Blanket chest - time to implement 'Plan B'

[pidgeonpost]

Those of you who read my previous post on this may have noticed the comment from 'dedee' that maybe the top was starting to bow. They were right, and how! It was fine according to a long straightedge when fitted too.
Not only has it started to curl from front to back, but is starting to develop a bend along its length. Clearly this is not mahogany as I thought, but banana wood.
This timber had originally been kilned, then stored in my garage (dry but unheated) for over 10 years, and was in the workshop for a week or so before use (I know that's not long, but I thought it would probably be pretty stable after 10 years).
The stock was around 1.25" sawn, which I took down to around 0.75" as it did have a slight twist in it. I guess at least some of the problem may be down to the release of stresses within the timber.
Question now is what to do about it. I do have enough stock left to make another top, but then I risk the same thing happening (though maybe I could reduce the risk by using M+T cleats on the ends - but you know what timber is like - if it wants to move it will do so one way ot t'other!).
Or maybe a slab of MDF painted reddish brown.
I'll post a photo if 'er indoors will release me from the decorating for a bit.

 

[woodbloke]

PP wrote:

I know that's not long, but I thought it would probably be pretty stable after 10 years

Even tho' the timber was originally kilned down to say 10% MC, storing it outside for a number of years in an unheated outside environment means that it will have absorbed allot of moisture and the content would probably have been more like 20% (timber behaves just like a bathroom sponge, soaking up and releasing water). Bringing it into a warmer 'shop and then into a warm house will cause the timber to rapidly start to loose moisture again which is probably the reason for the movement in the top of the chest. Its only my theory.... if you do decide to remake the top I'd suggest that the timber is kept for much longer in a warm room before machining - Rob

 

[PowerTool]

I go along with Rob's theory - which is why I keep my woodturning blanks in the house for several weeks before I use them (even though they are already dry,they should end up at the same moisture content as the house before I use them,and therefore much less likely to split/warp when turned)

Andrew

 

[pidgeonpost]

Useful info Rob. Unfortunately my workshop is only about 8' x 12', which makes storing timber lengths of timber (these were about 10') in anything like room temperature very difficult. Guess I should have at least cut the boards to length and tucked them in a corner somewhere for a few weeks.
I guess there's nowt for it but to remake the top at some point having followed the advice above, but it'll have to wait a while.
I'll borrow a moisture meter and check the moisture content of the stuff that's in the garage too.

 

[Alf]

Useful timber acclimatisation places to consider also include such venues as "under the bed" and "behind the sofa". It may require an understanding SWMBO though. Even TPTBs at Alf Towers have been heard to mutter about the beech that's been behind the chest of drawers in the guest room for the last couple of years (I know, I don't see what the problem is either :roll: )

Incidentally, when you reduced the thickness by 1/2", did you remove material evenly from both sides? Not doing so can cause trouble too, but I may be giving instruction on sucking hen fruit in which case disregard.

Cheers, Alf

 

[woodbloke]

Useful timber acclimatisation places to consider also include such venues as "under the bed" and "behind the sofa". It may require an understanding SWMBO though. Even TPTBs at Alf Towers have been heard to mutter about the beech that's been behind the chest of drawers in the guest room for the last couple of years (I know, I don't see what the problem is either :roll: )

Incidentally, when you reduced the thickness by 1/2", did you remove material evenly from both sides? Not doing so can cause trouble too, but I may be giving instruction on sucking hen fruit in which case disregard.

Cheers, Alf

Behind the sofa or under the bed are great places to store timber....do agree again about an 'understanding SWIMBO' tho' - Rob

 

[Paul Chapman]

Interesting discussion. Just a thought - even if one is able to store wood indoors, many of us have to take it out into an unheated workshop and leave it there during construction. Is there any rule of thumb about how quickly wood re-absorbs moisture in this sort of situation?

Cheers :wink:

Paul

 

[woodbloke]

Paul - I don't know of any 'rule of thumb' that says how quickly timber will re-aclimatise to its surrounding environment (great words for a Sunday morning :lol. I glued up the back panels for the elm chest last night and then brought them indoors overnight for the glue to set before re-machining. There has been some slight movement of the timber so it has moved in the drier conditions of the house, even though the 'shop is heated (tho' not hot) and dehumidified - Rob

 

[Paul Chapman]

Paul - I don't know of any 'rule of thumb' that says how quickly timber will re-aclimatise to its surrounding environment (great words for a Sunday morning :lol. I glued up the back panels for the elm chest last night and then brought them indoors overnight for the glue to set before re-machining. There has been some slight movement of the timber so it has moved in the drier conditions of the house, even though the 'shop is heated (tho' not hot) and dehumidified - Rob

Well, the answer is obvious - I'll just have to move all the woodworking clobber into the house and we'll have to live in the garage. Wonder what the wife will say when I tell her 8-[ 8-[ :lol:

Cheers :wink:

Paul

 

[pidgeonpost]

Some interesting thoughts there. My Domestic Assistant is very understanding about the storage of timber, though her preference is that individual pieces be assembled to create at least some semblance of furniture before it enters the house. Amazingly, when I manage to transfer quantities of sawdust and shavings from workshop to living room, kitchen, or bedroom (sometimes all three) she doesn't view this in the same way as she views mud etc., instead refering to it as 'clean dirt'.
Back on the blanket chest front, I believe that when I prepared the timber I flattened one side, then thicknessed it from the sawn side to within a mm or two of finished size, then turned it again to achieve the final thickness and remove any slight marks from feed rollers, squashed spiders etc.
I have about 1 metre of 1.25" x 8" stock still lurking in the workshop, and several chunks in the garage. I'll try and get them tested for mc on Friday and see what they turn out at.

 

[promhandicam]

Well, the answer is obvious - I'll just have to move all the woodworking clobber into the house and we'll have to live in the garage. Wonder what the wife will say when I tell her 8-[ 8-[ :lol:
Paul

The only problem will be (other than persuading wifey) is that once you've made something in your new workshop, if you take it to the living quarters you'll have the same problems of temp / humidity change, but in reverse! #-o

Steve :lol:

 

[dedee]

PP.
I have no pleasure, whatsoever, in being right.

This happen to me many years ago on a blanket chest made with that awful laminated pine board. I've learned to live with it satisfied that at least the kids can't catch their fingers under at least 1/3 of the top.

One thing I wondered about at the time is whether I should have turned the slats on the underside of the top on their edge which would have made them less likely to bend as the top bowed.


Andy

 

[user 2070]

Remaking is probably the sensible choice. Putting a cleat on the ends may simply result in the wood splitting.....but if designed to avoid this it will certainly result in an undesirable gap between the cleat end and the main section sides. (Due to expansion/shrinkage.)

Keeping the wood in its destination climate only works completely IF the destination climate is uniform (constant). In winter, we tend to take cold (fresh) air from outside and heat it to make the house liveable. This means that the RELATIVE humidity of the air in the house is drastically llowered and as a result any wood will give up its moisture much faster, to the surrounding air - until it reaches "equilibrium", than it would if the relative humidity was higher. (The difference between the wood's actual moisture content and the wood's equilibrium moisture content dictated by the surrounding air is the key here.) If the house has low relative humidity (winter) then your wood will tend to dry out from >>10% MC (not immediately but slowly), irrespective of whether you have machined it or made something with it. If the house has high relative humidity (summertime?) the wood will follow this with a higher moisture content. Finishes tend to slow down the exchange of moisture, so the wood "follows" even more slowly.

There are some reliable ways to counteract this, the conventional ones listed in Joyce:
1 Get the moisture content of the wood down below 10%, machine it and then seal it with enough of some finish which drastically slows the exchange of water (moisture) with the surroundings - BEFORE it absorbs more moisture. Performance of wood finishes vary widely in effectiveness as moisture barriers. They vary from almost worthless to nearly perfect.
Some moisture barrier (finish) is probably always desirable even if other methods are applied.
2 Use quarter-sawn wood (which is an approximation to the ideal of radially sawn wood) - because this eliminates the wood's tendency towards cupping, but not the overall expansion ....which you still need to allow for.
3 Plank the wood and alternate the ring directions - if the planks are narrow enough, the total cupping distances are much reduced, but then you lose much of the visual impact of the wood figure.
4 Use laminated materials - or perhaps laminate them yourself from solid.
(Veneering).

Simon

 

[pidgeonpost]

OK....I checked a couple of pieces of unprepared stock from the same batch on Friday. The stuff that was in the garage (undercover, unheated) was a shade over 15% mc. Another piece that had been in the workshop a month or so was around 13%. So, mc way too high, as suspected by those who responded above.
Looks like a remake of the top is the only answer. Plan is to cut a couple of boards to approximate length and move them to the workshop for a few weeks, then into the house for a few more weeks before checking the mc again. May be some time before I get chance to remake the whole top though. Rest of the chest seems OK.