taken off twice. On a table top the risk runs the other way. There is no way to add 20 mm to a finished piece of toughened glass, so decide the overhang before you order.
Measure at more than one point and use the smallest figure. The full method is in our help page on measuring an opening, with product guides such as how to measure a shower screen. If the opening is out of square or the glass is structural, have it measured on site before you order: you can book a measure visit.
Enter your sizes, holes and edges in the configurator and check the drawing before you order.
No. A toughened panel cannot be trimmed, drilled or notched after toughening, so a screen that does not fit has to be remade. Measure the opening, choose the hinges and fittings, then order.
Not once it is made. Every glass shelf we cut is toughened unless you ask otherwise, so add any holes in the configurator when you order and we drill them before toughening.
Laminated glass can be cut and drilled after manufacture, within limits. Ask us before you plan any work on it.
Every order comes with a dimensioned drawing to check before anything is made. If you are unsure of your measurements, book a measure visit and we take them ourselves.
Ready for the next step?
Find measuring instructions and order support in Help and advice, or ask the team about your project.
From this guide
Keep reading
27/10/2026 · 4 min read
Tinted mirror carries a colour; antique mirror has an aged look to its silvering. Here are the finishes we cut to size, what to check before ordering, and how to see the live price.
22/10/2026 · 4 min read
Shower enclosures are covered by BS EN 14428, and a compliant screen is toughened or laminated safety glass. Every shower and bath screen we make is toughened, 8 or 10 mm, with polished edges.
19/08/2026 · 4 min read
An alcove is never as square as it looks. These are the ten things that most often turn a confident measurement into a panel that will not go in, and the check that catches each one while it is still a pencil line rather than cut glass.
