01The five numbers you can actually change
Everything else is a consequence. Ask for these five and the drawing is complete.
| Number | Range we hold | What it decides |
|---|---|---|
| Length × width | 300–1200 × 300–700 mm | How many pans fit flat on the base |
| Depth | 150–400 mm | Splash, and how far a tap must reach |
| Corner radius | R10 / R20 / R30 | Cleanability against usable volume |
| Drain position | centred or offset to 150 mm | Whether a trap fits in the carcass |
| Overflow | none / slot / rear box | Where the water goes before the rim |
Two of these are free, one is nearly free, and two change the price. Length and width are cutting — nothing extra. Depth up to 300 mm comes off the same sheet with no extra weld. Corner radius is the one people assume is decorative and is not.
02Corner radius: the honest trade
Every bowl corner is a weld or a fold, and radius decides which.
We will build R10, and we will say on the quotation that the four corners are hand-dressed. That is a real cost and a real fatigue point on a bowl that gets used forty times a day. Our default radius is R20 unless the drawing asks for something else, because R20 is the number that keeps a commercial bowl both usable and quick to clean. For domestic work R10 looks better and nobody notices the cleaning; for a service kitchen R20 saves minutes every shift.
03Drain and overflow, decided by the carcass
The drain hole is where a custom sink stops being a design exercise and starts being plumbing.
- Centred drain — simplest trap layout, but the trap lands in the middle of the cabinet, which is where the shelf wants to be.
- Offset drain — up to 150 mm towards the back, so the trap hugs the rear panel and the shelf survives. This is what most commercial drawings specify.
- Slot overflow — a machined slot on the front wall. Cheap, invisible, and it needs the bowl to be at least 180 mm deep to sit above the water line.
- Rear overflow box — welded box behind the bowl, connected to the drain pipe. Used where the bowl is shallow or the tap is deck-mounted on the rim.
Whichever you choose, the overflow has to discharge below the drain fitting or it will not drain at all. We check that on the drawing, not in the workshop, because moving a welded box afterwards is cutting the bowl apart.
04Welding the bowl into the plate
A bowl is never just dropped into a hole and welded round the top. There are three joints and each one has a job.
- Rim to plate, top face — full penetration, dressed flush, then grained in the same direction as the surrounding surface. This is the joint you see.
- Rim to plate, underside — fillet weld, not dressed. This is the joint that carries the bowl when it is full of water.
- Bowl wall to bowl base — welded and passivated before assembly, because after assembly nobody can reach it.
After welding, every joint is pickled and passivated so the chromium oxide layer is restored, and the bowl is checked under oblique light: a dressed weld that has not been passivated shows as a dull band inside a bright grain and will be the first place to tea-stain.
05What to put on the drawing
One page is enough, and these are the lines that stop a round of questions.
Send that and the quotation comes back in 24 hours with the bowl priced as its own line, the plate as another, and the finish as a third — so you can see what the radius is costing you. Lead time is 15 working days from a confirmed drawing, all in one building, packing on-edge with formed edges protected, and an inspection sheet recording bowl position and edge tolerance.
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