Looking for tips. Fiberglass box building

[Kelvartis]

Took some time reading about it, watched build logs but still would welcome any suggestions.

Final design isn't set in stone yet but I would like to mold a pair of 12's around the wheel wells in my trunk, blending a slot ported mdf kerfed with a fiberglass volume maximizing shape on the sides.

Is there any way to really accurately measure the volume? box it out a little, seal and measure with water?

What final thickness will the fiberglass need to be at to tolerate subwoofer abuse (600-1000rms subs)?

How does the very odd shape of the volume inside the box affect the sound waves and performance of the subwoofer?

Finally, when I'm finished with the basic structure of the box will I be able to add a single layer of carbon fiber to really make it shine? I would like to lexan window the back of the boxes and have the inside carbon where needed, mirror where not with some LED lighting.

I think looking at a kerfed port from inside the box with carbon fiber and mirror would be the final touches to make it look as amazing as it could.

Background: 10+ years carpenter, never touched fiberglass. Built a few slot port boxes with 3/4 and 1 inch mdf.

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[calebkhill 10+ year member]

Good thread. I'm tuned in

 

[Kelvartis]

Something like this

But molded into the side wheel wells too since I don't have much space.

 

[hispls 5,000+ posts]

Very ambitious if you have never touched fiberglass before.

First of all FG is expensive, particularly when you get into thickness that is really adequate for 1000W of power. From there the stuff is just awful to work with. It stinks for weeks, is sticky as hell, itchy and just gross. Getting it smooth enough to paint or try to lay up a final layer of CF over is going to take plenty of bondo, sanding, and time. The more complex the shape the shittier it's going to be to get all those angles right.... same issues but multiplied for CF. It's even more expensive, you will need to get a whole different epoxy for it, and it'll really show any imperfections.... unlike fiberglass, CF laid up with epoxy is permanent, as will be your mistakes. And that weave is so easy to put a run into or pull out of alignment, you'll really not want to try that in any tight angles or whatever.

I'd suggest if you're married to this whole notion, start small with some tweeter pods or door trim rings for your mids and scale up as your skills and comfort level with the materials grow and you get more of a feel for what your limits are and what the limits of the materials are.

 

[Kelvartis]

fair enough. the trial run to it is throwing some stuff in my wife's car for practice. See how molding around trunk spaces works, layering up and smoothness. At least I got a lot of contractor grade tools on my side =D

 

[JKDriver]

Well, I will disagree with some of what hispls stated. He is right that fiberglass is more expensive than MDF. However it is not awful to work with if you are set up right. You say you have contractor grade tools? A good vac system, like at least a big Rigid shop vac? Compressor and air tools? Random orbital sander with vac attachment? Those can make life a lot easier.

Even if you don't, the main thing that will make life easier is to use 100% solid epoxy resins, and get the correct speed cure for your environment. This will mean very little odor, less amine blush, and using quick cure can greatly speed up the process. Look at MAS or West Systems. Also, I almost never use fiberglass chopped strand, which is the itchy crap used to create bulk. It is also what takes tons of sanding. I use Coremat in 2 and 4 mm for adding bulk and rigidity. Get epoxy rollers, small spiked metal rollers that help you get bubbles and voids out of your laminate. Always!! use good respirators when sanding fiberglass and epoxy resins!

I build wood/epoxy composite canoes and kayaks as a side business and make my living with a decorative concrete and commercial coatings company. So I deal with epoxy on a daily basis. If you need to make curved panels, don't overlook the possibility of bending up okume plywood to the shape needed, then laminating with epoxy and fiberglass.

Dave

 

[JKDriver]

Hey Kelvartis. I just caught the 10+ years as a carpenter. I don't know if you have spent time on cabinets and furniture, but if so you have most of the skills and tools needed. Between kerfing, bending 3-5 mm plywoods and proper jointing, you will only need to fiberglass the portions of your enclosure that you can't emulate with wood. If you can varnish, you can definitely fiberglass!! Also, that picture you posted is probably not actually skinned in carbon fiber. That appears to be a vinyl wrap, like the 3M stuff. Much easier and less time consuming.....

Dave

 

[slammedincouch 10+ year member]

For your volume question- packing peanuts are your best friends: Sticky Packing peanut volume measurement

"It really isn't that difficult. If you fill a container that is 1' x 1' x 1' with packing peanuts, you get 1 ft3 of volume. Moving this amount of packing peanuts into another container that is of a different shape, but the peanuts still fit will yield the same cubic volume.

Othewise, if you have an oddly shaped enclosure (fiberglass, let's say), fill it with peanuts the same way. Then you need to take those peanuts out and put it into a cardboard box that has easy dimensions to measure, and find the volume the peanuts consume in that box. That is the interior volume of your glass enclosure."

 

[Kelvartis]

Dave gave some valid and worth reading tips. Future readers might look closely at those as something to look into.

I have some test subjects to work with and then move on to this project with what I have learned.

Still having a field of work that requires hands on figuring **** out helps... and having pro grade tools.

 

[JKDriver]

I am not saying my way, or the products I use are necessarily better for box building. They are definitely more expensive, but less mess, odor, and work to finish out. People continue to use chopped strand and vinyl ester resins because they are cheap and readily available.

I am like you, I have a full work shop with everything from saws, bandsaws and planers, to a Bridgeport milling machine. They make many projects much easier. I am amazed looking at the cool boxes and builds people show on here, then look at their build thread and you see they did it all in their driveway and garage with hand tools!

I know it's off topic, but I do floors like this:

100% solids epoxy with urethane top coat.

And boats like this:

Lapstrake construction, one layer of 3 oz fiberglass, wetted out with 3 coats of epoxy to fill the weave, then 10 coats of spar varnish.

 

[Kelvartis]

Nice looking projects you took pictures of there. This will get me practiced a bit with epoxy's and resins at least too. I've got a 42" x 2" burl slab I need to turn into a table at some point. I did do some work with learning to hand cut dovetails this spring and made some nice joints.

I jump around a lot... seems like a contractor habit lol.

Time to jump into epoxy and resins. You say you like the 2 and 4mm coremat, do you use any other product in the building or just layers of that with resin?

Anything I should look for in a respirator you want to put your 2 copper in on? I've never really had one and I figure I'll buy a nice one so all those ****** times I'm told to crawl under a house or in some attic... I'll have it. Again, haven't researched it yet, just figured if you post again why not put your thoughts into the mix.

Table saw

12 inch planer

6.5hp shop vac

orbital sander

jigsaw

skillsaw

impact drill

air compressor (not big enough to paint a car.. 4.9 gpm @ 90)

bunch of misc hand tools and such.

Unfortunately I lack any shop space. I'm room'ing with a friend from highschool rent free for a few months.

Doing this with only half the garage floor as my entire space. =\

 

[cheapsunglasses]

My experience is it's hard to work with. You need at least 7-8 layers of fiberglass. I made molds on rear seat floor for two 8" 400W Kickers in my '98 Sunfire and fiberglass/resin does not like to bend and make clean, tight 90-110 degree corners. Took a lot of hours to finish (more than 10 hrs per 1.0 cu ft box) but they sound very decent (and definitely complete the audio system). I measured volume with foam peanuts.

Make sure you get the right respirator. Look at 3M specs and half-face respirators only last a certain no. of hours. After 40 hrs or so they are no good. Resin fumes can irritate your eyes, as well.

 

[JKDriver]

Time to jump into epoxy and resins. You say you like the 2 and 4mm coremat, do you use any other product in the building or just layers of that with resin?

Anything I should look for in a respirator you want to put your 2 copper in on? I've never really had one and I figure I'll buy a nice one so all those ****** times I'm told to crawl under a house or in some attic... I'll have it. Again, haven't researched it yet, just figured if you post again why not put your thoughts into the mix.

Table saw

12 inch planer

6.5hp shop vac

orbital sander

jigsaw

skillsaw

impact drill

air compressor (not big enough to paint a car.. 4.9 gpm @ 90)

bunch of misc hand tools and such.

Unfortunately I lack any shop space. I'm room'ing with a friend from highschool rent free for a few months.

Doing this with only half the garage floor as my entire space. =\

I pretty much just use Coremat, It can be cut and placed just like chopped strand, but less mess.

I like the 3M respirators with replaceable filters. That way one mask and you can get filters for whatever you are doing.

A die grinder attachment for your compressor comes in real handy. You can get sanding pads/ heads,and grinding/ cutting bits that will make cleaning up edges or removing a lot of material quickly a breeze.

 

[JKDriver]

You need at least 7-8 layers of fiberglass. fiberglass/resin does not like to bend and make clean, tight 90-110 degree corners. Took a lot of hours to finish (more than 10 hrs per 1.0 cu ft box) but they sound very decent (and definitely complete the audio system). I measured volume with foam peanuts.
Make sure you get the right respirator. Look at 3M specs and half-face respirators only last a certain no. of hours. After 40 hrs or so they are no good. Resin fumes can irritate your eyes, as well.

The time savings of Coremat is that at 2 or 4 mm thick, you can save 4 or 5 of these layers...makes things much quicker.

To make clean sharp corners, you need to use bias cut fiberglass mat. Or just cut a strip 1 1/2 inches wide at an angle to the weave of your mat. Layer a few strips along the sharp corners, then continue as normal.

 

[bubbagumper6 5,000+ posts]

Fiberglass really isn't that bad. If you have any type of skill with some tools and being able to follow directions you'll do fine. I just built my first glass enclosure and yeah I had a few hiccups and learned a few things along the way but in the end it turned out great. It's definitely not cheaper or easier than just using MDF but in the end you'll end up with a new skill and a new material you'll know how to build things with. Make sure to post up a log, I love looking at others' work. //content.invisioncic.com/y282845/emoticons/smile.gif.1ebc41e1811405b213edfc4622c41e27.gif

Also there's some good tutorial videos out there, especially if you know how to use bittorrent.

Lastly, here's the stuff I learned along the way...

Be conservative with your mold. I glassed my enclosure into the side of my trunk but made my initial mold WAY too big. It went way too far up the wall and was very difficult to remove/replace. I ended up having to cut at least the top 6" or so off of it, wasting time and materials.

Protective yourself. They tell you that fiberglass is itchy, well I prepped for it very well with tyvec suits, talc, etc but after laying a few layers, I thought I'd be fine without it. That's because when you're laying it, that's not the itchy part...it's when you're doing any kind of cutting/sanding on it, THAT'S when you need to cover every exposed bit of skin with either clothing or talc. Otherwise you end up with tiny little pieces in your skin that just look like red bumps and they're annoying as f***.

Pay attention to your MEKP ratio, I got sloppy and mixed a batch of resin with too much MEKP and it hardened within like 5 minutes, haha.

That's all I've got for now...good luck!