The artist for whom the dollars are in the detail

Stephen Biesty's new book of illustrations took 2,314 hours to complete. He knows this because, as he inked and drew and tinted, with small eyes narrowed in his burrow of a studio, he made a precise hourly note of progress. Every pinhead figure, every freehand curve and shaded sliver, went down, as it always has, in Biesty's log.

It is the record of a kind of genius. Incredible Explosions, or Exploded Views Of Astonishing Things, is a children's book to boggle adults too. It takes a dozen scenes and objects - a traction engine, an airport, the Grand Canyon - united only by their scale and internal complexity, and pulls them apart into intricate pieces.

With subtle perspective, Biesty shows each airport escalator, each bolt of the traction engine, even the sandwich under its driver's cap. Arrows and factual paragraphs swarm round the chopped-up machines.

Since 1992, when he published Incredible Cross-Sections, Biesty has sold 2 million volumes, a vast quantity for such traditional children's books. For his intended readers, he offers beguiling worlds in miniature, to be traced, lived in and learnt from; for their parents, reassuringly warm draughtsmanship in an age of computer games. Biesty books shine on the coffee table and, somewhere in their Lilliputian panoramas, there is always a tiny man on the loo.

The artist himself is not quite as immediately engaging. Biesty is 35, with the smooth face and straight jeans of a Microsoft programmer. He lives in a Somerset cottage of grey-gold stone between a village church and a pair of wandering geese.

Biesty's garden glows in the late-summer sun, yet he leads the way straight up to his studio and questions about his business. The room is almost bare of artist's clutter, more an office with fax and easel and three paintbrushes laid parallel on a tissue to dry. "I don't collect stuff," says Biesty.

He talks about his illustrating with a stern set to his chin, as if filling out a tricky detail. He doesn't sketch - "There isn't time to be doing reams of doodles" - but expands his work straight from thumbnail ideas to full-scale final pieces. These he completes, eyes close to the paper and hand in rhythm, layer by repetitive layer, between 7.30am and 5.30pm every weekday. "At lunchtime I go downstairs for half an hour and a sandwich."

Biesty makes all this sound like mass production. "You're employed to do one thing," he says, straight as a factory manager. "Something that's going to sell." There are no posters of his pictures on his studio walls.

More than most authors perhaps, he is part of a process. The research for his Incredible Explosions, all of which are based on reproductions or composites of real objects, arrived pre-digested in an envelope from Dorling Kindersley, his publishers in London. His ideas for books are vetted and directed by the marketing department, with an eye to the dominant American market.

Biesty seems happy to play the ego-free technician. Dorling Kindersley turn his books into CD-Roms, sell them in Tupperware- style evenings, and generally delight the middle classes; they have plenty of other well- paid illustrators. "Sometimes the pictures look better printed than in the original artwork," he says. London has sent him a "media chunk" suggesting answers to press questions. Often, he answers with "we" rather than "I".

There is a struggle at the back of this. Biesty comes from a family of frustrated artists. His brother trained as an illustrator, but "doesn't like commercial projects". His father was a fine draughtsman, but had to settle for a painting job at Rolls-Royce. When Biesty was growing up in Coventry and Crewe during the Sixties, he had to take his inspiration from the television.

"I used to watch the battles in films like Ben Hur and Spartacus and draw them up afterwards," he says, with his first hint of relish. In 1980 Biesty went south to Brighton Polytechnic to study graphic design. He discovered Victoriana: "There used to be guided tours of the sewers. That was brilliant - seeing the bits you don't normally see."

Biesty chose reconstructing castle designs as his speciality. At first, when he went freelance in 1985, demand was not overwhelming. He drew advertisements for tower blocks and stately homes for the Sunday Telegraph. Then, late in the decade, Dorling Kindersley started a children's sideline and he was rolling: fleshing out books on the Middle Ages, on Ancient Egypt, on so many subjects he can't remember the titles. In 1991 Peter Kindersley asked him to slice up an ocean liner into cross-sections. "I tried it lengthways," says Biesty, "And he said, 'Fine. But try it the other way, like a loaf.' "

From here, though, Biesty did more than fulfil a brief. To his detailing he added the dirty stuff of life. Drinking and whoring sailors reeled through his book on HMS Victory. Bodies rotted in the moat of his Castle. Like his young readers, Biesty finds glee in grubbiness. He cites Hogarth and Hieronymus Bosch, then pulls out a fax from Richard Platt, who writes the text for his books, about a mite that lives in human eye-lashes. "We're going to have to include it in the next one," he says.

Meanwhile, out in the gardenanother interest becomes apparent. Biesty's cherry tomatoes are hanging like grapes; his three-year-old son roars about on a toy tractor; his wife Liz emerges for tea. Would he rather be leading any other life?

"No," says Biesty quickly.

"Yes you would," says Liz. "He wants to build a garden, get some land."

"Well I might buy a wood," says Biesty. A little world of his own forms for a moment, beyond the page.