Ripping a bunch of boards; they bow away from the saw, now what?

[Pete S]

I have about forty 15/16" thick soft maple boards that are about 6 feet long. I need to rip them into 1 1/2" wide strips. They have been rough planed to this thickness and that finish is good enough for the job at hand. In my humble experience, they seem to be pretty nice boards. Most of them are pretty straight. The edges are rough off the sawmill. So--- I jointed one edge to make them dead flat. Now I take them to the table saw. It's a pretty new Delta hybrid saw with a nice sharp carbide blade. When I rip the board, the 1 1/2 inch strip that I am cutting is closest to the fence. About 1/3rd of the time the slat bows away from the blade, pushing the still uncut part of the board away from the fence a little bit, let's say as much as 1/8". This, of course, keeps the slats from having a consistent width. The slats that did this, when the cut is complete, are, indeed, warped. But, if I wait an hour or so, most of the warp is gone from the slats. What can I do to prevent this bowing away from the blade?

Pete Stanaitis

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[-MIKE-]

My first thought would be to make the cuts with the widest part of the board against the fence... in other words, cut off the 1-1/2" on the non-fence side of the blade. that way it bows away from the blade and has nothing to bind against.

Yes, this means you have to set up the fence for every cut. If you're worried about then not being exact duplicate cuts, cut them a little proud, then set the fence to 1-1/2" and cut them again to be exact duplicates.

Before I had a good table say and wanted a bunch of duplicates like this, I would cut them all proud, then run a bunch of them, side-by-side as a group, though the planer.

[Lew Hodgett]

-------------------- HOw wide are the boards on average?

Lew

[Limp Arbor]

Feahter board:

rarely have the splitter in my saw but when I am ripping long boards it always goes back on.

[Bill]

Try to clamp them flat as you cut them? with sacrificial boards (maybe screws?). I don't even have a TS, this is just a thought. GL!

Bill

[Sonny]

I have had lots of logs milled and the lumber air dried. Your problem is common with air dried lumber (similar with what I have experienced, also), i.e., the wood still has some elevated moisture content. Kiln drying would help reduce the amount of bowing/warping you are experiencing. Try cutting the boards at a much slower feed rate. This will/should help, some.

The wood may also have stress within, so your cutting relieves the stress and bow one way or the other. If you flip the board around and cut from the other end, does it bow the same way? If so, then the main problem is the moisture in the wood, not so much the stress factor.

The cut line is heating up, as you cut, drying out the wood along that cut line. As it dries, during the cut, it will shrink along the cut line, pulling itself toward the cut line.... similarly to a wet board left in the sun (drying mostly/faster on that exposed side) and it bow or warp on/toward the sun side.

Run the boards throught the saw at a much slower feed rate, make sure your blade is sharp and make sure the fence is parallel to the blade.

Sonny

[Swingman]

What he says ... use a feather board in front of the blade, and a splitter behind it.

From your description it is the wood that is most likely the issue, not your table saw.

If the distance from the front, cutting edge, of the table saw blade to your fence is 1 1/2", then your rip will be exactly that, _providing you keep the wood against the fence_.

With reaction, or case hardened, wood you sometimes have to force the issue of contact with the fence in front of the blade, thus the _feather board_.

A _splitter_ is a good idea to use when cutting any kind of reaction wood, not only for safety, but particularly with maple, as it burns easily.

[Larry Blanchard]

Read the title of this post - the boards are pulling *away* from the cut line. That's called reverse case hardening and IIRC has something to do with the wood being overly dried at the kiln.

[dpb]

As others have said, you _might_ be able to force them to stay against the fence but 1" maple is pretty thick and if it is going to want to move the amount of force required may be more than you can exert and still move them past the blade.

I'd ask how they've been stored, whether were kiln-dried or air dried, how long, etc., etc., etc., ...

My first inclination would be to

a) run them thru the planer again and then let acclimate for a while if can afford to lose a little thickness, or

b) rip them a little wide and then to final thickness after they do reacclimate.

Almost certainly a moisture equilibrium problem--whether case hardening owing to bad kiln temperature cycle or uneven air drying or storage problems after the fact is indeterminate w/o knowing the history, obviously.

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[dpb]

On 1/26/2012 12:18 PM, SonomaProducts.com wrote: ...

Not his problem; it's moisture inequilibrium from one of many possible causes which one (or more) of which is/are indeterminate for lack of complete information.

It's moisture because he notes that after they strip that has flexed/bent/bowed/whateveryouwishtocallit has had time to reachieve a surface equilibrium it reverts to straight (or nearly so). Reaction/stressed wood will not recover in that manner.

[dpb]

On 1/26/2012 5:50 AM, dadiOH wrote: ...

Bingo! on the latter...

The former a bandsaw won't make any difference either; they'll still move when the stress is relieved (altho one could avoid the fence problem which may be all you were intending; just pointing this out to OP in case not obvious to him).

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[John Grossbohlin]

As others have suggested feather boards, or a power feeder, could be used. Alternatively, cut the boards with the fence set to 1 5/8" to allow for the problem you describe. Then run them, on edge, through your thickness planer. The planer will make the edges parallel. If as you say they straighten out after a while you'll be able to get your desired, consistent, 1 1/2" width without having to wait for them to dry further. You might want to joint the board between slices... though you might not need to.

I just did something similar as the magnetic switch on my table saw failed. Rather than do nothing while waiting for the new switch to arrive I cut everything on the bandsaw. Then I jointed an edge and ran the boards through the thickness planer. It worked fine and my project got done.

John

[clare]

Sounds to me like the heat of the cut is causing the bow. Your blade is sharp - is it clean? If it has resin buildup on it , it will run hotter.

Another possibility is a "short fence" Just fasten a 5/8" plywood or whatever to the fence - stopping about mid-blade so the bow can go wherever it wants without moving the work away from the fence or the blade.

[Larry W]

Attach a board to your fence that is about 1/2 the length of the fence. The end farthest from the front should be right about where the cutting edge of the saw blade is. Naturally reposition the fence as needed to cut the 1.5" strips with the board attached. The space behind the board will allow the maple strip to curve or bow without pushing on the stock. I think you find some examples by googling something like "table saw half fence"

[Swingman]

That works great, and is an excellent tip for ripping reaction wood.

Big caveat, though. The OP will definitely want to use a splitter in case the reaction wood closes up behind the blade, which can put you big trouble once you push past the end of the half fence with no splitter.

[Larry W]

Absolutely right of course. I am in the habit of ALWAYS having the splitter installed except for dados or other cuts where that's impossible. I guess I should be more mindful that others may not follow the same practice. That's the best thing about a riving knive setup, there's much less need to ever remove it compared to a splitter.

[Lew Hodgett]

RE: Subject

This is a natural for a "Board Buddy" with yellow wheels.

Try ripping 1-1/2" x 5/8" x 24 ft long strips from wet Doug Fir, nominal 2 x 12 x 24 ft wet construction timbers without one.

BTDT.

Lew

[Swingman]

Me too ... Mine is what's left after you take off the plastic shields, pawls and springs from a unisaw blade guard. Works good though, and removes and installs in seconds. Rare is the rip made without it.

[John Grossbohlin]

Over the past 10 years or so I've had Biesemeyer T-Splitters on my contractor and cabinet saws. I am very good about making sure they are installed on through cuts. They are easy to take on and off and work well... the potential alternative is painful. ;~)

John

[Pete S]

They vary from about 4 1/2" wide to about 7" wide. Pete Stanaitis

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