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I have been under the impression that if you want to resaw lumber, the tool of choice is a bandsaw. I don't have a bandsaw, but I do have a contractor-style table saw. However, I have read elsewhere that it isn't safe to resaw lumber on a table saw.

But looking through Mathias Wandel's site, I found a couple places where he resaws lumber using his table saw; like here, for example.

Is this considered safe? If so, what are the rules of resawing on a table saw? I presume I should treat it like a rip cut. Is there a minimum safe length of board, where going shorter would become unsafe? Are there other safety considerations specific to resawing I'm not aware of? (Obviously all the standard rules of table saw safety should still apply: Don't stand directly behind the board being cut, use push sticks, etc.)

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Is this considered safe?

It can be done safely. A tall fence, featherboards, and good push stick make a big difference. Not everyone takes the time to set all that up, though, so it's worth pointing out that (like any TS operation) it can also be done unsafely.

If so, what are the rules of resawing on a table saw?

Equipment:

  • tall fence: The big difference between a normal rip cut and resawing is when you're making a regular rip cut, the wide part of the board bears on the surface of the saw. If you're going to stand a board on edge and cut it, you want a similar surface for the board to bear against. A normal TS fence is maybe 4" tall; if you're trying to stabilize a 8" board, you want something taller.

  • featherboards: Use them at least to keep the bottom edge of the board tight to the fence. If you can manage a tall featherboard to keep the board flat against your tall fence, even better. Remember that featherboards should be set up before leading edge of the blade -- you want to push the stock against the fence, not against the blade. Featherboards also add some kickback protection, which is important when making a non-through cut and you don't have the benefit of anti-kickback pawls. (A riving knife is great if your saw has one, but not every saw does.)

  • push stick: Excellent for exerting control over the stock while keeping your fingers well away from the blade.

  • zero clearance insert: If you're resawing, you're likely creating thin stock that could slip into the gap in a regular throat insert. A zero clearance insert will avoid that.

  • infeed and outfeed: Featherboards and a fence control the lateral motion of the stock. If you're working with long boards, you'll also want help controlling vertical motion. An outfeed table or rollers keep things safe by eliminating the need for you to reach over or behind the blade. Something on the infeed side, even just a single roller, lets you comfortably manage the board from a fixed position at the saw instead of trying to feed the first part of the board from several feet back.

  • clean, sharp blade: Heat is always a concern when ripping, but even more so when half the blade is spinning in an enclosed space. If your blade is dull and/or covered in pitch, it's going to run a lot hotter than a good clean and sharp blade. A blade lubricant made for saw blades helps too. A rip blade is the right tool for the job here.

Technique:

  • straight, flat stock: Don't try to resaw a board that curves in any direction; work only with straight, flat boards that are well dried.

  • work in steps: If you try to make a 3 1/2" cut down the length of a board, you're probably going to run into trouble. Typical home shop saws will bog down trying to make such a deep cut in hardwood. Even if you have a saw with plenty of power, you run the risk of generating a lot of heat, possibly scorching the wood. Instead, take smaller bites, raising the blade after each pass; you'll be able to feed the stock faster, which means things stay cooler.

  • cut from both sides: Even if you're resawing stock that's narrower than the capacity of your saw, cut partway in from each side rather than trying to cut all the way from one side. This reduces the risk of pinching the blade as internal stresses in the wood are released. Just remember to always keep the same face of the board against the fence so that both cuts are the same distance from that face.

  • don't cut through: If you leave a little wood (maybe 1/4"-1/2") in the middle rather than completing the cut, you'll be able to manage both halves of the board together through the entire operation. It's easy to finish the cut with a handsaw, and you're going to clean up the cut sides of each board with a planer (or a plane) anyway.

  • stay out of the line of fire: Standard TS operation advice, but always worth repeating: don't stand in the way of a potential kickback.

The main idea, as with any TS operation, is that you want to keep everything well controlled and keep your body parts out of harm's way.

Is there a minimum safe length of board, where going shorter would become unsafe?

As with ripping, I'd want the width of the stock to be a good deal less than the length.

  • 3
    Great answer, Caleb. Another advantage of taking small bites ("work in steps") is that any internal tension is released incrementally rather than all at once. Also if you have a rip blade, this would be the time to install it. – rob May 12 '15 at 3:14
  • Absolutely agree with both point, @rob. I'll edit to mention the rip blade especially. – Caleb May 12 '15 at 3:16
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The danger when resawing on the table-saw lies in kickback due to the internal stresses which may cause the log to pinch the blade.

This is less of a risk on a band-saw because if it does pinch then the log will be pulled down into the table.

  • When you say "log," do you mean a log being cut into boards for the first time? Would this answer also apply to a rough sawn lumber that you wish to resaw? – Charlie Kilian May 11 '15 at 21:50
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    Likely he means a log being milled for the first time; I think there is some confusion around the terms. The stresses won't be as great if you're just resawing thinner boards, but they still apply. A riving knife or splitter would help to alleviate this, but you still wouldn't be able to handle workpieces more than 10ish inches because of the limited blade size. – Daniel B. May 11 '15 at 22:59
  • more like 8", assuming a 10" blade with hub a bit below the surface and two passes that won't line up perfectly ... Bandsaws with 12" resaw capability are available at not-unreasonable prices. – keshlam May 11 '15 at 23:16
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    You can handle boards wider than that I'd you're willing to finish the job by hand. 3.5" on either side cut out with the table saw acts as a really good guide for a ryoba or bowsaw. – aaron May 11 '15 at 23:16
  • If a sawmill is cutting a log into boards for the first time, that's not resawing, it's head sawing or primary sawing. – Steve Nov 18 '17 at 0:11

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