Cardboard sub box w/ resin...not good

[honfatboy]

I started a new post for this because I didn't want it to get lost in the shuffle of oldloder's other post.

I had the idea of just making a sub enclosure out of cardboard for the following reasons:
1. Ease of use. I already had a box to fit the exact dimensions I needed.
2. Lack of space. Single cab Tacomas have no space behind the seat. So, I couldn't use 3/4 MDF.
3. Thought this would be easier...HA!

This box, while I'm still using it, is a wretched disaster of cardboard, MDF baffle, duct tape, foil, Great Stuff, and MDF scraps. I won't scare you with pics. It sounds like poo.

I did use 3-4 layers of mat and resin, but you would have to use I would guess about 10-12 layers on the long side of the enclosure, the cardboard even reinforced is not strong enough.

There are other issues, too. The "bread" of the cardboard box sandwich will not soak up enough resin like I thought. Cardboard = good water sponge; bad resin sponge. If you're going to do it, it does help a bit to tear off the outer layer of cardboard to get to the corrogated "meat" of the box. The ridges do soak up more and the resin can get down in the gaps.

The big probelm is how to attach the baffle for the speaker to the box. This is a very messy and time consuming process of reaching in the speaker cutout and trying to lay up mat without looking. Then you have to try and fill in the inevitable holes. That's where more resin, duct tape, MDF scraps and Great Stuff come in. It is NOT fun.

In the end, I would use something like 1/4 MDF or even the 3/4 styrofoam sheets you can find for insulation over cardboard for a structural mold. Again, though, with styrofoam you have the problem of trying to attach the baffle for the speaker. I think 1/4 MDF is the way to go and I would redo the box if I weren't selling the Taco soon.

Sorry for the long (some might say duplicate) post; but I wanted to save oldloder from the trouble and heartbreak.

David

Questions?

[AzGrower]

In the end, I would use something 3/4 styrofoam sheets you can find for insulation over cardboard for a structural mold. Again, though, with styrofoam you have the problem of trying to attach the baffle for the speaker.

the polyester resin will melt the styrofoam like a hot knife to butter...It wont hold up...

[honfatboy]

MDF it is then. :)

[mvw2]

It sounded like...fun :p

Yeah, it'll be tough to build something both thin and sturdy enough to handle what you're trying to do. It's easier if you're aiming for a light box as you can get away with a large thickness.

If you want to give glassing another try, maybe look at getting some purpose built 1/4" paper honeycomb mesh. They just lay up a couple plys of woven glass fibre for each side. It's helpful if you can vaccum or pressure seal the glass to remove excess air and resin. Some large 1/4" steel plates and a few hundred pounds of weights will do wonderfully, lol.

I'm just not sure how you'd box it all together, maybe lay up some glass along the seams to seal and hold the large faces together.



MDF is just so easy to work with though, no hassle, no mess.

I guess you could try plexiglass too, but I have no clue about stiffness properties versus thickness.

[oldloder]

Thanks for the post, David. I figured I wouldn't go there once AZ posted.

I'm gonna go with 1/2" MDF (I have some laying around), I think I can make it work. I may have to add some bracing front to back and if in the end it's not rigid enough, I'll try the the 1/4" MDF and glass it. I'd rather throw away $7 worth of MDF for the mockup if it doesn't work. :)

MVW2 : "It's easier if you're aiming for a light box as you can get away with a large thickness."
^^^^^^^^^ was the key all along.

Actually , I went to Home Depot this afternoon and I flexed a 2x4' piece of 1/4" MDF and a 2x4' piece of 1/4" pegboard. There really wasn't a whole lot of difference. Maybe with the resin filling the holes it would give an extra bit of strength ... could be an interesting expermient.

How long ago did you try it?

[ryanlloydmiller]

AFAIK, resin has nearly no inherent strength...point being: filling holes with resin will do nothing to add rigidity.

[chuyler1]

^^^
second. What makes fiberglass strong is not the resin...it's the fibers of glass.

[AzGrower]

seriously folks, you guys are talking about using pegboard, plexi, cardboard, paper mache, etc.... stick to the basics and just use the thickest possible MDF you can, then reinforce it with a few layers of fiberglass...

its not rocket science, so make it easy on yourselves.

[honfatboy]

AFAIK, resin has nearly no inherent strength...point being: filling holes with resin will do nothing to add rigidity.

No kidding. Where were you about six months ago? Would have saved me a lot of time...and resin. :D

[mvw2]

Yep, resin's purpose isn't strength. It just holds the fibers in place. Resin alone is soft and flexible. Mix wrong one way, it's like sugar candy, hard and brittle. Mix it wrong the other way, it's like rubber, easily bendable by hand, even a thick piece.

[Jakester77]

yes but when you coat an MDF box with resin it does give it a bit of strength am i wrong? I have a hard time believing it does nothing.

[chuyler1]

I think it helps seal the MDF more than anything else. (an MDF box is never air-tight)

I've coated the inside of my box with resin before. It doesn't really soak in like you would think.

[sigma6]

I would think you'd have to add at least one layer of mat to an MDF box to see a difference in stiffness. I doubt just adding resin would do anything.

[GlasSman]

I think it helps seal the MDF more than anything else. (an MDF box is never air-tight)

I've coated the inside of my box with resin before. It doesn't really soak in like you would think.

The ONLY thing resin is good for is to suspend the fiberglass fibers in placed.....THATS IT.

It is a mistake many of us make when we don't know the facts of this material.

Wood glue is more effective at say coating the inside of MDF....and it doesn't require a catalyst.

It's also cheaper than resin which has sky rocketed in the last few years.

[Nathan P]

Cardboard? You've got to be kidding me...

[Ge0]

I started a new post for this because I didn't want it to get lost in the shuffle of oldloder's other post.

I had the idea of just making a sub enclosure out of cardboard for the following reasons:
1. Ease of use. I already had a box to fit the exact dimensions I needed.
2. Lack of space. Single cab Tacomas have no space behind the seat. So, I couldn't use 3/4 MDF.
3. Thought this would be easier...HA!

This box, while I'm still using it, is a wretched disaster of cardboard, MDF baffle, duct tape, foil, Great Stuff, and MDF scraps. I won't scare you with pics. It sounds like poo.

I did use 3-4 layers of mat and resin, but you would have to use I would guess about 10-12 layers on the long side of the enclosure, the cardboard even reinforced is not strong enough.

There are other issues, too. The "bread" of the cardboard box sandwich will not soak up enough resin like I thought. Cardboard = good water sponge; bad resin sponge. If you're going to do it, it does help a bit to tear off the outer layer of cardboard to get to the corrogated "meat" of the box. The ridges do soak up more and the resin can get down in the gaps.

The big probelm is how to attach the baffle for the speaker to the box. This is a very messy and time consuming process of reaching in the speaker cutout and trying to lay up mat without looking. Then you have to try and fill in the inevitable holes. That's where more resin, duct tape, MDF scraps and Great Stuff come in. It is NOT fun.

In the end, I would use something like 1/4 MDF or even the 3/4 styrofoam sheets you can find for insulation over cardboard for a structural mold. Again, though, with styrofoam you have the problem of trying to attach the baffle for the speaker. I think 1/4 MDF is the way to go and I would redo the box if I weren't selling the Taco soon.

Sorry for the long (some might say duplicate) post; but I wanted to save oldloder from the trouble and heartbreak.

David

Questions?

Now isn't this in the true DIYMA spirit!!!

I had a similar situation. With plastic, not cardboard.

Do yourself a favor and install some 1/2" diameter dowel rod inside the box to give support. For now, hold it in place with hot glue.

Use 3m Super 70 spray adhesive to adhere fiberglass wolven matt to the box. You can buy this cheap at Home Depot, Lowes, Wall mart, etc... Cover the box with strips of mat cut into strips approx 3" by 6". Overlap strips where possible. Apply your first layer of resin. Build up 2 or 3 more layers after that. You should be golden.

Make sure you then fix the dowels in place by securing them with screws and/or kitty hair style body filler.

On a side note, I know a damn good enclosure can be built using traditional methods in aTacoma. Write DIYMA user "goestoeleven" for details.\

Ge0

[Jethro]

Cardboard sub boxes, now why didn't I think of that!

I've got about 300,000 square feet of corrugated out in my warehouse... maybe I should start experimenting with subwoofer enclosures. :D Shoot, ain't nobody buying shipping boxes in this economy, so I may as well use it for something... :(

Let's see, if I laminate 4 layers of doublewall together...

[capnxtreme]

It's also cheaper than resin which has sky rocketed in the last few years. . .

. . . since the OP was made

[GlasSman]

. . . since the OP was made

It was $18/gal in early 2000's went up to around $25/Gal THREE years ago and is even HIGHER now.

So that comment applied back then......AND now.

Step off Willis.;)

[GlasSman]

Polyester resin:

http://www.mertons.com/Epoxy/polyester_Resins/index.html

[GlasSman]

High Quality wood glue:

http://www.amazon.com/Franklin-International-Titebond-16-Ounces-5004/dp/B0000223UR

[TallTexan]

I thought about cardboard at one time. What I found cardboard to be good for in relation to fiberglassing is making cheap/quick molds after being covered in foil like I did on my pocket sub project for my Impala: Quick Prep/Build (http://www.diymobileaudio.com/forum/showthread.php?t=39646)

Thinking about it, if fiberglass strength is not in the resin, I would not trust cardboard for said strength. Plus if one could possibly soak cardboard in enough resin, the resin would probably do the same things as water does to cardboard: make it a mess.

[GlasSman]

The ONLY way a cardboard box would be good is as a form...not as a structural form.

If you could remove the carboard box and be left with a good outer shell.....yes.

Otherwise......a cardboard box is MORE TROUBLE than it's worth.