Joint help.

[Sea Chief]

Hi folks on here. This is my first thread so looking forward to any help, & thanks for any replies.

I've got a connundrum with jointing pine, an annoying facet plaguing me. I use a fingerjoint jig to rout say 9x 1/2" wide joints. Call it a 19"x 17"x 10" box. I then glue ( hand 'painting-on' each 3 inside rout faces of each finger) & clamp for a day. Router-trim off all 1/16th joint excesses. Sand. Shape edges with a 1/2" roundover bit. Final sand. All fairly standard. Then I brush on a contact glue to surface, also onto on the backing (like a fine cotton mesh) of a vinyl covering. Cure both until gone off, timed as as per instructions. Press on.

What I have now is a nicely finished, smooth edged, covered box. Sometimes though, after a week or so, the 4 jointed edges.. become uneven. The joints show through. Maybe a 2mm H difference, in-out-in etc. So something has happened. But I just don't know what. It's 21mm pine, & the solidity remains ( no compromise here) just this annoying edge 'shift' of some kind.

Can anyone help? Thanks, Sea Chief.

 

[Phill05]

Might help to do a test joint without the vinyl to see what is happening, sounds like the board is shrinking?

 

[profchris]

Simply, the water in the glue is swelling the wood a little. Over time, it shrinks back and changes shape.

If you shape the edges too early, then the wood will carry on moving afterwards, producing the effect you describe.

The solution is to wait longer before the final shaping - how long is hard to say, because each piece of wood reacts differently. Maybe make up a few test pieces and shape them at different intervals.

My guess would be that 48 hours should be enough, but no promises!

 

[Sea Chief]

Might help to do a test joint without the vinyl to see what is happening, sounds like the board is shrinking?

Hi Phil,

well this, funnily enough, is what I had only just this morning ( after long protracted consideration) thought seems most plausible.

You see I only get a photo, sent from a customer, whose had the 'box' for a while. So I can't inspect. But only today looking at his photo, I counted the joints (knowing where my first 'IN' one was made)... & came to conclusion, that perhaps the side had -shrunk- as opposed to the top having "enlarged". I'm fairly sure now it's one of the two surfaces -diminishing- slightly.

Ok this is a step on. Gratefully, SC

 

[Sea Chief]

Simply, the water in the glue is swelling the wood a little. Over time, it shrinks back and changes shape.

If you shape the edges too early, then the wood will carry on moving afterwards, producing the effect you describe.

The solution is to wait longer before the final shaping - how long is hard to say, because each piece of wood reacts differently. Maybe make up a few test pieces and shape them at different intervals.

My guess would be that 48 hours should be enough, but no promises!

Hi profChris, well this is the alternative theory as to what is actually happening: & until today what I was thinking.

But if it seems like there is shrinking going on, as opposed to swelling, then it seems you'd be spot on.

Evidence shows - it seems to me- a shrinking of the side though, causing this offset. Which points away from looking at the glue as an added factor.

Yes tests.. are my next step. But tricky, as some I make do this, others don't. It's infuriating tbh: as I send each off in perfect shape ( of course).

Any other thoughts, ideas, anything at all.. really welcome folks.

Chris- many thanks, SC

 

[Sea Chief]

Here are my joints after glueing. Trim off excess with router ( I use the bottom edge of a 3/8" straight bit, with template, to "skim" along & trim along this excess), & roundover to do.

And an eg of a good 'box'. No issue. This one ( mine ) is the same pine as pic 1, same glues, no wait period after jointing or immediate edging, to covering. Quickest I've made as it was my own.

So you see there's this inconsistency... which is infuriating as I can't glean clear answers.

 

[Sea Chief]

And a typical eg of a troublesome one: from this photo sent to me, I counted joints along establishing the top seems to remain as is.. & its the side that drops down.

But I cannot factor out of course, that it's not the -whole- top's thickness, that's moved 'upward' instead. IE 21mm to 23mm.

It is making me go insane, let alone the customer. Thanks, SC

 

[Phill05]

If there is inconsistency a few question's to ask is something being stored in the box that could affect the wood? is the box finished inside?

 

[Sea Chief]

If there is inconsistency a few question's to ask is something being stored in the box that could affect the wood? is the box finished inside?

Hi Phil, no.. nothing inside. Its an amp cabinet, but mostly empty in fact. It's definitely some way the wood is behaving irrespective of anything inside. For eg, the bottom of the wine coloured box Im told is the same as the top, & the amp (& speaker) is yet to be housed into it anyway.

Thanks, SC

 

[Inspector]

If the wood is at equilibrium in your environment (dry in your shop/home) it will change in your customers home if they have a different humidity than yours. Wood will always try to move as the moisture changes. If the boxes stay in your place there will be no movement unless you move. Your customer is in a dryer place than you have and the wood has lost moisture making the fingers show. You are down to putting a finish inside the speaker box or changing the material to something else, plywood/MDF, or change the joint you use so movement won't show. I would change the joint to splines or biscuits (keeping them to the inside corner because you are rounding them) and shellac/lacquer/varnish the inside and see if that's better.

Pete

 

[Sea Chief]

Hi

If the wood is at equilibrium in your environment (dry in your shop/home) it will change in your customers home if they have a different humidity than yours. Wood will always try to move as the moisture changes. If the boxes stay in your place there will be no movement unless you move. Your customer is in a dryer place than you have and the wood has lost moisture making the fingers show. You are down to putting a finish inside the speaker box or changing the material to something else, plywood/MDF, or change the joint you use so movement won't show. I would change the joint to splines or biscuits (keeping them to the inside corner because you are rounding them) and shellac/lacquer/varnish the inside and see if that's better.

Pete

Hi Inspector Pete.

Understood, but for one thing- I have had one which remained here without anything fitted inside it, & showed an identical unevenness after a while.

One thing I've been thinking, is whether the pine choice is a factor. It seems possibly ( annoyingly inconclusive), that jointing glue laminate pine, results in a box less prone to this issue.

Another thing is whether using 1/4" joints instead might help. But alot of expense on jigs & router bases to try this idea, just to end up in the same boat.

Or could I apply something to the finished edge prior to covering, that'll "fix" the wood in place preventing it move-?

 

[Fitzroy]

I made a coffee table with box joints last year. At the time and for several months afterwards they were completely flush, after the first winter some of the joints now are proud of the surface sufficiently that I can catch them with a nail, say approx 0.1mm. If I were to sand them flush then I would fine them below the surface at somepoint as the wood moves with the seasons. Wood moves more in one grain direction than the other. Your 1mm movement does seem excessive for what looks like a 20mm thick board, mine is c.30+mm.

However as Inspector said with such a joint you will always get seasonal movement that will threaten to crack or disrupt the covering you have on your enclosure. Moving to MDF and/or a different joint should eliminate the problem. A lock mitre router approach may work and would be easier than the box joints.

 

[Fitzroy]

Or could I apply something to the finished edge prior to covering, that'll "fix" the wood in place preventing it move-?

No. If wood wants to move it will move. Furniture design needs to work with this movement rather than constrain it.

 

[Inspector]

You need to read up on wood movement more. You will find that it never stops moving. When I lived on the west coast my furniture moved a little seasonally. Moved here to a much dryer climate and it shrunk and the joints all loosened up and it still moves seasonally a little.

Trying a different wood may help, some having less than others. Here is a shrinkage calculator you can play with to see how much different species move. The Shrinkulator – WoodBin

Going to smaller finger joints are not going to change the wood movement only the spacing of the bumps.

You can't fight the wood and prevent the movement. No amount of extra glue or different glue is going to hold it.

Pete

 

[Phill05]

Yes I would agree you can't stop wood moving a change of timber looks like could be the best move, If the timber is not seen could it be replaced with ply more stable and you could still make the same joints.

 

[TheUnicorn]

as others have said, it seems like this is an innevitable trait of wood. if you are not keen on mdf or ply, which I can see would complicate the roundover, I wonder if you could use a covering with a bit more bounce (like adding underlay to carpet) that would compensate for (hide) the movement

 

[Sea Chief]

You need to read up on wood movement more. You will find that it never stops moving. When I lived on the west coast my furniture moved a little seasonally. Moved here to a much dryer climate and it shrunk and the joints all loosened up and it still moves seasonally a little.

Trying a different wood may help, some having less than others. Here is a shrinkage calculator you can play with to see how much different species move. The Shrinkulator – WoodBin

Going to smaller finger joints are not going to change the wood movement only the spacing of the bumps.

You can't fight the wood and prevent the movement. No amount of extra glue or different glue is going to hold it.

Pete

Hi again Pete. Thing is, some cabinets buck the trend & are stable. I can't try a different wood because it's a requirement that these are made in pine, also fingerjointing & shaping edges of even 18mm ply is a nightmare re chipout. And the cost.. birch ply it would have to be, is massively costly. No alternative to the pine guage I use, hardwood?.. ridiculously costly.

So I'm really left still wondering why some do this, & some don't. Once they do this irritating trait, they then don't shift again too. So I can't see any evidence of them changing at all, say after a month from made.

The only glimmer of hop, it seems, is the glue laminate pine boards. These -seem- to have a much lesser habit of doing this shift. Now the reason thoug? It can only be the addition of glue, acting like 'support struts' say 5x across a 10" board. I'm only throwing ideas out here tho. But based upon logic nevertheless.

Thanks, SC

 

[Sea Chief]

Yes I would agree you can't stop wood moving a change of timber looks like could be the best move, If the timber is not seen could it be replaced with ply more stable and you could still make the same joints.

Hi Phil, thanks but unfortunately I can't change woods.

 

[Sea Chief]

as others have said, it seems like this is an innevitable trait of wood. if you are not keen on mdf or ply, which I can see would complicate the roundover, I wonder if you could use a covering with a bit more bounce (like adding underlay to carpet) that would compensate for (hide) the movement

I agree it's a trait of wood, but disagree it's innevitable: from most of the cabinets I've made & those bought even decades old, they just do not & have not changed. Even changing hands many times over decades. All fingerjointed pine, all the same thickness, all covered by a very similar cotton-backed vinyl. Oldies used hyde glue for the covering but I don't think this covering-glue is the cause, whichever it may have been.. or -all- my cabinets would show this trait.

So there is a way to do this, with 21mm pine, or say 3/4", for a stable box.. it's just knowing how. But I guess I'm on my own to figure it out. SC

 

[TheUnicorn]

I agree it's a trait of wood, but disagree it's innevitable: from most of the cabinets I've made & those bought even decades old, they just do not & have not changed. Even changing hands many times over decades. All fingerjointed pine, all the same thickness, all covered by a very similar cotton-backed vinyl. Oldies used hyde glue for the covering but I don't think this covering-glue is the cause, whichever it may have been.. or -all- my cabinets would show this trait.

So there is a way to do this, with 21mm pine, or say 3/4", for a stable box.. it's just knowing how. But I guess I'm on my own to figure it out. SC

maybe you need to have a look at the wood you are using then, in terms of how it is stored, sourced, seasoned, run a moisture meter over etc. Also maybe a sealing coat on the inside of the cabinet might help to minimise movement. I'd do a whole bunch of test pieces and see what makes things better worse