Bowed wood - How to straighten

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Forum topic by garberfc posted 03-28-2013 12:27 PM 33203 views 0 times favorited 22 replies Add to Favorites Watch
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57 posts in 2491 days

03-28-2013 12:27 PM

I have a couple of boards that are bowed and I’m wondering if they need straightening / how to do it, or, are they okay.

I’m building a faceframe out cherry. The stiles and rails are two inches wide and are going to be joined using mortise and tenons. The faceframe is going to be attached to the carcass using biscuits and Titebound III glue.

As seem in the photos I’ve been attempting to straighten these boards by bending them in the direction opposite their bow. They’ve been clamped for about a week and at least half the bow is gone. I’d say the bow in the middle is about 3/32. The rail is ~21 inches. I’m wondering if all the bow will eventually be removed and if it’ll return to it’s original shape over time.

Another question: Do you think that M&T joints, biscuits and glue are strong enough to hold a piece of bowed wood flat over time?

Please advise…

Thanks in advance for your help,

22 replies so far

View knothead's profile


163 posts in 4185 days

#1 posted 03-28-2013 12:48 PM

Wood does what wood does no matter what we try to make it do…..If they are already milled to final width and thickness you are not going to be able to fully correct this, you gotta either live with it or work the bow into your project somehow or remake them from better material.

IF, ON THE OTHER hand they are still oversized and long, Charles Neil has a trick that he uses that appears to help a great deal, He would rip a centered slot in the inside edge of the stiles and rails that is nearly all the way thru the width of the piece and then mill a piece that fills the entire slot you just milled out of the same material and glue it in. Clamp it up tight and straight, say against your bench or assembly table, anything that is flat and wait overnight for the glue to completely dry and then re-mill your pieces. Actually I would let them reacclimate to the shop again for a few days as you have just added a lot of moisture from the glue to the pieces The 2 additional glue joints really arrest any future bow or twist.

I suspect there are folks here with much more experience than I, and if there are better solutions I bet they will post them for you to consider. But this is what I would do if it were in my shop.

Just 2 cents worth of opinion no more – Have a good’n

-- So Much Wood - So Little Time! --

View redSLED's profile


790 posts in 2129 days

#2 posted 03-29-2013 12:55 AM

I am watching this with interest since I would love to “correct” some maple 1×4 and 1×6 pieces in my shop if possible.

Also, in the photo I think that’s too much pressure for those types of clamps. Might be better for some annoying-to-use big-arse C-clamps to take on that job – and extend the life span of the quick-grip clamps.

-- Perfection is the difference between too much and not enough.

View garberfc's profile


57 posts in 2491 days

#3 posted 03-29-2013 12:04 PM

A friend of mine mentioned adding some humidity as that’s how a lot of wood is bent. I don’t have the equipment for that. This is all in my basement shop where the humidity is pretty low (~40%) this time of year.

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Miles King

28 posts in 2929 days

#4 posted 03-29-2013 12:48 PM

That minor bowing of the wood doesn’t look too bad to me. As “knothead” said wood does what wood does. As an example look at some cabinet doors that were “flat” when originally made and after a few years some will exhibit some bowing but for the most part they still function and on some rare occasion some will need a little repair. It’s wood.

-- Miles

View garberfc's profile


57 posts in 2491 days

#5 posted 03-29-2013 01:27 PM

I think I’m just being stubborn (as usual). There’s nothing special about the pieces in question (other than their lengths exactly match their corresponding rails). It must just be another personality flaw…

View Woodknack's profile


12464 posts in 2617 days

#6 posted 04-01-2013 05:35 PM

If it really bothers you, rip them down the center, flip one and reglue. As for bending, humidity will cause wood to warp or bend because it is absorbed unevenly so if one side is ‘wetter’ it will bow up. Wood bending is done through heat, the steam just acts as a carrier but does not help bending.

-- Rick M,

View Net55's profile


78 posts in 1824 days

#7 posted 02-26-2014 04:05 PM

I’m removing the bow from a beautiful piece of milk chocolate colored walnut. This piece had about a 1/2” crown to it. Place a damp rag underneath it to add moisture to the wood. Raise the 2 ends, clamp down (both sides, just one side is shown in my image) in increments, in my case about an 1/8” per day. Use a household drape steamer or iron. You’ll need to over-correct, each piece will be different. This does not always work perfect. Let the wood sit flat for a few weeks, if it goes back a bit, repeat.

-- Bill, SW Florida

View runswithscissors's profile


2924 posts in 2262 days

#8 posted 02-26-2014 08:27 PM

A crude, simple but effective old trick is to lay the board cupped side down on the ground. Moisture in the earth will expand the concave side and straighten out the board. Of course, that doesn’t address what’s going to happen to it when it dries out again.

If you have sufficient thickness, jointing and planing would be a surer way to go.

-- I admit to being an adrenaline junky; fortunately, I'm very easily frightened

View Grandpa's profile


3261 posts in 2912 days

#9 posted 02-27-2014 04:25 AM

straighten the board by moistening the cupped side. Clamp it as shown in the lead photo above so it is straight. Wrap it in black plastic and heat it by placing it in the sun on a hot Oklahoma afternoon. Let the board cool and take it out of the plastic and unclamp. It will often stay pretty true. Try it on a scrap and see what happens.

View fernandoindia's profile


1081 posts in 3180 days

#10 posted 05-16-2014 08:01 PM

Hi Garber,

How did the straightening go. I´m having the same problem. so far after several attempts mine are still bowed

Thank you

-- Back home. Fernando

View ragf18's profile


1 post in 1218 days

#11 posted 09-19-2015 12:52 AM

what i do whit complete lumber piezes is put my car over the lumber in a nearly perfect straigt concrete floor, and then rinse a lot of water on it and left overnight. It really helpme aligning 4”x6”x20’ lumbers. sometimes requires a more than one night.

View BurlyBob's profile (online now)


6030 posts in 2502 days

#12 posted 09-19-2015 01:16 AM

I spent over a month trying to straighten some beech for a tv cabinet. I’d get one straightened out, put it aside to do another. By the time it was done the first had cupped again. Finally gave up and built the tv cabinet out of Oak plywood.

View Eugd's profile


65 posts in 1348 days

#13 posted 07-03-2016 01:52 PM

I need advice, I just built these doors about a few weeks ago, and I notice that one of the stiles are beginning to cup, when I built them they were straight, they are kiln dry 4/4 the panels are 1/2 plywood, do you think if I sand off the paint and wet the one that is Bowing, then clamp it to my bench for a week or two it will fix the problem? Or should I just make a new panel? Thanks for your advice

View JBrow's profile


1366 posts in 1157 days

#14 posted 07-03-2016 06:43 PM


If you can clamp the bowed boards that will make up the face to the carcase so that the bow disappears, then I would use the boards as they are. Once glued to the carcase, the boards will likely remain straight. However, close attention is required when cutting mortise and tenons into these boards. When these are cut, the boards should be kept flat, otherwise the mortise and tenon joinery may not come out well.

Mortise and tenon joints to build the face frame work well for me. I prefer a dado/rabbet joint for attaching the face frame to the carcase, but see no reason why biscuits would not work well. In either case, plenty of clamps with cauls to distribute clamping pressure when gluing the face frame to the carcase are more likely to result in tight seams all along the carcase and face frame, especially with a slight bow in a rail or stile.


If you post your problem as a new topic, you will likely get more ideas.

A lot of work has gone into your doors. If you can just live with the cup in the stile, this may be best. The cup could disappear this winter when humidity in the house drops.

Your idea to try to re-establish moisture equilibrium within the wood may or may not work, as long as plenty of paint is removed from the stile. I suppose whether this fixes the problem permanently depends on where moisture has entered or left the stile. But repairing the stile creates the problem of re-finishing the door so that the repair is invisible. In the end, re-making the door or replacing the stile may be required.

You did not say, so I will mention that it is best to apply finish to all six surfaces of the door. The ends, edges, and faces should all receive the same finish and the same number of coats. Also, when making the frame and panel doors, I like to apply finish anywhere that moisture could enter the wood and where finish cannot be applied after the frame and panel is assembled. This includes all six sides of the panels and the grooves in the frame into which the panel sets, but nowhere that receives glue. Lastly sanding all edges, ends, and sides to the same grit I believe also helps. All these tips are suggested as an effort to ensure that moisture will enter and leave the wood at the same rate wherever moisture finds an entry point.

View Aj2's profile


1949 posts in 2034 days

#15 posted 07-03-2016 08:00 PM

I need advice, I just built these doors about a few weeks ago, and I notice that one of the stiles are beginning to cup, when I built them they were straight, they are kiln dry 4/4 the panels are 1/2 plywood, do you think if I sand off the paint and wet the one that is Bowing, then clamp it to my bench for a week or two it will fix the problem? Or should I just make a new panel? Thanks for your advice

- Eugd
Did you use rift sawn wood for your doors.Careful selection and milling of your stiles are the only things you can do.
Once they have cupped maybe they will straighten out next year when you made them.
Forceing the wood to bend back is Fruitless and usually attempted by beginners.

-- Aj

showing 1 through 15 of 22 replies

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