Resawing and going to the kiln

[David Nelson1]

I'm having a difficult time making this decision. I have quite a few Bd/ft of 2 inch thick rough sawn oak of various widths. Some, if not all of the wood has some kind of cupping. I tried re-sawing a few of these pieces and didn't like the result due to not having a flat surface to reference from.

Here is what I'm thinking of doing instead. I take all the wood to the kiln first. When I get it back, joint an edge then make a few passes on the table saw for the approximate board width. Face the board, rough plane it just to get it flat, then re-saw.

Now here is my original worry that it will warp after it has been re-sawn. I plan on stickering it in the shop for a few weeks + or - a few to mitigate this factor, then run it back through the planer for final dimensioning. This wood has air dried for quite a few years and is anywhere from 8' to 14'.

Is my thinking flawed? Opinions please. Or should I just use it for another project?

[Nelson Howe]

If it's been air dried for many years, I don't see any need to put it in a kiln. I'm pretty sure oak dries fairly fast anyway, and as long as it has been kept dry, it should be good. It will move a little if you bring it into a climate controlled space, but all wood moves with the seasons. Kiln dried will move also, and gradually take moisture back on. I may be wrong, but my understanding is that if your air dried wood is several years old, it won't get any dryer air drying. In addition, if you kiln dry some of it this month, and then store it back with the other wood (i.e., in the same environment) the two will be at the same moisture content after a little while. Do you have a moisture meter? (I actually have one I've been meaning to sell, for what that's worth.)

Also, if you have any thoughts of bending or doing bent laminations, air dried wood seems to be preferred.

As far as the rest of your plan, I'd be cautious about ripping it on the table saw if it's too cupped. That sounds like kickback to me.

If you ripped your boards down the middle (bandsaw would be better, I think), you could joint and plane them with less thickness loss. I don't know if that would leave you with wide enough boards for your project, but they would match nicely if you glued them back together after flattening.

Either way, giving them time to move after initial milling sounds prudent.

Nelson

[Frank Drew]

David,

There's always a risk of the boards moving when you resaw, but you can control that to some degree by immediately stacking and stickering them with some weight on top, and you already plan to do.

I agree with Nelson that kiln drying might not add much at this point; have you checked the moisture content of the boards with a meter?

[David Nelson1]

If it's been air dried for many years, I don't see any need to put it in a kiln. I'm pretty sure oak dries fairly fast anyway, and as long as it has been kept dry, it should be good. It will move a little if you bring it into a climate controlled space, but all wood moves with the seasons. Kiln dried will move also, and gradually take moisture back on. I may be wrong, but my understanding is that if your air dried wood is several years old, it won't get any dryer air drying. In addition, if you kiln dry some of it this month, and then store it back with the other wood (i.e., in the same environment) the two will be at the same moisture content after a little while. Do you have a moisture meter? (I actually have one I've been meaning to sell, for what that's worth.)

Also, if you have any thoughts of bending or doing bent laminations, air dried wood seems to be preferred.

As far as the rest of your plan, I'd be cautious about ripping it on the table saw if it's too cupped. That sounds like kickback to me.

If you ripped your boards down the middle (bandsaw would be better, I think), you could joint and plane them with less thickness loss. I don't know if that would leave you with wide enough boards for your project, but they would match nicely if you glued them back together after flattening.

Either way, giving them time to move after initial milling sounds prudent.

Nelson

Hey Nelson, Thanks for comments. I'm doing hardwood flooring and a bit of it at a time. So when I get wood back from the kiln its going to get milled up and stored in a climate controlled area prior to being installed.

The general consensus here was the wood should be dried to 6-8 percent. The other thought was to sanitise the wood. It's an added expense but I feel it worth it. The wood had a MC of about 12-14%. Gotta be some added value there. BTW the cupping is not to terrible bad and I'll be using a power feeder.

[Scott T Smith]

David, do you have a way of checking the MC on the shell of the boards, as well as the interior? In order to check the interior MC of an 8/4 board, you'll need insulated pins about 3/4" - 7/8" long on your meter. You should take your measurements (ie insert the pins) from the face of the board, and not the side or ends.

Frequently, slices resawn from thick oak boards will cup when there is a difference between the core and shell MC%. If the humidity in your storage area goes up, the shell will increase MC% quickly, but the core of the board does not. Then, when you resaw the wood cup will occur due to differences in MC% between the two faces of the board.

For optimum resawing results, measure both the shell and core MC%'s, and increase/decrease the environmental humidity as needed to bring the shell in synch with the core. Then, joint/plane an equal amount from both sides of the board, and then resaw. You should experience minimal wood movement.

For flooring, I concur with the advice re kiln drying the boards down to 6% - 8%, as well as sterilizing them. Let your kiln operator know of your intent to immediately resaw the boards, and ask them to do a conditioning run at the end of the kiln cycle (if needed) to bring the core and shell MC%'s in synch.

[David Nelson1]

David, do you have a way of checking the MC on the shell of the boards, as well as the interior? In order to check the interior MC of an 8/4 board, you'll need insulated pins about 3/4" - 7/8" long on your meter. You should take your measurements (ie insert the pins) from the face of the boar, and not the side or ends.

Frequently, slices resawn from thick oak boards will cup when there is a difference between the core and shell MC%. If the humidity in your storage area goes up, the shell will increase MC% quickly, but the core of the board does not. Then, when you resaw the wood cup will occur due to differences in MC% between the two faces of the board.

For optimum resawing results, measure both the shell and core MC%'s, and increase/decrease the environmental humidity as needed to bring the shell in synch with the core. Then, joint/plane an equal amount from both sides of the board, and then resaw. You should experience minimal wood movement.

For flooring, I concur with the advice re kiln drying the boards down to 6% - 8%, as well as sterilizing them. Let your kiln operator know of your intent to immediately resaw the boards, and ask them to do a conditioning run at the end of the kiln cycle (if needed) to bring the core and shell MC%'s in synch.

HI Scott,

Insulated pins ....... nope can't say that I have them. I'll have to research that. Conditioning run???? How do that do?

[Scott T Smith]

HI Scott,

Insulated pins ....... nope can't say that I have them. I'll have to research that. Conditioning run???? How do that do?


Typically during the kiln cycle there is a delta between a boards shell and core moisture content, sometimes as much as a percent or two, with the shell being lower than the core.

At the end of the kiln run, a conditioning cycle is one where the relative humidity in the kiln is increased slightly in order to bring the shell MC% up to match the core MC%. This can be accomplished with steam injection or sometimes just by turning the compressor off (if it is a DH kiln).

If your boards have a uniform moisture content throughout, then movement after resawing may be reduced. The operative word here is "may", as any internal stress related movement will still occur.

Frequently, a separate conditioning cycle may not be needed as the kiln operator usually stops removing moisture during the sterilization cycle. The elevated temperatures in the kiln for sterilization help any residual core MC to permeate outward, bringing the core down further and the shell up slightly (as long as the RH% in the kiln is not too low).

To know for sure, you have to measure both core and shell MC%'s in various locations of several boards.