Replies

1. 
   john_c2 | Jun 11, 2020 06:29am | #1

   Some boards just dont behave well after resawing. They usually stay flat if you take the same amount from each side. So if you want 1/2 inch from a 4/4 board, take 1/4 inch from each face. A lot of wood ends up in the dust collector, but you should get one good board. If you resaw and it gets wonky, you end up with nothing.

2. 
   DRBWWing | Jun 11, 2020 10:19am | #2

   Bowing occurs because of tension release and cupping is due to unequal moisture balance. Both are issues resawing lumber. Air dried lumber is probably better because kiln dried lumber tends to have more issues with tension. This is because kiln drying does not allow a board to de-stress gradually like air drying does.

   Do not mill resawn boards right away - even it they look perfect coming off the bandsaw because a lot can happen in just a few hours!

   The resawn boards need to re-acclimate before milling. Put them in stickers with bows opposing each other, and clamp the whole stack between two thick, straight boards. Or put on the floor with heavy weights on top. Hold them for several days up to a week, preferably in a climate controlled room, out of the sun and out of air drafts.

   When you start the milling process, go slowly, no more than 1/16" off each side per session - then immediately back in stickers and clamps for another few days.

   Even doing all this, you may not be successful, because may be into some lumber that particular tree is tension filled and not going to behave.

3. 
   geedubbee | Jun 11, 2020 12:35pm | #3

   I have had batches of ash, mahogany and even hard maple that contained some lively boards. It happens despite our best efforts to handle things properly.

4. 
   peterj_nz | Jun 11, 2020 06:30pm | #4

   Thanks for the advice, I will give it another go and let it rest. If you leave kiln-dried timber to air dry does it eventually relax a bit?

5. 
   mdorsam | Jun 11, 2020 07:41pm | #5

   Peter:
   My experience is that the quality of the kiln drying - the process and care - is important and unknowable. There are many ways to kiln dry lumber... some very effective and others whose sole virtue is expedience. The stuff from Big Box stores is kiln dried, and will bow horribly if you process it too quickly.
   My answer to your second question is that shop-acclimation is important. Anytime you purchase lumber, let is sit in the shop long enough for it to acclimate to the ambient temperature and shop humidity... minimum 3 days, more if your climate requires it.
   John's recommendation is spot-on. When you first re-saw lumber, you expose new grain to the air and stress-relief begins. You can partially mitigate waste wood by planning to use the first cuts on smaller project elements (bowing will be less of an issue, the shorter the needed finished part), and utilizing what should be the best portions for larger project elements. The innermost piece will have freshly exposed wood on both sides
   Finally, you should re-saw heavy (a good 1/4") on the outside cuts, as they will bow the most. The heavy cut allows you more planing alternatives.
   My apology for the very long answer...

6. 
   peterj_nz | Jun 12, 2020 05:22am | #6

   Thanks for the great responses, everyone. I will use these tactics on the next project

7. 
   chipsawdust | Jun 15, 2020 12:17pm | #7

   I've had that problem with just ripping thick white oak. Tension makes it close back up after the riving knife and sometimes can cause the cut to burn. I ended up putting wedges in the kerf after the blade to stop that from happening, which is a tricky business.

   Since then I've resorted to ripping on the bandsaw, but that doesn't mean there's no tension. Good discussion here.