Thread: Merbau thinned to 10mm - how to stop it curving?

How old is it? Is it the current humidity we have here in Melbourne?

I have some 40 year old Merbau thicknessed down to ~13mm that does not bend (at least from what I have seen). But perhaps it’s the way I store it, flat stacked one on top of the other.

It could be the timber, I have found American Maple does that when thicknesses to that sort of thicknesses. It also could be the way it is sawn

Originally Posted by cava

How old is it? Is it the current humidity we have here in Melbourne?

I have some 40 year old Merbau thicknessed down to ~13mm that does not bend (at least from what I have seen). But perhaps it’s the way I store it, flat stacked one on top of the other.

I would say that it is fairly new - was bought at Bunnings recently but has been kiln dried. The recent humidity in Melbourne possibly hasn't helped - its been a bit brutal!

I have found this to be a fairly common problem when machining down to thin sizes on many species of timber. My method of alleviating it is to ensure the thin strips are stacked with weight on them and both sides protected from the environment. Sitting another piece of thicker timber on top usually works fine. When the coasters have been cut, I do the same. Once the coasters have been finished the problem rarely occurs because both sides have the surface sealed.

Was equal amounts removed from each side or just from one side?

If just from one side, the freshly cut side will dry out a bit more even if kiln dried, best to cut slightly oversized and let sit over night on stickers then flatten

To my mind this depends greatly on whether 'twas rift-sawn, plain sawn or whatever. For timber that thin this should not be ignored, regardless of timber choice.

Look at the end-grain and see if you can determine which direction the rings are going. If the rings are more or less vertical (ie. short parallel lines between the top and bottom faces) the board should be fairly stable in and of itself. For coasters this is definitely the orientation you want!

If the rings are 'across' the board, ie. you can see long arcs across the width, then I'm sorry but that's a bad choice of timber orientation; that sucker'll move with almost any change in humidity, let alone a wet glass put on it.

Rings on the diagonal lie somewhere in-between, the closer they are to vertical the stabler the board.

Originally Posted by DJ’s Timber

Was equal amounts removed from each side or just from one side?

If just from one side, the freshly cut side will dry out a bit more even if kiln dried, best to cut slightly oversized and let sit over night on stickers then flatten

It was put through a thicknesser - I might run an experiment where I put both sides of it through and see what happens - will report back!

Originally Posted by Skew ChiDAMN!!

To my mind this depends greatly on whether 'twas rift-sawn, plain sawn or whatever. For timber that thin this should not be ignored, regardless of timber choice.

Look at the end-grain and see if you can determine which direction the rings are going. If the rings are more or less vertical (ie. short parallel lines between the top and bottom faces) the board should be fairly stable in and of itself. For coasters this is definitely the orientation you want!

If the rings are 'across' the board, ie. you can see long arcs across the width, then I'm sorry but that's a bad choice of timber orientation; that sucker'll move with almost any change in humidity, let alone a wet glass put on it.

Rings on the diagonal lie somewhere in-between, the closer they are to vertical the stabler the board.

Lots of good information there - will take a look in the morning and see which way the rings went. I put it through a thicknesser to reduce it from 19mm to 10mm

It will be extremely difficult and I would imagine near impossible to stop the cupping. The old man always used to say that the only board you could safely plane down thin is one that is quarter sawn, and has been cut to 3/4” thick then stickered and seasoned for at least 12 months. He used to make a lot of wooden aeroplane parts and that was the way they prepared the stock for those, mostly spruce, which is much more dense and stable than merbau.

What about planning down to ~5mm and glueing together at 90 degrees to make a 2 ply product. I believe that Matthias Wandel (Canada) has done this but with more layers successfully. It’s much more work, with more waste, but an option.

Originally Posted by RSD

Lots of good information there - will take a look in the morning and see which way the rings went. I put it through a thicknesser to reduce it from 19mm to 10mm

Just took a look and it appears to be somewhat quarter sawn - the ring lines are about 30 degrees from the vertical.

I've just started an experiment now where I have put both faces of the original 19mm piece through the thicknesser and reduced it down to 13mm, and then I will let it sit for about 2-3 days and then further reduce it to the required 10mm - will be interesting to see what difference that makes. I'm also going to try some different species of timber as well to see if any of them are better.

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Originally Posted by cava

What about planning down to ~5mm and glueing together at 90 degrees to make a 2 ply product. I believe that Matthias Wandel (Canada) has done this but with more layers successfully. It’s much more work, with more waste, but an option.

It might work, but it sounds like far to much work just to make a coaster.