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MDF edges and screws
MDF edges and screws
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Old 20th June 2008, 06:42 AM   #31
Shaun is offline Shaun  South Africa
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I like using biscuits for the alignment benefits and easier setting up. That is the only (but not insignificant) advantage I see compared to not using it. For me, the term "biscuit joint" is misleading. As per chiily's comments, correct gluing and clamping are still required.
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Old 16th August 2008, 02:37 PM   #32
critofur is offline critofur  United States
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Post Toughen your MDF screw holes?

I have a biscuit jointer, I have a nice brad nailer and a nice big compressor, and I have a lock miter bit.

If you're producing quantities of speaker cabinets, the brad nailer is a godsend, it's SOOOO much faster and easier than clamping.

One problem with using the brad nailer: I think the brads would dull router bits fast? The last pair of speakers I put together (for myself) with the brad nailer I later realized I wanted 3/4 roundovers on the front edges. I'm hesitant to route the edges with the brad nails in them...

I thought the lock miter bit would be cool, but, I haven't tried it yet because: I don't want tons of MDF dust. If you are worried about the glue joint showing through the finish (and that does seem to happen in most cases, eventually, from what I've seen others post), then the lock miter joint would be a good option (unless you're going to do roundovers?).

The biscuit joiner ~ hmm, If I was building furniture, I would definitely use it. If I was building PA speakers for road use, I would use it there too. But for home speakers I usually just glue and clamp with yellow wood glue. I prefer to use the white Titebond Molding and Trim glue: http://www.titebond.com/IntroPageTB.....asp?prodcat=1 because it doesn't drip and it dries fairly quick, the stuff is a real pleasure to work with compared to other messy, drippy wood glues, but, it costs more so I don't use it as much as I'd like to.


- but -

The point of my post is something entirely different, I was searching for "screw" + "MDF" because I've thought of something potentially very useful for MDF speaker cabinets:

When mounting drivers on MDF baffles it's easy to over-tighten and strip the MDF so the screw just spins. This is particularly true if you are removing and re-mounting the drivers multiple times. I was trying to think of an easy solution (including situations where it's not convenient to use T-nuts) and I think I've got it: I'm going to use a little syringe to put thinned polyurethane into each screw pilot hole and let that harden before putting in the screws. I think that will toughen up the MDF sufficiently?

I'll use 50/50 thinner + poly so that it will soak in readily.
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Old 16th August 2008, 03:36 PM   #33
richie00boy is offline richie00boy  United Kingdom
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MDF edges and screws
Just fit threaded inserts, if you find t-nuts too difficult. Have a look at http://www.modelfixings.co.uk/threaded_inserts.htm You can get flanged or non-flanged versions. I would think the non-flanged ones would be just what you need.

As for the original problem of the joints showing and general assembly, I agree with MJL that cleats are just not needed, butt joints with glue are fine. Shock breaking an MDF joint I guarantee you will not happen. If a loosely nailed and PVA glued large MDF box can roll around in the boot of a car whilst crashing and rolling down a carriageway from over 70 MPH and nothing at all happen other than being chewed up and smashed in on the corners then I think that says it's good enough to me.

The only reason to use screws is if you can't use clamps. I'd rather use clamps then I can roundover the edges if I want. And of course I don't have to mess about drilling holes. Screws create yet another different surface that can show lines as well.

The lines appear because of different expansion properties. The whole box inside and out needs to be sealed properly.
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