How to deal with reaction wood?

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Forum topic by jacobgerlach posted 10-15-2013 06:00 PM 1289 views 0 times favorited 9 replies Add to Favorites Watch
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29 posts in 1734 days

10-15-2013 06:00 PM

Topic tags/keywords: jig poplar milling

I previously posted here asking for help choosing lumber for some projects.

Fast forward to now, and I am working on a pair of bookshelves. I’m building the case from birch plywood and picked up some S2S poplar today for the trim. I built this jointing jig for my tablesaw and have been happy with it so far, especially because it gives me some options outside of expensive S4S home store stock.

I need to rip most of the poplar to 1 1/2”, but the first piece I ran through came out with 3/4” of bow over about 5 feet. I have heard this called reaction wood. What’s the best way to deal with this? Specifically, is there anything I can do besides just cutting it wide and jointing the bow out with my jig? My boards are 7-7.5” wide, so I was hoping to get 4 pieces of trim out of each.

9 replies so far

View pintodeluxe's profile


5623 posts in 2781 days

#1 posted 10-15-2013 06:08 PM

I have seen it happen many times. Sometimes the wood has internal stresses, and you just have to work around it. In a bookcase, the trim will be attached to the sides or frame so you may be okay.

I have largely resolved this issue in my shop by using rough lumber. I dry it and let it acclimate to my shop, then joint it. That way any movement happens before the milling operation.

Two related topics I guess, wood movement and reaction wood.
The reaction wood problem is tough when you need long, straight lumber.

-- Willie, Washington "If You Choose Not To Decide, You Still Have Made a Choice" - Rush

View jacobgerlach's profile


29 posts in 1734 days

#2 posted 10-15-2013 06:16 PM

Pinto – are you saying just clamp/glue it to be straight when I attach it?

I thought that using kiln dried lumber I didn’t really need extra drying time. The lumber was in a warehouse nearby and I’m working in my garage, so both are the same climate. I have read about letting wood acclimate but I assumed that only applied if you’re working indoors.

I tried milling down the bowed piece from my first attempt. Straightening out one edge worked fine. When I ran the second edge through the saw to get it parallel I got 1” of cup and more bow!

View bondogaposis's profile


4688 posts in 2319 days

#3 posted 10-15-2013 06:25 PM

Some boards are just like that. I recommend using a different board for the trim and saving that board for some other use.

-- Bondo Gaposis

View JustJoe's profile


1554 posts in 2006 days

#4 posted 10-15-2013 06:27 PM

I just looked at that jig you linked to. When you say bow, is that side-side or up/down?
If it’s side-side. You say the first cut is good and the second one it goes all wonky. I’m assuming that means you use the jig to make one edge straight, and then remove the jig and rip the second edge normally just using the fence. If that is so, when you’re making the second rip cut can you see the board physically twist/bow once it goes past the blade? Is the kerf getting much wider, or closing up? If that is the case then there is no cure. It might be reaction wood, it might be that the kiln operator was in a hurry and cranked it up to the “toast, dark” setting. If you’ve only cut the one board, you may consider returning the other boards and finding a different source.

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View jacobgerlach's profile


29 posts in 1734 days

#5 posted 10-15-2013 06:38 PM

When I say bow I mean side to side. I initially got bow when ripping a smaller piece off of the large board. I used the jig to straighten one side of the smaller piece. Joe, your assumption is right – after getting a straight edge with the jig I used a regular rip cut with the fence to get the second edge straight. The kerf was visibly opening up as the board went past the blade (for both my initial cut off of the large board and when cutting the second side of the cleaned up piece). For the last cut, the kerf was opening and the piece was also bending up away from my outfeed table as I went along.

Bondo – is there any reason to think the other boards from the same source will be any different?

View pintodeluxe's profile


5623 posts in 2781 days

#6 posted 10-15-2013 06:41 PM

It is a personal decision as to whether the board is usable. If it is held in place with a rabbet and glue, it may never be a problem.

-- Willie, Washington "If You Choose Not To Decide, You Still Have Made a Choice" - Rush

View jacobgerlach's profile


29 posts in 1734 days

#7 posted 10-15-2013 11:30 PM

I had planned on just gluing the trim to the case. It seems like any joinery used to take out that big of a bow would be pretty stressed.

I’ll need to spend a little time thinking about how to adjust my design so that I have a better way to take the bow out.

View Clint Searl's profile

Clint Searl

1533 posts in 2329 days

#8 posted 10-15-2013 11:53 PM

Throw it in the fireplace.

-- Clint Searl....Ya can no more do what ya don't know how than ya can git back from where ya ain't been

View runswithscissors's profile


2725 posts in 1993 days

#9 posted 10-16-2013 07:59 AM

Rather than toss your wood, here’s a trick that might work for you. Clamp one end of your stick (the one you just cut, with the bow in it) into your bench or woodworker’s vice. Hold on to the other end. Using a heat gun, play heat over most of the length of the board (or where the bow seems to be most pronounced) until the wood is good and hot (5 to 10 minutes worth). Be careful not to scorch the wood. Then start flexing the wood to work the bow out of it. Do this somewhat gradually. Apply more heat if it seems necessary. Overbend (beyond merely straight). Now hold it in that position for a few minutes. It won’t take long to cool.

I haven’t tried this with poplar, so can’t say how it will react.

I did this one time with a 12’ length of crown molding that was like a ski at one end. I got a discount on it at the lumberyard because obviously about 3’ of it were useless. Of course that was oak, which is inherently a good bending wood. After straightening, that molding never did resume its ski shape, but stayed straight. The whole process probably took me no more than 7 or 8 minutes. You can do this even to remove twist or corkscrewing. In that case, grip the free end with a clamp so you can twist as you flex.

What do you have to lose? Better than tossing the wood and taking a chance on another piece.

Good luck!

-- I admit to being an adrenaline junky; fortunately, I'm very easily frightened

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