unscientific ply/mdf movement experiment

[Phil Sewell]

Given that the general consensus on the forum is that ply moves and therefore shouldn't be glued into panel grooves I thought it would be worth seeing exactly how much it does move in extreme circumstances (my belief being that it's movement is neglible and therefore it's ok to use glue if required).

Very unscientific but I cut 2 bits of 9mm ply and mdf 300mm x 100mm. I left an mdf pce and a ply pce in the freezer for 12 hours.They both stayed at 300mm.

I hung the other 2 pces a couple of inches above my woodburning stove last night for 4 hours. The ply reduced in length by 0.75mm, the mdf reduced by 1.0mm.

Obviously normal household conditions are no where near as extreme as this and the fact that the ply has moved a very small amount over the stove means I think that ply (and mdf) will hardly move at all in normal situations. Not to forget that there will also be some finish applied (i.e paint, lacquer etc) which will further restrict the movement of moisture. To conclude, in my humble, do the glue if you want to!

So what d'ya think about that matron, controversial eh!

I await the barage of critism , it's all good fun!

Phil.

 

[Oryxdesign]

Mmmm, I would say that's it's quite dry in a freezer and also quite dry above your stove. Maybe try somewhere damp too.

 

[9fingers]

Whilst you are at it, information on thickness changes would be interesting and I suspect, of greater significance.
I agree with Simon, humidity rather than temperature is a key factor in wood movement.

Bob

 

[motownmartin]

I make a lot of chess boards and I glue the squares to a plywood base because I thought Ply was a very stable material and unlikely to move, they end up bowed like a Banana, so I started to use mdf, the same thing happens, now I am thinking that its the wood squares that swell and bow the board because there is little movement in both the ply & mdf.

 

[Dodge]

I make a lot of chess boards and I glue the squares to a plywood base because I thought Ply was a very stable material and unlikely to move, they end up bowed like a Banana, so I started to use mdf, the same thing happens, now I am thinking that its the wood squares that swell and bow the board because there is little movement in both the ply & mdf.

The main problem with your chessboards isnt the ply or mdf but the fact that the timber squares are only glued to one side.

To prevent movement you really need to apply the same to each side of the ply - chessboard one side, backgammon the other?

Basically what you apply to onve side exerts movement on that face therefore you need to counteract that with the same on the opposite side. Same principle as veneering or infact thicknessing timber. If you planer more off one side that the other movement issues will occur.

Rog

 

[Mattty]

I make a lot of chess boards and I glue the squares to a plywood base because I thought Ply was a very stable material and unlikely to move, they end up bowed like a Banana, so I started to use mdf, the same thing happens, now I am thinking that its the wood squares that swell and bow the board because there is little movement in both the ply & mdf.

The main problem with your chessboards isnt the ply or mdf but the fact that the timber squares are only glued to one side.

To prevent movement you really need to apply the same to each side of the ply - chessboard one side, backgammon the other?

Basically what you apply to onve side exerts movement on that face therefore you need to counteract that with the same on the opposite side. Same principle as veneering or infact thicknessing timber. If you planer more off one side that the other movement issues will occur.

Rog

The other strong possibility and contributing factor is type of glue. If your using a waterbased glue then the substrate will expand on the veneered face with the increase in MC and become convex.

 

[motownmartin]

I make a lot of chess boards and I glue the squares to a plywood base because I thought Ply was a very stable material and unlikely to move, they end up bowed like a Banana, so I started to use mdf, the same thing happens, now I am thinking that its the wood squares that swell and bow the board because there is little movement in both the ply & mdf.

The main problem with your chessboards isnt the ply or mdf but the fact that the timber squares are only glued to one side.

To prevent movement you really need to apply the same to each side of the ply - chessboard one side, backgammon the other?

Basically what you apply to onve side exerts movement on that face therefore you need to counteract that with the same on the opposite side. Same principle as veneering or infact thicknessing timber. If you planer more off one side that the other movement issues will occur.

Rog

The other strong possibility and contributing factor is type of glue. If your using a waterbased glue then the substrate will expand on the veneered face with the increase in MC and become convex.

What glue would you reccomend Mattty

 

[Mattty]

I would prob use a waterbased glue! A titebond or similar, depending on what timber and section size etc. I also use a lot of PU glue now but this is possibly unsuitable for what you are doing.

My point, was really to point out the fact that you are probably adding moisture to the substrate so movement should be expected and counteracted with a backing veneer as Rog suggested.

 

[motownmartin]

I was initially backing up Philip by saying there was little movement in plywood and thats why my boards warped, they are ok after a month or so

 

[sometimewoodworker]

Given that the general consensus on the forum is that ply moves and therefore shouldn't be glued into panel grooves I thought it would be worth seeing exactly how much it does move in extreme circumstances (my belief being that it's movement is neglible and therefore it's ok to use glue if required).

So what d'ya think about that matron, controversial eh!

I await the barage of critism , it's all good fun!

Phil.

My opinion is not so much that it moves, it does but not much, more that the frame will move differently.

 

[Jacob]

What I don't get is why people want to glue their panels into the frames in the first place.
Loose panels in frames is traditional, well established, proven way of avoiding these little movement problems, whatever the causes or the extent. Why waste glue trying to prove it's not necessary? And the extra work cleaning off etc.
Completely pointless waste of time, effort and glue, and an inferior result.

PS loose panels and frames have been used for hundreds of years and world wide. Whatever you use, some movement is inevitable. We just have to keep repeating the obvious until it sinks in! Don't glue panels into frames, it's pointless and can cause problems.

 

[motownmartin]

What I don't get is why people want to glue their panels into the frames in the first place.
Loose panels in frames is traditional, well established, proven way of avoiding these little movement problems, whatever the causes or the extent. Why waste glue trying to prove it's not necessary? And the extra work cleaning off etc.
Completely pointless waste of time, effort and glue, and an inferior result.

I suppose we can't all be as good as you Jacob :wink:

 

[9fingers]

I tend to just put a couple of spots of glue on panels of whatever material - man made or natural - just to minimise the risk of a rattle developing later on. No real evidence if it works or not.

Bob

 

[Jacob]

What I don't get is why people want to glue their panels into the frames in the first place.
Loose panels in frames is traditional, well established, proven way of avoiding these little movement problems, whatever the causes or the extent. Why waste glue trying to prove it's not necessary? And the extra work cleaning off etc.
Completely pointless waste of time, effort and glue, and an inferior result.

I suppose we can't all be as good as you Jacob :wink:

Not sure what that means.
You mean you glue things unnecessarily because you are no good at woodwork? Just stop doing it then! What is the problem FFS?

I tend to just put a couple of spots of glue on panels of whatever material - man made or natural - just to minimise the risk of a rattle developing later on. No real evidence if it works or not.

If no evidence then don't do it! Rattling panels isn't a problem often encountered, if ever. If they rattled it would mean they were too loose in the slots to start with.

 

[motownmartin]

What I don't get is why people want to glue their panels into the frames in the first place.
Loose panels in frames is traditional, well established, proven way of avoiding these little movement problems, whatever the causes or the extent. Why waste glue trying to prove it's not necessary? And the extra work cleaning off etc.
Completely pointless waste of time, effort and glue, and an inferior result.

I suppose we can't all be as good as you Jacob :wink:

Not sure what that means. You mean you glue things unnecessarily because you are no good at woodwork? Just stop doing it then! What is the problem FFS?

No problem Jacob, don't take offence, just the fact its your profession and others don't have the same experience.

 

[No skills]

@ Phil

Quite interesting to see so little difference in size with the wide variation in temperature, if you do try a similar experiment with varying humidities then please post up your findings.

 

[Doctor]

No problem Jacob, don't take offence, just the fact its your profession and others don't have the same experience.

Is that where you got your twig jig from Jacob, "a fence" :lol:

 

[bugbear]

Whilst you are at it, information on thickness changes would be interesting and I suspect, of greater significance.

Even a 10% change in thickness on 6mm ply is only 0.6 mm, which I keep being told isn't very much!

BugBear

 

[Jacob]

No problem Jacob, don't take offence, just the fact its your profession and others don't have the same experience.

Is that where you got your twig jig from Jacob, "a fence" :lol:

Of course not. It was a hedge.
Trip down memory lane (looking for twigs)!
In case anybody doesn't know what this is about I've copied and pasted:

Basically any old bit of stick will do for many things. With a hole for a chisel or knife-tang for instance, or a slot, as in this handy spokeshave sharpening jig.

Hope this helps.

This image was featured elsewhere a few months ago but seems to have been substituted.

 

[bugbear]

You mean you glue things unnecessarily because you are no good at woodwork? Just stop doing it then! What is the problem FFS?

No problem Jacob, don't take offence, just the fact its your profession and others don't have the same experience.

Grimsdale just likes shouting the odds. Don't worry about it. He also likes "ruffling feathers".

It's a shame, because in some specialised areas of woodwork he's quite experienced and knowledgeable

BugBear