Resawn wood bowing/cupping

[HeathRobinson]

Hi all,

I don't think this is a pure hand tools problem, even though that is what I used to arrive at this point. I resawed some inch thick maple into 1/4" thicknesses last Sunday. It was a day long, titanic wrestling match between me, my few hand saws, the wood and my workmate! A great workout! :lol: I left the pieces still rough sawn on one side until this weekend when I found that one piece has bowed/cupped.

A bit disappointing considering the amount of sheer physical effort I put into separating them. Is there anything I could have done to avoid this effect? I had let the wood sit for about 2 weeks before the resawing thinking that this would have sorted out most moisture problems.

Thanks in advance for any wisdom bestowed upon yours truly!

Simon

 

[woodbloke]

Simon - it sounds to me like there were internal stresses in that particular piece that were released when it was sawn - Rob

 

[WellsWood]

What exactly are you planning to do with boards that are sawn to 1/4" thick I wonder? After planing out the saw marks you'll be lucky to be left with veneer, in which case a little cupping won't be much, if any, of an issue as you're surely going to attach it to a substrate substantial enough to hold it flat once glued.
Cupping of boards on resawing is extremely common, be it through internal stresses being released as Rob says, or the differential moisture levels between the newly exposed face and the existing one (2 weeks isn't anything like long enough to reliably negate this), and is simply something you must expect to some degree and allow for in your sawn thickness. Resawing to the thickness you have and expecting it to stay flat and true is an extremely tall order methinks.

 

[HeathRobinson]

Hi Mark,

I was just thinking of making a small box to practice technique. Resawing being one of those techniques. The rough sawing still left me enough thickness to plane down to 1/4" thickness but not now that the one board has bowed.

If you're wondering how I lost nearly 1/4" during resawing then I doubt you've tried hand resawing using the tools I had at my disposal. :lol: Think cheap dovetail saw, slightly undersized but very coarse cutting tenon saw and an extremely coarse cutting B&Q general household saw which made short work of a lot of wood. If I could have stationary power tools I would get myself a band saw but as I work in the house that isn't possible at the moment.

Cheers for your input though guys.

Simon

 

[WellsWood]

If you're wondering how I lost nearly 1/4" during resawing ....

Simon

Not really Simon, even with the bandsaw I'd be allowing (and expect to lose) about that much, or more if the boards are of any length or both faces are sawn. All in all then it sounds like you did a pretty bang up job.
Resawing by hand? Nah, that's just a bit too masochistic for my taste 8-[

 

[Digit]

Assuming that a piece of timber has a moisture content of zero Simon, resawing would have no effect, but timber gives up and absorbs moisture via its external faces. Therefore the interior will always have a different moisture content to the outside faces, thus when you resaw, one face must be dryer/wetter than the other and movement will occur.

Roy.

 

[woodbloke]

Simon - are you sure this happened?..we could do with a coupla pics :wink: - Rob

 

[HeathRobinson]

Hi Rob, wasn't sure if you were joking about the pictures or not but decided to oblige anyhow. I'm sure everyone knows what bowed wood looks like :lol: I assume that you are asking about work in progress pics. Pitty I don't have any shots of the work in progress. No doubt the camera would have got bloodied. I have got one or two battle scars myself. The maple is unquestionably harder and gets much sharper edges when planed than my usual pine - my gashed little finger can attest to that!

The other board has also bowed a little but not as much as this one.

 

[Paul Chapman]

Hi Simon,

If you look at the end grain in that bowed plank it's clear to see why it has bowed the way it has. It's sawn through and through rather than quarter sawn. The only thing you could do is to rip the board along its length into narrow strips, turn every other strip over and glue them together. However, by the time you have done that and cleaned them up you will have probably lost too much thickness.

Cheers :wink:

Paul

 

[Richard T]

When a plank is sawn, tensions in the wood are released , the thing that was a tight tube in life is suddenly sliced into flat bits in death. Those growth rings, when cut, will try to get straight; that's why the cup is always on the frowny side and the bow is on the smily side.
Just cut planks wide enough to take off possible bow/cupping and still have enough width left in the middle.
This is a perenial problem and probably the reason that the most talked about things on this forum are planes and planer/thicknessers.