Thread: Joining table top - advice needed

It will probably be OK if the only problem with the glue up was that one board was bowed along its length. If you joined two convex edges together (join tight in the middle, and open at the ends), that will definitely give you a broken joint in very quick time with Spotty. A quick test to see if the joint has opened at the ends even slightly, is to sand the end grain with 240 or 320grit sandpaper. The sanding dust will fill the gap and leave a white line.

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From Bunnies kitchen section.

I'd be happier with some mechanical connection between the bowed and straight boards -- biscuits, dominos or dowels.
What i think will happen is that over time, the bowed board will induce a slight bow into the entire desk top.

It might perhaps be best to let the bow happen and then flatten the top to take it out.
5 mm is not all that much and a slight difference in thickness would be "hidden" if you chamfered the edge of the top

Originally Posted by ian

I'd be happier with some mechanical connection between the bowed and straight boards -- biscuits, dominos or dowels.

OK, well hopefully my first joint will have got the bowed board flat enough for me to use biscuits on the next joint on the other side. I guess I could then cut yesterday's non-biscuit joint in two and redo with biscuits.

Before I see if this will work, do you think it is worth changing the glue I'm using? I see people recommending Titebond whereas I am using Selley's Aquadhere Interior at present. (Although I see the nearest Titebond distributor is 20km away in Auburn). Would there be a significant difference in the strength?

Originally Posted by tony2096

Before I see if this will work, do you think it is worth changing the glue I'm using? I see people recommending Titebond whereas I am using Selley's Aquadhere Interior at present. (Although I see the nearest Titebond distributor is 20km away in Auburn). Would there be a significant difference in the strength?

There wouldn't be enough difference in the strength between these two glues for anyone to realistically guarantee "you won't have that problem if you use this one."

Titebond III is my preference, in my opinion it's the best all-rounder PVA in it's price range, but Aquadhere Interior is a good glue and more than suitable for this job.

Maybe once you've finished the bottle it'd be worth your while to change and give Titebond a go, esp. if a distibutor is so close to hand.

But for now?

Ive been making furniture for fifty years. I have never used any form of connector in table tops. A rogue board is a common problem and the trick is to place it or them with a straight board on each side. My suggestion would be to place yours in the centre. The most important boards are the two outer edge boards as these are supported only on the one edge so the straighter they are the better.

Originally Posted by Skew ChiDAMN!!

There wouldn't be enough difference in the strength between these two glues [Selly's Aquadhere, Titebond] for anyone to realistically guarantee "you won't have that problem if you use this one."

Originally Posted by tony2096

OK, well hopefully my first joint will have got the bowed board flat enough for me to use biscuits on the next joint on the other side. I guess I could then cut yesterday's non-biscuit joint in two and redo with biscuits.

given that you've already glued this joint I wouldn't bother with ripping it apart to re-glue. Too many opportunities for problems to develop along the line of the rip cut.

my thinking is that PVA glues (Aquahere & Titebond) can creep a bit, and a mechanical connector across the joint would sort of mitigate against the creep allowing one board to raise above the other.

It's not going well. When I took the clamps off today it all looked good but an hour later one of the bowed ends had separated back into its original position. Here is a picture (the 2 boards on the left are the ones I glued, the far 2 are still loose and just there to show that they are still flat.

I'm not sure what to do now: should I try and prise them apart (I'm afraid that they might not separate down the glue line - isn't glue supposed to be a stronger bond than the rest of the timber?) or should I use a circular saw to cut them apart?

Then to try joining them again, I'm thinking about Ian's advice to leave the board bowed while I glue them together and then take off the excess timber that is sticking up. I'm not keen on this option as I don't have many useful tools (no jointer or planer - just hand plane and ROS) so am afraid of having to spend many hours getting rid of the 5mm which would be sticking up, or ending up with a messy surface (the reason I bought dressed timber in the first place was due to this lack of any big machinery).

What about trying to unbend it? A couple of days ago I tried forcing the board into an arc that was the opposite of the bow and leaving a hose dripping on it overnight in this position - but no effect...is there anything like this that is worth trying (given boards are 32mm maybe too thick to work?)


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When you buy dressed timber, it just means that it's not rough sawn, it doesn't meat flat or straight. You will not be able to bend it flat or straight by any method, especially something as hard as spotted gum. If you want to pull it apart you will have to cut it.

IMO, your only possible chance of getting it flat without a jointer is by using biscuits, polyurethane glue and leaving it to dry in clamps at least overnight.

Edit , sorry I skipped through to quick and didn't see your post no 10.
Ill leave it all as I wrote it though. 11.37 pm



The problem is that its Spotted Gum . I don't think it will stay together.
Plenty of traditional cabinet timbers that are dry stay together when just butt joined and glued and it takes a period of neglect to make them let go . Hard Aussie hardwoods don't do so well . And spotted gum is hard and durable as well as being known for being slippery and possibly waxy feeling I'm told .
A wood I have used in a top which you cant really compare to spotted gum is the WA Karri. Its hard heavy stuff and bone dry . I know its dry because Its a top I used in my work table opposite my work bench . Over 15 years Ive had to re glue it back together three times , because the butt joins , done with two pack sometimes , let go .
The last time I think I added biscuits . And its holding . What I'm saying is , its another heavy hard Aussie hardwood that doesn't glue so well like that.

I have a mate that just build a table laminated from Spotted gum . I'm sure his problem was also that the moisture content was wrong for what he tried to do . The table left the workshop and a few months later has had to be rebuilt . Every joint let go. It was 60mm thick base and top .

What he should have done is built and connected in a way to allow each board to move with the non glued boards showing as an intended part of the design .

If you know your boards are properly dry then biscuits or tenons as connectors . I use a domino like a biscuit now, as a tenon . Up to 14mm thick and as wide as I like . The last job I used 60mm wide x 14 thick Oak Dominos I made for the job . Either that or a loose boarded top . A top where biscuits are used but no glue. And bread board ends either tenoned on . Or pegged on , where you can see the peg ends in the top end edge. Or doweled on . All glued . The middle boards move and the BBE hold them at the ends. Ive done a lot of tables like this and seen Original very old Oak 17th century ones that are still working fine.
If you are pegging on a BBE the BBE cant be to wide . You have to get a peg through say 100mm BBE and then 100mm into the top . Not so easy on thin 19mm tops buy not so hard on a 30mm one .

Originally Posted by tony2096

It's not going well. When I took the clamps off today it all looked good but an hour later one of the bowed ends had separated back into its original position. Here is a picture (the 2 boards on the left are the ones I glued, the far 2 are still loose and just there to show that they are still flat.

I'm not sure what to do now: should I try and prise them apart (I'm afraid that they might not separate down the glue line - isn't glue supposed to be a stronger bond than the rest of the timber?) or should I use a circular saw to cut them apart?


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Hi Tony

My preference would be to place the rogue board in the centre, get the ends level with the other boards, and allow the bowed section to be higher in the middle section.

It is easy enough to plane the raised section away (planing across the grain first) - no one looks under a table to see how level the top is. What is important is that the top is level and the edges are the same thickness.

I do not use biscuits or dominos to align boards. If you do, make sure that they are positioned just under half way (from the bottom), otherwise they could telegraph through the surface at a later time.

Regards from Perth

Derek

I agree with Derek. The offending board should be fitted bow up and later planed to flush. If you can push it down well and good, but dont over do it as the stresses will only give problems at a later date. Your pic shows that later date was not long coming.
Your failed glue up may be attributable to waxing of the edges. This is a common problem with oily timbers of which many eucalypts are guilty. This build up of oils will prevent a good bond in many cases. A wipe down with thinners along the edges to be glued immediately prior to glue application helps a lot. My prefered glue for spotty was Selleys 308 or, if I wanted to get in a real mess, epoxy.
The reason for not using connectors in the joint is to prevent running the risk of unequal forces coming into play created by the difference in structure of the two timbers. Add to this the fact that biscuits are designed to swell with glue impregnation only means more push and shove. I can assure you a biscuit is not going to stop a 30mm thick bit of spotty going any which way it wants to.

Originally Posted by rustynail

Your failed glue up may be attributable to waxing of the edges. This is a common problem with oily timbers of which many eucalypts are guilty. This build up of oils will prevent a good bond in many cases. A wipe down with thinners along the edges to be glued immediately prior to glue application helps a lot.

This is so true, and I just encountered a perfect example. I am making a vice handle, so last night I laminated some scraps suitable for the handle using Titebond III. Found a couple of pieces of spotted and a thin strip of Blackwood. They had been machined flat probably 2 years ago. I just glued them up as is, because it's only a vice handle. I turned it to a cylinder on the lathe well enough (one end the joint had came apart from the tailstock wedging it open, but I got it turned well enough anyway). Then I wanted to drill a ~35mm deep hole into each end to accept an insert nut so I can bolt the end lugs on. Well...I managed to drill the hole ~2mm deep before the thing split all the way. It's a perfect split. The Blackwood has a lot of glue residue on it. The Spotted Gum has ZERO residue. It is still silky smooth, just as it was when it came out of the thicknesser years ago.
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