Wood screws vs wellnuts vs T-nuts

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I also have a 3-way cab that's unfinished MDF and very solid (the vendor is professionally a triple glazed window manufacturer) - from ebay. 25mm front but not predrilled so T-nuts are out.

Why do you think they are? Just drill holes of suitable diameter, fix the T-nut to the inside per Hand, and secure it, one after the other, using a screw that pulls them into the wood.


OTOH, I've made the experience that common machine screws work very well in MDF even without nuts, unless you're planning to losen the screws too often.


Best regards!
 
… I was hoping to make something that would allow driver removal for maintenance…

In that case I would certainly recommend using threaded insert nuts. It is what they were invented for, after all. Just make sure you get the ones designed to go into wood/MDF (rather than into plastic or metal).

Once in, they stay put, and you will never again have to worry about stripping or breaking up the MDF when you screw/unscrew a driver. If you reinforce the edge of the driver cutouts you will make the job of drilling the holes and fitting the inserts easier (painting with diluted wood glue [PVA] will do the trick; make sure you allow it to dry completely before continuing).

Use a drill stand to drill the holes so the drill cannot wander about, and use a proper wood drill bit (one with an inverted V face and a guide tip) of the right size for the inserts. Lower the drill slowly to prevent tearing the MDF apart.

If you use inserts that take an Allen or Torxx driver for fitting, you can put the driver bit in your drill stand chuck and _slowly_ help the insert on its way into its pre-drilled hole to make sure it goes in straight. If you don't trust the drill to do it slowly enough, turn the chuck by hand. If you can only get inserts for a slotted driver, instead of the driver bit fit a length of threaded shaft into the drill chuck onto which you screw a nut followed by the insert. Tighten the nut against the insert, start the insert on its way, and when you are done, undo the nut a quarter turn (using a spanner tapped with a metal hammer so as not to disturb the insert) and unscrew the threaded shaft from the insert.

As I noted in my earlier message, the great advantage of inserts (apart from the easy maintenance part) is that you have a wide choice of good-looking and safe, slip-free fasteners (i.e. Allen or Torxx rather than Pozidriv, or even worse, Phillips). It only takes one slip of the screwdriver bit to ruin a speaker surround.

Another advantage of using screw inserts is that you can fit them from the front without any need for access to the rear of the baffle. You could even fit them into the front-facing edges of the top, bottom, or sides of the cabinet, should you want to. And you can use them in otherwise fully finished cabinets, too. I should know, because I have.

One more advantage of using inserts is that there is no need to drill all the way through the baffle (provided, of course, that the baffle material is thick enough). This avoids air leaks (of minor consideration, I think, since the speaker mounting bolts will provided enough of a seal anyway), but more importantly, it avoids weakening the edge of the driver cutout too much before you fit the inserts.

Oh, and do practice on a piece of scrap MDF. @;-)

HTH,

Marcus
 
Why do you think they are? Just drill holes of suitable diameter, fix the T-nut to the inside per Hand, and secure it, one after the other, using a screw that pulls them into the wood.

I was thinking about this earlier on the train as it happened.

I had assumed that for M5 bolts, I would drill a 5mm hole and drill out the back to 6mm diameter to 8mm depth and that this can only be done prior to installing the front of the cabinet.

But I guess I could drill 6mm all the way through.

So indeed yes it was an assumption.
 
So, nobody’s ever had a T-nut go loose enough for the spikes to completely disengage from the material core while still threaded on the machine screws? When as close to the driver opening as they could be here, you might not get all of those little spikes to engage. I’d only ever use them when I could easily get access to the backside of the panels.
Use threaded inserts if you want, but I’ll ask - what type of maintenance are you envisioning that would require frequent removal of the drivers? If you blow up any driver more than once, there are other problems to solve, I think.
 
I'm with chrisb! The main problem with T-nuts is over-tightening them, which can make them chew up materials such as MDF and chipboard,

The more often they are unscrewed and tightened back up again, the more the likelyhood of them failing and leaving you in a dilemma!
 
So, nobody’s ever had a T-nut go loose enough for the spikes to completely disengage from the material core while still threaded on the machine screws? .


Has only happened to me twice in 20 years of playing about with speakers. The speakers had been used for 11 years before I tried to unload the drivers. 2 t nuts stripped in mdf. A screwdriver gently levered against the chassis pulled the t nut spikes tight enough to undo the bolt. The t nuts were fitted with a good blob of glue when I built them.
 
So, nobody’s ever had a T-nut go loose enough for the spikes to completely disengage from the material core while still threaded on the machine screws?

Yep, my name is Nobody. @;-)

Mind you, I have never used them in a speaker cab. If I ever were to, I would make sure they could not go off on their own, by glueing or taping (or whatever) them in place.

When as close to the driver opening as they could be here…

Which is exactly why I do not like to use them. They offer a cheap and cheerful solution, but not in this case. MDF is very useful stuff, but T-nuts necessarily put the material into compression, which will cause it to crumble when near the edge. Simple screws and inserts don't and won't.

Use threaded inserts if you want, but I’ll ask - what type of maintenance are you envisioning that would require frequent removal of the drivers?

I think the OP was thinking in terms of experimentation rather than maintenance, which might involve multiple unscrewing/rescrewing sessions (yes, I've been there). Hence my suggestion of using threaded inserts to avoid wearing out the base material.

BTW, I agree that in some cases simple screws will suffice (provided they are suitable for use in MDF), but I think the added luxury of being able to choose nicer screws plus the ability to unscrew/rescrew them time and time again without the risk of damage outweighs the – very slight – added expense and effort of using inserts.

Marcus
 
I’ll ask - what type of maintenance are you envisioning that would require frequent removal of the drivers?

At very least, I was going to make sure I can fit the drivers, and only when that's all OK will I add extra bracing, stuffing, deflex or whatever. (And changing the stuffing might be more than once). And only when I think the sound is going to be reasonable, remove the drivers for finishing the outsides of the cabinet.
 
Try these style-

Knife_2.png



https://www.ezlok.com/e-z-knife-inserts-for-hard-wood


Worst case, drill the holes for them all the way through, put a stud through both sides of the MDF, and throw a lock washer and a cap nut on either side.
 

PRR

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Joined 2003
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Nobody uses speaker clamps?

They grip the edge of the driver but the bolt goes an inch+ outside the hole. It was THE way to mount PA drivers when I was in the racket. No strain at the hole-edge, easy to remove front-mount drivers quickly. Clamps do not have to go where the speaker holes are.

Penn-Elcom G0727/NO Speaker Clamp Only 4 Pcs.

Grill Clamp Kits in the Speaker Components Department at Parts Express | 316
(Some of these are grille clamps; PartsExpress can't tell the difference.)

Ah, those are plastic.
US Speaker Parts- Speaker cabinet hardware
Halfway down, "G0790 NEW Speaker Clamp Heavy Duty $2.15"

Also, JBL MA15 Speaker mounting kit is the real deal and can be found on secondary sites.
 
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You can use a router to make a 2mm deep well for the t nut to sit in so it is flush with the back of the baffle before you glue the baffle on. Cut down the mounting bolt so it doesn't poke out the back of the t nut and you should be good to go.

Sure and for the smaller Wilmslow cabinet that seems to be the way to go. I'm not sure I need 2mm (seems less I think according to my calipers, but I guess its safe) - and QTA sell 20 and 25mm long M5 bolts.
 
Note that some speaker clamps are thin plastic, and really intended for holding surface mounted metal grilles, and note that lower down on the page linked by PRR above are woodscrews that are close to the sheet metal types I suggested above. They are similar to one’s I’ve bought from both Parts Express and Solen. The SK8 roundheads would be great for either the clamps or, provided the head clears any recess in the driver frame, the woofers directly.
 

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