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Old 6th April 2009, 02:32 AM   #1
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Default plywood joins

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...
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Impedance varies with frequency, use impedance plots of your drivers and make crossover calculations using the actual impedance of the driver at the crossover frequency
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Old 6th April 2009, 06:02 AM   #2
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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!
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Old 6th April 2009, 06:23 AM   #3
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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?
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Old 6th April 2009, 06:39 AM   #4
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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?prodcat=1
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Old 6th April 2009, 07:45 AM   #5
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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.
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Old 6th April 2009, 08:05 AM   #6
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Default Re: plywood joins

Quote:
Originally posted by 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...
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.

Quote:

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.
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Old 6th April 2009, 11:47 AM   #7
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Quote:
Originally posted by 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?
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!
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Old 6th April 2009, 12:14 PM   #8
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Glue them (with PVA),
and find something heavy.... ...it works!

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Old 6th April 2009, 12:28 PM   #9
HK26147 is offline HK26147  United States
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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
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Old 6th April 2009, 11:50 PM   #10
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Default Re: Re: plywood joins

Quote:
Originally posted by Drew Eckhardt
Using cleats


Quote:
Originally posted by Geek

After those joints have dried, add cleats.
I'm not sure that's the right order.

Quote:
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?
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