Welded, Undermount or Top-Mount Sink

A brushed stainless worktop seen from above: a wide shallow basin on the left, a deep bowl with a drain on the right, a spring-mounted pull-out tap between them, a flat channel along the front edge and a shelf of glasses behind. — The welded version of the joint: bowl and deck were one part before the first cut. The other two methods leave a line at this seam that a fingernail will find.

01The two questions that decide it

Ask them in this order and the table becomes almost unnecessary.

Fig. 1 — The cleaning regime decides the joint before appearance gets a vote.

If nobody cleans the joint deliberately — a rental, a serviced kitchen, a busy pass — then the answer is the joint with the fewest places for anything to sit. That is the welded bowl, not because it is better made, but because it has no bead.

02Second question: who replaces the bowl

Bowls get beaten up. A commercial bowl in a service kitchen has a working life measured in years, and what happens on the day it fails is decided now, on the drawing.

Replacement, by joint
Joint	To replace the bowl	Downtime	Cost of failure
Welded-in	Cut it out of the top; the top is usually replaced with it	The whole top comes off	High — the top is the bowl carrier
Undermount	Release the clips from below, lift the bowl out	An hour, from underneath	Medium — access decides it
Top-mount	Lift the bowl out of the aperture	Minutes	Low — the reason busier kitchens pick it

This is the column that decides commercial work and is missing from most comparison tables. A welded bowl in a client's home is a lifetime object; the same bowl in a cafe is a future removal job, and pretending otherwise is how a specification becomes a complaint.

We ask the replacement question on every drawing we quote, and we write the answer on it: bowl welded in, or bowl replaceable from below. Our clients in hotel and hospital work almost always choose welded; our clients fitting out rental property almost always choose top-mount, and both are defensible once the reason is written down.

If the choice is still open, the comparison of a welded bowl against a separate one follows the water path instead, which is the other half of the same decision.

03The tolerance chain, which nobody explains

The aperture is one link in a chain, and the chain is why a sink sometimes does not line up even though every number on the drawing is right.

Sink template — supplied by the sink maker, and it changes between model years.
Aperture cut — we hold ±0.5 mm from the template.
Bowl position from datum — also ±0.5 mm, so worst case is ±1.0 mm before the bowl is involved.
The bowl's own tolerance — a pressed bowl is not a machined part.
Carcass position on site — usually the largest term in the chain.

The ±0.05 mm figure is an edge tolerance on a machined edge and has nothing to do with this chain. Anyone who quotes it for an aperture is quoting a number they cannot measure on a cut-out.

04What each one costs, in shop operations

Not prices — shop operations. Once you see the operation count, the price difference stops being mysterious.

Fig. 2 — Relative shop operations. The welded bowl is not expensive because of the plate; it is expensive because dressing a weld inside a grain is hand work.

We fabricate bowls from 1.2 mm sheet in 304 or 316L and weld them into 5–10 mm plate, or cut an aperture for a bowl you supply. The quotation comes back in 24 hours with the joint priced as its own line, so the weld appears next to the clip rather than hidden in a total.

Lead time is 15 working days from a confirmed drawing, all operations in one building, packing on-edge with the edges protected. The inspection sheet records the aperture position from the datum and the edge tolerance, and that sheet is what the written warranty is settled against.

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