Cup & Twist Prevention in Thin Stock

[Paul Fitzgerald]

I'm planning on resawing and planing either 4/4 or 5/4 stock down to 1/4" to make boxes.

Every test I've done so far has failed. The stock looks great immediately after prep, but cups and/or twists after sitting overnight. I've been searching through the forums on and off for for a few days trying to find out what I'm doing wrong.

The first thing I found was I need to rough out the stock oversized, let it reacclimate, then mill to final dimensions. That sounds good to me, but I recently had some 13/16" thick hard maple cup and twist overnight after taking only 1/32" off each face. I can only assume it's going to be worse with thinner stock.

The second thing I found was the species of wood makes a difference. For example, I've read that white oak doesn't permit the passage of moisture nearly as well as other species so the internal moisture content could be much greater than the surface moisture content. Therefore, cupping and/or twisting after resawing or planing white oak could be more prevalent. I've only tested with pine, poplar, and maple... and have had issues with each.

The third thing I found was I probably ought to get a moisture meter.

I'm leaning towards making these boxes out of cherry and don't want to waste money because I screw up milling the stock.

Any insight ya'll can provide would be much appreciated.

Paul

[Jason Beam]

First question: How are you settin' those freshly milled pieces overnight? Are they laid flat? Stacked on one another? I've had major warping happen when I effectively sealed off one side from the air - I will always lay things upright or leaned against something to permit airflow on both major surfaces. That's helped a bit.

Second question: What kind of quality is the wood you're using? BORG wood and some other places that kiln dry their wood too fast can create internal stresses that will cause cupping when resawn, too. Usually drying too fast will cause honeycombing, but sometimes it just doesn't pull apart. Also, if it's limb wood, you'll have nothing but trouble. Good straight trunk wood will usually behave more predictably.

Third question: What cut was the board? Is it flatsawn? Generally, the best behaved wood goes in this order: quartersawn, riftsawn, flatsawn - the first being best, the last being least. Flatsawn wood loves to cup. Flatsawn twisted grain really loves to cup.

Anything thinner than about 1/8" will probably cup pretty easily if ther's much stress or moisture difference in the piece. It'd be much more finicky than a board with enough thickness to resist some of that force. So the thinner you get, the better quality wood and storage techniques will be needed to keep it flat.

[Paul Fitzgerald]

First question: How are you settin' those freshly milled pieces overnight? Are they laid flat? Stacked on one another? I've had major warping happen when I effectively sealed off one side from the air - I will always lay things upright or leaned against something to permit airflow on both major surfaces. That's helped a bit.

Ah! I've been laying them flat and face to face.


Second question: What kind of quality is the wood you're using? BORG wood and some other places that kiln dry their wood too fast can create internal stresses that will cause cupping when resawn, too. Usually drying too fast will cause honeycombing, but sometimes it just doesn't pull apart. Also, if it's limb wood, you'll have nothing but trouble. Good straight trunk wood will usually behave more predictably.

The pine was borg wood, but the hard maple and tulip poplar was from my hardwood dealer. I'd certainly hope stock from my hardwood dealer to be good quality considering the price I've been paying for it. :D


Third question: What cut was the board? Is it flatsawn? Generally, the best behaved wood goes in this order: quartersawn, riftsawn, flatsawn - the first being best, the last being least. Flatsawn wood loves to cup. Flatsawn twisted grain really loves to cup.

Yes, as far as I can tell, the pine, poplar, and maple were all flat-sawn.


Anything thinner than about 1/8" will probably cup pretty easily if ther's much stress or moisture difference in the piece. It'd be much more finicky than a board with enough thickness to resist some of that force. So the thinner you get, the better quality wood and storage techniques will be needed to keep it flat.

Thanks for the tips!

Paul

[Jared Cuneo]

For some reason (commisions I guess :rolleyes:), I have become a part time boxmaker, so I have been resawing a LOT of thin stock. Usually, 4/4 maple, cherry, walnut, sapele, into 1/2 and 1/4 pieces, and I can tell you that sometimes, there is nothing you can do. If I notice a piece of material is coming out of the bandsaw pinched, it's not going to be pretty. At this point, I usually stop and plan to use the piece for 3/4+ material.

Now I try to buy planks that are not flatsawn if I am doing any amount of thicknessing.

I stack the strips on top of one another with a 25lb weight on top and that helps a good bit.

As for grain, I echo above, it you look at the board and its close to the heart or has grain moving in the same direction on either end, thats bad news.

My .02

JC

[Scott Banbury]

Paul,

Use my AD wood as it's acclimated to Memphis EMC and won't warp after you resaw it.

Scott

[Paul Fitzgerald]

Paul,

Use my AD wood as it's acclimated to Memphis EMC and won't warp after you resaw it.

Scott

Work kept me pretty busy today. I'll give you a call tomorrow.

Paul

[John Fry]

I think an improvement in the way you are storing your slices would improve your problem.

I sticker and clamp everything immediately after resawing and leave it there until it is used in the project. You are exposing freshly cut, internal wood, to a new external environment and it will immediately try to adjust.

Here is a picture of how I store resawn material. (It is how I store all freshly cut and milled material actually, even up to 8/4.)

http://www.chiselandbit.com/armoire/armoire6.jpg

Stickering with weight is fine too, but I use clamps so I can move the stacks around the shop and keep working without too much hassle. Otherwise they are always in the way.