Limiting wood movement

[Deadeye]

I had a go at resawing.
The resawing part went fine (from inch and a quarter to two x half inches)
However, I started with a flat board and ended up with two bowed, cupped, twisted ones overnight.
Is there any way to minimise this or even to know if it's likely and use the board for something else?

 

[Glynne]

Unfortunately there is no way to predict the internal tensions in a board, other than if you have several boards from the same tree you can expect something similar.
Whilst your resawing went well in that you only lost 1/4”, you need to be less ambitious and aim to get a single board from your inch and a quarter which isn’t really that thick. If you need some thin stock, say for a small box, then resaw oversize, allow the timber to settle and then try planing / thicknessing alternately from both sides but continue to let it settle. If the timber you have has cupped and bowed to such an extent then perhaps forget the resawing and use it in its current thickness.
It will seem a waste, but better to get one usable board then several unusable ones.

 

[Droogs]

Rather than type a whole lot here is a linkto some good introductory information about resawing and its problems

hth

http://honeydowoodworking.blogspot.com/ ... upped.html

 

[profchris]

I do a little resawing for musical instrument making. Basically:

1. Any plank which doesn't have vertical grain is highly likely to cup. The exception might be where the board was narrower than about 1/3 of the tree, so all the grain slants in the same direction. The more like a cup/dish the end grain looks, the worse it's likely to be.

2. Vertical grain wood behaves best as a rule.

3. But any plank can have internal stresses so it twists, bananas, or whatever. Just luck if it doesn't.

4. If you find a plank which has some chance of resawing well, help by ensuring it's moisture content matches your workshop (including waiting a few years!). If it doesn't match it will surely move around

 

[Sgian Dubh]

Unfortunately there is no way to predict the internal tensions in a board, other than if you have several boards from the same tree you can expect something similar.

Neither of those statements are quite true, Glynne, although there is decent logic in the second one.

The fork or prong test is a good way of testing for internal stresses in the wood.

This test reveals if there is transverse stress within a board. Take a short but full width and thickness section 25 mm (1”) long out of a plank. Ideally take the piece out at least 450 mm (18”) from the end. You want a piece from a representative section of the board, not near ends where changes in MC are more volatile.
A. Turn the cut out section end grain down on the bandsaw table.
B. Bandsaw two forks about 7-10 mm (1/4”- 3/8”) thick.

The result of cutting a section out are:
1.If the forks remain parallel this indicates stress free wood.
2. Very slight bending of the forks shows minor stress.
3. The forks or prongs curve inwards showing transverse stress or case-hardening.
4. The forks bend away from each other indicating reverse transverse stress or case-hardening.
5. The bending of the forks may not happen immediately, and can take a few hours to develop.

Note 1: This test does not specifically indicate longitudinal stress or case-hardening, although if the test shows the wood is transversely stressed or case-hardened, then longitudinal stress or case-hardening is most likely also present.
Note 2: Observe that I have consistently referred to stress or case-hardened here. Case-hardened wood is artificially stressed through improper drying techniques. There are also natural growing features or faults in living trees that can lead to stress that can or will show up when undertaking the fork or prong test. Slainte.

The image below is from Woodcraft: https://www.woodcraft.com/blog_entries/ ... kiln-dried

Edit. Note that the description in the below image describes case-hardening in terms of the wood being wetter and dryer. This is incorrect. Case-hardening is a condition whereby the outer layers of the wood are in compression and the core in tension. Reverse case-hardening is the opposite. As such, therefore, the wetness or dryness of the wood, whether at the core, the intermediate zone, or the shell, has no real bearing on the condition.

 

[Glynne]

Thank you for the comprehensive reply. It’s always good to have an expert view on things and I hope to be able to catch up with you at Harrogate to say thank you in person.
So whilst fully accepting your explanation, the difficulty I have as an amateur, and I suspect many others on the forum share, is that cutting a board 18” from the end effectively cuts it in half and so for the effort involved in cutting forks, I may as well try and mill the whole board. The difference between professionals and an amateur!
Thank you for taking the time out for your reply.

 

[Sgian Dubh]

I appreciate your difficulty if you're working only with a small quantity of wood - not enough to cut a bit out of somewhere away from the ends. On the other hand, if you need to cut even just two or three longish boards into shorter lengths for a project, you can frequently sacrifice an inch or two from somewhere in the middle of the length.

I'll be at Harrogate on all three days because Classic Hand Tools asked me to join them, primarily to keep an eye on the Lost Art Press bit of their stand whilst my pen works nineteen to the dozen (probably not that much, ha, ha) signing copies of my book. I'll be more than happy to meet and chat a bit if you drop by. Slainte.