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Those would probably work well if you were screwing into the flat section of the MDF sheet. I have never had a problem there. The problem is when you screw into the end of the sheet as I did on the layered egg construction. Behind those holes which were created with a pilot drill was the interior opening of the egg. Therefore there was only a little over an inch of material. Although I never had a problem before it made me realize how close to problems I had been in the past and decided against wood screws. When mounting drivers on the flat surface of the inside of an enclosure I always glued backup pieces of scrap MDF to increase the thickness of the wood at the mounting surface to prevent splits. There is no need for screws for the main assembly if you use biscuits and with them no need to fill surface holes. Also, with driver mounting the machine screw inserts allow many insertions and removals of the screws without having problems with holes enlarging as is often the problem with wood screws. Lots of different methods that work depending on the individual situation.

To follow up, designers of knock-down furniture made of MDF have more control over the design of joints, grade of MDF, backed up against assembly and stress tests in the lab in order to refine what will work reliably given the jointery demands. As DIYer trying to get it to work right first time (so it does not have to be re-made), need to be more wary of endgrain spltting, which cheaper MDF grades (like the Georgia-Pacific MDF) that one gets from Home Depot. Many MDF & Particle Board construction screws that claim to require no predrilling really only work cross grain, not end-grain. Even pre-drilling endgrain will cause splits since the fibers are so much weaker in tension than compression. That many of these screws are flat-heads means you are driving a wedge into the grain.

Agree that the best solution is use biscuits, dowels, etc. with glue for endgrain joints in MDF, or use wood battens glued to the MDF if you need to have a removable panel (screwing into the batten, not the MDF). Nothing else is reliable enough to hold without potentially destroying the work.

Nails as registration pins worked great. The pictures show the clamp extenders I made for gluing the top and bottom on the enclosures. Worked like a charm.

Looks like this weekend I start patching, sanding, and sealing the cabinets.

David

Very cool idea with the clamp extenders. Another one of the many fixtures you need to build with a complicated project. Glad the nails worked.

Router Fun!

I patched and routed out the edges of the cabinets over the weekend. For patching I used Bondo wood filler. The pot time on this is a few minutes, had to mix up a couple of batches just to do the face of one speaker cabinet. However, it sanded down nicely and really holds a good edge, better than any other wood filler I have used. For routing, I used a 30 degree bevel bit on the front (and back) baffle, and 45 degree on the top and bottom edges. Need to do some hand work to cut faceted corners. Should start final filling and sealing of the raw MDF edges later in the week.

David

Looking good. That bondo filler is what I also used on the eggs. Great stuff.

Clever clamp extenders. Impressive project, looking forward to hearing them.

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I took the day after my birthday (Wednesday) off to work on the speakers (being stuck in a 6-1/2 hour meeting on my birthday was no way to enjoy it). So I patched, sanded and finally applied shellac as a sealant on the raw MDF. Used wax-free clear shellac (Zinsser Seal-Coat). The MDF really soaked up the shellac, I went through a quart of the stuff, with two coats on each of the MDF edges and a single coat on the flat surfaces. I could have used another quart, I think. After it dried, I sanded the surfaces down with a 180 grit sanding disc, and they turned out pretty smooth.

I decided to use Duratex to paint the cabinets, based on my satisfactory experience with it on a another project. It drys and cures super hard, and tends to cover-up minor surface imperfections. I like using a fine foam roller to apply to get a relatively smooth (matte) surface rather than the highly textured surface used on road cabinets. I bought a gallon of white spray grade (based on reports of it being easier to apply with a smooth foam roller) and tinted it to a blue-grey color using concentrated Cal-Tint lamp black and blue liquid tints that I picked up on Amazon (I have lots left if anyone wants to experiment). I just added equal amounts of the black and blue tints to get the desired color. After thoroughly mixing with a drill powered impeller (trying to avoid splattering the paint all over), I let it sit a day. Last night I painted the first coat on all but the back surface of the speakers. Really easy to get a smooth (fine textured) surface with no overlap marks. This is the initial coat, which will probably be sanded down before applying the next coat.

David

Can't wait to hear these! Color looks very cool! I went back and did a big double take while looking at the impedance and phase curves. Usually in my field, when you see something that good, it is a result of fraud!

Just finished with all the painting as of a day ago. Working on the crossovers (done, actually) and wiring harness. I hope to start assembly of the speakers on Sunday, finishing over the next week. So expect to have them in the system by next weekend!

Now need to go down to the basement and cut and tin lengths of Cardas 15.5ga litz for the internal wiring. Will use a smaller gauge for the tweeter, however, the terminals are pretty fragile looking.

David