NEW YORK (AP) _ Tim Allen is back on the set of ``Home Improvement,'' clean and sober after a tough court-ordered alcohol rehabilitation program.

``It was a boot camp,'' Allen says in Sept. 19-25 TV Guide. ``It was horrible. But (rehab) is the best thing I have ever done.''

Allen was arrested last year in Michigan by police who clocked him doing 70 mph in his Ferrari in a 40-mph zone. He pleaded guilty to drunken driving, was fined $500 and got a year's probation. Allen checked into the California rehab center in April as part of his sentence.

``Home Improvement'' co-star Patricia Richardson has noticed a dramatic change in Allen's personality on the set. Before, ``he would fume quietly, and it would come out in a mean streak of humor,'' Richardson said.

Now, he's ``sober in more ways than not drinking. He's more grounded. He doesn't back off or go away and fume,'' she said. ``The fact he could make such a major life change in the middle of all this is a miracle.''

In 1978, Allen was convicted on drug dealing charges and served 28 months in a federal prison. He went on to become one of the richest entertainers in America, ranking sixth on Forbes magazine's latest list with $77 million in 1998 earnings