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I joined four 1x6x32" boards.  The boards were flat and all lay flat together before joining.  After joining, the middle was bowed.  I drilled all of the holes on the left side of the boards.  Should I have alternated sides?  Or is there another reason for this?

Thanks for any help!

Dolores

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Hi Dolores,

A board or joined boards bow because of uneven drying. If the moisture content in your boards was high and you joined them and left them flat on a table for a while, the boards will bow. To prevent this happening, you must do 2 things- alternate the growth rings on adjoining boards (so one boards' growth ring goes up and the one next to it goes down) and keep them elevated after joining them on small scraps of wood so all the boards dry evenly on both sides. the location of pocket holes doesn't matter. hope this helps.

Thanks for your reply.  I did alternate the growth rings.  When I removed the clamp after screwing in the last screw the boards were already bowing.  This was for a top for a dresser I am making.  I now have them laying flat on the floor with the dresser setting on top of them.  

Dolores,

Can you make rip cuts, between the joined boards, and then rejoin them?---

so as to salvage what you have invested.

  What joinery method did you use?

Dolores,

Can you post photos?  What kind of material did you use....oak, pine, etc.? 

Thanks for your replies!  Yes, I will post photos later this evening. And it is pine.

Wood doesn't shrink, swell, or warp except for one reason---

change in MC, which is related to changes in relative humidity (not temperature).

  THE CAUSES OF WARP IN LUMBER SEASONING

http://ir.library.oregonstate.edu/xmlui/bitstream/handle/1957/4870/...

Hate to ask the obvious, but how did you edge the boards?  Could one of the boards be cut not true at 90 deg?

with a jointer.  The individual boards are not cupping - it is the whole joined board that is cupping.

Rick said:

Hate to ask the obvious, but how did you edge the boards?  Could one of the boards be cut not true at 90 deg?

flip the boards, so grain goes different each board....anything i think over 30 long needs support, 32's right on the line :)

The types of wood warping include:

  • bow : a warp along the length of the face of the ood
  • crook: a warp along the length of the edge of the wood
  • kink: a localized crook, often due to a knot
  • cup: a warp across the width of the face, in which the edges are higher or lower than the center of the wood
  • twist: a distortion in which the two ends do not lie on the same plane
  • check: to split along the length of the board (often due to improper drying)

When edge joining boards, using the Kreg joinery fasteners, 

I'd suggest alternating the direction of the screws. 

REASON:  so as to obtain more equal clamping pressure on the joint.

Thanks for all the replies.  

@Ken - you said earlier that the direction of the pocket holes made no difference and now you suggest alternating the direction?  That is what I will try as it seems that it would equalize the pressure.  Thanks!

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