Hey, just a quick question, I am in the proccess of build a set of line arrays with internal bracing , made out of MDF and will be veneered. The question remains if when using butt joints, will wood glue be strong enough? Or will I need to use screws as well? The front baffle is 1" and all other sides and braces are 4/5" thick.
TIA
TIA
Let me add a caveat...glued butt joints can be adequately strong provided the underlying construction is accurate. If the parts are flat (not warped, twisted or bowed) and the cutlines are true, straight and square so that all of the mating surfaces meet closely without gaps then a good quality wood glue will provide a quite strong joint. It won't be as strong as a screwed and glued joint or nearly as strong as a biscuited glued joint, but it will be adequate. This is because wood glues provide the highest strength in very thin layers but are not good at gap-filling. It is interesting that at diyAudio we regularly obsess over capacitor brands, cable and connector features and esoterica such as thin coatings applied in intricate patterns to speaker cones; conversely when it comes to the fundamental structure that is the foundation of a speaker we ask what is "good enough"!
Throw a old cabinet off your house, or hit it with a sledge hammer. The butt joints will be the last to give. So good enough means the joint is stronger then the panel. Another question would be does a butt joint sound better then a biscuit joint...
On the other hand whats the hardest to align, a butt joint.
On the other hand whats the hardest to align, a butt joint.
Yes, you would be correct, it is PVA glue.
And I think I may be able to source some here. Is this the stuff you are talking about?
An externally hosted image should be here but it was not working when we last tested it.
He means multi-ply, as in plywood.Thanks guys.
@Planet10, forgive my ignorance, but what is multiply?
Re: aligning butt joints - I like to dry clamp everything together and drill pilot holes. That way, I can simply glue along the joints and tighten/align at the same time with drywall screws. After the screws are tightened, I still put the bar clamps on, though.
Whether one removes the screws afterwards is up to personal preference and finishing method.
Yes, that Titebond III would be the stuff! Remember, you're getting your information from some joker in the internet, so test with some scrap pieces to be sure you like it.
Hint- Whenever I buy a bottle of wood glue, I write the date on the bottom using permanent marker. I just don't use it that fast and sometimes it can pretty old between projects. I don't know the shelf life, but at 2 years I usually buy another bottle.
Hint- Whenever I buy a bottle of wood glue, I write the date on the bottom using permanent marker. I just don't use it that fast and sometimes it can pretty old between projects. I don't know the shelf life, but at 2 years I usually buy another bottle.
I have repeatedly found that glueing to end grain of wood is not anywhere as strong as gluing to the the side face.
This applies even more when gluing MDF.
I don't know why. Could it be dust contamination?
Dowels or biscuit or similar do "add strength" but just as important "add shock resilience" to end grain joints.
I would never expect any glued end grain to end grain joint to be as stiff nor as strong as the parent material. A butt joint that includes one end grain face must similarly be limited in strength. Q.) why did someone invent and why do we see scarf joints?
Is it strong enough?
That is completely different and requires testing, probably destruction testing.
This applies even more when gluing MDF.
I don't know why. Could it be dust contamination?
Dowels or biscuit or similar do "add strength" but just as important "add shock resilience" to end grain joints.
I would never expect any glued end grain to end grain joint to be as stiff nor as strong as the parent material. A butt joint that includes one end grain face must similarly be limited in strength. Q.) why did someone invent and why do we see scarf joints?
Is it strong enough?
That is completely different and requires testing, probably destruction testing.
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AndrewT,
Your observation on end grain is spot on...the problem is that the end grain of wood constitutes the openings of the channels which used to carry sap through the (living) wood. Glue spread on end grain tends to have the moisture drawn away prematurely through this pore structure interfering with proper curing. Most joinery techniques in woodworking (rabbets, biscuits, mortise & tenon, dovetails, etc) have as one of their objectives increasing the area of long grain to long grain glue surface which greatly increases joint strength. Of course with plywood the end of a panel is a mix of end grain and long grain which gives a better outcome than solid wood end grain.
Your observation on end grain is spot on...the problem is that the end grain of wood constitutes the openings of the channels which used to carry sap through the (living) wood. Glue spread on end grain tends to have the moisture drawn away prematurely through this pore structure interfering with proper curing. Most joinery techniques in woodworking (rabbets, biscuits, mortise & tenon, dovetails, etc) have as one of their objectives increasing the area of long grain to long grain glue surface which greatly increases joint strength. Of course with plywood the end of a panel is a mix of end grain and long grain which gives a better outcome than solid wood end grain.
Much of the strength in butt joints in speaker cabinets comes from the fact that the joint is supported on more than one side. I have never seen a well-constructed speaker box made with butt joints fail. A closed box that basically just sits there its entire life doesn't need the sort of strength that a drawer does which is subjected to tensile and compressive forces on a regular basis. Save the dovetails for the drawers unless you are doing it for aesthetic reasons.
To answer the question about clamp pressure, a few years back one of the woodworking magazines did some testing to see if a joint could be starved of glue from too much clamping pressure. They found the exact opposite to be true which makes sense because glues joints are strongest when the film area is largest. Extreme clamping pressure pushes parts more closely together resulting in a larger contact surface area and more glue film.
To answer the question about clamp pressure, a few years back one of the woodworking magazines did some testing to see if a joint could be starved of glue from too much clamping pressure. They found the exact opposite to be true which makes sense because glues joints are strongest when the film area is largest. Extreme clamping pressure pushes parts more closely together resulting in a larger contact surface area and more glue film.
Yes. They are installed on one panel first (fully glued) so there are no alignment concerns. You use clamps to hold the panels together nice and snug then fire your nails on the inside through the cleats. Quick, easy and strong like Ox. You can make it even easier by nailing through from the outside as the holes made by the nails are so small they don't need filling if you are going to veneer.
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