Best practices for fastening speaker parts

[Rick Sykora]

This topic started on another thread and was initially about creating a speaker with a removable back…

First pass at removable back failed predictably. Tried to countersink some wood screws and most stripped on the first attempt to tighten. Have some nutserts and planning to try them next. Likely need to strengthen the MDF. @carbidetooth know you suggest epoxy but thinking I need something that harden the surrounding MDF better. Maybe wood hardener or some thinned wood glue? Suggestions?

 

[cavedriver]

I have removable front baffles on the 0.5 cu ft MDF housings that PE used to sell that use 1/2" MDF. I'm using 1.25" coarse thread drywall screws in pre-drilled holes. With carefully selection of the drill size and application of torque I can get a solid connection but I will still split the MDF over time if I'm not careful. I used a countersink bit to make room for heads. I matched the hole drills to the root diameter of the screws. I used some 1 or 2 mm foam gasket on the face to ensure there were no air leaks. If the cabinet walls were 3/4" MDF I'm sure I could use this approach indefinitely. Not sure where the guy that used to make these housings for PE got his MDF but it's pretty strong. The black screw heads are of course ugly on the unfinished MDF for now but could look about as good as any other exposed screw next to any darker stained veneer.

 

[Rick Sykora]

I have removable front baffles on the 0.5 cu ft MDF housings that PE used to sell that use 1/2" MDF. I'm using 1.25" coarse thread drywall screws in pre-drilled holes. With carefully selection of the drill size and application of torque I can get a solid connection but I will still split the MDF over time if I'm not careful. I used a countersink bit to make room for heads. I matched the hole drills to the root diameter of the screws. I used some 1 or 2 mm foam gasket on the face to ensure there were no air leaks. If the cabinet walls were 3/4" MDF I'm sure I could use this approach indefinitely. Not sure where the guy that used to make these housings for PE got his MDF but it's pretty strong. The black screw heads are of course ugly on the unfinished MDF for now but could look about as good as any other exposed screw next to any darker stained veneer.

Thanks, this is questionable MDF. The reason I have spare cabinetry is that the milling was so poor, PE kept sending replacements until I got some clean ones.

 

[somebodyelse]

First pass at removable back failed predictably. Tried to countersink some wood screws and most stripped on the first attempt to tighten. Have some nutserts and planning to try them next. Likely need to strengthen the MDF. @carbidetooth know you suggest epoxy but thinking I need something that harden the surrounding MDF better. Maybe wood hardener or some thinned wood glue? Suggestions?

I've hardened MDF with cyanoacrylate in the past when I was out of wood hardener.

 

[Rick Sykora]

I've hardened MDF with cyanoacrylate in the past when I was out of wood hardener.

Do or use anything special? Found most stuff that really hardens does very locally and then just breaks free around the nutsert.

 

[Salt]

For the purpose of dismount front or back I insert a frame to the enclosure for the screws and leave the walls alone.

 

[Rick Sykora]

Am think (thinned) polyurethane might be the trick.

 

[Rick Sykora]

For the purpose of dismount front or back I insert a frame to the enclosure for the screws and leave the walls alone.

Agree, this is best except am trying to keep it a C-Note as much as possible and may it easy to place damping panels.

It may come down to some added framing though.

 

[ryanosaur]

Agree, this is best except am trying to keep it a C-Note as much as possible and may it easy to place damping panels.

It may come down to some added framing though.

It seems like you are just trying to recreate the old finished Dayton Cabinets from PE with the removable front baffle. This only have four screws in each corner. Perhaps a block inside each corner of the cabinet which you can screw into, perhaps even using threaded inserts to mate it easier to remove the panel for various testing purposes...

 

[carbidetooth]

First pass at removable back failed predictably. Tried to countersink some wood screws and most stripped on the first attempt to tighten. Have some nutserts and planning to try them next. Likely need to strengthen the MDF. @carbidetooth know you suggest epoxy but thinking I need something that harden the surrounding MDF better. Maybe wood hardener or some thinned wood glue? Suggestions?

Kinda depends on what you started with. Pithy core MDF is never gonna be great to work with if "removable" is the target. I have tested inserts to some extent with a single #8 insert and screw in the face of Ranger Board high density MDF. Held 25 lb. bag of shot with no issues. The only way to know if it'll work on whatever you have is give it a go. At least that's what I'd do.
The key to consolidating core of MDF is penetration and consolidating material viscosity and strength. Penetrating epoxy would be my first choice. Cyanoacrylate (Super Glue) second. Some sort of hardwood inserted in edge perhaps third, but not sure juice is worth the squeeze. Wood glue would have little effect beyond the surface of material no matter what.
I may have some pithy core MDF to experiment with. Just to be certain, you're attempting a threaded insert into edge of 3/4" MDF?
FWIW, I have experimented with penetrating dye into MDF to see how far it would penetrate. Honestly, I was completely disappointed in result. Probably less than .010". With this in mind, I really think inserts with epoxy on outer diameter in going to give best result.

 

[Rick Sykora]

Kinda depends on what you started with. Pithy core MDF is never gonna be great to work with if "removable" is the target. I have tested inserts to some extent with a single #8 insert and screw in the face of Ranger Board high density MDF. Held 25 lb. bag of shot with no issues. The only way to know if it'll work on whatever you have is give it a go. At least that's what I'd do.
The key to consolidating core of MDF is penetration and consolidating material viscosity and strength. Penetrating epoxy would be my first choice. Cyanoacrylate (Super Glue) second. Some sort of hardwood inserted in edge perhaps third, but not sure juice is worth the squeeze. Wood glue would have little effect beyond the surface of material no matter what.
I may have some pithy core MDF to experiment with. Just to be certain, you're attempting a threaded insert into edge of 3/4" MDF?
FWIW, I have experimented with penetrating dye into MDF to see how far it would penetrate. Honestly, I was completely disappointed in result. Probably less than .010". With this in mind, I really think inserts with epoxy on outer diameter in going to give best result.

Thanks, it is 1/2” mdf btw.

What do you consider penetrating epoxy? Can I buy in small qty?

 

[Rick Sykora]

It seems like you are just trying to recreate the old finished Dayton Cabinets from PE with the removable front baffle. This only have four screws in each corner. Perhaps a block inside each corner of the cabinet which you can screw into, perhaps even using threaded inserts to mate it easier to remove the panel for various testing purposes...

Yes, but is the back and would require gluing wood blocks in each corner though.

 

[carbidetooth]

Thanks, it is 1/2” mdf btw.

What do you consider penetrating epoxy?

Lots of stuff out there primarily aimed at the "wood stabilizer" or "Wood Rot Fix" world. While I'm no chemist, it appears to be low viscosity epoxy. Also used in the wood boat building world. I think I have some 1/2". I'll give it a go in the next few days.

 

[ryanosaur]

Yes, but is the back and would require gluing wood blocks in each corner though.

Yes. Might not be absolute best solution; perhaps easiest functional?

 

[Rick Sykora]

Yes. Might not be absolute best solution; perhaps easiest functional?

Cannot really be done without affecting how damping sheets would be applied, but is better than fuller framing.

Am willing to deal with some maintenance before having add blocks

 

[ryanosaur]

Cannot really be done without affecting how damping sheets would be applied, but is better than fuller framing.

Am willing to deal with some maintenance before having add blocks

Of course! That’s the fun of spitball problem solving from afar, though!

 

[carbidetooth]

You piqued my interest, Rick. This epoxy takes 24hrs to cure, so we'll see how it works out. #6 insert, 1/4" hole, 1/2 material.

 

[Salt]

If suitable I prefer to use these: https://www.rampa.com/eu/en/RAMPA-INSERTS-TYPE-SKD30/43961500102500
On front of MDF this does not work, except you drill the hole in dimension of outer diameter and fix it in epoxy or you cut the thread by hand (and epoxy it, nevertheless).

 

[somebodyelse]

Do or use anything special? Found most stuff that really hardens does very locally and then just breaks free around the nutsert.

It wasn't anything special. I thought cyano would be worth a try as the viscosity was low like the wood hardener, so it might have a chance of penetrating rather than sitting on the surface, and it seemed to.

 

[carbidetooth]

If suitable I prefer to use these: https://www.rampa.com/eu/en/RAMPA-INSERTS-TYPE-SKD30/43961500102500
On front of MDF this does not work, except you drill the hole in dimension of outer diameter and fix it in epoxy or you cut the thread by hand (and epoxy it, nevertheless).

I've tried all manner of thread-in and drive-in threaded inserts and they all have shortcomings when it comes to insertion in MDF. On the flat, they create a hump because the threads displace material, and it has to go somewhere. On the edge, they tend to split the material. To make it viable, I think one would need to have a tap that mimics the exterior threads of insert.
The method I show is best I've found at not creating more problems and I suspect stronger than you might guess. If I had a strain gauge, I could test to failure. What I'll do is rig up a weight bearing test as I've put an insert in both ends of the material