how flat?

[Digizz]

The 4 pieces of lovingly thicknessed, planed and cut Maple for my table top surround have been sitting in my (fairly hot) workshop for 1-2 days now. Unfortunately a couple of the boards (25 mm thick, 120mm wide and 1m long) have bowed very slightly by 1-2mm over the 1m length.

They are going to be joined together to make a mitred square surround into which a glass top drops in (into a rebate).

I guess they're warping because the moisture content was probably something like 12% (kiln dried to 8%, gained the rest in transit to UK and storage in a timber shed). They were also through and through cut rather than quarter sawn (which I couldn't find a supplier for). I should have stored them in the workshop for a while before machining I guess (how long for though I don't know???)

Is there anything I can do? is 1-2mm anything to worry about? Should I just glue them up and rely on the legs and frame to pull them back straight?

Anyone know how to gain 30 years experience in woodworking in 24hrs!

Ta.

 

[Chris Knight]

Digizz,

I should try and be patient. Leave it for several more days before doing anything. Then take out the bowing and anything else like cupping that develops. You will find it very hard to make nice joints if your pieces are not absolutely flat and I wouldn't rely on the rails pulling the mitred frame flat.

As you observe you would have been better to leave it sometime before milling the wood but in any case, try to do it always in two stages. Stage one is rough sizing, leaving a further machining allowance for stage two when, after a further period of drying/stress relieving, you machine to final size.

 

[Digizz]

Yeah - too eager to get started!

How long would you normally leave the timber in the workshop for - days, weeks?

Maybe a moisture meter would have been a good idea to guage how much it needed drying out?

 

[Chris Knight]

Digizz,
A moisture meter is useful but not essential. I normally leave kiln dried wood in my shop for a month or two before cutting anything. Then mill roughly to size and leave for another week as distortions from both drying and stress relief need to be taken account of . The initial period of acclimatisation is for moisture, that after the initial machining is for stress relief. Stresses relax fairly quickly normal - within a few hours generally but I like to leave it a bit longer to allow for any extra drying that wants to take place. This is most important when resawing boards from thick stock - they will almost always cup and may bow.

 

[Digizz]

Thanks Chris,

Is there any way of speeding up the process i.e. do any suppliers offer a re-kilning process (if such a thing exists) or any other way of quickly getting the wood to a machinable state rather than waiting a couple of months?

Sounds like planning ahead is key here - something that's alien to me!

 

[Alf]

Of course in the long term what to do does rather depend on whether the climate of your workshop is anything like the place the finished piece will end up in. It's no good acclimatising anything to your workshop if it's cold and damp while the finished project is intended to go within 2 inches of a radiator <shudder>. And vice versa. This is how I justify a guest room with its own timber stack... :wink: Welcome to the wonderful world of wood movement, Digizz. A slow, drawn-out mental breakdown starts here... :roll:

Cheers, Alf

 

[Digizz]

mmm - if anything the workshop is currently hotter than the room the piece is intended for - but I don't think I can justify stacking it in the living room for a few weeks, especially with new carpet coming this week!

All the other spare bedrooms already have piles of my other work and hobbies kit in - computers, video camera kit and various electronic bits! I'd be very unpopular if I started stacking timber in there too!

 

[Chris Knight]

Digizz,

Alf of course is spot on - try and make your workshop the same as the room where the furniture will go. I have a B&Q dehumidifier and aim to keep temperature and humidity in the shop more or less the same as the main rooms in our house where most of my stuff ends up.

You can't really speed things up I am afraid and because kilning operations are governed by strict schedules that relate to the amount , type and condition of timber, I doubt very much if you could find anyone willing to "re-kiln" a few boards, I have certainly never heard of it.

It helps if you can work in a restricted range of timbers. Then buy as much as you can afford and store this somewhere appropriate. That way, when you want to make something, you have already got wood that has been acclimatised to your conditions. Wood will never get cheaper so you can see it as an investment. I have a few boards of oak and other woods that I bought years ago and, even if you could buy wood of that quality these days, it would be vastly more than I paid for it.

 

[Digizz]

good point - I'm planning on making a load more furniture out of Maple - guess it's time to buy a load more in and store it somewhere. Maybe I can find some under bed storage!

 

[Digizz]

Just measured the humidity in the workshop - quite a lot drier and hotter than the living room where it's going to end up.

How soon would you start to see a difference if you're taking timber from one extreme to another - days, weeks?

I presume the warping I'm seeing is down to stress relief as it was only a matter of 24-48 hours or so from being a flat board to a warped one?

 

[Chris Knight]

Digizz,

I would expect to see moisture related distortion that appeared in a few hours to disappear in the same time if conditions can be restored - this applies to eg a flat panel that becomes non- flat if one side becomes drier than the other.

In your case, as you have machined the wood from larger pieces, you cannot restore the conditions exactly. I would guess that you are indeed seeing stress related movement since it has happened quite quickly but if you machined the pieces out of a significantly thicker piece of stock, then possibly you are getting some moisture related movement as well as the interior of a piece may be expected to be significantly wetter than the outside of a piece that is in an environment now drier than the environment from which the wood was previously stored in.

It really helps if you can plan to make your joints and assemble things soon after they are cut or shaped. I often leave certain operations until I know I will get a clear run at them for this reason. The longer bits hang around waiting for assembly, the longer time and opportunity they have to distort.

 

[Digizz]

Do you think I should press on with making up the top now rather than leaving it a while then? I'd already finished it to the correct sizes - any more warping and i'll end up with a much thinner top.

The alternative is to get some more timber and let it adjust before I make a new top - and use the stuff I cut for something else.

 

[Offcut]

Digizz,
From what your saying it sound like the wood has destressed when you cut it down to size. I don't think you should see much more movement, unless your work shop is particulary wet or dry.
If your joining several boards to make the top then joining them now will help reduce the warping as long as you alternate the grain.

I would crack on and get the top made otherwise you could be waiting for ever....

Buying your stock earlier is a good idea but I always find I am itching to get started.

Have a look at this album of a bathroom door
The oak was quartered. The last photo shows what happened when I cut the planks from 50mm thick down to 25thk. They warped badly leaving me having to plane them down to remove the warping.

http://uk.pg.photos.yahoo.com/ph/homeau ... ?.dir=1ba3

I don't think leaving them any longer would have stopped this

Andy

 

[johnelliott]

I agree with Chris, what you are seeing here is the natural movement that comes with cutting a board from a larger piece. Consider the strain a tree is under when it is growing, having to resist the effects of wind, slope, more branches on one side than the other etc etc. When the tree is cut down and sliced up some of those stresses are released, and as the cutting process continues so more stresses are relieved until you get to the sawdust which is relatively stress free!
Best way to deal with it is to try to cut your required pieces somewhat oversize and gradually take them down to the finished size. It also helps to design your piece with these problems in mind- because there is always going to be some movement. When I am making a frame and panel door I check each rail and style with a straightedge. This reveals that each has a very slight curve along its length. I then assemble the door so that the curves are all the same way. Then, if there is any further movement it doesn't cause the door to curl
John

 

[Digizz]

But the stresses can take a short while to appear right?

Generally how long would you leave it between converting a thicker plank to thinner and final planing/finishing? - couple of hours/days?

 

[Offcut]

Hard to say really, i'm sure that 'rules of thumb' will come into this one.
In my experiance the warping has happened straight off the saw. I usually leave the items overnight and then plane them the next day. I haven't had any items warping further - touch wood - .

Andy

 

[Alf]

until you get to the sawdust which is relatively stress free!

Right up until you start treading it into the living room carpet... :roll:

 

[Anonymous]

But the stresses can take a short while to appear right?

Generally how long would you leave it between converting a thicker plank to thinner and final planing/finishing? - couple of hours/days?

I would cut to a few mm oversize and then leave for a week (or two) before final dimensioning. When finally dimensioning, remember to machine both sides evenly