Precisely how precise?
During a visit to a woodworking friend's home, my pal asked me to check out his tablesaw. He was having "issues" with the setup and wanted a second opinion.
There in his garage shop was a nice contractor's saw, complete with a shiny top, perfectly lubricated handwheel threads, and not a speck of dust on it. While I admired the gleaming saw, my friend passed me a board he had ripped on it. I sighted down the cut edge and noticed the smallest amount of roughness on the cut. Trust me; you really had to squint to see anything.
Next, he removed the saw's throat plate and blade, and went to a special drawer where he stored his precision measuring devices. Armed with his machinist's dial indicator, he mounted it to the saw top, and gingerly pushed the instrument to the arbor flange. "There," he said, his voice heavy with disappointment, "The arbor's off by .002", and I'm having a bear of a time getting it perfect."
I looked at the board, noted the measurement, and studied the board again. "Looks good to me," I said.
He sighed, reassembled the saw, made another test cut and held the result up close to my face. "You see?!?" I looked again, and if I squinted just right, turned my head to the side, and positioned the board in the proper raking light, I could barely make out some roughness.
"I dunno… Still looks good to me."
He turned, shook his head and said, "You just don't get it, do you?" It was then that I remembered what he does for a living: My friend is an engineer.
Wood is pretty amazing stuff. It seems so substantial, yet it constantly moves in response to changes in temperature and humidity. Woodworkers for centuries have understood this and adapted their methods of work to account for it.
I get a kick out of woodworkers who routinely turn to machinist's tools to perfect the thickness of a tenon or the fit of a set of dovetails. If you cut the joint on a rainy day and assemble on a sunny one, you'll see the magic—and feel the frustration—of our preferred medium of work. Hey, we aren't machining parts for the Space Shuttle.
And, getting back to my buddy's beef: Trying to get a perfect "glue-line rip" right off a tablesaw is an act of magic you don't need to attempt. Many experienced woodworkers will joint a board, rip it an extra 1⁄32 " wide, then joint the ripped edge to smooth it and bring the board down to size.
Remember, when wood is involved, "close enough" is usually close enough. It's more fun to build projects than to worry about thousandths of an inch.