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Old 17th March 2012, 12:58 PM   #1
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Thumbs down Cracks in Sub box bracing.

I am building a sealed sub box with dimensions of 20" H X 30"L X 30"W. I am using 1" MDF all round and a 2" MDF baffle and 1" MDF bracing with cutouts. I using the glue a screw method as I don't have clamps.

I started on the bracing today even though the holes are pre drilled I am getting very little cracks in the MDF after I have screwed the screws in. It is only on the bracing that this is occurring.

I was wondering if this is going to affect the integrity of the box? They are also glued, so I was thinking that it won't make a difference, but I thought I should ask the experts anyway.

Cheers

Dave

Edit: I am using a single 18" TC sounds LMS Ultra driver

Last edited by JapanDave; 17th March 2012 at 01:51 PM. Reason: Added sub specs
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Old 17th March 2012, 04:14 PM   #2
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Quote:
Originally Posted by JapanDave View Post
I am building a sealed sub box with dimensions of 20" H X 30"L X 30"W. I am using 1" MDF all round and a 2" MDF baffle and 1" MDF bracing with cutouts. I using the glue a screw method as I don't have clamps.

I started on the bracing today even though the holes are pre drilled I am getting very little cracks in the MDF after I have screwed the screws in. It is only on the bracing that this is occurring.


Dave

Edit: I am using a single 18" TC sounds LMS Ultra driver
The cracked material may buzz at high power.
Since the cabinet is sealed, the buzzing may not be audible, but the cracks may get worse under hard use, and become audible.
If the material is cracking, the pilot hole is not large enough.

Injecting glue or caulk into the cracked areas would be a fix.
Printer cartridge refill syringes work well for that type of fix, drill a hole the size of the syringe "needle" and inject until the crack cavity is filled.
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Old 17th March 2012, 08:58 PM   #3
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The other reason that it is cracking is that you are screwing into the "end grain" of the board. MDF doesn't actually have a grain, but the ends do split more easily. A couple pipe clamps would only set you back about 30 bucks or less, and would be the best thing to do. And lots of glue! (wipe off the squeeze out) Jim.
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Old 17th March 2012, 09:28 PM   #4
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Sounds like you need to up the pilot hole size.
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Old 17th March 2012, 10:16 PM   #5
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I should have also mentioned the proper screw to use for MDF is a "Confirmat" screw. There is a special drill bit that corresponds with the the size screw you are using. Available from woodworking stores like Rockler, or Woodcraft. If you needed them in bulk, then someone like Mcfeeley's online is a well respected supplier. Hope this helps. Jim.
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Old 17th March 2012, 10:53 PM   #6
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I am in Japan, so I don't have those stores you are talking about. But , I am sure I can get some somewhere.

Looks like I am going to start from scratch.

The braces are not that good anyway.

Can anyone tell me how much wood needs to be taken out of a brace to allow good air flow of a sealed box? Eg, in a piece of MDF that is 30"H X 20"W. This would work out to a surface area of 600 Sq Inches, does the surface area of the brace need to be say under 300 Sq inches?

@Cal Weldon , I am already getting slippage when screwing, as the screw stops biting and does not seem to grab anymore. Maybe I am using the wrong screws?

Last edited by JapanDave; 17th March 2012 at 10:59 PM.
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Old 18th March 2012, 12:04 AM   #7
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Where at in Japan? I know a Canadian transplant on one of my wood forums that runs an L shop in Tokyo. Depending on where you live, he might know some places to find them. I'd be happy to ask him. Jim.
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Old 18th March 2012, 12:28 AM   #8
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I live in Osaka. But, most shops sell over the net, so it still might be worth a shot.

BTW, what is a "L" shop?
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Old 18th March 2012, 12:40 AM   #9
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Liquor shop. He went to Japan maybe 20-22 years ago to study martial arts, fell in love with a local, and this is her family's business that Stu is running now. I'll PM him and see what he knows. Jim.
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Old 18th March 2012, 01:02 AM   #10
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Thanks, looks like I am starting from scratch. This time hopefully I can do it right.

I have also lived here for nearly 20 years.
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