Anyone have experience or preferences for securing screws in MDF? ie: T-nuts, hurricane-nuts, threaded inserts, etc. I want to re-do my box top (5/8" MDF with 3/4" MDF ring) to accept a new 12" driver and this time be able to remove/install the sub later without stripping out the MDF.

Thanks

 

Predrill holes &/or hammer in t-nuts ..

some ppl use epoxy to hold the t-nuts in too

 

Thanks Dave, I was able to get some T-nuts in tonight by pre-drilling the holes like you said, and then I also used a C-clamp to push them in. Worked well!

 

Glad it turned out well for you. Be sure to test them out a few times before you use them on the final run. (Make sure they STAY)

Also .. make sure they are clean so you don't get locked threads & ruin a t-nut hole.

 

Actually, if you've got an air compressor, a 2-inch air stapler used for building furniture was the best tool I've ever used for box building. Really simplifies the process and cuts the box building time in half. No pre-drilling and counter-sinking and it's just as secure as screws IMHO. Otherwise, 1.5 - 2-inch wood screws pre-drilled and counter-sunk. The latter is quite important. So what's up Dan, you gonna show us some pix or what? Guess that's the pot calling the kettle black...

 

I hear ya... thanks guys!
well, I made some great progress last night. Got the whole thing drilled out, T-nuts in, and ready for the top to be glued and tightened down. And then it hit me! The ring cover that connects to the sub top and hides the screw heads has an MB Quart label on it and it needs to be aligned with the front of the box. In my haste I didn't even think about that and it was lop-sided!

So today I have to remove the (8) #10 1 1/2" machine screws holding the sub/ring/MDF and the T-nuts. Somehow fill in the screw holes, and drill out 8 new holes. What a waste of time! Well at least I got the other 15 screw holes (that hold the top to the fiberglass bottom) all ready to go and counter sunk (King Dremel to the rescue!).

I should have some pics by the weekend, I'm a slacker about batteries for the cam. I also got a Kenwood KDC-X879 head unit in yesterday which will be another adventure.

 

What do you guys recommend for internally sealing MDF to fiberglass? Besides numerous screws and wood glue to hold the top down tight, I want to use a bead of Silicone II inside...good enough?

 

liquid nails or silicone is good, but make sure to air out silicone for at least 24 hrs before putting the sub anywhere near it .. the fumes are corrosive.

 

What dremel tool did you use to do countersinking?

The way I picture it is you use a small bit and predrill the hole then use a very large bit (the size of the screwhead?) and go in 2 mm for the "countersinking"....

But I am getting a dremel today.. so any help?

 

Home Depot sells countersink bits. It's like $5 and totally worth it. The bigger bit will attempt to drill through whatever you are using it to countersink. I've messed up some projects doing that. I'd just spend the $5 for the peace of mind, but then again I'm addicted to tools. Good luck!

 

Wow, I never knew that. What degree of 'corrosive' does it exhibit? I'm sure it won't eat through your woofer, but will it damage a spider or something? I'll keep that in mind when I build my next box. Thanks for the info Dave! Guess you learn something new every day...

 

Yeah, I wish I had known about that last night! Oh well, I'll take the sub out and let it air out a little more.

Regarding the counter-sink..I also wish I knew about the special bit because getting it to look perfect was painful. The dremel will only hold a bit to a certain size so you will likely need to use a real drill too. I tried to use the larger bit 2mm down technique and it didn't really work well, doesn't create a V type groove just straight down. I ended up using the dremel to sort of route out the sides to a V pattern. I also used oval top counter-sunk screws which seem to be more foregiving and don't look so lopsided if not in the hole perfect.

Be careful when drilling the holes too. A large bit can tear up the underside of the MDF you are drilling. I found using a pilot hole with a smaller dremel bit and then drilling slowly with a larger bit helped. The T-nuts worked like a champ.

 

I was out testing the sub last night. Someone in the neighborhood (kids) left a large rock out in the middle of the street. Stupid Dan drives right over it without seeing and it did a number on my muffler and maybe some of the metal bracing under the car! I'm ticked..this stupid rock is only about 5" tall and it sounded like I was running over a boulder!

 

Use the same cloth and fiberglass and just overlap the MDF to the fiberglass. That is how I did my box and it it working great. It is a little hard to work through the hole, but worth the time I think.

Before glassing MDF, picture.

After glassing MDF, picture.

With this you not only get a ton of strength at the seam but it is also 100% air tight. And if you just use silicone then you run the risk of the mdf flexing away from the fiberglass with the silicone give that you get (silicone is rubbery so it isn't rigid). So if you go the silicone route you will still need a rigid fastener for strength.


Here's a good info site on box stuff
http://www.jlaudio.com/tutorials/boxdesign/index.html

but about the fumes, at this site JL says.....
"Fortunately, most JL Audio subwoofers have a specially treated surround that protects them from hungry acetic acid fumes which is cause #1 not to be overly concerned with using silicone to seal your box. Secondly, the fumes are only released during curing (the time when the caulk goes from a free-flowing gel to an amorphous solid) so all you have to do to prevent damage to the drivers is to wait until the silicone has cured (8-12 hours usually) before dropping the subs in."


Hope all this helps out.

 

omfg, I'd be talking to some parents, 'cause that ain't cheap to fix. On the plus side, time for that aftermarket exhaust!

[stupid kids]

This would be me with their damn parents. Actually, if you wanted to replace with factory, you can usually find them in the classified section for like $50 or so. Not exactly in high demand.... Dude, kill those kids. That's not even cool. Sorry to hear that happened. Well, how'd the sub sound? Hopefully that at least was good...

 

Gundam, that's great info. I like your sub mount and glass work. I was thinking of fiberglassing to the MDF also. But my issue was the height of the box had to be exact to fit under the false floor in the wheel well. I made it fit exactly flush and level so the trunk liner has no gaps and doesn't wobble or rattle.

It seems good enough using wood glue, 15 counter screws, and then sealing a few times from the inside with silicone. Actually, my plan was to fiberglass on the "inside" with a couple strips of cloth after screwing the top down..which is probably possible since I have a small box with a large (12") hole..but I'm tired of working on it.

 

Thanks Motown. I was really mad and felt like throwing the rock through their window. I guess I just grin and bear it though, after so many years of trying to keep my vehicles looking and driving like new, I've come to the realization that driving in general is hazardous and other people simply don't care. It's ironic how much time and care we put into our cars when at any second they could be totalled in an accident and all that work goes down the drain.

I don't know if I need a new muffler or not, the dents in it are pretty shallow..probably 1/4" or a little more. Still sounds the same and drives the same..I don't know.. I'll bring it over to the dealer and see what they recommend.

I was also worried about a bend in one of the metal sections under there. Not sure of the name, but it's the large cross-member piece towards the rear that looks like two muscular arms flexing. Do you know what I'm talking about? it has circular holes in it. Anway, it is bent in a spot.

 

I can relate to that 100%!!!!!!!!!!

I want to make my box prettier, but....

With what you are securing it with you should be good. You have enough rigid constraints to support the silicone. Let me know how it turns out.

 

thanks, I'll have some pics up this weekend. It was a PITA to get the height of the box on all sides to match the drunk depth..I learned the hard way that just because it's level outside of the car, doesn't mean it's level Inside the car.

 

Here are some countersunk bits - very interesting and I love this forum for educating me everyday. Off to home depot I go to get some MDF and countersunk bits. Every iteration of my sub enclosure is tighter and better!