MDF box, what kind of screws to use?

Im building a 3/4 mdf box and im wondering what you guys would recommend using for screws. i tried using #8 1-1/2 and predrilling with a standard 7/64 drill bit, but that split the wood. Is this a good size screw to use and i just need to do a larger predrill? if not recommend a different size screw and predrill hole. would a countersink bit make a big difference?

also, what would be good placement for the screws?

8 is too big, you need to be using a 6 with a 7/64" predrill. Also try switching to a 1+1/4" long screw.

The screws are pretty much just there to hold the box together until the glue dries, so you don't need too many of them. I always countersink and just be careful how much you tighten them down. No need to go crazy and crack the mdf, just make them nice and snug where you see a little bit of glue ooze out of the seam.

I've always used a brad nailer.  Its alot easier then predrilling and using screws.

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TEX

I would have to disagree about the screws being only useful for holding the box together for the glue to dry. The screws will also help keep the box from falling apart should the glue not be applied correctly, or not enough being used. The type of glue used could also be a factor. True, it shouldn't take many screws to help hold things together, but they should be used regardless, IMO.

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1-1/4 isnt going to give the screw much to hold on to once it goes past the 1st board, anyone else this ?

correction: anyone else recommend using the #6 1-1/4 screws?

Thats' all I ever use when dealing with 3/4" MDF. I've built a lot of boxes this way and never had a problem. If you use the proper type glue, and proper amount, you can place your screws about 6" or more apart. If you're not too sure about your glues holding power I wouldn't  space them farther than 4" apart.

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Gettin' deafer by the day.......96' GMC yukon-Eclipse CD 5442HU
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spread the glue then shoot some brads in it. 

The glue is much stronger than any screws, brads, or even the wood itself.  You only need the screws or brads to keep the wood tight together until the glue dries. Once it dries it's not gonna fall apart.

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TEX

A tip for making the best bond:  Clamp with many large clamps as hard as you can with glue.  Wait a couple minutes, tighten the clamps a little more, and then screw. 

I make my speaker enclosures without any screws.  With enough clamps and careful planning screws are unnecessary.

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New Project: 2003 Pathfinder

whats the minimum distance i should keep the screws from the edge of the wood (so it wont split)? Oh, im using Liquid Nails ultra quick grip construction adhesive,. Is this the best liquid nails adhesive for this application?

davidh_r wrote:

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whats the minimum distance i should keep the screws from the edge of the wood (so it wont split)? Oh, im using Liquid Nails ultra quick grip construction adhesive,. Is this the best liquid nails adhesive for this application?

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Depends on the temperature and the exact brand of MDF you have. 

Experiment.  Predill slightly undersized holes if you are concerned.

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New Project: 2003 Pathfinder

You need to have the screw centered on the vertical board. So basically you need to be predrilling your holes ~.375" from the edge (1/2 of .75") for 3/4" MDF. Line the horizontal board up with the edge of the vertical board and predrill away.

I realize you need to drill in the middle of the vertial board, but im talking about how far away from the edge you should stay from