Joint help.

[Scruples]

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.

A hard wood would move less?

 

[sawtooth-9]

Pine will always have a movement problem - it's a soft porous wood that can absorb and release moisture. This is particularly so because of the open pore structure and pine oils are not compatible with water.
I have done several very fine finger joints ( 4 mm ) in relatively soft woods ( well seasoned ).
I always cut the finger at least 2 mm deeper than the base wood - and ONLY use epoxy glue. Why ? - NO moisture introduced into the join and the joint strength is much greater.
Once the epoxy is cured, just sand off the excess.
Particularly with soft woods, the stability of the final product will depend on sealing out moisture - either by varnish, oils, or waxing

 

[MorrisWoodman12]

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

Just an observation but in your last photo it looks like the side piece has shrunk BUT the top piece hasn't, well at l can't see corresponding shrinkage marks on the side - bit difficult to be sure though. If that is the case and it is wood sourced and cut at the same time is there a clue there or is it just another bit of inconsistency? I assume btw that the very definite line along the joint and across the box is between two pieces of vinyl.

 

[Sea Chief]

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

Hi Unicorn,

good points. I agree this is sort of my avenue of thought, exhausting other avenues really. I might be inadvertently aiding the shrinking, somehow, sometimes. Its a costly timber now @£12 a metre so not gonna be a cheap set of tests.

Appreciate all the replies chaps, anymore thoughts on the glue laminate pine ( this is 5x 2" widths of 3/4" thickness pine, strongly glue together making a "10 x 1 " board.. the glue seems stronger than the wood so the structural box is ticked ok).

Thanks y'all, SC

 

[Sea Chief]

Pine will always have a movement problem - it's a soft porous wood that can absorb and release moisture. This is particularly so because of the open pore structure and pine oils are not compatible with water.
I have done several very fine finger joints ( 4 mm ) in relatively soft woods ( well seasoned ).
I always cut the finger at least 2 mm deeper than the base wood - and ONLY use epoxy glue. Why ? - NO moisture introduced into the join and the joint strength is much greater.
Once the epoxy is cured, just sand off the excess.
Particularly with soft woods, the stability of the final product will depend on sealing out moisture - either by varnish, oils, or waxing

I might try changing my glue to Titebond, from the reviews (I use a basic everbuild 501 currently ) but epoxy I think isn't that conjusive to doing so many 1/2" joints (25-30) on each box.

And using less of it maybe too.. I do scrape off a lot of excess as a habit, just being super sure I've covered my bases, & as it's not costly stuff.

Stillthe fact remains -some- boxes, just don't do this trait ( bucng the notion that all softwoods simply WILL do this: it has to be concluded therefore that shifting is -not- a certainty after all you see). If only I could establish why this is.. I'd have my answer.

Thanks, SC

 

[Sgian Dubh]

You're dealing with an intractable facet of wood's behaviour in that it is always adjusting its size in response to changes in relative humidity (RH), i.e., it shrinks as it loses moisture in response to lower RH, and swells when RH rises. RH changes hourly, daily, weekly, etc, all the way up to there being generally repetitive annual patterns. Those box lock joints are always going to shrink and expand over the seasons and they will always eventually telegraph through that leatherette(?) covering - is it leatherette? I've seen many examples of exactly this phenomenon, e.g., the through dovetails at the corner of cabinet carcases telegraphing through the overlaid veneer.

Your only option to essentially prevent this telegraphing is to redesign the construction to eliminate through joints, which basically means don't use your chosen box lock joints, and to incorporate some sort of joinery that ends at the outer corner of each the two parts as a mitre. There are various ways of doing this, all the way from the relatively complex hand made secret mitred dovetail joint to the simple mitring of each piece, plus additional internal and therefore hidden reinforcement, e.g., splines, dominoes, biscuits, and so on.

An additional element that will help is to make sure you use wood that is at an appropriate MC to start with, probably about 10 - 12% MC at the time you build, assuming these items are for indoor use, and not wood that is at a higher MC, e.g., 18 - 20% MC. Slainte.

 

[peter-harrison]

I agree with TheUnicorn- it's most likely that your timber isn't dry enough when you get it. If you can afford to, it would be a good idea to get a moisture meter and check a new bit of timber against one that's been in your workshop for a while.

 

[Jacob]

Wrong joint for the job?
I would have tongue and grooved it, with glue blocks on the inside. Would leave just one line visible and OK even if showing through.
Also a lot easier - those DTs are over the top really.
P.S. Wrong material for the job too. Ply or MDF?

 

[deema]

Slainte is spot on, wood expands and contracts at different rates longitudinal and laterally. The joint you have chosen is wrong for the application. You need a joint with no end grain showing.
For exemplary joinery you should look at hidden mitred dovetails. However, although not difficult to execute it’s all hand work and time consuming.
You need a mitred joint, so something that’s locked for instance with biscuits is quick and easy, however for shall or production runs a locked mitre joint is very effective. You can get a cutter for both spindle moulders as well as routers. That would be my choice.

 

[Jacob]

You don't need a fancy joint at all, as it's covered and out of sight.
Here's a pic of a T&G box joint. I've made hundreds of boxes like this, over the top of a TS.

A rebate would be even simpler to machine but harder to join as it would need careful clamping or pinning.
Either way rubbed glued blocks would add strength and very easy to do.
You flood each side with PVA glue, press and rub it into position and let go after a few seconds. That's enough to hold them in place as the glue goes off. They are sometimes shown drilled and screwed but this isn't necessary.
They are widely used in boxes like yours, or under stair treads and all sorts of cabinets.

 

[Doug71]

If they have to be made from softwood and you want to finger joint the corners you could try Accoya which is treated Radiata Pine, it won't shrink but is expensive and a bit brittle in use.

Think I'd be mitring them.

 

[Sea Chief]

A hard wood would move less?

I'm adamant it would, but I cannot sell my boxes if hardwood, as the expense to make them is prohibitive, the customer doesn't want hardwood, & I cannot source hardwood out here anyway.. without travelling huge distances that is. It'd add msybe £25 to each box. I make no profit as it is on the pine one.

 

[Sea Chief]

I agree with TheUnicorn- it's most likely that your timber isn't dry enough when you get it. If you can afford to, it would be a good idea to get a moisture meter and check a new bit of timber against one that's been in your workshop for a while.

Understood thanks. Thing is out here, it's not only wild, but very moisture heavy too.

I can't keep a stock of timber in, as it cups if cut into manageable sizes.

I can only persue my idea, even if it has no followers, thst the laminated pine 'struts' of glue might be acting as a countermeasure to the shrinking. I can only hope really, along this avenue.

 

[Jacob]

I'm adamant it would, but I cannot sell my boxes if hardwood, as the expense to make them is prohibitive, the customer doesn't want hardwood, & I cannot source hardwood out here anyway.. without travelling huge distances that is. It'd add msybe £25 to each box. I make no profit as it is on the pine one.

If they are covered in vinyl you can make them of any old rubbish as long as it does the job. I strongly recommend the simple T&G joint plus rubbed glue blocks I've described above.

 

[Sea Chief]

Wrong joint for the job?
I would have tongue and grooved it, with glue blocks on the inside. Would leave just one line visible and OK even if showing through.
Also a lot easier - those DTs are over the top really.
P.S. Wrong material for the job too. Ply or MDF?

Unfortunately an amp cabinet, needs to be both super-strong in the join type, & have no internal extra wood, as amp hardware goes up to the very inside edges. And 'fingerjointed' is just expected as it follows amp cabinet custom going back to late 1940's too. Pine is also inherrant to the sonic signature. And light enough. And affordable - just, still-. No other alternative alas.

 

[Sea Chief]

If they are covered in vinyl you can make them of any old rubbish as long as it does the job. I strongly recommend the simple T&G joint plus rubbed glue blocks I've described above.

The inside is seen Jacob, mostly empty really, but thanks for your thoughts.

 

[Jacob]

Unfortunately an amp cabinet, needs to be both super-strong in the join type, & have no internal extra wood, as amp hardware goes up to the very inside edges. And 'fingerjointed' is just expected as it follows amp cabinet custom going back to late 1940's too. Pine is also inherrant to the sonic signature. And light enough. And affordable - just, still-. No other alternative alas.

The wood is going to make no difference to an amp. Maybe it would for a speaker.
More research!

 

[Sea Chief]

If they have to be made from softwood and you want to finger joint the corners you could try Accoya which is treated Radiata Pine, it won't shrink but is expensive and a bit brittle in use.

Think I'd be mitring them.

Hi Doug71. I just don't have this exotic option, here though. I'd have to travel 100m to cardiff or something.

No the problem is only with the pine I can get here, & fingerjointing it.

Thanks, SC

 

[Sea Chief]

The wood is going to make no difference to an amp. Maybe it would for a speaker.
More research!

The amp has a speaker in it.princeton for eg.

 

[Sea Chief]

You don't need a fancy joint at all, as it's covered and out of sight.
Here's a pic of a T&G box joint. I've made hundreds of boxes like this, over the top of a TS.

View attachment 138687
A rebate would be even simpler to machine but harder to join as it would need careful clamping or pinning.
Either way rubbed glued blocks would add strength and very easy to do.
You flood each side with PVA glue, press and rub it into position and let go after a few seconds. That's enough to hold them in place as the glue goes off. They are sometimes shown drilled and screwed but this isn't necessary.
They are widely used in boxes like yours, or under stair treads and all sorts of cabinets.

View attachment 138690

Hi again Jacob,

the rebating idea is interesting, but I just couldn't add the internal brace. This needs to be clear, hence f-joints chosen really.

Thanks, SC