Undoing a bow in a panel

[danst96]

Hello,
I'm making some round end tables and i have glued together some panels. The panels have sat for a week and have developed a slight bow, I don't have the thickness to flatten them, is there anyway of undoing this in another way?

It's probably related to the fact I left them in my very cold shop which was probably dumb.

 

[D_W]

acclimatize them to whatever the conditions were before a week ago (though if it's stress relief, that may be hard to fix).

I've not experimented much with moving wood back (rather I'll glue it thick, let it sit for a while - and then remove the movement later - if it moves again, then I just let it go), but have a friend who plays around with panels by sunning one side of them (probably creating stress on one side by differential drying) to get them to move back.

On a more industrial scale, I've seen machines that will press the wood and heat it or press with heat and steam and actually flatten boards before use. This is attempted sometimes to flatten guitar necks that don't have a simple problem (that is, heat pressing something that has become misshapen oddly, like an S or a twist, but had a repair shop quote doing it for a defective gibson guitar that I had and their comment was "it probably won't completely fix the problem and if it doesn't, you have to pay, anyway".

 

[deema]

The panel needs to be raised so air can get all around. It needs to be away from any heat source. Now, wipe on the cupped side a damp cloth over it so it’s wet without water standing. Repeat daily until it’s flat.
if it’s a moisture imbalance it usually works. If it’s released tension in the wood it won’t.

 

[baldkev]

As deema said

I made a 'box' out of a lump of 2'' stock and when i brought it home the lid bowed. Its 5mm thick... after a couple of days it settled back down ( sigh of relief )

Looking at the end grain, it looks as if they are all glued with the annular rings in the same direction? Its best to alternate that wherever possible. I accept that sometimes it doesnt visually work, but reduces the overall effect of movement as you get a mild wave rather than a long cupping edge

 

[danst96]

The panel needs to be raised so air can get all around. It needs to be away from any heat source. Now, wipe on the cupped side a damp cloth over it so it’s wet without water standing. Repeat daily until it’s flat.
if it’s a moisture imbalance it usually works. If it’s released tension in the wood it won’t.

Thanks, I'll try that.

I'm a little worried it's released tension because it was 8 quarter before and I've resawed to 4/4.

Will see how we go

 

[danst96]

Its best to alternate that wherever possible.

I did think about it but I figured with the panels being so small it wouldn't have much influence and forgot to do it in the end... I'll pay more attention to that next time and see if it makes a difference

 

[MARK.B.]

Sage advise given above let mother nature play with it for a while and see what happens As a last resortwould it be possible if unseen in the finished piece to put a series of relief cuts that stop short of the edges might help or it might just hasten its journey into the fiery flames of Hell

 

[baldkev]

Burn baby burn...... disco inferno!

Anyway..... the other thing could be to route in a rebate , clamp dead flat and glue in a 20x10 oak strip or similar
Doesn't look deep enough for a 20x20 angle iron

 

[MARK.B.]

Angle iron Angle iron ya Damn Heathen

 

[baldkev]

Oops

Edit: stainless, not mild steel due to possible tannic reaction

 

[Fitzroy]

Will it pull flat on the leg frames?

 

[Ttrees]

I'd chance wetting the shrunken cupped side and hope for the best.

 

[Bojam]

I made some quick panel clamps this week. The image below shows a pair with two panels clamped. Each clamp consists of two 35mm thick planed hardwood bars (each 1m long) with matching 20mm holes drilled through to accept 18mm dowel rods. Put the panels to glue up between the bars then add spacers as required. Then drive in wedges between the panel/spacer and the end dowels to apply lateral pressure against the sides of the panels. This has the effect of closing the joints and simultaneously skewing the clamping bars enough to get a friction fit on the dowels pulling the top and bottom bar together. This stops the panels from slipping out of alignment. The pressure is such that I can pick up the whole arrangement and carry it around without any other clamps being used to hold it all together.

Note - not visible in the picture - I predrilled 3mm centering holes at 96mm intervals (using the Parf guide mk2 ruler) along the inside faces of the bars. I can then go back and drill out other 20mm holes with a forstner or TCT boring bit as required for different sized panels.

This won’t stop cupping if the panels are not stored carefully after glue up - e.g. stickered to allow air circulation, etc. But it will stop that annoying occurence of uneven glue ups, which is common when gluing more than two boards together (usually when the middle board gets forced slightly out of alignment).

I got the idea from Izzy Swan. The Renaissance Woodworker has done something similar but using more complicated hardware. I think the system is ingenious and dates way back to when wedges were the go to way to exert clamping pressure. Combining wedges with cauls just makes a lot of sense. Plus I can’t afford to pay the silly money for sash clamps out here and parallel clamps and pipe clamps aren’t even available in the shops.

Hope you manage to get the table top flattened! Definitely try the damp cloth trick.

I should mention that the panels shown in the picture were just used to test the clamps. They are not glued and no effort was made to match colour, grain, etc!

 

[Bojam]

Deleted.

 

[TRITON]

Soak in water, and put some serious weight on it. Leave that for a week or longer and hope for the best.

 

[Sgian Dubh]

The piece is cupped, not bowed. Pull it flat with a screw attached cross-grain bearer(s) or rail(s) incorporated within the tables undercart. Slainte.

 

[John Hall]

Very common problem, when wood has been stored in a cold damp environment, then moved into a warm house with central heating etc…wood that looks fine in the timber yard can soon change its shape once it’s in a warm house. Unless you have a planer thicknesses to get it flat it can be a real pain…using cross bracing helps, but doesn’t always fit in with the design details. Can be heartbreaking when hours of work are ruined before your eyes.

 

[Citracal]

The panel needs to be raised so air can get all around. It needs to be away from any heat source. Now, wipe on the cupped side a damp cloth over it so it’s wet without water standing. Repeat daily until it’s flat.
if it’s a moisture imbalance it usually works. If it’s released tension in the wood it won’t.

This is the correct thing to do. Wet it on the cupped side, sit a weight on top of it and leave it over night.

If this doesn't work flatten it by hand.

If it's been resawn as you mentioned than there will be a lot of tension released and you won't be getting it out with some moisture.

 

[recipio]

Going from 2" to 1" and then using it without more seasoning is probably the main problem. It would be worth checking the moisture levels. After sanding you may be able to clamp it to the underframe and hold it down with a threaded insert and bolt. That's woodworking for you !