Warping wood

[Keefie]

I have had the same trouble every time I make an 8" x 10" x 3/8" thick blank for portrait work. I have bought kiln dried timber planks that were absolutely flat, then I would resaw them 8" wide and just over 3/8 thick then put them through the thickness planer to bring them down to the 3/8" thickness I want, then finally cur them 10" long. They come out perfect, the right size and flat too. then within an hour or so they have warped so much there is almost a 1/4" gap under the middle when it is laid on a flat surface - this makes it awkwatd to cut patterns as the wood "bounces" where it's not supported in the middle and also it spoils the finished items. It is for this reason I mainly use birch ply for portraits/ pictures etc. I have tried oak, beech, walnut, maple and a few other woods and they all seem to warp. Does anyone know what I'm doing wrong??  I know in the USA you can but these blanks already cut to size (and flat too) but in the UK I have yet to find a supplier that will sell them ready sized and planed. I look forward to hearing what I have been doing wrong

[dgman]

Hey Keffie. The #1 reason your boards warp is unequal moisture absorption on the top and bottom of your board. Here are a couple of things I do to help prevent this. Plane equal amounts from each side of the board.
After planing, do not set your board flat on your bench or any other surface, you need to let air circulate evenly around the entire board. What I do is lean the board from the top against a wall or bench to allow for air circulation, or if you are planing a lot of boards, stack the boards with stickers between them to allow for the air circulation.
You will want to let the boards equalize for several days before using.
If you use tape on your blanks, do the same on the bottom especially if you are not going to finish cutting in one sitting.
Good luck!
P.S. Even if you buy ready to saw boards online, you still have to take these precautions!

[daliclimbs]

My man Dan is right as usual  ... I mill most of my lumber and resaw a lot of reclaimed wood. Air flow is essential! I generally don't lean my lumber like Dan to help me save some space. But I put stickers between all my lumber always! Even if its down to EMC of 7% or below. I put enough stickers on my bottom boards to get them at least 6-8 inches off the floor and then a minimum of 3/4" between each row. This allows plenty of airflow and lets them dry evenly. Some woods have a life of their own and I will leave them thick and allow them to dry to about 7% moisture, then if they cup I can plane it out and they stay stable from that point.

[BilltheDiver]

I agree with Dan & Dali, however there is another factor as well.  When you saw a piece do wood you often release inner stresses inside the wood which will result in some war page.  I still think uneven moisture is the main culprit though.

[dgman]

So Keith, did this help?

[Keefie]

I cut my last section of the plank yesterday so I now have 2 x 1/2" planks and stacked them on 1" square strips of wood to let the air get to them. they have both warped, so I'll wait for them to stop moving then plane them to size(I left them oversize just in case). I checked the moisture content and it was 5.9      How long would you recomment to leave the planks before planing them?

[dgman]

I would give it three or four days. When you plane the boards, make sure you take equal amounts from each side. What I do is take very small cuts at a time and flip the board after each pass. After planing, do not set the boards flat. Stack and sticker or lean them to allow for air flow around the board.

[BilltheDiver]

Remember you need to run a face across a joiner before putting them into a planer.  Otherwise you will still have twisted or bent boards.  If you don't have a joiner make a sled and use wedges to stabilize the underside and then the planer can face the top side.

[wha]

I use to have the same problem after planning my boards to 1/2" thick.
To prevent it from happening I cut 2 pieces of 3/4" ply 12x12 and clamp my planed piece between and leave it for 3 to 4 days before I use it.
This has helped a lot. I do the same thing for all my blanks for ornaments, I leave them clamped until I need them.

[Keefie]

I'll have to give the clamping a try, thank you all for the help.
Keith.