Yeah, and just to make sure we are on the same page, it wouldn't be a substitution in hopes of higher stiffness, just equal to the glass layup, and a bit of easier (or at least more conventional) finishing.
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DIY Lightweight Composite Cab Build
- Thread starter zac2944
- Start date
Yeah, and just to make sure we are on the same page, it wouldn't be a substitution in hopes of higher stiffness, just equal to the glass layup, and a bit of easier (or at least more conventional) finishing.
- Dec 18, 2000
- 13,201
- 340
- Disclosures
- greenboy designs: fEARful, bassic, dually, crazy88 etc
Want some wood? You can buy panels with wood plys on the outer edges and foam glued in between (googled it ages ago), thus gaining many of the rigidity benefits and lighter weight of layup constuction. This presents a few quandaries on panel joining and edge constuction, but not so hard to solve.
This is probably what FLITE is doing.
This is probably what FLITE is doing.
Wouldn't it be better to make them like Zac did for stiffness and weight reasons, and then just put wood veneers on for appearance, if that's what you want for looks?
- Dec 18, 2000
- 13,201
- 340
- Disclosures
- greenboy designs: fEARful, bassic, dually, crazy88 etc
Sounds like a lot of people would like lighter cabs, some hoping Zak will make a bunch (or at least for them). But if one were to pursue this commercially, the wood/foam/wood panels would be looking good due to the time/cost/performance ratio. And if you've ever seen the weights of some FLITE products, they are very very light - with Neo drivers they'd be right in the ballpark where for the buyer paying half or less for a pound or two more (assuming identical drivers and handles and such)... well, it begins to make sense.
+1
These panels are fairly expensive to buy, but you could make your own pretty easily for a lot less money. The trick here, as Greenboy pointed out, is in how you join the panels.
Here a link to my local plywood/lumber supplyer. They have foam core plywood. You can get some data there. Click on Marine Plywood, then scroll down. They sell a 4'x8'x1" sheet that has 1/8" Okoume (wood) skins, 29lbs, $265.
If I were to make an equivalent 4'x8'x1" sheet using fiberglass/epoxy it would weigh about 15lbs, and cost significantly less. I can't compare stiffness because I don't have any data on their panel. I did some rough calculation using unverified data for plywood and the two panels would have similar stiffness.
Just as a point of reference, a 4'x8' sheet of 3/4" Baltic Birch plywood weighs in at around 75lbs, 50lbs for a 1/2" sheet, and 25lbs for a 1/4" sheet.
Wow.. neat project. I just got on TB a week ago and honestly do not have the time to read nearly 500 posts on this one.
Some info that may be of use: these guys http://www.fibreglast.com/ sell all kinds of composite stuff and are very hobbyist / DIY friendly, but they will spam the heck out of you so do not give them an email address.
A Mech-E friend of mine worked at a company (Crane) making similar stuff. "FRP" - fiberglass reinforced plywood, extremely common and popular for trucks, RVs, etc. They came up with an idea to do the FG over poly-something in continuous panels, for large semi-trucks. Spray down the foam, run through planer, spray resin, lay roving, spray more resin, run through press rollers. Incredibly rigid. Think about 3/4" think. They did tests with stiffening beams embedded in the foam, and they didn't add much; they were NOT used in the final product. It was all just really strong on its own.
Some info that may be of use: these guys http://www.fibreglast.com/ sell all kinds of composite stuff and are very hobbyist / DIY friendly, but they will spam the heck out of you so do not give them an email address.
A Mech-E friend of mine worked at a company (Crane) making similar stuff. "FRP" - fiberglass reinforced plywood, extremely common and popular for trucks, RVs, etc. They came up with an idea to do the FG over poly-something in continuous panels, for large semi-trucks. Spray down the foam, run through planer, spray resin, lay roving, spray more resin, run through press rollers. Incredibly rigid. Think about 3/4" think. They did tests with stiffening beams embedded in the foam, and they didn't add much; they were NOT used in the final product. It was all just really strong on its own.
It's actually even better than that. Stiffness is proportional to the thickness cubed (a.k.a. to the third power).
Great cab!
Are you sure? Correct me if I'm wrong, but I believe you are talking about ordinary Beam Theory, which is a little different than Sandwich Beam Theory.
I posted most of this back on page 22 but I'll go through it again for my own benefit.
From what I've read, ordinary beam theory stiffness (D) is the product of the modulus of elasticity (E) and the second moment of inertia (I). In sandwich beam, D is the sum of the flexural rigidities of the different parts about the centroidal axis of the entire section.
So for ordinary beam theory, you are correct. D = E * [(b*t3)/6]. Here the stiffness does indeed very with the cube of the thickness of the beam. Where b = width of beam cross section and t = thickness of beam cross section.
With a sandwich beam your stiffness equation is the sum of the parts of the beam. You've got to consider the local stiffness of the facings, then the stiffness of the facings about the centroidal axis of the entire cross section, then finally the stiffness of the core. The equation looks like this:
Where:
Ef = Elastic Modulus of the Facings (Skins)
Ec = Elastic Modulus of the Core
b = Width of the Beam
d = Distance Between Facing Centroids
t = Thickness of a Facing
c = Core Thickness
In most cases the first and third terms of that equation can be neglected. More specifically, when d/t > 5.77, the first term amounts to less than 1% of the second. When (Ef/Ec)*(td2/c3) > 16.7, the third term amounts to less than 1% of the second term.
I plain(er) english, this means that if you have facings (fiberglass skins) that are significantly thinner than the core and the modulus of elasticity of the facings is higher than the core, your stiffness boils down to: D = Ef * (btd2)/2
Therefore, I would say that the stiffness of the composite panels I'm using is proportional to the square of the thickness and not the cube.
Here's where I got most of this info: [Invalid or Expired Link Removed], BoatDesign.net article
Please let me know if I'm wrong here. I'm still trying to figure all this stuff out, and am a total novice.
i really didn't need to see that. i just got out of my thermodynamics class and i surf on talkbass to get away from equations and formulas.
jk man, and i believe my statics professor would agree with your reasoning. btw good job taking the math out of the lab and doing something with it.
jk man, and i believe my statics professor would agree with your reasoning. btw good job taking the math out of the lab and doing something with it.
That is an interesting (albeit non-intuitive) result. I didn't think that the fact the material is a composite would change the proportionality of the moment of inertia to stiffness.
I understand you are neglecting the insignificant terms in the equation. That's cool.
Is d the distance from the centroid or the distance between the two faces?
I have to admit, I have not read the references you linked too. I'm on the run as usual.
Jeff
Just went through the thread - great watching this come to life.
Zac such and awesome Project and Result!! High 5!!!!!
Zac such and awesome Project and Result!! High 5!!!!!
great project! I'm glad to see your process - back on the 4 of 5th page you said you were learning the hard way what you can and cannot do with glass, and I know what you mean. I do fiberglass a lot, just not in this application.
I just started a thread (http://www.talkbass.com/forum/showthread.php?t=478077) about this - but I would have taken a very different approach. I come from a different background (car audio) but I do boat fiberglass as well - very different techniques. I'm confident your enclosure will be a little bit lighter than my concept, but I'd like to see some rounded edges to reduce the standing waves a bit.
I hope you get lots of use out of it! thanks for sharing!
I just started a thread (http://www.talkbass.com/forum/showthread.php?t=478077) about this - but I would have taken a very different approach. I come from a different background (car audio) but I do boat fiberglass as well - very different techniques. I'm confident your enclosure will be a little bit lighter than my concept, but I'd like to see some rounded edges to reduce the standing waves a bit.
I hope you get lots of use out of it! thanks for sharing!
Hey Zac,
I just started an experimental light cab build. I'll be making a BFM 10.5. I am using 1" thick pink foam with laminating film over it. This is a technique based on what us RC sailplane guys are doing. It is basically just like FG over foam, but much easier, cleaner and quicker. It gives about the same structural results, although the laminating film can't go around compound curves like FG - which is not a huge issue with a cab. Also you have to use certain paints to get them to stick well.
I cut the cab and glued most of it together in <2 hours. I started covering it too. I'm at 1.5 pounds right now, but it will be probably 3-4 total for the box and another 4.5 for the driver.
Right now, I am NOT recommending anyone else do this since I have no idea how it will sound.
Zac, how it yours doing with wear? I'm assuming it will dent if you throw it around too much. I figure at 8 lbs, I can carry it a lot more carefully than at the 25 lbs it is spec'ed at.
If it doesn't work, at least I didn't spend a lot of time building it!
Andreas
I just started an experimental light cab build. I'll be making a BFM 10.5. I am using 1" thick pink foam with laminating film over it. This is a technique based on what us RC sailplane guys are doing. It is basically just like FG over foam, but much easier, cleaner and quicker. It gives about the same structural results, although the laminating film can't go around compound curves like FG - which is not a huge issue with a cab. Also you have to use certain paints to get them to stick well.
I cut the cab and glued most of it together in <2 hours. I started covering it too. I'm at 1.5 pounds right now, but it will be probably 3-4 total for the box and another 4.5 for the driver.
Right now, I am NOT recommending anyone else do this since I have no idea how it will sound.
Zac, how it yours doing with wear? I'm assuming it will dent if you throw it around too much. I figure at 8 lbs, I can carry it a lot more carefully than at the 25 lbs it is spec'ed at.
If it doesn't work, at least I didn't spend a lot of time building it!
Andreas
http://www.talkbass.com/forum/showthread.php?t=493485
zac, come on over to the Homebuilt/Converted Amp/Cab club and showcase your wwork along with others who've decided that DIY is better! Very impressive what you've done!
zac, come on over to the Homebuilt/Converted Amp/Cab club and showcase your wwork along with others who've decided that DIY is better! Very impressive what you've done!
Hey Zac,
I just started an experimental light cab build. I'll be making a BFM 10.5. I am using 1" thick pink foam with laminating film over it. This is a technique based on what us RC sailplane guys are doing. It is basically just like FG over foam, but much easier, cleaner and quicker. It gives about the same structural results, although the laminating film can't go around compound curves like FG - which is not a huge issue with a cab. Also you have to use certain paints to get them to stick well.
I cut the cab and glued most of it together in <2 hours. I started covering it too. I'm at 1.5 pounds right now, but it will be probably 3-4 total for the box and another 4.5 for the driver.
Right now, I am NOT recommending anyone else do this since I have no idea how it will sound.
Zac, how it yours doing with wear? I'm assuming it will dent if you throw it around too much. I figure at 8 lbs, I can carry it a lot more carefully than at the 25 lbs it is spec'ed at.
If it doesn't work, at least I didn't spend a lot of time building it!
Andreas
Andreas, great to hear about your build. It is always nice to see someone try something new.
Can you tell me more about your laminating film? Who makes it? Where can you buy it? What is is made of?
The stiffness of you composite will be determined stiffness of the skins and the thickness of the foam. 1" thick XPS is a good place to start, but if the film you're using for skins isn't stiff enough or strong enough you might have issues.
If I can find out some material properties for the film I'll be able to do some quick calculation and give you an idea of how stiff it will be compared to plywood. I have a spreadsheet set up for just these types of calcs.
My composite ZL210 cab is holding up just fine. I've probably done 15-25 gigs with it and no issues what so ever. I'm still amazing people with how light it is. They think it is a joke until I stand on top of it. It wolds my weight without any issues.
You might want to do some testing by making some sample boards with some foam and your film before going through with the full built. Just lay up a 3"x24" piece and compare it to a similar sized piece of plywood. That should give you an idea of how well it will work. If it bends much easier than 1/2" ply I'd say you're out of luck. If it feels just as stiff or stiffer than you're probably good to go.
At any rate, be sure to take pictures and document such a cool build here on TB!
I cooked the wife a nice meal and made her a couple of strong G&T's yesterday evening and was able to sneak in some time on the cab while she passed out on the couch.
I am only on page 5 of the thread, and I am very into all that has been said by everyone, but this quote here really made my day. Shows a new perspective on the character of Zac.
BTW, I used to own a video production company and I was privvy to a lot of new and futuristic technology by making videos for Ford top management and their design center. Around 1990 they had a multimillion project designing the best race car after their famous GT60 that won three years in a row at Grand Prix in the 60's. The new car was the GT90 and they were using a very high composite system that was a honeycomb nature for the body that was compared to the airline industry.
Nice job so far Zac. 20 more pages for me to read on this thread. Like a novel wondering how it ends.
http://www.laminatorwarehouse.com/di_films.shtml I'm using the 7/3 DI (10 mil), but I have a few others here. It is polypropylene. You can get this stuff a number of different places, but each has its own qualities. The CP is less stiff, for example. The nice thing is that it is just iron on, so it is 100 times quicker than FG/epoxy.
I did a test and one ply is near as stiff as plywood, but less strong (kind of like what you found out during your testing). Luckily I can put multiple layers of the film over each other and that will substantially increase stiffness and strength. I can do the calculations too (we do them to calc wing strength), but I have no idea how strong or stiff they need to be! Do you have any info on that?
I just went back and read that you put 27 ozs of E glass on each side. Yes, that would be strong. That would make a good strong slope fuselage.
I did the testing as I mentioned before. I looked around my shop for plywood, and found that one piece was really stiff and the others were quite a bit more flexible.
This box is 14" x 20" x 16" and has inherent internal bracing in the design, so that should help with strength/stiffness.
I was going to make a build thread once I figured out if it would work or not. I have a couple of pics.
