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Old 18th June 2008, 02:33 PM   #11
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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.
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Old 18th June 2008, 02:59 PM   #12
Shaun is offline Shaun  South Africa
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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.
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Old 18th June 2008, 03:08 PM   #13
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I think the bigger issue he is having is the joint eventually showing even after going over it with spackle. This has more to do with the properties of MDF and not necessarily the joining method. I believe there is a fairly large thread around here about this specific issue.
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Old 18th June 2008, 03:21 PM   #14
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Quote:
Originally posted by Shaun
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.
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...-glue-showdown

Regards,

Dennis
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Old 18th June 2008, 03:28 PM   #15
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Quote:
Originally posted by rinx
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
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Old 18th June 2008, 03:38 PM   #16
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Quote:
Originally posted by Shaun
I think that some of the views expressed here about PVA glue are unnecessarily paranoid.

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.
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Old 18th June 2008, 04:32 PM   #17
badman is offline badman  United States
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Default Second the yellow wood glue

Quote:
Originally posted by djarchow


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...-glue-showdown

Regards,

Dennis

My best results have been with Titebond II, which I've found to be bettter than I or III or urethane glue.
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Old 18th June 2008, 06:24 PM   #18
chiily is offline chiily  United Kingdom
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You could always try a biscuit joiner. Makes lovely flush joints, lots of glue area.

Click the image to open in full size.
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Old 18th June 2008, 06:39 PM   #19
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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.
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Old 18th June 2008, 07:05 PM   #20
Shaun is offline Shaun  South Africa
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Quote:
Originally posted by theAnonymous1
I think the bigger issue he is having is the joint eventually showing even after going over it with spackle. This has more to do with the properties of MDF and not necessarily the joining method. I believe there is a fairly large thread around here about this specific issue.
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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