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Sure, "stronger than the material" ...but how "strong" is the material?

It seems to me that, compared to plywood, even the highest quality MDF can relatively easily come apart in ways which screws might help to prevent.

YMMV

Titebond II or III is used for the same reasons by all types of custom woodworkers and cabinet makers that use hardwoods and extremely strong Baltic Birch marine plywood, etc.

It's strong enough, even for the hardwoods and BB ply.

But, if you think you need something stronger, use Loctite PL400 Subfloor Construction Adhesive. Use a caulking gun to apply it.

IMO, it doesn't really matter much what you use to clamp the panels together while gluing them up...screws, a brad nailer, or good ol' clamps. As long as the panels are held together tightly and aligned properly while the glue dries, you are good.

IME, a brad nailer is the fastest and easiest, and also leaves the smallest divot which is quick and easy to fill and sand. If you need to add extra strength to the joints, use blind biscuit joints or oak dowel pins.

If you want a really strong and dense material for your subwoofer enclosures other than high-quality Baltic Birch, try the Huber Woods AdvanTech Subfloor sheets, available up to 1-1/8" thick.

AdvanTech Flooring, AdvanTech Subflooring, AdvanTech Floor | Huber Engineered Woods

 

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By "come apart," I wasn't referring to the adhesive, but rather the panel material (i.e. MDF, plywood, etc.).

My premise is that MDF can much more easily separate/delaminate along its length than plywood (or natural wood). For example, when creating an MDF corner joint, by gluing "end grain" to panel surface, the end grain would be well bonded to the adjoining panel surface; however, that panel surface is not so well bonded to the rest of that panel itself (compared to the plies of plywood); and to that extent, more liable to come apart.

Yeah, I understood what you were trying to say previously, i.e. the glue isn't the limiting factor.

 

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In my view screws are the best extra insurance needed for the not so well built enclosures.

us back yarders build. We don't all have the highly accurate table saws and jigs in our
tool boxes. Our cuts cannot be perfect.

Wood glue is super strong when used properly but by itself, in an imperfect cut, is fairly weak and brittle. Screws can keep things together when all else fails.
If a crack in a seam develops it will propagate, unless screws stop the destruction.

I just had a carpenter friend assemble a 2.25 cuft ported box for my 12" jbl gti mkii.
The panels were double thick 3/4" mdf, the thing weighed a ton.
I had asked him to use lots of long screws and gave him good reasons why, but he didn't. It blew to bits.

The destruction only took about two minutes at high volume and every panel had come
apart. The carpenters glue had had lots of time to dry but failed miserably
If he had used the appropriate screws in the appropriate numbers this would not have
happened.

This is the third time i have witnessed glue joint failure involving a car enclosure.

I know many will disagree but in my experience screws matter, especially in the mobile
environment.

Don't have your carpenter friend build anymore subwoofer enclosures for you. Do you know if he even clamped the panels together while the glue was drying, and what type of "carpenter's" glue he used?

Even with the most basic of tools that any "back yard builder" should have (budget list below), with a little bit of time and care, you should be able to achieve Perfectly Straight and Smooth Cuts, assuming you are using a decently sharp and appropriate blade for the material you are cutting.

And Yes, the quality and type of adhesive matters. Don't skimp there.

Titebond III Ultimate Wood Glue 16-oz...Note that some woodworkers still prefer Titebond II especially for finish work where a wood stain will be used .

The Original Gorilla Glue is also incredibly strong and has excellent gap-filling properties....

Original Gorilla Glue ...but use this very sparingly as it expands quite a bit and can make a mess. I prefer the Loc-tite PF or PL adhesives for gap-filling.

TOOLS:

Harbor Freight 16" x 24" Steel Carpenter's Square

Black & Decker 4.5 amp Jig Saw

or

A Circular Saw/"Skil saw"

Harbor Freight 48" I-beam Level (as a Straight Edge Cutting Guide)

or

Harbor Freight 40" Aluminum Ruler/Straight Edge Cutting Guide

and

Harbor Freight 3" C-clamps (to secure the straight edge cutting guides)


I'm not saying "DO NOT USE SCREWS". But if this type of enclosure is properly cut and assembled with the appropriate glue and clamping, screws should not be needed.

I think that there could be a few disadvantages to using screws, other than the obvious extra time and cost. Care has to be taken to make sure they are centered in the material and are driven straight so as to not cause edge chip out or splits. And if you use too many screws too close together in cheap or thinner MDF, it can easily cause a long linear split in the panel. This is why I prefer the brad nailer... it is MUCH faster and less likely to cause splits.

 

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I wish I had a 60" level in addition to or instead of my 48" level, so that when I'm making full-width cuts, I'd have that extra length to guide my Skilsaw as I begin the cut (as this is where I've ended up with issues from time to time).

Totally agree. You should have the appropriate guide overhang for the length of the panel you are cutting and for the saw you are using. A backer or supporting board on each end is helpful as well.

Also, despite my best OCD efforts, my straight edge + Skilsaw cannot achieve (or at least have not yet achieved) the degree of dimensional parity provided by the locked fence of a table saw (often requiring rework of one form or another), further necessitating the use of screws.

True, a good table saw will be better in nearly all circumstances. But with a circular saw, this problem is usually down to having a cheap/not sharp/not appropriate type of blade, in addition to the shaft bearing run-out or lateral play in the drive shaft/motor, which causes the blade to "float" left-to-right. It will help if you keep a very consistent speed and forward pressure on the blade through the entire cut.

For those reasons I'd rather use a jigsaw with a guide as opposed to a cheap circular saw with a meh blade.

Incidentally, I've found jigsaws (even my very nice Bosch unit) to produce woefully inferior cuts (mostly due to blade flex, particularly in thicker materials such as 3/4" MDF), despite the use of a straight edge, fresh blade, and careful attention to technique.

Again, it's mostly down to using the correct type of blade. Use a thicker, good quality hardened blade that's appropriate for the material. AND, you need to make sure you start the cut true, and Go Slowly!

As soon as you think it is "cutting well" and then try to push the blade too aggressively through the cut, that's when it will flex & drift. VERY Slow and steady (consistent speed) wins the race. If you feel like you have to "push" the saw through the cut, you're going too fast. You should just be using "fingertip pressure" to advance the blade. Not a lot of people have the patience for this, including myself at times. Too often I'm in a rush and just want to get 'er done.

 

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I have some loctite PL 500. Is this ok to use?

IMO, I don't think it would be the most appropriate adhesive to use. If you need a gap-filling adhesive, go with one of the previous suggestions.

But if your cuts are clean and straight, just go with the Titebond II or III wood glue.

My MDF that is left over from the previous box build is now small enough that two people can handle it on a table saw. I'll be using it to cut the pieces for my new box tomorrow. It will be ported and will have a 4 x 6 aero port firing upwards. The dimensions for the box will be 21x10x17.5 outside measurements. The inside measurements will be 19.5x8.5x16 for a volume of 1.53 cu ft.

Measure thrice, cut once, and take your time to do it right the first time. Have fun with it.