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bending a long piece of 2x4

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  • bending a long piece of 2x4

    Hi guys! I'm building some stair rails and I bought two clear fir 2x4x16'. However, they both have a bit of a bow to them. I think it's called crown. So, how would you go about making them straight and staying straight. I didn't think it mattered that much when I bought them because I figured they would bend a bit. When I placed the 2x4 on the steel posts it was quite a bit of difference. Being clear fir, I guess it's a bit dryer and doesn't have much give. I rigged up some clamps to try to bend the 2x4's. What is the proper way to get them straight without waiting decades?

  • #2
    I don't quite get what you are trying to do. Are you trying to encase the 'steel posts' in fir? are they 16' long of are you cutting them into shorter sections. Can you just bond the fir to the steel posts and fill the anchor holes with wood filler? Even with all my tools I would have trouble straightening a 16' long timber. The longest you can do with decent results is twice the length of your jointer bed and even an 8" jointer can only do about 13' successfully. You also need to be sure that the board is dry ~8% moisture content and evenly dry by allowing air to flow around it.
    Please clarify what you are doing and perhaps we can provide a clearer answer

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    • #3
      Hi Wayne! I'm using the 16' fir as the top handrail for the stairs. I have four steel 1.5x1.5 vertical posts with a small section of flat bar welded on top. The flat bar is at a slope and the 16' fir will be bolted to that from underneath. I ran a string to make sure all the vertical steel posts lined up. If I were to try and bolt that 16' fir on top of the vertical steel posts, the 3.5" side of it would be really offset on the flat bar about 5/8". I didn't want to bolt it at the bottom and try to bend it in place as I get to each vertical post. I think that will either split the 16' or rip out the vertical steel post. Let me know if this is still not clear. I'm incorporating steel into the hand rail just to make it as sturdy as possible and still use wood ballusters/spindles. Any suggestions?

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      • #4
        You could use a jointer to take the bow out but then you would have a 2 1/4 wide straight piece (3.5 - (2 X 5/8)) so that is not a good plan. I really don't think you will require much force to straighten a 16' piece by 5/8". I would pin both ends then allign it at the 8' make and pin it (screw to steel flat bar), any varriance in the two 8' sections will be so small it would not be visible.
        There is one trick you can try but no guarantees. The reason for the bow is that the short side has lost more moisture than the long side, if you have some unfinished concrete in the house lay the board on the floor cup down ( ends touch floor, gap in middle) and check it at least every half hour. The board will absorb moisture from the floor into the side that lost it and begin to elongate thereby reducing the cup. When it is straight enough bolt it on and add the finish to help balance the moisture gain/loss

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        • #5
          Thanks! I'll try the moisture trick first. Then I'll do as you suggested and bolt both ends first and then work the middle straight. I'd be happy to get the rail within 1/4". It didn't occur to me bolt both ends first. I was thinking bolting one end, then bend and bolt as I go up.

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          • #6
            If you fasten both ends, then bend/flex the board so it is straight, won't the two ends be forced apart due to the added length? If the board has a bow in it, then it is an arc, however slight that may be. It has to be (the length of the arc) longer than a straight line through your four points (your steel supports).

            When you lay the board on a flat surface with the cancave side down, what is the gap in the center of the 16' board? Also, what is the orientation of the board. Is the wide face of the board horizontal or is it vertical? The former would be tougher to straighten I would think.

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            • #7
              Bob, you do have a point there about the ends pushing out. However the ends that they will be bolted to are the steel flat bar and are pretty solid now. Maybe once bolted on both ends, the board won't bend at all! I'll have to measure the bend again. The first time I checked, the arc was 5/8". I measured that while the board is laying on the 1.5" side and the 3.5" side is vertical. Brooks gave me the idea when he mentioned moisture. I have the wood rigged up with clamps and I'm trying to soak it a bit to help it bend.

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              • #8
                Thanks for the advice. The moisture trick worked. I rigged up the clamps and sprayed the arched section with water and got it to bend. It took a few days, but it worked. It wasn't perfectly straight, but it got to be 1/4" of where it needed to be. Much better than the 5/8".

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