Driver mounting hardware

[palmtree]

Actually got some cabinet building done this weekend. After my Jasper jig mishap last time I had to build a homemade jig which seemed to work just fine. I will post some pictures after lunch--it seems my SD card has died. It was an all out clamp-o-rama.
My question is about driver mounting hardware. I bought the 1/4" kit from parts express but now I see that there is no way they are going to be long enough. With 2 layers of 3/4" MDF and some 1/4" plywood on the inside and the thickness of the cast frame on the RL-p15 the 1.5" bolts are going to come up short by quite a bit. What have you guys used in the past for a set-up like this?
Thanks

[---k---]

I took the t-nut to Ace Hardware and bought the matching 3" long hex bolt. It is silver and not black, and easy to over torque and break the t-nut free, but if you're gentle, it works.

[dlneubec]

I'm not sure what you are using on the other end of the bolts, but I would think a 1/4" to 3/8" counterbore, for the whatever kind of nut you are using, might work.

[palmtree]

I have t-nuts planned on the other side. Thanks for the info guys.

[oxcartdriver]

I used 3 inch bolts into t-nuts, mounting a rl-p15 in 2.25in (2x 3/4 BB, 1x 3/4 MDF). There was no recess for the rl-p15, only a through hole. I found 2.5in to be to short and only grabbed the t-nut with a few threads. With a driver recess one could probably use 2.5in.

I used the parts express premium/deluxe t-nuts in 1/4 inch, and the 3 inch bolts were stainless. I went to my personal max the torque limit with a screw driver, and then used a rachet with a screw driver socket to raise the torque a bit more. Yes there are limits, but the deluxe t-nuts seem to go a bit deeper and the stainless bolts take high torque levels. Compared to the costs of the driver the premium t-nut and bolt costs were minimal.

[Martyn]

As an alternative to T-nuts, you could counterbore the inner face of the baffle and then press and glue nylon-insert lock nuts in the counterbores...

[---k---]

Also, in case you haven't seen the warnings else where - T nuts do not hold well MDF. It is easy to over torque the bolt and rip the t nut out of the MDF, then you are screwed. It is best to glue small scabs of plywood on the back and then pound your t nut in the to plywood.

Some people also just put gorrila glue on the t nut and claim success.

[steve nn]

I don't know why you guys even bother with the T-nut's?? Sure they look fancy-dancy, but a good 2.25 - 2.50" course thread wood screw is overkill and five times faster not to mention cost. What am I missing except for a nicer looking pic :P

[kirknelson]

Ability to remove and replace the driver if necessary and that wood screws don't hold very well in MDF.

Has anyone used hurricane nuts? How do they do in MDF?

I guess one could always just counter sink and glue a plain ole nut and washer back there. As long as it's glued to the MDF it shouldn't fall in if/when the driver is removed.

[dynamowhum]

Another alternative is to build the front baffle with baltic birch plywood. You could then use wood screws and not worry about them coming out.

[steve nn]

Ability to remove and replace the driver if necessary and that wood screws don't hold very well in MDF.

That's just not so. I have removed and replaced some drivers into subs up to 20-25 times with no problem at all. Wood screws do great in MDF if your just as careful with them as you are with T-nuts not to strip the threads. Especially if you back the baffle with ply and use longer than your standard 1.25-1.50" ct screws. I got some 1.50" No. 9 course thread that I seriously doubt you could make strip with a screwdriver and they're only 1.50". I don't mean to rant, but that's the way it is.

[Dennis H]

I'm with Steve. Squirt a little yellow glue in the screw hole and it will harden the MDF nicely but not stick very well to the screw if you ever want to pull it out. If you do strip out a hole, yellow glue plus matchsticks or toothpicks will make it as good as new.

[steve nn]

If you do strip out a hole, yellow glue plus matchsticks or toothpicks will make it as good as new.

I just about came back to say the very same, but I'm glad you did instead Dennis. That's all it takes if a guy does by chance mess one up. He can also elect to move up a notch in screw diameter. It just hardly ever ever happens if you set your torque correctly and predrill small.

[nick77]

I don't know why you guys even bother with the T-nut's?? Sure they look fancy-dancy, but a good 2.25 - 2.50" course thread wood screw is overkill and five times faster not to mention cost. What am I missing except for a nicer looking pic :P

Boy I have to agree Steve. I have removed drivers also and just for saftey I went up a size but dont think it was neccessary.

[oxcartdriver]

Its good to know the functionality of screws as I have to dis-assemble a few speakers to glue in in the cross overs (originally velcro'd during development and testing) and get the cabinet veneer applied.

I would still choose t-nuts for mounting a sub driver of my own, but if cost were a consideration I would now (based on above) use screws. Another advantage of screws is that one could potentially due a full circumvential taper on the back of the driver through hole. With t-nuts I could only round the regions between t-nuts..

[Hank]

If you are intent on using T-nuts, then put good epoxy into the holes and around the "spikes" after you pound them in. I've done that for subs/guitar speakers. For drivers that may be subject to removal/reinstallation, I MUCH prefer threaded inserts. My 1/1/2 cents.