# Screws or not in a sub box



## bigone5500 (Jul 11, 2018)

I built my last box with 3/4 MDF and used Titebond II glue at all joints followed by silicone at the inside seams. I used a brad nailer to hold it together until the glue dried. I've not had any trouble with it so far. I had one guy ask me why I didn't use screws. In my mind, the glue will create a strong bond and be stronger than the material itself. This is evident in some videos where the glued joint was placed under stress and the material failed before the glue joint.

This brings me to my question. Do you really need to use screws in the joints? Is there a point at which the enclosure's size could determine whether screws are necessary? I would think that larger enclosures with greater surface area on the panels would benefit from them and smaller (~1 cu ft) could be fine without. 

What are your thoughts on this subject?


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## minbari (Mar 3, 2011)

bigone5500 said:


> I built my last box with 3/4 MDF and used Titebond II glue at all joints followed by silicone at the inside seams. I used a brad nailer to hold it together until the glue dried. I've not had any trouble with it so far. I had one guy ask me why I didn't use screws. In my mind, the glue will create a strong bond and be stronger than the material itself. *This is evident in some videos where the glued joint was placed under stress and the material failed before the glue joint.*
> 
> This brings me to my question. Do you really need to use screws in the joints? Is there a point at which the enclosure's size could determine whether screws are necessary? I would think that larger enclosures with greater surface area on the panels would benefit from them and smaller (~1 cu ft) could be fine without.
> 
> What are your thoughts on this subject?


exactly this! the wood will fail before that glue does.

I used screws on mine only to hold it together until the glue dried. hell on a small enclosure I think 3/4" MDF is overkill. I used 1/2" saved alot of weight


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## Onyx1136 (Mar 15, 2009)

Glue bonds the panels together. The screws or brads or clamps are just to hold the boards together until the glue dries. I’ve seen people use screws to put an enclosure together, then remove them and fill the gaps once the glue was set. Use whatever temporary fastener you prefer, but know that the screws don’t add any strength to the final product once the glue is completely set.


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## diy.phil (May 23, 2011)

I've actually done it both ways over the years. The screws are useful if we keep working or adding panels non-stop and don't have time to let each section dry. Clamping or appropriately placing heavy objects over it to make the glue joints tight is very important if not using screws and have lots of time to spare.

Edit/add: Back then i went thru the trouble of using a countersink drill bit so that the screw is recessed. Then hammer in a hole plug (with glue) in each and then trim it with a router (furniture style). All the lines/edges with glue too (not just screws). Now... just glue and waste time on the internet while it dries lol.


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## Driver of 102080 (Sep 19, 2016)

Depends on how you care about the looks I stained my slot ported box so no screws show on mine.

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## Grinder (Dec 18, 2016)

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


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## bbfoto (Aug 28, 2005)

Grinder said:


> 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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## FordEscape (Nov 23, 2014)

Grinder said:


> 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


IMHO if you've got that concern even 1/2" x 1/2" x 'length of joint' internal corner-blocking glued with Titebond II is easier and adds as much reinforcement as the screws would with MDF (or plywood).

Adjust enclosure volume if you must but the volume displaced will be minimal if you rip triangular x-section blocking strips.

'Screw-less' is the way to go, IMHO. :laugh:


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## Grinder (Dec 18, 2016)

bbfoto said:


> _Titebond II_ 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.
> 
> ...


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.


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## 04quadcab (Dec 31, 2017)

I like to line everything up with clamps and then use my brad nailer to keep everything together while the glue dries. This allows me to move to the next panel rather than waiting for the glue to dry. The other alternative would be to buy a lot of clamps.

I'm also a big fan of internal bracing.

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## dgage (Oct 1, 2013)

For my commercial subs (18 and 24” subs), I use PL Premium 3X and that is all. I haven’t had any issues with it. When I build cabinets or furniture I use Titebond 3 and fasteners, if used, are pretty much just for the glue to setup. I sometimes remove screws after the glue dries since the glue is stronger than the material. The reason I use PL Premium for sub enclosures is it also acts like a caulk to ensure the enclosure is air tight.


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## SPLEclipse (Aug 17, 2012)

If you're designing an enclosure and think: "This is large enough that maybe screws would make it stronger", you need to add internal bracing, not screws. Besides making sure it's air-tight, bracing is the single best thing you can do to make sure your enclosure performs well.


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## bbfoto (Aug 28, 2005)

Grinder said:


> 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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## Grinder (Dec 18, 2016)

I started out using screws because I had no clamps, and because I had no table saw (i.e. somewhat less than absolutely perfect cuts with Skilsaw) and wanted to be sure of consistently tight glue joints.

So, my first four MDF speaker cabinet projects had a LOT of screws (every 2 – 3 inches). However, when contemplating my fourth build (3ft.^3 cabinets for a pair of Dayton HF 15s), I decided to cut way down on screws (still more than sufficient, I thought). But when a knowledgeable friend saw these pictures, he advised me to add more screws (to “go nuts” with the screws, as I had with pervious projects).



















(to be continued)


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## Grinder (Dec 18, 2016)

...and so, I did (as these pictures show). 

…and as a result, I concocted a theory that might explain the forgone conclusion that screws are somehow essential (i.e. my MDF delamination theory).


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## Grinder (Dec 18, 2016)

...and then I added additional bracing.










In any case, I am quite happy with the result.


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## minbari (Mar 3, 2011)

Made allot of enclosures over the years. Never had one come apart due to the wood failing. Always just did a basic glue and screw

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## Grinder (Dec 18, 2016)

...and here's the finished product.

...ahem, minus exterior finishing, of course.


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## dgage (Oct 1, 2013)

Grinder said:


> ...and here's the finished product.
> 
> ...ahem, minus exterior finishing, of course.


Now that's the proper way to add subwoofers to a room. So many people try to hide them and you find a way to feature them. Love it!


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## dgage (Oct 1, 2013)

And not sure this really helps but it does show some of the bracing in my Mariana 18S so I thought I'd attach. I had a quick animation done to show how the subs are constructed. 

https://www.youtube.com/watch?v=2vMNYk6zyQ0


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## Grinder (Dec 18, 2016)

dgage said:


> And not sure this really helps but it does show some of the bracing in my Mariana 18S so I thought I'd attach. I had a quick animation done to show how the subs are constructed.
> 
> https://www.youtube.com/watch?v=2vMNYk6zyQ0


Nice!

Seems like that stack of inset rings would eat up a lot of material (unless you've got other uses for the rest of it). Yep, too bad folks seem to want their speakers to disappear.


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## lampinlance (Apr 15, 2018)

My issue is the number of times I’ve seen furniture, especially chairs with spindles or leg bracing, come loose. The glue became brittle with age and with the stress of being used, it falls apart even when it’s tacked. That’s why I’m hesitant to use brads for sub boxes.


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## dgage (Oct 1, 2013)

The issue is the type of joint and grain of the wood. First, wood is organic and real wood has pores and grain patterns. Some of these grain patterns are prized and others are considered defects such as knots. If you glue real wood long grain to long grain you will get a very strong bond because the glue is able to marry the pores of the wood, which are going in the same direction. In that orientation, with modern glues, if you try to break a glued long-grain joint, the wood will usually break somewhere else, the joint is that strong. Now if you try gluing a long-grain joint perpendicular to the long-grain of another board, that is called a cross-grain joint and is actually pretty weak, like your chair example. That is why 19th century craftsman often used mortise and tenon construction often with pins. 19th century chairs often went through the seat and were then wedged from the top to gain strength. Modern chairs are built cheaply and to aesthetics, long term strength is usually a lower priority than appearance. 

But none of that matters as you’ll either be using MDF, which has no grain, or plywood, which has grain going in both directions. Glue will give an incredibly strong bond with plywood and a pretty strong bond with MDF. You can use screws if you want but the only thing you really need is clamping pressure until the glue sets up and bonds the 2 pieces of wood. Clamping could come from actual clamps, brad nails, or screws but most of the strength will come from using a modern glue and that glue should last for decades and decades.

Edit: I forgot to mention wood being organic and is often heavily affected by changes in humidity. If you’ve ever had a door stick after heavy rains, it is due to humidity and the wood cells expanding. This expanding and contracting of wood over time has a tendency to loosen joints. It will also loosen around fasteners over time, which is why gates sag, the screws aren’t tight in wood anymore because the movement of the wood reamed out the screw hole.


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## bigone5500 (Jul 11, 2018)

Sorry for the delayed reply, and thanks for all your replies. I'll simply glue it and use my brad nailer to hold it until the glue sets. All the information in the replies alleviates my concerns. Now to save up for the new sub...


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## Patrick Bateman (Sep 11, 2006)

SPLEclipse said:


> If you're designing an enclosure and think: "This is large enough that maybe screws would make it stronger", you need to add internal bracing, not screws. Besides making sure it's air-tight, bracing is the single best thing you can do to make sure your enclosure performs well.


Keep in mind, all braces are not created equal. The optimum brace is decoupled from the enclosure.

Kef does this in their LS50. The trick is finding the right adhesive. Liquid Nails for floors was a safe bet, but Home Depot has ceased stocking it. You can still get it at HD Supply.


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## lampinlance (Apr 15, 2018)

dgage said:


> The issue is the type of joint and grain of the wood. First, wood is organic and real wood has pores and grain patterns. Some of these grain patterns are prized and others are considered defects such as knots. If you glue real wood long grain to long grain you will get a very strong bond because the glue is able to marry the pores of the wood, which are going in the same direction. In that orientation, with modern glues, if you try to break a glued long-grain joint, the wood will usually break somewhere else, the joint is that strong. Now if you try gluing a long-grain joint perpendicular to the long-grain of another board, that is called a cross-grain joint and is actually pretty weak, like your chair example. That is why 19th century craftsman often used mortise and tenon construction often with pins. 19th century chairs often went through the seat and were then wedged from the top to gain strength. Modern chairs are built cheaply and to aesthetics, long term strength is usually a lower priority than appearance.
> 
> But none of that matters as you’ll either be using MDF, which has no grain, or plywood, which has grain going in both directions. Glue will give an incredibly strong bond with plywood and a pretty strong bond with MDF. You can use screws if you want but the only thing you really need is clamping pressure until the glue sets up and bonds the 2 pieces of wood. Clamping could come from actual clamps, brad nails, or screws but most of the strength will come from using a modern glue and that glue should last for decades and decades.
> 
> Edit: I forgot to mention wood being organic and is often heavily affected by changes in humidity. If you’ve ever had a door stick after heavy rains, it is due to humidity and the wood cells expanding. This expanding and contracting of wood over time has a tendency to loosen joints. It will also loosen around fasteners over time, which is why gates sag, the screws aren’t tight in wood anymore because the movement of the wood reamed out the screw hole.


Thank you for the explanation. It makes sense!


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## lurch (Jan 20, 2014)

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.


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## minbari (Mar 3, 2011)

Then your "carpenter" friend was a hack

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## dgage (Oct 1, 2013)

I’ll give you extra insurance of screws but the reason your friend’s box failed was the wrong choice of glue. Carpenters glue, my favorite being Titebond 3, is for accurate joints like on a kitchen cabinet or furniture. It doesn’t have any gap-filling capabilities so if the cabinet isn’t damn near perfect, the glue won’t work where there are gaps. That’s where construction adhesive comes in as it has gap handling properties if the cabinet isn’t perfect, while also adding the benefit of making our sub enclosures air tight. As I stated, even though my subs are cut on a CNC and are accurate and repeatable, I still use construction adhesive and the best I’ve found for the money is PL Premium 3X. I say for the money because I haven’t tested out the $7 plus tubes but after using Liquid Nails Heavy Duty for a time, I switched to PL Premium 3X and find it to be better. If your friend’s imperfect cabinet would have used PL Premium that was fully cured, the enclosure wouldn’t have come apart. So screws without the right glue isn’t the right method either. As I said, I don’t use screws, I use ratchet straps and clamps until the glue cures for 24 hours and then release, but as you said, you view screws as insurance and many of us buy insurance, even when not required.


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## bbfoto (Aug 28, 2005)

lurch said:


> 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.
> ...



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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## bigone5500 (Jul 11, 2018)

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


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## Grinder (Dec 18, 2016)

bbfoto said:


> Don't have your carpenter friend build anymore subwoofer enclosures for you.
> 
> 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 decent and appropriate blade for the material you are cutting.
> 
> ...


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).

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. 



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.


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## Grinder (Dec 18, 2016)

bbfoto said:


> ....
> 
> 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.


Agreed.


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## bigone5500 (Jul 11, 2018)

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.


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## bbfoto (Aug 28, 2005)

Grinder said:


> 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.




Grinder said:


> 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.




Grinder said:


> 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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## Grinder (Dec 18, 2016)

bbfoto said:


> 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.
> 
> 
> 
> ...


Trust me, I have been there and done that... LOL My barely used worm drive Skilsaw and Diablo blade are definitely not the problem. It is entirely a matter of slight layout disparity/error (despite my best efforts/OCD).


I agree 100% about the jigsaw technique and proper blades (and I can still mess it up. LOL).


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## bbfoto (Aug 28, 2005)

bigone5500 said:


> 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.




bigone5500 said:


> 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.


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