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Dealing with rough sawn timber that has a bow

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wobblycogs

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Hi, I'm building a couple of doors and one of the pieces of timber that I'll be using for a stile has a bit of a bow in it. The timber is 54mm thick rough sawn meranti and I need to get a 44mm thick stile out of it, the bow is about 9mm over the 2m length of the stile!

On paper at least the stile I need is hiding inside the rough sawn timber sitting on my bench but I'm not sure of the best way to extract it. I've got a planner thicknesser but the tables aren't anywhere near long enough to handle timber of this length (1100mm total table length vs 2000mm of the stile). I suppose I could build extensions but I was really hoping to avoid that if possible as I very rarely work with timber this long.

I did wonder about trying to unbend the timber. A single clamp easily pulled the bow out when I clamped it against another piece of stock. In fact considering how easy it was to pull the bow out I've even wondered about just leaving it bowed and letting the joinery pull it straight in the final glue up. That seems risky though.

Any ideas gratefully received!
 

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It can be flattened on the 1100 table of your machine without making any extension tables. Once flattened the wood may move from the stresses in it being relieved and still end up bowed but you can try if you want. Better would be to get another piece that is flat and use it for shorter parts.

The way to work it is to lay the middle of the board over the cutter head and push it through without pushing down on the board. That will cut some of the end of the board. Now flip it around and do it again to the other end starting from the middle. Now your board will have a little off each end removed. Repeat the process several more times and you will see the flat areas at each end get bigger until there is very little rough wood in the middle. Now you orientate the board so the grain will tear out the least and put it through normally. The board will be flat after a pass or two and you can go to the thicknesser. The method works better when you have more thickness to work with. You can skip the thicknessing if the ends are too thin after flattening. Take some construction lumber and bandsaw a bow into the edge and practice until you get the hang of it.

Your other way to do it is to put it on a thick piece of sheet stock (plywood/MDF) with a strip across the front so the board takes it along as you feed it. You'll need to put shims under it along the way to support the bow. Double sided tape works. This way with the board on the sled you cut the hump away with each pass until flat. Then you remove it from the sled and thickness to size.

Pete
 

MikeG.

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I'd buy a new piece.

Doors aren't something you want to take a risk with, and even if you plane this flat you risk it not staying flat. To answer your question, though, you hand-plane the bow out of one side, then flatten the other side with the thicknesser.

The idea of letting the joinery (ie the rest of the door) pull the bent piece flat is a non-starter, because as much as the straight stuff will be pulling on the bent piece, the bent piece will be pulling on the straight pieces. You'll end up with a door all over the place.
 

wobblycogs

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Thanks guys,

Ideally I would use / buy a different piece of timber but that's not an option at the moment as I need to get this done and I don't have any other suitably sized timber to hand. It'll probably move a little after planning but I think I can deal with a few mm of bow once it's to size. Long story short these doors will basically never been used, perhaps once a year at most, so I'm willing to risk them being awkward.

Anyway, the sled idea sounds good though, I think I'll give that a go. I'm going to get a good workout putting a sled and the work piece though the thicknesser :D .
 

deema

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The bow can be caused by a few things, you need to consider what has caused it to know whether to use it or not.
Uneven drying out. If the board has been stored with one or more faces exposed and one or two not you can have a moisture imbalance that will have caused the bow. Placing it in stick for a week or two can straighten it. This is most common with slab sawn stuff, and you need to get the moisture balanced before using it otherwise is will more than likely cup afterwards and ‘straighten’. This will result in a bow in the opposite direction after it’s been straightened.

If the stuff has been stored correctly and climatised to your workshop it’s likely to be stress in the stock and it’s also likely to be twisted. What ever you do it will move afterwards and is not really suitable for a style. As already stated get another piece. The cost time and effort in making a door can be ruined by a single style twisting.
 

wobblycogs

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Some very good points. I don't think storage will have been an issue as it comes from a big reputable dealer. At this point I've got basically nothing to lose by flattening it and seeing what happens as I've already made a sled and mounted the board. If nothing else it'll be an interesting experiment.

The daft thing is I don't even want this doorway, I'd rather just brick it up and have the additional wall space but it's on the plans so it's got to be put in, sigh.
 

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wobblycogs":11j3qsgc said:
......... I don't even want this doorway, I'd rather just brick it up and have the additional wall space but it's on the plans so it's got to be put in, sigh.
It sounds like this is for yourself. Is that right?If so, the fact that it is on some drawings is irrelevant in terms of "got to". If you don't want it, no-one can force you to have it, (unless it is some sort of re-instatement issue, or it is a requirement for a secondary means of escape).
 

thetyreman

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yep any timber that bows like that usually can't be saved, just get a new piece and start again, I don't fully understand why you can't do that? can't you laminate a new piece to the correct size? if you've spent this much time and money anyway, it's not much more work.
 

wobblycogs

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Yeah, the door is for our house. As it's external I'd have to get the drawings updated and go back to planning and listed building for modified consent which is likely to take weeks. Right now this door is the only thing between us and final sign off which is something that I'd really like to see happen!

I work full time so going to get more timber is a bit of a mission and the wood yard would charge me significantly more than the cost of the timber in delivery. It's not that I can't / won't I'd just rather avoid it if at all possible.
 

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wobblycogs":2cd8w0ry said:
Yeah, the door is for our house. As it's external I'd have to get the drawings updated and go back to planning and listed building for modified consent which is likely to take weeks. Right now this door is the only thing between us and final sign off which is something that I'd really like to see happen!.........
Could you explain the situation more fully. Was there a door there before? Is this in a new extension, or a replacement door in an existing part of the building? If it is an existing door, are you replicating it, or doing something new?
 

wobblycogs

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The door is in a new extension. The design is to match other doors and windows in the house. The reason it won't ever get used is because it's from my workshop to the patio. I had it added to the plans thinking that I could move equipment in and out more easily but in all honesty now I'm in the shop I'd rather have just had a blank wall so I'll probably fix shuttering over the door once it's signed off.

The doorway isn't considered an escape route so closing it off would be accepted by planning but one day I'll be selling this house and I think it would make a nice feature and at this point just fitting doors is the path of least resistance.
 

deema

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If you don’t want to source a new piece the ‘best of a bad job’ would be to thickness both sides (not flatten) cut it down the centre (Bandsaw) and then glue the outside faces together. Once the glue has dried, flatten and thickness to size taking care to remove the same amount of material from both sides. This will produce a style where as far as possible the internal tensions have been balanced giving you the best chance of it keeping straight. You won’t know it’s a laminate especially if it’s used on (should be) the hinge side as the glue line is not on the face sides. Using three hinges will also help keep it straight.
 

wobblycogs

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Yeah, I've considered that and if I had a handsaw I'd definitely do it. Best I can muster is a circular saw from both sides and then finish the middle off by hand.
 

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wobblycogs":8dqlqook said:
The door is in a new extension. The design is to match other doors and windows in the house. The reason it won't ever get used is because it's from my workshop to the patio. I had it added to the plans thinking that I could move equipment in and out more easily but in all honesty now I'm in the shop I'd rather have just had a blank wall so I'll probably fix shuttering over the door once it's signed off.

The doorway isn't considered an escape route so closing it off would be accepted by planning but one day I'll be selling this house and I think it would make a nice feature and at this point just fitting doors is the path of least resistance.
You don't have to do everything that you have planning permission for. You can't do more, but you can do less. So in terms of planning consent, you don't need to insert this door. Neither Planning nor Listed Buildings "sign things off".......that's only Building Control with a Completion Certificate. Building Control have no interest in the existence or otherwise of a door which has no safety or disabled access implications. Your works will be signed off as complying with Building Regs whether or not you have this door.

So, unless there is something else you haven't told us about, I can't see why you couldn't omit this door.
 

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Being able to step outside in the summer to sand something, do other work outside or just have the door open for air is a good thing. Now if your shop has other high doors to do the same that's different.

Pete
 

toolsntat

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I find it better to know the bow and use it to your advantage by making the hollow or flattened hollow the face to meet the rebate when hung.
Cheers Andy
 

Jacob

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wobblycogs":2ymztupz said:
Hi, I'm building a couple of doors and one of the pieces of timber that I'll be using for a stile has a bit of a bow in it. The timber is 54mm thick rough sawn meranti and I need to get a 44mm thick stile out of it, the bow is about 9mm over the 2m length of the stile!........
54-9=45 hence 44 is theoretically possible. Might just do it!
There is a technique where you plane from the middle of the convex side by passing it over the planer with pressure only in the middle. Difficult to describe but if you get the idea it will remove the minimum for an all flat surface. It's more reliable than hoping to flatten the concave side, though this can work too.
 

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Jacob I guess I've been doing it wrong all these years eh? :wink:

My Dad, a Dane who learned his craft before the second war, showed me ho to do it concave side down. I always found it easier than from the convex side especially because it is easier to take out the twist at the same time. Each to their own as the outcome is the only thing that matters. The OP might as well try to flatten what he has and if it doesn't work he'll have to buy more stock. Faced with the same task I would have bought a few extra long boards so that I wouldn't have to deal with one that wasn't straight after flattening and thicknessing. Straight boards can warp after they are prepared too. #-o Besides when I don't have extra I'm more likely to screw one up. :roll:

Pete
 

Jacob

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Inspector":3i6f0z39 said:
Jacob I guess I've been doing it wrong all these years eh? :wink: ....
No, but there's more than one way to skin a cat. The convex side down takes out the twist automatically. It's hard to describe but it works. You apply pressure in the middle - if the board is very bent then the ends don't get planed at all until enough has been taken from the middle.
....The OP might as well try to flatten what he has and if it doesn't work he'll have to buy more stock....
I agree
 

Doug71

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Don't just flatten one side over the planer and take the rest off the other side under the thicknesser as it will come out bent again.

Over the surfacer you need to flatten BOTH sides a bit. Take a bit off one side then flip the board and take a bit off the other, keep doing this so it releases the internal tension equally (best if you can let the board "rest" a bit now and again), then when you are nearly down to size you can start on the thicknessing.

When thicknessing still keep looking down the board and if it moves you can go back to surfacer and straighten as needed.
 
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