Correcting a bowed board on a desktop

[Ross J]

IMG_3976.jpgIMG_3975.jpgIMG_3974.jpgI'm making a 1700 x 750 redgum desk using 140mm wide timber and edge gluing. One of the outside boards has bowed since I did the glue-up and I'm seeking help on how to fix the problem.
I purchased the timber from a reputable specialty timber merchant in September here in Melbourne. To allow for climatisation I delayed the glue-up until November. I did not biscuit joint nor put a spline in. I just used glue. Due to other work I haven't been able to get back to finishing the desktop. Last week I noticed that one of the outer boards has bowed. How do I fix the problem? Do I try separating the offending board, or saw and then dress the edges before re-joining. Any suggestions on how best to separate the board and how to re-join?

[Wimmera Jack]

Your problem lies in the fact the board has a knot area in about the centre.
When edge joining timber like that I use dowels. You will need to use an accurate dowel jig.
But a lot will depend on how much you can pull that board back to flat without it causing the attached boards to bend.
Use your circular saw to separate the boards using a thin toothed blade.

[Camelot]

You should have really let the 2 end pieces run the full width of your table their job is to hold the longer boards in place by using a loose tongue cut short at each end by say 25mm this would stop you from seeing the loose tongue is your finished table. The tongue could have been made from some say 12mm birch ply. If you have used PVA it as a creep factor which means it can allow the timbers to move without breaking the joint.

If you have a track saw then just cut down the joint and this will dress the surfaces at the same time, but I would glue it back together using some sort of loose tongue like a biscuit jointer or domino

[Fekit]

To be honest, there are so many problems going on there .......

The design layout of the boards was always going to fail, and it will continue to fail until such time as it has managed to pull itself apart back to individual boards.

The idea that timber stops moving .............. what ??????

And that just using glue ........ eh? what?

[Camelot]

To be honest, there are so many problems going on there .......

The design layout of the boards was always going to fail, and it will continue to fail until such time as it has managed to pull itself apart back to individual boards.

The idea that timber stops moving .............. what ??????

And that just using glue ........ eh? what?

I think he was keeping the timber in the room where the table will be used, this is good practice if the room as a controlled environment which does not fluctuate in moisture and temperature levels.

[China]

No problem with just using glue, so long as the boards are edge prepared properly, 40+years as Cabinet Maker I have joined thousands of boards Just using glue with out problems.

[Skew ChiDAMN!!]

Redgum is one of those timbers that just keeps on moving all over the place.

I love the stuff, but when it comes to building up panels, well... it's one of the few timbers I prefer to put biscuits or splines in. You also should be very picky about using 'select' pieces so the grain is all nice and parallel.

All that being said, I'd use a thin kerf blade to seperate and leave the piece aside for a week or three to see if it'll move further by itself. Possibly it'll straighten but it may curve worse.

If it stays the same then I'd simply re-glue with an abundance of biscuits or a spline.

If it does move again, it'll probably need re-dressing before gluing up, if not straight out replacing.

[Tung tied]

That does look a bit big to sand out. Do you have a biscuit joiner or dowel jig or a domino to align it in place if you cut the offending board off and letting it sit for a while?

If knot , I can help, although "investment" in something like a biscuit joiner or dowel jig is worthwhile. Domino joiners are fantastic if you don't mind selling a kidney....

Also, have read here too. Dowel jigs

Let me know how you go.

Cheers

Bryan

[aldav]

You are a victim of the vagaries of River Red Gum and the unusually humid summer we've been having. As Skew pointed out River Red Gum is one of those timbers that never seems to settle down. Once you've cut the offending board off you can use your router and a mortising bit to create the same joint as a Festool Domino. The board will undoubtedly fight back but you might have a win.

Finally got to your first post after 15 years of lurking. I suspect we've been telling you things you already knew.

[riverbuilder]

Cut it off, glue another piece in with no knots in it. Use dowels or dominoes into the header boards. Red gum is cranky timber, it moves heaps.

[ian]

Is it just me ?
or has Ross J glued up a desk top that looks like it is frame and panel construction, but is really all solid wood?
If that is the case, my advice is to start again.

If I am right -- I won't claim that I am always right -- Ross will never get a flat top from the glue up he's shown.
Frame and panel construction involves making a panel which has tongues on all four sides that fit into corresponding grooves in the rails and styles. The panel floats so there will always be some gap between the panel and the rails and styles. (The rails should have tenons into corresponding mortices on the styles.)
Gaps, even small ones, are not what I'd want on a desk top.

In my view, rather than toss the top he has made and start from scratch, Ross should cut the individual boards free from the glue up,
then use the "rails" to extend the short boards in "the panel" in a way that creates a pleasing pattern on the top -- perhaps use a pattern of staggered scarf joints that step across the finished board.

[GraemeCook]

... And that just using glue ........ eh? what? ...

No problem with just using glue, so long as the boards are edge prepared properly, 40+years as Cabinet Maker I have joined thousands of boards Just using glue with out problems.

Agree with China. As I write this I am sitting at a desk that I made in 1983 - hell, its 39 years old! The top consists of three planks, each 2300 mm long and 250 mm wide, which were butt glued together with epoxy. It is still flat and has not split, and the Danish oil finish is still in great good shape. There are no end caps.

Timber shrinks as it dries and expands as it rehydrates, but it moves at different rates radially, tangentially or longitudinal. This is well documented in standard references such as Bootles or Wood Database. Sorry, Ross, but Ian is right. The tensions created by movement will continue to cause problems. The longitudinal planks will expand and contract a lot more then the longitudinal expansions of the end caps; then tension must go somewhere and it will stress the glue lines.

The best way to dismantle it is to saw along the glue lines.

[Camelot]

I see where you are coming from, but in a traditional frame & panel construction you either have a fielded panel or a raised & fielded panel, both require the panel to sit in the groove and not be glued to allow for movement, thus in a fielded panel the panel in thinner than the frame and in a raised & fielded panel the panel can be as thick as the frame, but it still looks better slightly thinner. So to make a raised & fielded panel work you need to introduce a moulding like a classic Ovolo to reduce the panel thickness around its perimeter to allow it to fit in the frames groove.

[ian]

I understand what you are saying about traditional frame and panel work. But Ross has not made a traditional frame and panel.

What I suspect Ross J has done is glue up what looks to be a frame and panel (which traditionally would use some form of raising to create the tongue on all four sides of the panel) but, unfortunately, Ross has used plain rub joints in his glue-up.

[Camelot]

Would be nice for RossJ to give further input now many members have posted their thoughts