plywood joins

[PeteMcK]

I want to build my next cabs out of 17mm plywood,
what's the easiest way to join the panels with minimal woodworking tools (& skill )? There will be a couple of 45 deg panels, cabs ~80 L.
I want to avoid screws from the outside (except on the back) if poss...

 

[Geek]

Minimal tools and skill, eh?

Well, before I could afford a toy... errr.... tool shop, fluted dowel joints usually kept thing together unless I sat on them.

All you need is a drill and dowel guides (assorted sizes for a pack for $5 in a typical hardware store).

Cheers!

 

[PeteMcK]

Thanks Geek, I knew there had to be an easier way than what I was thinking of....
What kind of glue do you recommend, is PVA OK?

 

[audio-kraut]

For doweling and edge gluing you need at least some good clamps.
I use both elmers yellow glue and tite bond, works extremely well:

http://www.titebond.com/IntroPageTB.ASP?UserType=1&ProdSel=ProductCategoryTB.asp?prodcat=1

 

[simon dart]

The uncomfortable truth is some skill and some tools are really what you need! My advice is to practice on something less expensive/critical before you commit.

 

[Drew Eckhardt]

I want to build my next cabs out of 17mm plywood,
what's the easiest way to join the panels with minimal woodworking tools (& skill )? There will be a couple of 45 deg panels, cabs ~80 L.
I want to avoid screws from the outside (except on the back) if poss...

Using cleats will let you mate panels at any angle without being too accurate on panel size or the angles on the edges.

When you have standard angles (90 or 45 degrees) lock miter joints cut with a router table take some intelligence to setup, but only require clamping in one dimension and are much easier to align than conventional miter joints.

Splined miters, biscuts, or dowels would be another alternative with positive alignment.

Thanks Geek, I knew there had to be an easier way than what I was thinking of....
What kind of glue do you recommend, is PVA OK?

PVA requires tight fitting joints (it doesn't have much strength accross gaps). It takes 200psi of clamping pressure to perform optimally (a clamp every 7" on 3/4" stock). It gives you at best (with something lik e Titebond Extend) 15 minutes to get everything lined up and will start to stick is soon as you get pressure on it.

It's very inexpensive, produces invisible glue lines, doesn't soak in, scrapes off, is non-toxic, cleans up with water, and lets you remove the clamps real soon (30 minutes for a lot of jobs).

You can't beat it when the above constraints are acceptable.

If not you have to look elsewhere.

Epoxy (as a structural adhesive like T-88 or filled with wood flour) will be strong accross .050" gaps and beyond, requires no clamping pressure, and can give you an hour to monkey with joints before it starts to cure. It's expensive, makes bigger glue lines, soaks in (bad if you want to stain or use a clear finish; you can use packing tape adjacent to joints and blue painters tape elsehwere to keep it off), requires gloves, and takes solvents (some benign; white vinegar emulsifies the components and uncured epoxy, and denatured alcohol isn't as nasty as acetone) to clean up. Epoxies with long open times won't stop being sticky for 6-8 hours at room temperature (colder temperatures lengthen cure times) and may mean a day in clamps when there are stresses in the assembly.

 

[Geek]

Thanks Geek, I knew there had to be an easier way than what I was thinking of....
What kind of glue do you recommend, is PVA OK?

The guys have already answered with great advice, but I'll add my twonie...

I've used regular white PVA, LePage's wood glue and Titebond. All seem OK, but they do need clamping. The wood clamps that slide on a bar, then tighten with a screw-type handle are best, but a bunch of "Quick-Grip's" will do fine too (the cheapie knockoffs are OK for non-repeated use, like by the weekend DIY'er).

After those joints have dried, add cleats. You can use 18mm square, or if you have a table or band saw, cut them so you have triangle shaped pieces so to not eat up so much volume in the box. Clamp them too while drying.

Though the glueing instructions may say "clamp for 1 hour", if you are in an area of highish humidity (I'm near Vancouver, BC, so I think Sydney has similar levels, maybe even more), I would clamp for a full 24H.

Cheers!

 

[longitude]

Glue them (with PVA),
and find something heavy.... ...it works!

 

[HK26147]

Expanding polyurethane adhesives work well.
I used plenty of pipe clamps.
On the inside of the speaker panels I pre-attach strips of wood ( approx 1" x 1" ), inset to the thickness of the panel material. This provides a ridge/stop to align the other panels to. Glue and shoot screws from the inside through the cleats into the adjoining panels, and use clamps and you have no visible screw heads

 

[Cal Weldon]

Re: Re: plywood joins

Using cleats

After those joints have dried, add cleats.

I'm not sure that's the right order.

Though the glueing instructions may say "clamp for 1 hour" <snip> I would clamp for a full 24H.

I thought there was a reason you release the clamps after 30 - 90 minutes and then let it continue drying for a minimum 24 hours. An old carpenter's tale?

 

[raypalmer]

For large areas it's cheaper to use 60lb bags of playsand rather than buying a platoon of clamps. I think I bought my bags for 8 bucks each, then stack them on whatever I'm gluing until the seams are all airtight. Just make sure they're well and sturdy bags so you don't have a sandsplosion on your hands.

 

[Geek]

Re: Re: Re: plywood joins

I thought there was a reason you release the clamps after 30 - 90 minutes and then let it continue drying for a minimum 24 hours. An old carpenter's tale?

Seriously, 7 out of 10 clampings I release in an hour, let go < 6 months, unless done in the heat of summer.

Furn. grade ply, $50/jug Titebond and gapless table sawed joints.

24H clamp, I can stand on it without as much as a settling crack.

Cheers!

 

[chilinski]

Rule about clamps:

You could own every clamp that was ever created by all the people in the world since the start of time and you'll still be one short.

Also, you probably ought to think about cabinet grade plywood and not the stuff you get at Lowe's/Home Depot. The good grade will cost you $60 plus per 4x8 sheet. If you use the standard grade available there, you probably will find there are voids between the top veneer layer and the layers beneath. You won't see these until it is way too late...usually after you put on the topcoat...and you'll see a wrinkle in the top veneer layer or a bump or a slight depression. In most cases, you can put your finger through it.

It would be really nice if you have access to a real woodworking store near you...someplace like Woodcraft where you can get the right materials for this kind of project and professional, knowledgeable advice on the woodworking part.

 

[hybridfiat]

Gussets

All the suggestions you have had are great. But if you want real strength use a strip of 1/4 round or bullnose moulding down the inside glueline and some 100mm gussets (right angled triangles made from bits of scrap) spaced at about 250-350mm on the inside.
The gussets will add a massive amount of structural strength and ridgidity and are THE easiest way to make any glued or screwed structure indestructable. They also help you keep the whole thing square.
I use liquid nails for the non visible stuff.
Happy building

 

[Cal Weldon]

Please read the thread, we've already covered cleats. Most of us use continuous ones, not spaced. If you use leftover plywood, you need not purchase chamfer strip as you have described.

 

[hybridfiat]

Mate, cleats mean something different here.

 

[Kravchenko_Audio]

Some more two cents

This is one way to do 45 degree mitre joints.

EDIT :

Messed up the links

http://i407.photobucket.com/albums/pp160/mwmkravchenko/IMAG0034-1.jpg
http://i407.photobucket.com/albums/pp160/mwmkravchenko/IMAG0035.jpg
http://i407.photobucket.com/albums/pp160/mwmkravchenko/IMAG0036.jpg
http://i407.photobucket.com/albums/pp160/mwmkravchenko/IMAG0038.jpg
http://i407.photobucket.com/albums/pp160/mwmkravchenko/IMAG0040.jpg
http://i407.photobucket.com/albums/pp160/mwmkravchenko/IMAG0043.jpg

This works very well. The secret to correct glue ups is not always immense pressure. To much pressure and you squeeze out all the glue and have a very weak bond. Good mating of the surfaces is what is really required. And enough pressure to keep them well mated.

There is also a way to use packing tape to works as clamps. But that I have to get some other pictures of. I use it when I have a large amount of edging to glue on in the shop. Works like a charm and can be applied to larger panels to. It even works on difficult shapes like curves and the like.

Mark

 

[strider75]

Re: Re: Re: plywood joins

I'm not sure that's the right order.

"Is it detrimental to add the cleats after the panels are glued in place?" he asks, thinking of his recently glued panels sitting in his basement sans cleats.....

 

[badman]

No, it's fine to retrofit them, but you can get the best glue and clamping done when they're present from the get-go.

I'm currently retrofitting some big ply cabs with bracing. Ribs and cleats all thrown in after the fact, and they certainly help a lot, but the gluework is sloppy compared to what you can do in initial assembly.

Plywood scraps are great. There's something to be said for just tossing them into place as panel thickening with some yellow glue.

Not the most effective thing but easy and an improvement.

Also, cutting 45 degree beveled edges onto some scrap stock, and making strips of it, then using it to brace across corners making triangles can be extremely effective (same idea as the corner chocks but with a larger affected section of panel)

 

[Pano]

All these and Mark is using tape?

Nice idea Mark, thanks.

Great thread. ("sandsplosion" LOL)