Bowed panels after glue up

[mr]

So having spent weeks prepping the wood and then gluing up to get my panel width. placing the "nearly to thickness" panels into a sticked pile as I go I return to the pile of panels to find that rather than nice flat panels (as once they were) awaiting final finish for the bookcase I was making I now have several long bowed panels. So bowed in fact they might make nice coopered tops for something.
No idea what to do now really, planing them flat probably not realistic, theyre not just a little bowed after all. Ive moved them from workshop to house in the hopes that some central heating might flatten them again. It will probably make them worse but then theyre already so bad that it doesnt really matter.

Oh well back to the drawing board.
Mike

 

[Matt1245]

I'm no expert on this, but did you place each board with the growth rings running opposite to each other? What wood are you using?

I've read somewhere about putting panels out on the lawn first thing in the morning, to absorb dew to help flatten them, but not sure of the details.

Matt.

 

[mr]

The wood is nasty reclaimed pine, given to me so no great loss but an iritation as Ive spent about 3 weeks preparing this lot all by hand. The plan was to try and finish the bookcase this weekend and at the moment it looks like I might be starting again. :/
Growth rings are mostly but not entirely running opposite to each other but that doesnt seem to have had any effect the bow is equal in places where rings are opposite and the same.
Havent heard about putting them out on the lawn but its an idea alright and short of any other its certainly worth trying.

Cheers Mike

 

[mack9110000]

Don't put them out on the lawn tonight !!

 

[Matt1245]

If i remember correctly, you had to apply the finish soon after bringing them indoors, but don't quote me on that as i may be well off the mark.

Matt.

 

[mr]

These are so far from a finished state now to be honest that that wouldnt be possible. Now that they ve curled up I expect that if they flatten out again there will be an amount of planing to get them properly flat. Very dispiriting really, the pieces I had sized and surfaced last weekend intending to put together the last couple of panels with have also bowed along their length, So Im having to plane them flat again, meaning the existing curly panels will be too think if they ever go flat again. Bah, I believe is the expression I was looking for.
Mike

 

[Lee Brubaker]

Mike: Go to www.woodcentral.com click on message boards & ask the question there. I have seen the lawn thingie but can't remember the details. Your bound to get a lot of helpful advice.

Lee

 

[mr]

Cheers Lee, Ill get over there shortly.
Mike

 

[mr]

Am beginning to think that the major cause of the cupping is that the wood wasn't /isn't dry enough to start with. Beign reclaimed from pine fencing stock I suspect it was never dried properly in the first place so that its moisture content was too high really to be useable.

Theres still a largish pile of this stuff and Im beginning to think its just taking up space.
Mike

 

[paulm]

Mike,

Think your last post probably explains the problem if thats the quality of the timber involved.

Could have been caused also by taking more off of one face than the other when you were cleaning it up as this would cause one face to be less dry than the other and lead to cupping, but suspect it's mainly due to being low grade timber to start with.

Cheers, Paul.

 

[mr]

As you say Paul I think that is the case. Shame really cos theres a mountain of the stuff that Im not sure what to do with now. Its certainly put an end to my plans for this weekend unfortunately. As for taking more off one face than the other, thats quite possible I wasn't counting passes with the plane if you see hwat I mean more aiming for clean square and straight - which at one point I had.
If nothing else its been planing practice I suppose. Best start looking for some proper materials for the boys book case eh, that way he might get it by christmas.
Cheers Mike

 

[mr]

After a weekend stood in the house the panels appear to have flattened themselves out to a large extent, not as flat as they were but possibly workable. Wonder what will happen when summer arrives
Mike

 

[Adam]

Or see here:
https://www.ukworkshop.co.uk/forums/view ... 14&start=0

Try putting lawn into the search engine of the forum, its come up a few times before.

Adam

 

[spadge]

Putting wood on the lawn just means wetting one side (the concave side) whilst keeping the other (convex side) dry. This has the effect of swelling the fibres on the concave side and hopefully flattening the bow in the wood.

"Understanding Wood" by R Bruce Hoadley will tell you all you need to know about movement in wood due to changes in moisture content.

If you want a really graphic illustration make yourself a Rittenhouse hygrometer. All it is, is 2 pieces of thin (say 2mm) wood about 150mm long and about 12mm wide glued together. On one piece the grain runs the lenght of it on the other it is cross grain. It works because the cross grained piece swells (moist air) or contracts (drier air) and causes the whole thing to bend. Just running a wet finger down the cross grain side will make the thing bend before your very eyes.

 

[user 2070]

Mike,

As everyone will confirm, Wood moves with varying moisture content - the trick is to get it dry and then seal it to slow down the moisture changes.

What you probably did by putting the wood into the house was change the moisture content of the wood, but one weekend is probably a short time for this. This weekend, the low temperatures outside meant that the air outside will have a very low misture content (in absolute mass terms - not relative humidity). Taking that cold-air into the house (ventilation process) and simply heating it to 20C will mean that the warmed-air probably then has a VERY low relative humidity and therefore can dry the wood out relatively fast. This is why centrally heated houses are so much of a challenge for solid-wood furniture making.

The good part of this is that, because the wood straightened out in the house, you perhaps started (when planing) with drier wood than after your glue-up = it probably moved in the right direction over the weekend. The bad news is that you don't yet know how dry it was and whether that will reflect the long-term moisture content AFTER finishing = it may move even further the other way as you dry it now.
Without measuring the moisture content of the wood the only easy way to tell what will happen next is probably to leave the wood in something which resembles its final environment (indoors). After a while (weeks rather than days perhaps) you may then make a less risky decision on proceed / saw&reassemble / scrap.

As far as the summer is concerned, by then you should have dried out the wood to something close to what you want (long-term) and sealed it so that the moisture no longer gets in and out at the same rate.

Simon

 

[mr]

Hi Simon
yes that all makes perfect sense to me unfortunately.
Mike

 

[Lee Brubaker]

mr: You can salvage that lumber with a little extra work. Reduce the boards down to 3/4" thickness then laminate them with a quality glue. This will prevent the cupping. There are a lot of things you can do with
1-1/2" material. If you are looking for thinner than 1-1/2" then of course reduce the lumber thickness to suitable thickness accordingly before laminating to the thickness that you are after. When I need thinner material I usually square one side of the plank, then resaw it allowing enough thickness to run it through the planer prior to glue up.

Lee