Thread: Cupped silky oak

I don't think it's a "was the timber dry" issue. Just a wood issue!

Couple of quick questions to better understand the scenario. How was the timber stored for those 3 weeks? To get the 10mm final thickness, I assume you ripped 10mm off one side of the 24mm thick board?

From my experience, timber has lots of strange internal pushing and pulling going on. Kind of like a family! Stable dressed timber is in a state of balance. If you cut a thin (eg 10mm) slice off a dressed and stable board, there's no guarantee the 10mm strip will not warp or twist a little. This new thin board has a new face which is no longer interacting with the fibers of the parent board, so it may twist a little as it finds it's own state of balance. Everything wants to be in balance! (insert zen buddhist style "hhummmmm" sound effects)

I find that if you take material away from each side it can help, but in this case would have been wasteful to dress 24mm down to 10mm. I just rip off pieces a little bigger than the final size required (all dimensions) and once the smaller piece has settled, dress it to final size. How much bigger I cut it will depend on the timber and how much I think it may twist. Eg euro beech tends to twist a lot, so I'd allow more. Silky not as big an allowance.

Cheers

Greg

Greg, I should have said that after jointing and thicknessing the board I resawed it into 2 x 10mm thick boards. One of the boards I stored as is, the other I cut into the sizes needed for the box. The amount of cupping is almost like a mirror image, ~0.5mm across the width of the board, which after jointing is 90mm wide (it was 100mm to start with, not 150mm as I stated in my first post).

I spoke with the supplier I bought it from (a very reputable mob in the ACT) who assure me that they buy and sell only kiln dried timber. So I'm hoping that you're right and it is only the timber settling after the resawing. In future I won't dress to final size until after allowing for a settling period.

I agree with what Greg said as well, best to let the timber settle for a few days before doing the final thicknessing.

Originally Posted by Harry R

About 8 weeks ago I bought a 24x150x1500 piece of silky oak from a supplier who sells kiln dried timber. Three weeks ago I jointed/thickessed the board and resawed it to 10mm thickness for making boxes and cut the resulting boards to the required lengths.

Today I was getting ready to cut dovetails when I noticed the pieces had cupped. The peices are not twisted, just cupped and not by much, around 0.5mm or so. Obviously the board wasn't as dry as they thought it was

I'm thinking of using the jointer to flatten the concave side, but leaving the convex side as is (ie. with slight outward bulge) as this would not affect the look of the box. However, before doing this I'd appreciate advice on whether I'm likely to get more cupping to the extent that it would separate the dovetail joints.

don't do this Harry

the convex side will rock as the timber goes through the jointer possibly resulting in a side to side taper or even a twist.
you need to place the concave side on the jointer's bed to avoid this rocking


ian

Originally Posted by Harry R

I'm thinking of using the jointer to flatten the concave side, but leaving the convex side as is (ie. with slight outward bulge) as this would not affect the look of the box. However, before doing this I'd appreciate advice on whether I'm likely to get more cupping to the extent that it would separate the dovetail joints.

Sorry I missed answering your actual question

If it's been 3 weeks you should be right. I don't think it'll move any more unless you're getting season shifting temp/humidity changes where you are. Today was like our first day of summer here...hot and stormy. But even it if did want to move a little more, silky only 10mm thick in small box sized pieces probably wouldn't have the mass to separate itself in a glued dovetail joint.

Jointing the inside concave side is the way to go. If you leave the outside convex face as is, be careful marking up your dovetails. Could play some havoc. Or fix both sides and have a box with a 8.5-9mm thick sides. Just tell people the delicate proportions were on purpose You might like it and decide on a permanent design change

Best of luck!

Greg

It's also possible that the wood was originally kiln dried correctly, but it has now actually Absorbed water from the air.

If the wood was dried to 8% moisture content, but you leave it in a high humidity environment (70-80 RH) it's moisture content will increase again, up to ~12%, and some movement may occur.

Likewise if wood is just air dried to 12%, then taken to a drier climate it will dry out some more, and move in the oposite direction.

Also check that the wood wasn't stored flat on a bench or similar. In that case the change in moisture will be uneven and it's almost sure to cup. If thats the case, stack it on some sticks so air can circuclate to both sides of the board and it should even out again.

Cheers

Ian

Almost all timber will move when re-sawn.
Time is your friend here. Our process in the store is:
Rough sawn board.
Joint one edge one face (for following fence and table of bandsaw)
Re-saw
stack is cool place out of the way. (sticks between and a small weight is a good idea)
Wait a week (or three)
Re-joint as movement is assured.
Dress to finished size.
Assable asap.

I hope you didn't give the timber dealer a hard time this is very normal and one of the joys of working in solid timber

Good Luck

No, I didn't give the supplier a hard time. I know that these guys have forgotten more about timber and woodwork than I know, so I was prepared to listen to their advice. They offered to run their moisture meter past the silky oak. However, given the above advice I didn't end up taking the wood back for measurement. I've flattened the pieces (both sides) and have been careful about storing them with plenty of circulation and they've stayed stable. Obviously it was just the timber settling in after resawing (it was my first go at this with my new bandsaw). Am about to assemble the box in the next day or so. That's one of the many things I like about woodwork, there's always more to learn. Thanks for the feedback and advice

great to hear...
Pics of the box please