Thread: Gluing supports perpendicular to desktop grain

I would think you will be pretty safe at 400mm. Well seasoned timber is more inclined to swell than shrink and shrink is what causes cracking.

Originally Posted by rustynail

I would think you will be pretty safe at 400mm. Well seasoned timber is more inclined to swell than shrink and shrink is what causes cracking.

Yeah I think I'll just role with it and hope for the best. It doesn't have to last a long time... though I always like to make things to last if I can. It's solving a problem that'll only exist for another couple of years which is a wall-mounted desk in a bedroom, but I'd like to repurpose it when the time comes of course.

Hey Wardrop, do you mean you laminated the lengths of timber or glued timber strips underneath?

Originally Posted by Wardrop

Hi All,

I'm working on a project and just realised while laying in bed this morning that I've make a rookie oversight. I've glued strips of timber across the width of a desktop instead of using fasteners that would allow movement. The width of the desktop is only 400mm and the piece will be kept indoors at all times so I'm wondering if I might just get away with it. I'll be finishing it with hard wax oil. I'm thinking now of maybe adding a couple of screws just in case the glue ever lets go from the expansion and contraction. Thoughts? Has anyone ever done this and gotten away with it longer term?

The timber is reclaimed tasmanian oak that was used for door jams in a house, so hopefully it's more dimensionally stable than "fresher" timber.

Depends. Well seasoned wood can also mean hard and unyielding. And well seasoned doesn't take into account seasonal change in dimensions. All wood shrinks and expands no matter how old it is. Some questions: Where in QLD? Indoor, do you use Aircon 24/7? What month was it glued up? What was the weather like? How long has it been glued up? To a much lesser extent, what type of glue?

Wax oil sounds like a finish that will allow humidity to penetrate and escape easily in wood.

In joinery my loose rule of thumb is expect movement at at least 2mm over 900mm. In a really wet season expect 3mm.

Other question to ponder. Can you disassemble and plane the cross piece(s) off?

You'd be surprised at how little such movement can cause a joint or wood to fail.

Originally Posted by rustynail

I would think you will be pretty safe at 400mm. Well seasoned timber is more inclined to swell than shrink and shrink is what causes cracking.

I beg to differ. I've done something similar with finger pull on a box lid just 100mm wide, and it bent significantly over that 100mm...

Here's a photo for those not clear on what I'm talking about; I haven't sanded it yet so please excuse the glue stains. There's an end piece like that on each end, and one in the middle. The endgrain is also glued.

PXL_20220908_221427485.jpg

I'm up in Far North Queensland. Aircon is probably on half the day in the warmer months. The harwax oil does let the timber breath, but it would certainly inhibit the rate at which it gains or loses moisture as it does create a polymer like structure that's only slightly porous. I'm just going to run with it and see how it goes. If I see the timber wanting to bow or those supports delaminating underneath, I'll address it then. Should be interesting experiment.

Next time I'll either screw such pieces allow a little room for movement, or create waterfall ends using off cuts from the top laminated panel.

Originally Posted by The Spin Doctor

In joinery my loose rule of thumb is expect movement at at least 2mm over 900mm. In a really wet season expect 3mm.

So that'd be barely 1mm movement in a 400mm board. I'm curious to see what will win, the glue joint or the expansion. Will the timber try to cup/warp, or will it try to peel away from the glue. It's the drier time of year here, so I'm not fearing contraction at all, only expansion.

The timber should come up nice when finished. Well done! Using stronger joinery would be worth considering on the next build.

Post a pic when your done, would be keen to see it finished!

Originally Posted by Wardrop

Here's a photo for those not clear on what I'm talking about; I haven't sanded it yet so please excuse the glue stains. There's an end piece like that on each end, and one in the middle. The endgrain is also glued.

PXL_20220908_221427485.jpg

I'm up in Far North Queensland. Aircon is probably on half the day in the warmer months. The harwax oil does let the timber breath, but it would certainly inhibit the rate at which it gains or loses moisture as it does create a polymer like structure that's only slightly porous. I'm just going to run with it and see how it goes. If I see the timber wanting to bow or those supports delaminating underneath, I'll address it then. Should be interesting experiment.

Next time I'll either screw such pieces allow a little room for movement, or create waterfall ends using off cuts from the top laminated panel.



So that'd be barely 1mm movement in a 400mm board. I'm curious to see what will win, the glue joint or the expansion. Will the timber try to cup/warp, or will it try to peel away from the glue. It's the drier time of year here, so I'm not fearing contraction at all, only expansion.

Barely 1mm... That amount of unyielding movement, and considering all the other factors you alluded to, puts huge pressure on glue joints. I'd be surprised if it doesn't pop.

Not to be an arrogant ass but everything about that is wrong. And has been for the last 2000 years of joinery, or at least as long was woodworkers have been using glue.

At such an early stage, not fixing it is such a woodworking sin.

1mm may not sound like much but it's a lot when you have 0mm of room to move. Should be easy enough to neatly trim off the offending pieces with a hand/jig/circular saw, clean up with a plane or sander and reattach with screws going through oversized holes. Note that the hole drilled through the apron piece needs to be wider than the screw to allow for movement across the grain of the table top, there will be negligible movement along the length of the boards. You can have one screw in the center of each apron piece that is drilled exactly to size - this is the anchor point and the remaining oversized holes will allow for movement.

Edit: The one time I took the "she'll be right mate" approach to wood movement I should've known better - a cautionary tale of wood movement

Another approach...

A japanese kataba saw (ie. one without a back) would make short work of splitting off those pieces with minimal damage.

If I were in your shoes I'd use a japanese flushcut instead. They're basically the same thing, but typically more flexible and with no set on the teeth. With care you'd most likely be able to remove the pieces with minimal kerf loss and practically intact.

Then you could simply screw them back on and only lose a mm or so in final dimensions.

The last time I looked, you could pick up a cheap, mass-produced one for about $AUS30.

Alright, you've all convinced me. Bought myself both a cordless oscillating multitool today and a flush cut pull saw; the Irwin one that Bunnings sells. I've got a strip of timber in the middle of the desk too where the flushcut saw won't work too well on, so multitool is necessary there at least. Both will be welcome additions to my tool arsenal.

Originally Posted by Dimo

Using stronger joinery would be worth considering on the next build.!

Yeah I've been resisting the temptation to make it more than it needs to be. It's a wall-mounted desk for a bratty teenager, so it's already "fancier" than I had planned, haha. The more effort I put into it the more I'll "care" if they don't give it due respect. The original plan was a benchtop from bunnings and some metal shelf brackets, but I've ended up making brackets out of the same timber too. If it was a piece of furniture that I cared more about, I would mitre the join and either use glue and a corner brace or a spline.

I also don't have a proper workbench yet. Working on saw horses leaves a lot to be desired. That'll be my next project I reckon. My local bunnings has a heap of nonstrural untreated pine 70x35 2.4m, so should be able to make a chunky cost-effective workbench from it. I'll get a quote from a local sawmill too, but they mainly do hardwood timber which I've heard isn't necessarily what you want for a workbench.

Here are some pics of the finished project for those interested. First two photos show the material in it's original state. Last 4 show the finished products. Very last picture shows the holes for the screw fixing which is what this thread was all about. Finished with Evolution Hardwax Oil in Classic sheen. It's Meranti by the way, not Tassie Oak as I previously thought.

Nice work Wardrop!