Hei please tell me some ideas:
-how big should be screws diameter (I am doing box 20cm x 45cm x 150cm box. And how often should I use screws.
Why I am asking, is that my last speakerbox I used screws diameter about 3mm and they arent long. I put MDF pieces together and used autospackel to cover connection places, but even when I spackled twice between one week, after waiting a week I felt under fingers that the line where two pieces of MDF were together has some stage. I was wondering , maybe the MDF is playing on this connection line and pieces are removing eachother?! Any ideas?!
-how big should be screws diameter (I am doing box 20cm x 45cm x 150cm box. And how often should I use screws.
Why I am asking, is that my last speakerbox I used screws diameter about 3mm and they arent long. I put MDF pieces together and used autospackel to cover connection places, but even when I spackled twice between one week, after waiting a week I felt under fingers that the line where two pieces of MDF were together has some stage. I was wondering , maybe the MDF is playing on this connection line and pieces are removing eachother?! Any ideas?!
Hi,
end grain of MDF does not glue well.
Use screws.
End grain of MDF does not screw well.
Use a timber batten inside all the corner joints. Screw the batten into the faces of each MDF panel.
You can use long screws into MDF end grain but they do not survive shock loads. The MDF splits and leaves the joint open/weakened/damaged/leaky.
Try 4mm chipboard screw (very deep thread profile) with 50mm of penetration into the end grain pre-drilled to about 3mm diameter and use glue in the hole as well as in the joint. But this does not give a robust fixing.
end grain of MDF does not glue well.
Use screws.
End grain of MDF does not screw well.
Use a timber batten inside all the corner joints. Screw the batten into the faces of each MDF panel.
You can use long screws into MDF end grain but they do not survive shock loads. The MDF splits and leaves the joint open/weakened/damaged/leaky.
Try 4mm chipboard screw (very deep thread profile) with 50mm of penetration into the end grain pre-drilled to about 3mm diameter and use glue in the hole as well as in the joint. But this does not give a robust fixing.
Hi Andrew,
By shock, do you mean dropped from a high place? A properly glued joint, using the right glue, even on MDF end grain will not fail from the loads put on it from the driver.
Your message makes it seem that glue will be useless and can be avoided with the use of corner cleats and screws. Not so.
By shock, do you mean dropped from a high place? A properly glued joint, using the right glue, even on MDF end grain will not fail from the loads put on it from the driver.
Your message makes it seem that glue will be useless and can be avoided with the use of corner cleats and screws. Not so.
I understand to use corner batten, like Andrew is suggesting. I have done it for PA speakers, but to start using it for tower-speakers its not for me best solution:
1) it takes too much time for every speaker (its faster without it)
2) still I believe some other option.
So, what do you think something about that:
I am using router to cut half of the edge and glue it like it shows (bold lines) and use screws 4mm and longer (50 f.e). of course I am gonna drill 3mm hole.
ps! I will upload picture a littlebit later
But still, do you have any idea, why this stage appear after when I have grind the surface and after couple of days?! Mystica!
1) it takes too much time for every speaker (its faster without it)
2) still I believe some other option.
So, what do you think something about that:
I am using router to cut half of the edge and glue it like it shows (bold lines) and use screws 4mm and longer (50 f.e). of course I am gonna drill 3mm hole.
ps! I will upload picture a littlebit later
But still, do you have any idea, why this stage appear after when I have grind the surface and after couple of days?! Mystica!
rinx said:
What type of glue did you use? Yellow carpenter's glue is best. It is basically white PVA with Aliphatic resin to increase strength.
For a box that will not be abused this glue will make a strong enough joint on it's own. As Shaun said above, make the joints tight and clamp it properly. Screws just create too many problems with MDF.
To reinforce the joints, if you think they are not strong enough, use cleats (battens) in the corners after the box is assembled (reach in through the driver hole). Just glue these in place without screws.
Thank You,
I try to find something similar from europe also. Well, and its not very excpensive compare with white PVA I am using.
Do you have any idea, how speakermanufactures are building boxes and what glue do they use. Do they use the technic we figured out, or do they use lots of screws (actually I do not like spackle the plases - other hand it will fix excact place)
I try to find something similar from europe also. Well, and its not very excpensive compare with white PVA I am using.
Do you have any idea, how speakermanufactures are building boxes and what glue do they use. Do they use the technic we figured out, or do they use lots of screws (actually I do not like spackle the plases - other hand it will fix excact place
)
MDF + Gorilla Glue = One hell of a bond.
I glued a U-baffle together using gorilla glue. If I stand in the "U" and press out with all my strength the joints don't even give a hint of wanting to separate. If I did the same test with PVA I'm pretty sure one of the joints would have broken.
Gorilla glue does "foam" some while it's curing, but since most MDF gets painted anyway it's no big deal to just scrape the excess off before it fully cures and then sand the rest later.
I glued a U-baffle together using gorilla glue. If I stand in the "U" and press out with all my strength the joints don't even give a hint of wanting to separate. If I did the same test with PVA I'm pretty sure one of the joints would have broken.
Gorilla glue does "foam" some while it's curing, but since most MDF gets painted anyway it's no big deal to just scrape the excess off before it fully cures and then sand the rest later.
I think that some of the views expressed here about PVA glue are unnecessarily paranoid. I have never had a butt joint fail since I've been building speakers with MDF and PVA glue. Consider the operating conditions of the box (PA or home Hi-Fi?) and build accordingly. Appropriate technology.
Shaun said:
Fine woodworking did a glue test a while back and their results were that a PVA glue like titebond III resulted in stronger joints than any other tye of glue including epoxy and pulyurathane like Gorilla glue.
Here is a link to the audio junkies site where they summarize the report from fine woodworking.
http://www.audiojunkies.com/blog/346/best-wood-glue-wood-glue-showdown
Regards,
Dennis
rinx said:I understand to use corner batten, like Andrew is suggesting. I have done it for PA speakers, but to start using it for tower-speakers its not for me best solution:
1) it takes too much time for every speaker (its faster without it)
2) still I believe some other option.
So, what do you think something about that:
I am using router to cut half of the edge and glue it like it shows (bold lines) and use screws 4mm and longer (50 f.e). of course I am gonna drill 3mm hole.
ps! I will upload picture a littlebit later
But still, do you have any idea, why this stage appear after when I have grind the surface and after couple of days?! Mystica!
If you are talking about using a joint where there is exposed endgrain of the MDF, the endgrain takes on moisture and expands and contracts differently than the surface of the MDF which is why you still feel the joint even though you thought you had sanded it smooth. I normally veneer all my speakers so this isn't an issue. If you paint the cabinets, it will be.
As other posters mentioned there are probably a number of threads here and on other sites about dealing with this.
Regards,
Dennis
Shaun said:
I, for one, was talking about yellow carpenter's glue (link posted above). This IS PVA glue, but it has aliphatic resin added for extra strength and moisture resistance.
I have used polyurethane glue for projects that will see a lot of moisture (a maple butcher block and outdoor projects, including speakers) and it is very strong. The drawback is that it takes a long time to cure and you need to be just as careful about clamping it as the PVA glue, except for longer.
For 99% of the things you would build, yellow wood glue is the easiest and best choice.
You could always try a biscuit joiner. Makes lovely flush joints, lots of glue area.
An externally hosted image should be here but it was not working when we last tested it.
I use Titebond Original, I assume this is no.1? Either way, when destroying or altering some boxes, usually the MDF rips away from the glue rather then the joint breaking. In other words the Glue joint is stronger then the MDF itself.
Glue + clamp is all you should ever need for normal domestic applications.
Glue + clamp is all you should ever need for normal domestic applications.
theAnonymous1 said:
Yep. That thread was about sealing MDF. I'm currently building some speakers using translam, and the MDF edges are exposed from top to bottom. I don't yet know how I'll be sealing the outside, but I have used acrylic roof sealer painted on the inside.
Another way to somewhat overcome the MDF edge expansion issue is to use 45 degree joints. I forget the name for this joint, but it is done by making a 45 degree bevel on the edges, such as used in picture frames.
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