DIY Wood cabinet corner joints advice please

[alaskaleftybass]

Hi all, I'm quite inspired by watching your own DIY posts, tso I'm going to rebuild some of my PA cabinets and some bass and guitar combos, replacing heavy particleboard with void free 1/2" plywood. I've done some home stereo cabinets, and I also built my own 215 cab that I covered with Tolex and sold with an Ampeg V4B.

I'm disassemblying my various cabinets, and taking precise mesurements to duplicate the cabs in lighter forms. These are Behringer and Peavey cabinets. All made from particleboard, quite heavy. I also want to upgrade the bass and guitar combos with better/lighter neo speakers.

My question: Please don't laugh, but I can't do a dovetail joint, and can do a butt joint but I think that the plywood corners will be too thin for me to route a round edge without running into tiny nails or screws used to secure the joints. If I use a butt joint, how can I bury the hardware so I won't run into metal when I route all the edges?

Also, I want to change out the speakers in one 410 8ohm cabinet, and one 110 cabinet. Both are ported cabinets. How can I tell if a speaker is designed for a sealed or ported cabinet?

Thanks for your advice in advance.

 

[Munjibunga]

Dado.

 

[alaskaleftybass]

Thanks Munjibunga! I'm attaching a picture I remember of a joint I did in high school, and I think this one will work but will have to be careful due to the thinness of the plywood..... called a boxjoint dado....

 

[Rune Bivrin]

Butt joints are generally fine, provided you use good glue (PL Premium comes to mind) and brace the cabinet sufficiently.

All the cabs at Bill Fitzmaurice Loudspeaker Designs are butt jointed 1/2" ply, and can be rounded over just fine.

Personally I use a pneumatic brad nailer to fix the sides while the glue cures. If you use good quality carbide tip router bits they'll eat through the brads no problem.

If you feel so inclined you can always use a 1x1" rod inside of the joint as a reinforcement.

As far as replacing drivers are concerned, you'll get a bunch of replies that tell you it's not as simple as that. A driver is designed for a rather narrow set of box parameters. If you can find the T/S parameters of the drivers you intend to use you can use something like WinISD Pro to model the performance.

 

[wcriley]

I've used drywall screws (pre-drilled pilot holes) to hold the joints together, then removed them before routing.

 

[1958Bassman]

A butt joint won't be very strong using any kind of material if mechanical fasteners aren't used (screws, biscuits, dowels, etc) when making a simple box. The BFM cabinets hold up because they all have multiple pieces of material that act to resist "racking" and this keeps the joints from breaking. Butt joints work best when long grain is meeting long grain, not end grain. A finger (similar to box) joint is very strong because of the increased glue surface, but plywood isn't made to be strong in this kind of joint without reinforcement- solid wood is better when using these joints. However, a solid wood cleat can be installed in the corners to A) add some material to support the corner through increased glue surface (especially if the corners will be rounded-over) and B) allows installing screws farther from the corners, which avoids blowing out the ends. These can be triangular or square/rectangular and can be glued-in or used with/without mechanical fasteners. Any additional pieces will make for a stronger cabinet and these can be glued in after the basic construction has occurred. Corner clamps make cabinet building much easier and they're pretty cheap.

 

[Nightlyraider]

The fearful 15/6s i built are only glue and 1/2" ply and there have been zero issues regarding structural integrity nearly two years into their life.

Using PL Premium, I think I'd be more concerned about the ply eventually de-laminating than the joints falling apart.

 

[teemuk]

How can I tell if a speaker is designed for a sealed or ported cabinet?

If it's good for ported system then the driver's Qts should be between 0.2 – 0.5. At least it shouldn't be higher than that. Anything over 0.7 isn't suitable for porting. Efficiency Bandwidth Product (Fs / Qes) should be greater than 90. If the EBP is less than 50 then the driver is likely more well suited for sealed enclosures.

 

[alaskaleftybass]

Thanks everyone for chiming in. I will post pics of my disasters lol as I progress. I'm almost leaning towards using 5/8" instead of half, but my bolder side says use 1/2" the weight difference will be worth it. I'm undecided on the dado vs. butt joint, being partial to the butt joint and making sure I have reinforcement internally.

Thanks!

 

[Commodore 64]

I use a Kreg Jig for pocket holes: Link Removed
I've done a few kitchen cabs, and 3 or 4 amp cabs using this.

 

[johng999]

Has anyone tried plastic resin glue for their cabs? I made a few cabs years ago with it and I found that it was incredibly strong as long as a lot of pressure was applied to the joings. Dado cuts and a couple of trianges glued into the corners held for years and years.

 

[Woodstockz]

Thanks everyone for chiming in. I will post pics of my disasters lol as I progress. I'm almost leaning towards using 5/8" instead of half, but my bolder side says use 1/2" the weight difference will be worth it. I'm undecided on the dado vs. butt joint, being partial to the butt joint and making sure I have reinforcement internally.

Thanks!

I like your approach to lightening your combo cabinets. I'm sure that 1/2" will be OK, especially if you reinforce it somehow.

I wouldn't use a butt joint without a reinforcemtent. I have used both dado and reinforced butt joints on speaker builds that have worked out OK.

 

[bgavin]

The screws used in butt joints for BFM cabs are only there long enough to hold the joint together.
They are removed after the adhesive is cured.
The secret sauce in Bill's boxes is PL Premium adhesive.
The wood will break before the joint comes apart.
PL Premium expands to fill voids, and is the adhesive of choice for speaker cabs.

1/2" baltic birch is more than sufficient. Larger is over kill in expense and weight.
I routinely build 3/8" BB, and brace any span wider than 6~8", depending on use.
Bass boxes are much more prone to resonance, than are top boxes.
Brace to suit the task at hand.

[ edit ]
There is a reason for cleating at the joint: use of crappy, thin veneer plywood.
If your plywood has a thin surface veneer, it is junk, and to be avoided.

 

[Jools4001]

A butt joint won't be very strong using any kind of material if mechanical fasteners aren't used (screws, biscuits, dowels, etc) when making a simple box. The BFM cabinets hold up because they all have multiple pieces of material that act to resist "racking" and this keeps the joints from breaking. Butt joints work best when long grain is meeting long grain, not end grain. A finger (similar to box) joint is very strong because of the increased glue surface, but plywood isn't made to be strong in this kind of joint without reinforcement- solid wood is better when using these joints. However, a solid wood cleat can be installed in the corners to A) add some material to support the corner through increased glue surface (especially if the corners will be rounded-over) and B) allows installing screws farther from the corners, which avoids blowing out the ends. These can be triangular or square/rectangular and can be glued-in or used with/without mechanical fasteners. Any additional pieces will make for a stronger cabinet and these can be glued in after the basic construction has occurred. Corner clamps make cabinet building much easier and they're pretty cheap.

The baffle and the rear panel will prevent racking, even on a simple box.

As others have pointed out, PL Adhesive is so strong that the wood will break before the joint will.

I just built an overengineered kitchen cabinet from 3/4" ply. It's simply butt jointed at the corners. When it was hung on the wall, just as an overexuberant demo to my wife of how strong the thing was, I swung off it's bottom shelf. I weigh 200lbs, the cabinet didn't even budge.

Good quality ply, butt jointed with PL glue, with the baffle and rear panel also PL'd, plus a little extra strength all round from a good bracing system will give you all the glue area you'll need to be plenty as strong as a cab needs to be