Side board Top wont stop cupping help needed to Tame it

[A-Marks]

Hi all!

I have a bit of a problem in as much as the top of a side board I recently made from Maple keeps warping and lifting up at one corner. Its actually quite bad and raises about 8 mm above the stretcher below it - but only in one corner at least.

I made the top from three pieces ie two joints which I pinned with biscuits, the timber was also very rough sawn and i planned it with a thicknesser I think from memory i only had to remove about 3-4 mm from each face though. I roted a small roundover on the edges and smooth sanded it.

I have fixed it to the frame with Z type table top clips which allow a bit of movement Do you think that if I was to pull it back into a flat state and them put some more Z clips close to the warping that It will stay put?

The top has not had a finish applied as yet mainly because I'm waiting to see what happenes to it.



Allan Marks

[Termite]

I think the problem is being caused because you don't have a finish on it.
The top is drying out faster than the underside.
When you do get it flat make sure you put a sealing coat on the underside as well.

[redwood]

if a top has no finish top or underside wont matter as much as some think. [ if its anchored down propperly] bit of a myth... but you shouldnt leave it to see what happens because that will only quicken a problem if its to occure

My guess is the offending board is flat sawn and the growth rings are arched downwards causing the timber to srink tangently with the grain making it cup upwards

[duchampski]

Consider sawing some kerfs on the underside of the top. Then secure it in place. That would offer some flexibility in its natural wood movement.

[Termite]

I just love the way you debunk some known timber facts as "myths", and then go on to "guess" what the problem is. Your guess is proof of the "myth" you made light of.

Unsealed timber, no matter how long it has been seasoned, will absorb moisture, and dry out, and move.

The unfinished top in question is exposed to the atmosphere, whereas the underside is inside a cabinet and has less exposure to the same atmosphere.
It would seem to me that in the temperatures we are having at the moment, the top is drying more than the underside and thus cupping upward.

If you don't believe me, then either use a wide board about 10-12mm thick, or edge join strips to about 200mm wide, plane down both sides so that it is dead flat, and then leave it on your bench overnight with one side flat down on your benchtop.

Tell me how flat it is in the morning.

[redwood]

I just love the way you debunk some known timber facts as "myths", and then go on to "guess" what the problem is. Your guess is proof of the "myth" you made light of.

Unsealed timber, no matter how long it has been seasoned, will absorb moisture, and dry out, and move.

The unfinished top in question is exposed to the atmosphere, whereas the underside is inside a cabinet and has less exposure to the same atmosphere.
It would seem to me that in the temperatures we are having at the moment, the top is drying more than the underside and thus cupping upward.

If you don't believe me, then either use a wide board about 10-12mm thick, or edge join strips to about 200mm wide, plane down both sides so that it is dead flat, and then leave it on your bench overnight with one side flat down on your benchtop.

Tell me how flat it is in the morning.

Termite i love the way you seem to delight in debunking my ideas

If the board has been connected securly to the base, the ammount of movement will depend largely on what type of boards are on the top.

if they are all qtr sawn, no finish wont make much difference, and thats not myth its fact. thats why the jappanes didnt have much problem with alot of their qtr sawn oak furniture that was only burnished with no finish at all.

If you use flat sawn timber with the growth rings facing down, radial shrinkage will force the timber to cup upwards. anchoring it will slow it and finishing it will slow it further, but mother nature is stronger and no matter what you do it will cup at the corners.

If you use flat sawn timber with the growth rings facing upwards, the radial shrinkage will force the timber down.

now as iv only been involved with wood for 20 years im just guessin with all this, so termite plz tell me if im wrong, but if you plan your top in the first place and all you have is flat sawn timber, to arrange the orientation so all the growth rings face up, then when you secure the top to the carcase it will be impossible to lift even with no polish because mother nature is forcing it down at the edges and the middle stayes flat because its securly anchord there. Some like to alternate the orentation, if thats what you want its ok, just make sure the two outer boards rings are facing up

And to answer your question

If you don't believe me, then either use a wide board about 10-12mm thick, or edge join strips to about 200mm wide, plane down both sides so that it is dead flat, and then leave it on your bench overnight with one side flat down on your benchtop. Tell me how flat it is in the morning

when a was raw at this caper that would happen alot. but it didnt take long to realise you have to cover or anchor your timber down or preferably lean it againsed a wall flipin over and around every day till its needed. i thought you would have also realised that after all the years youv been doin it. never to late to learn somethin new is it

[Termite]

Can't argue with some of what you say, but you're only halfway there regarding some of it.
If you consider time associated with timber as a measure then I outrank you by a factor of 2.3.

I have no argument with the fact that quarter sawn timber is by far the most stable, but it is usually about as decorative as a sheet of MDF, that is why a variety of other sawing methods are quite often used for furniture timber to show the grain features to their best effect.

Now we have the conundrum of unstable timber that can't be glued ,screwed, nailed, or otherwise immobilised to the point where it can't move. It has to move or we suffer the consequences, so we use the various methods of fixing which will allow movement, so we are back to the problem the bloke that started the thread has.

One of the ways to help overcome the problem is to put a finish on both sides of the timber. This will not stop movement, but it will go a hell of a long way to equalising or slowing down the changes in moisture content that cause the cupping in the first place.

In all but exceptional cases you won't find noticeable cupping caused by moisture differential in a dresser top treated this way and held in place by Z fasteners.

Or would you prefer featureless quarter sawn stuff, and don't think quarter sawn timber won't cup either.

[outback]

I only have 0.12% of your combined experience, but I know if your'e not careful with the orientation of your ring, all sorts of bad things can happen. You'll be flat quartered and finished, both top and bottom, before you saw it coming, and then no type of fastener will help.

[redwood]

Termite your getting away from the initial point. Allans sideboard top cupped in one corner only. so if it was because of a lack of finish why didnt it move in the other three corners:confused: blind freddy knows sealing timber slows movement.

understanding shrinkage, again a bit of a "myth" because the fibrils dont srink, they just move closer together. cell walls compress when moisture enters and when it leaves the compression causes the cell to be slightly larger. over time it absorbs more moisture and the release makes boards react more severly (thats why dowells constantly fail after 10 or so years)

the greatest movement occurs at right angles to the direction of the fibres, as in radial and tangential (tangential the most) , so expeirienced woodworkers can usualy tell by a quick look at the growth orientation how that particular board will move and be used. its not rocket science just experience and commonsence. i just find it funny how every one just jumps the to old addage that if something goes wrong with movement its cause their is no finish. so if a board cups only in one corner, it is more than likely that the lack of finish isnt the cause. thats why i was assuming it had more to do with the orentation of the board.

I will be interested for Allan to let us know about the three boards in question because we are all assuming on this one because we cant see what is going on.

and on tops that "the conundrum of unstable timber that can't be glued ,screwed, nailed, or otherwise immobilised to the point where it can't move" well breadboard ends were invented to overcome that.

and flat sawn vs qtr is a matter of taste. it depends on the timber. qtr sawn oak`s medullary rays are as good as it gets, nuthin better . and flat sawn was not devised for its feature, it was mainly for ecanomic reasons. each to their own

[Termite]

Anyone got a smily showing a bloke bashing his head against a brick wall.

And I did learn something, I always thought it was "Back sawn" not "Flat sawn".

[Iain]

And how about Outback with the orientation of his ring

[redwood]

Anyone got a smily showing a bloke bashing his head against a brick wall.

And I did learn something, I always thought it was "Back sawn" not "Flat sawn".

plain sawn - back sawn - flat sawn, same thing.

and why do you want to bash your head up againsed a wall:confused:

[Termite]

and why do you want to bash your head up againsed a wall:confused:

Cause it feels so good when I stop.

[Termite]

And how about Outback with the orientation of his ring

I'm starting to have some humorous thoughts about that old rhyme "Ring around the rosie".

[Iain]

Al's providing the posies tomorrow