Dealing with cracks in pine board for a desk

[Duane...]

Hi all,

Making a desk, and using reclaimed pine scaffold boards (about 33mm thick) for the surface. I've got 3 lengths, biscuit jointed together.

There are quite a few cracks on the boards, most superficial, but on one of the boards the cracks work their way along the majority of the board, so there is a bit of flex along it's length. I'm not too worried about this, as I am having steel legs made which will run across the width of the surface, so will stiffen it up.

However, I would still like to stiffen up the surface, even just for while I'm finishing it. Two ideas;
1. Screw and glue a length of wood (maybe 10x70mm) from front to back of the underside of the surface, at each end of the surface. Easy option, but protruding wood is a bit messy.
2. Router in 3 channels (both ends and middle) 10mm or so deep, into the underside of the surface, and glue and screw wood stiffeners in these channels. A lot more work, but much tidier.

Which of those sounds more effective?

Couple more questions;
3. While doing the above, would it be OK to sash clamp the surface tight to close up the cracks, and fill with glue? Or will they just spring open once unclamped (and then cause the surface to bow as it will be constrained from the new stiffeners on the underside)?
4. Even more fundamentally, is restricting the boards and cracks with the stiffeners a bad idea due to expansion/contraction of the wood? The desk will be in my bedroom (in the UK), so not a huge amount of temperature variation).


And then... we have the matter of filling the remaining cracks, but maybe that's for another thread!


Any input or suggestions would be much appreciated!


Thanks,
Duane.

 

[Penny]

I would go for option 2. Router the channels and fix strengtheners below.

As to the cracks: How about (once the top is sanded smooth) filling the cracks with a coloured resin? It could add a nice touch to the desk and make a feature of the cracks instead of doing a fill with a wood filler that would stand out anyway.

 

[blackrodd]

How about router in some of these?,--

http://www.ebay.co.uk/sch/i.html?_from= ... r&_sacat=0

Regards Rodders

 

[Racers]

If the cracks close up with a clamp just put some glue in and clamp it.
You can blow the glue into the cracks with a straw.

Pete

 

[Eric The Viking]

I'm with Pete, for practical reasons: building boards are full of grit. Even after some clean up there's quite a lot left, ground into the surfaces. It will take the edge off router cutters pretty fast*, and the result will probably be burning, not the clean finish you're after.

And anyway, constraining the natural movement across the grain is a bad idea. Your steel frame needs slots in it and probably to be used with dome headed screws, so they can move with the wood.

I make things from scrap wood sometimes. If it's been outside, I usually clean up (before machine thicknessing) with a two-handed wire brush, used with the grain. But for building boards you can't reach the grit deeply embedded. Heck, I use a grinder to cut concrete tiles, brick and steel up on scaffolds, so that's grit, carbide and possibly diamond dust embedded!

I'd use a belt sander on it diagonally to start with, then work down grits with an orbital. You might get to the point where a hand plane will work, but expect it to blunt quickly, because of the grit.

E.

*it can be surprising: I was rebating some melamine-faced chipboard a while back, and the finish started going off (burning and chipping of the surface). I was surprised to find the melamine facing had fairly quickly worn a notch in the cutter.

 

[Paul Chapman]

*it can be surprising: I was rebating some melamine-faced chipboard a while back, and the finish started going off (burning and chipping of the surface). I was surprised to find the melamine facing had fairly quickly worn a notch in the cutter.

Chipboard often has bits of metal in it - horrible stuff.

Cheers :wink:

Paul

 

[Eric The Viking]

*it can be surprising: I was rebating some melamine-faced chipboard a while back, and the finish started going off (burning and chipping of the surface). I was surprised to find the melamine facing had fairly quickly worn a notch in the cutter.

Chipboard often has bits of metal in it - horrible stuff.

Cheers :wink:

Paul

I know - I was wondering why my rail saw blade was dulling so fast when doing flooring, then I saw the glinting along the cut edges.

In the case of the MFC, it was definitely the melamine causing the problem - sharply defined nick at the exact depth of the cut. I tried two passes -- two nicks :-(.

I can't remember now, but I don't think it was an especially cheap cutter (I Think I was using a 15mm Wealden plunging cutter for that job - had to do holes for knock-down fixings too), and it certainly wasn't a lot of work.

 

[Duane...]

Thanks for all the replies, interesting stuff.

Is the wood likely to experience much movement? As I said, it will be in my bedroom, which doesn't have much temperature range throughout the year.
Isn't glueing the cracks restricting the wood's movement? And is glue likely to be strong enough to hold the cracks closed together?

The boards are pretty new to be honest, not brand new but not weathered and old like you normally see.


Apologies for all the stupid questions, very much an amateur!


Thanks,
Duane.

 

[Eric The Viking]

Is the wood likely to experience much movement?

Yes. It's more moisture content changing than temperature, and the former varies dramatically during the year.
As I said, however you fix it to a steel frame, arrange for movement across the grain.

Isn't glueing the cracks restricting the wood's movement?

Not significantly. it's the sides of two sets of fibres. that originally had a weakness. All it does is distribute the stresses more evenly really.

And is glue likely to be strong enough to hold the cracks closed together?

Certainly, if you do it properly. PVA-based glues, and my personal favourite is Titebond (Titebond II, but there's a variant with a longer 'open' time, which would probably be easier for doing a long crack).

The boards are pretty new to be honest, not brand new but not weathered and old like you normally see.

In which case you may well find it hasn't stabilized yet, especially if you've planed the surfaces. You may well find it continues to open up cracks over time.

The best answer is to start from a different place (yes, I know). Get it roughly to size and shape, and let the boards sit around for a while, to adapt to the environment. Wood is almost always too wet for a house when it's fresh, and the drying out will cause it to change shape - sometimes predictably, sometimes not. So if you straighten and flatten it too early it will move around again afterwards, which is really frustrating (it's happened to all of us!).

A "while" in this context is a really long time that's hard to be specific about. Hardwoods and thick bits of softwood need ages - months to years. Generally the thinner it is, and the more open the grain, the less time it needs.

We also usually paint the ends of the boards, so that drying doesn't happen too fast at the ends and cause splitting. You can't always win this one!

It's one reason why a lot of modern "solid wood" furniture is made up of wooden 'staves' -- long thin blocks of stock, glued together. The individual pieces move around less, so overall the worktop or whatever is more stable. Craftsmen (less so in big factories) can arrange the grain so that adjacent pieces conflict, so a tendency for one piece to warp one way is counteracted by the opposite tendency in its neighbours.

The other reason, incidentally is cheapness - you can glue offcuts back together into usable boards.

It's also a reason for the existence of chipboard - the 'random' grain makes it more dimensionally stable, although it has a lot less strength usually than the equivalent board of unmolested wood. Likewise plywood (much stronger because of the crossed grain and thin layers) and MDF (generally nasty, but very dimensionally stable, in the moisture resistant version).

Apologies for all the stupid questions, very much an amateur!

I'm an amateur too. We're all learning, even the pros.

E.

 

[Duane...]

Thanks again. Going to be difficult to resist the temptation to just get on with the project..!

Here are a couple pictures of the cracks.

How much movement should I allow for when I put bolt slots into the legs, a few mm?


Thanks,
Duane.

 

[Eric The Viking]

Those go through the heartwood - where the tree is oldest and where the wood is weakest. You won't remove them easily by glueing - they are indeed because of shrinkage though.

The good news is that either side you have 'quatersawn' wood - about the most stable and the strongest boards. The middle bit is pretty much rubbish though.

I'm sure others will suggest alternatives, but I would rip down the boards, discarding about an inch or perhaps two from the middle (equidistant from the centre of the tree, where the growth rings emanate from). Then glue the gap together. Repeat for the other boards too.

Cutting a bit out and re-glueing the one you showed will give you a quite stable board - or it should. Boards that don't go through the centre of the tree, or on a radius, will tend to cup. The fix there is to cut the board in half lengthways, then swap one piece end-over-end and glue up. You'll need to look at each piece and decide how to get the best from it.

Also when you glue up, unless you have a huge quantity of powerful cramps, it may be best to glue one joint at a time, adding thickness piece by piece. That makes best use of the squeezing power you have available, and it's a lot easier to do than trying to juggle lots of pieces of wood simultaneously..

If you look on the net, especially Marc Spagnuolo's site (the Wood Whisperer), you'll probably find explanations of the best way to join boards to make tabletops - taking the grain into account to best effect. Also search on here for 'rubbed joints' - you don't need biscuits and lots on here don't use them (I'll admit I do!).

E.

 

[blackrodd]

The scaffold boards would have been kiln dried before final sizing and cut to length and end banded.
But, it makes sense to let the boards acclimatise to the new environment at least before taking action regarding the splits and shakes you have.
On the sample you have pictured, That piece is western white spruce, commonly used for scaffolding boards, some door linings, etc.
Sorry to say its far from a first choice as it's so very hard, stringy and very very woolly, and difficult to get a decent fine finish for staining, as you can easily get with regular softwood.
In the true spirit of recycling, there's perhaps a good case here of accepting the piece as it is in rustic form, and either leaving the split as is and getting the chosen finish deep in the split, or fill with a contrasting element.
Just as long as you remember that Recycled Scaffold boarding is ideal for rather rustic work, and are happy with that finish including any repairs and filling still evident then you will probably be delighted.
There's quite a lot on utube a Google that you have probably seen.
The main thing is get stuck in and enjoy you're self!
Regards Rodders

 

[Duane...]

Thanks guys.

I'll be honest - I'm not looking for perfection with this project, and it looks like my choice of material/grain location isn't helping! I'm just trying to make a simple desk, learn a bit, and have some fun along the way!

So, how does this sound - realistically, what is the worst that could happen?
Get Titebond deep into all cracks (blow in with a straw), and lightly clamp up (more for rigidity across desk width rather than to hide the cracks)
Belt sand and orbital sand the surfaces as flat as reasonably possible
(If filling cracks rather than leaving exposed) - fill with suitable filler, sand again
Finish wood with suitable finish
Attach steel legs using wood inserts and M8 bolts, with either oversized, or slotted holes in the steel to allow for movement.


How does that sound?

Rodders, why do you suggest using filling with a contrasting element, rather than trying to match the wood colour? Simply because it's impossible to perfectly match the colour, or to "embrace" the imperfections? What kind of darker filler would you recommend?


Thanks,
Duane.

 

[Racers]

Belt sand, empty the bag, mix the contents with glue and work into the cracks, leave until set and sand again.

Pete

 

[blackrodd]

I mentioned a contrasting repair as Just a different approach other than trying to "blend" in a fill or repair.
This is not my Idea, some of the turners in the forum have an interesting approach, keep an eye out for you're self.
Regards Rodders

 

[Paul Chapman]

As Eric The Viking said, you really need to rip the board in two where it is split, plane away an inch or so on both pieces and then glue together. Trying to repair the boards by gluing the split parts together is not really the answer.

Cheers :wink:

Paul