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Why use plywood?

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Peter G Denmark

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Ok - i've used plywood in construction, and i liked it because it's very tough and rigid. But these properties only apply when it's supported and fastned along it's entire edge - at least that's what i found to be true.

Plywood is normally made by mounting a tree trunk on a gigantic lathe, that peels of a sheet of wood from sap to core in at long band, that is then clipped, and glued together with an irregular number of ply's.

Now - that might have been cool when most trees where old growth, but with the trees they use now - there is a big difference in the way the sap wood and the core reacts., so a lot of plywood sheets are inhenrently unstable.

Because there isn't a lot of woodworking ressorces available in my language, i've of course watched Norm and similar woodworkers, and thought i was missing out, when i saw them using plywood.

But damn - i've tried to buy 3 different batches of birch plywood, from different recommended suppliers, where the last one was 11-ply at £100 a sheet, but still they warp. I have a very controlled environment in my shop, and has stored them perfectly. I'm not saying they warp a lot, but warp they do.

In the woodworking community i find a lot of people that treat their machines like they were meant to mill metal parts for at space shuttle (parly including myself), and then they accept that they have to wrestle with sheets of wood, that almost allways warps?

I understand plywood from a production point of view, if you have to batch out 1000's of kitchen cabinets, but for the average hobbyist, like myself??

I find that construction grade 2x4's that has been laying in my shop for a couple of weeks, resaws, stickered, milled, left for 2 days, then milled down to final dimension and glued up as a panel, to be a much more predictable material than most plywood. It might not be as pretty right of the bat, but with a bit of white pigment in a wood oil, it shines right up. If you know how to do glue sizing, it can take stain pretty evenly too.

I have seen plywood from years ago that seems to be really good, but i simply think that the quality has gone into the toilet.

MDF is heavy, has really unpleasant dust, takes a screw really badly and really can't be used with tradtional joinery, but at least it's flat. Even IKEA's 10mm melamine sheets can deal with a lot of abuse.
One sheet product that i really has become fond of, and that is cheap as chips, is OSB. It might be made from saw chips swept of the floor, but it's a mixture of the same chips through the board. I've left some sheets of 18mm OSB outside for 3 years, and granted - the edges where frayed, but as soon as i cut of 5 cm of the edge, what was left, was a flat usable board.
If i have to build any shop furniture i a hurry, i will definately use that, and if you google "OSB furniture", you will see that it can look really cool, and can actually be beltsanded down to a smooth finish. And contrary to popular belief, it is very strong, and as long as you go for the 18mm stuff, it holds a screw very well.

If i lived i a country with a home depot, where you can get 3/4" birch ply for $23, then i could afford to throw out a lot of material, but living i Europe, that's simply not the case. Here i have to make it work, and the funny thing with plywood is, that once it's warped, it holds the warped position really nice and strong. I have - with moderate succes - sprayed the concave side of a bent sheet with water, and put the sheet outside in the sun with the convex side up, but most times i've just gotten an S-shaped peice out of it.

Sorry - had to went my frustration, because tomorrow i have to drive 300 km to return the warped birch, and i have to pay for the gas, :).

BTW - check out this article on Plywood vs. OSB http://bct.eco.umass.edu/publications/b ... d-plywood/
 

Woodchips2

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Thanks Peter for the link to the article, very interesting. Lots of pros and cons for various uses.
Regards Keith
 

Benchwayze

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I have found that it warps.
I use it, but only for small section stuff, and like you say, supported at all edges.

But I don't rely on woodwork to earn a living, so I can get on with these kinds of inconveniences. It does seem as if there is better material available in the USA though, and more choice. Which is understandable, given the size of the country. :)
 

Peter G Denmark

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As stated, i understand it from a production tempo standpoint, but for furniture, there is no reason to spend more money on this stuff, than it would cost laminating spruce lumber to the same size.

Now that i've started to notice, i look at a lot of table saw sleds on youtube, and notice, that the ones not supperted by a fence on both sides almost always has a slight warp, because you can se the edges or corners lift of the table. so for making jigs, it's just hopeless, unless you brace it, and then - what's the point?

From a eco standpoint i would like to se MDF core with a veneer of wood be available, since you would get the looks of wood, and still have a better yield from the trees.

The reason i'm writing this is, that a lot of would be woodworkers seek information on the internet, and think they can't build stuff with the lumber from the nearest store, which is just not true. Wood doesn't need to have max 8% moisture content or be hardwood. All wood can be made to work in a project, and the lumber at the home centers are down to about 20% moisture, and will be relatively stable after 2-4 weeks in your shop. It will definately be as predictable as plywood, if you brace it the same way.

Any days of the week i would chose a 3 week dried construction 2x4 as a sacrificial fence on my TS mitre gauge over a strip of 3/4" plywood.

If you ask regular woodworkers in the USA, it seems everybody are struggeling with the warpage, but this has just become part of the deal. A lot of the wood used comes from Europe (Finland, Sweden, The Baltic countries), and there are 500 million people in the EU, so the marked is there, but has just never caught on, as anything but a structural sheet.

I have found one exception on the plywood front. That brown phenolic covered 9 to 11 ply stuff that is used in the bottom of lorrey, trailers, and used for concrete casting - that stuff usually stays really flat. Here it costs around £35 for a 12 mm sheet, so if i'm ever going to build a TS sled from anything but MDF, that would probably work. The phenolic helps to seal it from the moisture, so it can be stored outside, under a roof, and still be flat when you need to use it.

So to all other newly started woodworkers - just spend the ekstra couple of days with real lumber, buy some melamine, particleboard, osb or MDF - you will be fine without plywood. Just remeber a dust mask and a good dust extraction system when working with mdf.
Once in a while i put my 2,5 hp LPHV dust extractor outside the shop with no filter or collection bag, with the hose in through the door. turn it on and blow all the settled dust in the shop into the air with compressed air, and whatch it sail towards the hose and outside, leaving my shop vitually dust free. Even after having sawed that black MDF stuff, where the dust i VERY visible.

Just my opinion.
 

Benchwayze

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Well I was planing some joinery grade softwood this morning. Even that was so 'green', I was continually waxing my bevel up LN 62. I did the job, and it's good enough for purpose, but I wouldn't want to make nice, pine furniture with the stuff. :|
 

Harbo

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I don't often use plywood or MDF but when I last did make a couple of Dolls Houses the thin ply I used for the hinged fronts and roofs warped quite badly - even though I had finished off both sides with the same paints.

Rod
 

Mr T

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Hi Peter

You said:
From a eco standpoint i would like to se MDF core with a veneer of wood be available, since you would get the looks of wood, and still have a better yield from the trees.
I'm interested, can you not get veneered MDF in Denmark?

Chris
 

Benchwayze

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I think Peter means a rather thicker veneer of wood than normal. More like plywood, but including a ply of MDF.
It might be a good idea, but I have had MDF warp, when I inadvertently leave it exposed to sunshine! So whether or not it would stabilise plywood might be debatable.
 

Peter G Denmark

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Precisely. What i'm talking aqbout is what the americans call MDO plywood. They use it for street signs etc.

But getting veneered MDF with a wood surface is not possible for the private consumer in Denmark and Sweden. You can get melamine covered MDF, which is very stable.

I can get MDF to warp as well if i'm careless and have done so. But if i store it properly, for instace against a wall with stickers between them, i have never seen it warp.

My point was, that a lot of woodworkers go out of their way to get plywood, because that's what we see other use, when it's just not that good a material for the average hobbyist, regardsless of skill level.

Another thing to bare in mind - when buying construction lumber, is to go for the wider boards. 2x4's tend to be from spruce, because they generally have smaller trunks, where as the 2x8's and 2x10's are often pine or duglas fir. If you go for the boards that have the core of the tree in the middle of the piece, you can rip it down the middle and essetially get two pieces of quarter saws pine. Ok - you will loose about an inch in the middle, but still a really cheap way of getting pretty stable wood. If you have a bandsaw use that for the ripping, or at least remember your riving knife. The core is very unstable and can bind the blade. A standard skil saw with a straight edge does a good job as well.

If you buy a cheap moisture meter, and find a lumber yard where the moisture content is 18-20% it's pretty certain that it has been dried in a kiln, which will make the pitch set, so it doesn't seep out.

Furthermore - i find i really cool when people take cheap and readely available materials and use regular tools to make something beautifull or usefull. Like the www.woodgears.ca guy.
 

kirkpoore1

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Peter, I get your point, and indeed I use solid wood for almost all my furniture, but for jigs and stuff around the shop I use plywood:

1. It's lighter than MDF. And since you can often use thinner plywood than the MDF you'd use for the same purpose, it's often a lot lighter.

2. It takes a beating better than MFD. Dents in plywood become chips in MDF, and if repeated bending happens (even if unintentional), ply will bounce back where MDF will eventually crumble.

3. Plywood will take screws where they'll strip out in MDF. As an example, I'm building a box under the table of my big bandsaw to contain the sawdust. The dust hose attachment piece will be fixed to a hole in one side of the box, and will be attached with screws. If that side weree MDF, the screws would pull out in short order.

4. I can burn my plywood scraps in my wood stove.

5. It takes a lot more water to destroy plywood than MDF. Painted ply will last for a while outside if not exposed to water too often. MDF, probably even veneered MDF, will be toast the first time it gets damp. Plywood's not a permanent solution in this situation, but sometimes "a while" is good enough.

I use OSB when I have to cover large areas and don't need to paint. Otherwise, I leave it alone.

Kirk
 

Peter G Denmark

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Kirk - you don't count, because plywood is cheap as chips where you live :). If i have to order a sheet of quality birch in Sweden, it will cost just short of $200, where as a sheet of 3/4" MDF costs $40,

If i could get plywood for $20, i would use it more often, since warpage wouldn't be a disaster.

But in Europe, i just don't think you get what you pay for.
 

kirkpoore1

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Peter G Denmark":2qxhgde4 said:
Kirk - you don't count, because plywood is cheap as chips where you live :). If i have to order a sheet of quality birch in Sweden, it will cost just short of $200, where as a sheet of 3/4" MDF costs $40,

If i could get plywood for $20, i would use it more often, since warpage wouldn't be a disaster.

But in Europe, i just don't think you get what you pay for.
Hey now, it ain't that cheap:
$45 plus tax for a 4x8 sheet. My friends who make cabinets tell me this really isn't the good stuff, which runs more like $100+/sheet, and I know some guys who build very high end furniture that make their own out of veneer (though not in 4x8 sheets).

That being said, given your cost I'd use it pretty sparingly too. The ability to put screws in it is the primary positive, I think, and I could get by with a half or quarter sheet every now and then for that usage.

Kirk
 

Benchwayze

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Peter G Denmark":25ghccgn said:
Kirk - you don't count, because plywood is cheap as chips where you live :). If i have to order a sheet of quality birch in Sweden, it will cost just short of $200, where as a sheet of 3/4" MDF costs $40,

If i could get plywood for $20, i would use it more often, since warpage wouldn't be a disaster.

But in Europe, i just don't think you get what you pay for.
An 8 x 4 sheet of 18mm thick, WPB plywood costs me £29.00.

At this moment that's about 37 Euro (Sorry, no Euro sign on my keyboard!) :)
 

Cheshirechappie

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When I was growing up about 35 years ago, there was a sheet material made up of strips of softwood (about 1" x 3/4" - 25mm x 20mm) edge-glued into a sheet, with the growth rings alternating to even out movement, then a thickish face veneer glued on both sides. I think it was called 'blockboard', and from memory was regarded as a good choice where stability was needed. Never seem to see it these days - is it still commercially available?

Edit to add - I've just checked the website of Richard Potter Timber (one of the better suppliers in my area) and blockboard is still available. Their price for 18mm BB grade birch ply is £42 a sheet, plus 20% VAT - so that's £50-40 a sheet, not including delivery charges.
 

Andy RV

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I've just had some timber delivered from Richard Potter, including sheets of 6mm and 18mm birch ply, it looks to be good quality, I'm using it for a router table that I'll start tomorrow, hopefully it will stay flat, this thread has got me worried!
 

Peter G Denmark

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Andy RV":1or5lnmf said:
I've just had some timber delivered from Richard Potter, including sheets of 6mm and 18mm birch ply, it looks to be good quality, I'm using it for a router table that I'll start tomorrow, hopefully it will stay flat, this thread has got me worried!
Don't worry about your router table. For that kind of construction the plywood doesn't have to support itself, but is braced al over, and if you find the birch ply to be worth the money and pleasing to look at, you'll be fine. Plywood is very strong structually.

Making higher cabinets with drawerslides, and no braces to force the plywood into submission, that's where i find the warping to be quite problematic. The same with shelves.
 

Benchwayze

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Andy RV":1jtsj0gn said:
I've just had some timber delivered from Richard Potter, including sheets of 6mm and 18mm birch ply, it looks to be good quality, I'm using it for a router table that I'll start tomorrow, hopefully it will stay flat, this thread has got me worried!
Andy,

I'd say it will be fine; especially if you construct the top as a torsion-box! :wink:
 
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