Bowed board

[memzey]

Hi gang,

I'm making a coffee table for our front room and have planed and thicknessed the oak boards for the top. They are 6" x 4' and 3/4" thick. I will glue them up to make a 2' x 4' top using biscuits to help alignment. Post-thicknessing one of the boards I plan to use in the middle of this glue up has done the old lignum disco manoeuvre and bowed along its length by about 1/4" or slightly less at the peak of its "hump" . I'd rather not replace this as it's a good match to its mate (cut from the same board) and was wondering what people on here would do in my situation? The bend is easily taken out with some downward pressure and I wondered whether the fact that it was going to be glued up to straight boards either side of it plus the use of biscuits would be enough to keep it straight in use?

All advice greatly appreciated!

 

[custard]

You'll be fine with that.

Personally I rarely use biscuits or splines when jointing up, but that's just a personal preference. However, faced with a situation like you're describing I'd be even less likely to use biscuits. It sounds paradoxical but it's not. You want to be in charge of the straightening process, the fact is abdicating that control to a few biscuits rarely works out as well. Set the boards up on bearers for a dry glue up, start in the centre tightening up the central sash cramp so the top is flush, then move out to the ends. If you can get the result you want then just repeat but with glue.

 

[morturn]

Leave it for a day or two in the workshop stickered first

 

[kevinlightfoot]

I would go for it if it was my job the bowing is not that significant over the length of the board the biscuits should do their job and the flatness of the adjacent boards will also help.Ive glued boards with greater deformation and had no problems.Of course the nature of any piece of wood is different from another so things going wrong cannot totally be ignored.Good luck and carry on regardless.

 

[memzey]

Thanks all. I was a little concerned that the forces being exerted by the bowed board would pull the others out of true over time but logically I suppose, the opposite is the case in that the three are more likely to true up their delinquent cohort.

Custard - thanks for the tip on process. Is your reluctance to use biscuits because you feel the bow might affect registration in some way and therefore lead to a built in misalignment? I had considered this and thought that by cramping the board down to my (dead flat) bench top while milling the slots I’d be ok and that the biscuits would then help get things right during the glue up?

 

[custard]

Is your reluctance to use biscuits because you feel the bow might affect registration in some way and therefore lead to a built in misalignment?

That's part of the reason. Another issue is how you get the biscuits correctly "plugged in" during the glue up, as all the biscuits need to go in together which is trickier with slightly warped boards. It's not a risk free process. Even if you plan on inserting the biscuits "dry" it's inevitable some glue will get transferred into the biscuit pockets, and as I'm sure you know biscuits start to swell the moment they touch glue. So in the worst case you're wrestling to get the boards aligned while the biscuits are swelling up and jamming in their pockets at unhelpful angles. I'm not saying that will happen, I'm saying it could happen.

Why not try a dry glue up first without biscuits and see how that goes? It would cost you nothing and the experience might influence your plans.

Incidentally, I'm not anti biscuits for edge jointing. I know excellent craftsmen who regularly use alignment aids, and I know other, equally excellent craftsmen, who don't. It's just personal preference.

 

[Beau]

My 10 pence worth is to do as morturn suggests first and leave it in stick for a couple of days in the hope it does correct. If no and you have a sub frame for the table that would enable you to pull out any curve then crack on and glue it together with biscuits would be my preference. One warped boards glued to two straight ones is unlikely to leave you with a perfectly flat top though as that tension is still there wanting to manifest itself.

 

[woodbrains]

Hello,

I'd agree with Custard here (as usual). I only ever use biscuits when everything is dead flat and I want to make sure everything stays in alignment to a fine tolerance. You actually want to shift the surfaces about. There is no advantage in biscuits here; you are going to have to press down, possibly with the help of a hammer and block, the boards during clamping anyway. The biscuits are not miraculously going to have everything just slide together. They won't add any strength to the joint, so why bother with the extra faff? The flat boards might not take out the entire curve, but they will get rid of most of it, enough to handplane back to flatness without losing too much thickness. Biscuits will do no better here, either.

Mike.

 

[memzey]

Thanks again everyone. Here are a couple of dry fit pictures to show where I am with this:

This shows the boards from the top down. Offending board is second from the top.

This one is at an angle to illustrate the bow a bit more clearly. As I tried to persuade them into alignment I realised that in order to show the face I’m after I’ll have to have the convex face showing, which means I must somehow persuade it up in the middle. Does anyone have any good pointers on doing so? Much easier to bang a high spot down with a rubber mallet!

 

[Ttrees]

I would think it might be possible to get the back piece straightened a bit, by introducing some
moisture on the concave side, but I wonder if this is just a quick fix, or practiced atall?

 

[Jacob]

Biscuits align but make a weaker joint. Plain glued is best - with glue spread 100% on both surfaces.
Multiple boards can be a problem in gluing up - you get one joint straight and another one pops out. Simple answer is just to do one joint at a time - glue two together, wait until gone off and glue the next one. You just have to schedule your work around it!

 

[Steve Maskery]

Excellent grain-matching there, memsey, lovely.
+1 for gluing one joint at a time.

 

[memzey]

Thanks again for the input everyone. It really is much appreciated. I think I will try Jacob's suggestion and break the glue up into sections. I should have thought of that already really. The simple solutions are almost always the best. I usually let glue ups cure overnight so this will mean things will take a bit longer than I had planned but then again so do all of my projects so nothing new there!

Steve - thank you for your kind words. I have tried to orient and order the boards in a way that is pleasing to the eye but I'm not 100% convinced I've done such a good job. I hope it works out but I guess I won't really find out until the finish goes on. It's funny that so much of the talk in woodworking is about things like sharpening and cutting dovetails, two skills which are really very easy (or at least straight forward) to pick up, whereas, very little time is spent talking about the really challenging stuff like getting your stock to work in harmony, designing visual weight/lightness into your work, understanding how to proportion the aspects of your design, etc. I wonder if some of that is due to a lack of interest from manufacturers as there is no gadget to flog that "solves" these problems? Anyway I will try to get some shed time on this tonight and report back my progress.

 

[Steve Maskery]

The mathematics of this is interesting, I think.
You have four boards to arrange harmoniously, let us call them A, B, C and D.

Board A can go in any one of the four positions across the table. I can also be top of the tree to the left or the roots to the left, and it can be heart-side up or heart-side down.
So board A has 4 x 2 x 2 possible positions.

Board B can go in any of the three remaining positions, but can also be roots L/R and heart U/D
So board B has 3 x 2 x 2 possible positions.

Board C can go in any of the 2 remaining positions, but can also be roots L/R and heart U/D
So board C has 2 x 2 x 2 possible positions.

Which leaves board D having 1 x 2 x 2 options.

So the total number of permutations is:
4 x 2 x 2 x 3 x 2 x 2 x 2 x 2 x 2 x 1 x 2 x 2 =
=
=
=
=
=
=
6,144!

So if you considered each one for just 30 seconds, it would take you over 52 hours to decide.

OK, for a coffee table, it's really only half that, because the table can be viewed from each side, but for a sideboard, say, which has a front and a back, it stands.

Enjoy!

 

[memzey]

You've just melted my brain Steve!

All I did was look at the face of each board in isolation and pick the one that looked the best. I then arranged them face side up on my out feed/assembly table to an orientation and sequence that seemed to work; the most figured boards (including the bowed one) are in the centre with the plain, straight grained ones to either side. I hope it will look nice with a few coats of Osmo on it. I was thinking of starting a WIP thread in the projects section once I've got this bowed board issue sorted. Would that be of interest to anyone or have my ramblings on this thread been enough to put people off?

 

[OscarG]

...Would that be of interest to anyone or have my ramblings on this thread been enough to put people off?

I'd certainly like to see it.

I'm also watching this bowed board issue with interest!

 

[SteveF]

I am watching
but I only counted 40 permutations :-(

Steve

 

[memzey]

I took the advice above and did a dry fit of two of the boards, including the bowed one, and was happy with the outcome as far as being able to manage the alignment. I did however dress the machine jointed edges with my No 7 first and gave the joint some spring while at it:

I then checked in a dry fit to ensure the joint was invisible:

On to glue up; a thick bead applied, some tapping with a raw hide mallet and a few cramps later:

Lovely. Those two cured and I have just glued up the other two:

They’ve been in for a couple of hours and am now thinking of glueing the two assemblies together. Do we think that it too soon or am I alright?

 

[custard]

They’ve been in for a couple of hours and am now thinking of glueing the two assemblies together. Do we think that it too soon or am I alright?

Looking good.

You're alright to move on, in fact at reasonable room temperatures you'd be okay to remove cramps after 30 minutes.

 

[memzey]

Thanks Custard. I’ve taken the cramps off but will let the glue cure fully on the second assembly before glueing the two together. I’m concerned that they may come apart during mallet assisted “persuasion”