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Constructing a Composite Bass Project!

Discussion in 'Luthier's Corner' started by Kickin'Fruit, Dec 5, 2006.


  1. Hey everyone,

    I'm about to take on a great project for my Composite Materials class. I am a Mechanical Engineering Student at RIT and we have the opportunity to pick an object we want to make out of composites and I thought a bass would be awesome!

    Of course I have to buy the materials. Any of you have any information on what would be the best materials for taking on this project?

    I am planning on modeling it after say a RainSong guitar or a Modulus but with a Fender style body.

    I don't think I'm in over my head as my professor even suggested this as a project. If worse comes to worse I could just make a replacement composite neck for my Fender J bass.

    I am looking for any insight into this project. If I don't get enough information, I'll just end up making a composite hockey stick or something else less interesting. Thanks for any help!
     
  2. I've read a couple of the patents for graphite basses and necks. One method (I think the one patented by G. Gould of Modulus) uses graphite pieces on a mold with epoxy. Other methods use graphite cloth over a core with epoxy and yet another uses graphite dust mixed with epoxy on a cast. Too bad those guys don't hang around here.
     
  3. Rodent

    Rodent A Killer Pickup Line™ Commercial User

    Dec 20, 2004
    Upper Left Corner (Seattle)
    Player-Builder-Founder: Honey Badger Pickups & Regenerate Guitar Works
    hey KF,

    Excellent idea for a project! :hyper: Here's a couple of thoughts -


    * For US Export Control reasons, you will not be able to discuss the engineering details of your part in this international forum. A Google search on US Export Control will keep you out of hot water

    * But ... at a high level we can discuss your choice for materials (just not the engineering details of application of this choice) So will you be utilizing a hand lay-up process, or are you looking more at a chop fabric or RTM process?

    * The original Steinbergers utilized a chop fabric approach from what I can see. Same thing for at least the outter ply on a Modulus neck. Most of the carbon fiber stiffening bars utilized in neck construction are of a pulltrusion origin

    * If you plan to utilize hand lay-up, will you also be working the design with a CAD system? I kinda know just a little bit about this subject ;)

    * There's a TON of good information available on NetComposites.com, and several other on-line resources for purchasing your materials.

    * Be aware that several large commercial aerospace programs are grabbing up most of the carbon/kevlar fabric materials available today, so you may be forced to adjust your design to utilize a fiberglass material with epoxy resin ... and fiberglass designs are not Export Controlled(!)

    all the best on this and do keep us posted

    R
     
  4. Angus

    Angus Supporting Member

    Apr 16, 2000
    Palo Alto, CA
    If you need help, I can definitely let you know where to get carbon composite materials- no need for the fiberglass that Rodent mentioned. I do huge amounts of carbon fabrication and can give you some pointers if you need.

    I would suggest the easiest way to go about it would be using dry or pre-preg uni (non-directional) carbon over a core. The most difficult part of the entire process will be the mold and core fabrication, not the layup part itself, which is fairly simple once you get the process down, but do expect to make more than 1 before you get it correct.

    A neck would be a good place to start, even if somewhat difficult. Beyond that, it would be easier to make an acoustic a la Rainsong than a full composite instrument like a Status. Either would be difficult, though.

    Subscribed.
     
  5. My first post was a little in haste as I was between classes and had to get goin. I'll update and edit the first post with generalized information from the other posts.

    A little more organized thought process would be this:

    Project: Composite Bass Fabrication

    Focus Options:
    -Composite Neck
    -Composite Body
    -Full Composite Bass

    Idea Tree:
    -Composite Neck
    +Smaller mold
    +less material (less expensive)
    +Bolt on replacement for a Fender Jazz Style Bass
    +Specification areas: neck radius, fretted (#) or fretless (#, lined unlined)

    -Composite Body
    +Hollow body or Solid Body (lost wax process, bladder inflation)
    +Could be any design
    +Would need space for electronics
    *Active or Passive, Pickup placement, pickup type
    +Complex design?
    +Can be coupled with composite neck for complete composite replacement options

    Full Composite
    +Largest mold
    +Increased chance for flaws
    +Increase in materials
    +Whole part possible for scrap

    This is a rough outline, and as it currently stands the bolt on neck sounds really enticing as I could put it on any Fender Bass and would look really cool. I'm thinking if I use an epoxy resin with a fretless neck that would not only be easy but sound very *mwah*

    I'm going to discuss this more with my professor over email.
     
  6. Angus

    Angus Supporting Member

    Apr 16, 2000
    Palo Alto, CA
    There's way more to it than that.

    I would not recommend either lost wax or bladder inflation for your part. Lost wax will melt during the curing stage (the temp of which depends on resin or prepreg curing temp, usually in the 175-300 degree F range) and will ruin your part. Bladder inflation makes very imperfect shapes when put in tight radius's or small areas- it's really only meant for large, open shapes.

    A full composite body not only requires lots of material, but more specialized materials, too- you'll need much much wider rolls of weave if you do not use uni, and you'll have to make a significantly larger oven. Stick with a smaller part the first time through, it'll save you a lot of cash. Carbon is very expensive and very easy to mess up, but still less of a pain than fiberglass!

    Either way, you won't be able to use carbon weave or uni for a fretboard. Epoxy or polyester resin will be part of the curing process, as it is part of what holds the carbon in shape, but it is not suitable for a fretless fretboard. You would be playing right on the resin, so when it starts to wear, you're wearing into the carbon, which is not really repairable. You'll want to adhere a fretboard of some sort (perhaps composite) onto the neck you make, especially if you want the adjustability of a truss rod.

    What you should be thinking, more than anything, is "how am I going to make the mold?" because that is by FAR the most difficult and time consuming part. 95% of your time will be spent with the mold, and the other 5% with making the actual part. I'd think about that before anything else.
     
  7. Alright, after a few classes and some research into the patent office I've come up with these ideas:

    Modulus uses carbon fiber and epoxy for their necks. It is a unidirectional fiber running longitudinally along the axis of the fret board for increased stiffness when string tension is applied.

    Also, Modulus uses a hollow core and affixes a composite fretboard.

    Modulus also claims that the use of carbon fiber eliminates the need for a truss rod.

    My Ideas:
    Same as modulus with unidirectional fibers, however, maybe using a honeycomb foam core.

    For the mold I am planning on buying a used Fender neck on Ebay (or maybe a friendly TB'er has a donation? :)) as a plug from which I will cast the mold. Tuning peg holes will be post manufacture machined via CNC.

    My questions:

    Should I incorporate a truss rod if I'm using carbon fiber?

    If so, I was looking into using a shape memory material such as Nitinol Tubing or a traditional mechanical truss rod.

    If I make a hollow core neck, I also may incorporate LED lighting for finger markers.

    What are some constraints on the neck I should pay close attention to? Should I go Fretted or Fretless and what factors will affect my itonation significantly?

    Thanks again for any insight guys.
     
  8. Angus

    Angus Supporting Member

    Apr 16, 2000
    Palo Alto, CA
    Ok...somewhere along the line, the enthusiasm is there but you aren't fleshing the ideas out to their full extent.

    The fibers that Modulus use are commercially available, but only ever seen them available in very, very large quantities from Aerospace supply companies. Even if that weren't a problem, the process is- part of it's strength comes from being subject to very high pressure during the curing process. You do not have technology available for this.

    The better option for you, in my experience, would be to use woven carbon cloth, like Status uses. You could achieve a similiar end result with unidirectionally woven carbon cloth. It's sometimes a bit hard to find dry (you aren't ready for pre-pregnated carbon yet), so you could achieve similiar stiffness using directionally-woven (standard) dry carbon and using a few layers oriented at different angles- requires a bit of calculation if you want to be sure of stiffness, but you could also just go with standard proven angles.

    The advantage here is that it doesn't require high pressure to cure to adequate stiffness. You could get away with only using a vacuum pump and a small, homebuilt oven to cure the pieces. The curing materials are much cheaper this way, too.

    The other thing to think about would be the honeycomb core- do you have a CNC machine to cut it to the internal profile of the neck? Got anyone to do the CNC programming and machining? It's very expensive. This is NOT a material you can cut or carve by hand, and a changing-radius/thickness/width shape is extremely difficult. You might want to look at something more like a hard foam (not at all similiar to sytrofoam) or something similiar. It'll be much easier for your first few attempts.

    Also, for what it's worth, both Modulus and Status use truss rods. Even carbon fiber will move in changing temperatures. Nitinol is not what you want.

    Avoid things like LEDs and stuff- it will overcomplicate your build to a huge extent. You'll have enough on your plate learning everything else anyway. These will only get in the way and increase costs.

    Do you have a budget in mind?
     
  9. I have experience in programming CNC and am ASTM certified in running a Computer Numerical Controlled mill, lathes and the like. So that resource is readily available in the machine shop. Also I do have access to an autoclave and heat treatment oven.

    Thanks for the idea about status, so far I've only looked at Modulus. Fortunately, commercial vendors for pre-preg Carbon Fiber is available.

    I have the next 8 weeks for this project and am estimating a budget from as close to $300 as possible.

    My ideas as the moment are still strictly brainstorming so the hatchet isn't ready to fall yet so to speak and I really appreciate the almost devil's advocate approach to get me thinking about alternatives.

    Edit: Also I have a rough sketch drawn up in AutoCAD and Mastercam, just the specifics such as fret placement are yet to be added. I saw in the Luthier's FAQ a calculator to find that.
     
  10. Angus

    Angus Supporting Member

    Apr 16, 2000
    Palo Alto, CA
    Pre-preg woven, though, right? Pre-preg doesn't specify how it's arranged.

    The modulus-style carbon shards still require high pressure during curing, which is unlikely to be available.

    If you are going to be using pre-preg, you'll need a very large freezer to keep it very cold (otherwise it'll be ruined), and it'll be quite expensive. It's also easier to screw up the lay-up, even if ideally it's lighter per stiffness.

    $300, though?! Not with pre-preg, and unlikely with dry. You might want to want to have a little more handy than that. And that's assuming it goes smoothly the first/second time! You could easily spend that much just on one lay-up.
     
  11. Sorry, I wasn't too well educated when I started naming materials. I talked to my professor today and like you suggested he said I should go with unidirectional Carbon Fiber, oriented at 0* and 90* and aligned at a 45* angle on the neck to account for the tension of the strings on the neck. He said that the problem with a person trying to make a guitar before is that the tension bent his neck like a bow.

    So for materials I will use unidirectional carbon fiber layers with an Epoxy resin.

    I want to make the neck hollow, so I'm think I will use blue-foam for the core, then when the part is cured I will wash away the blue foam with acetone.

    I can use CAD and CNC to machine the blue foam and other methods to get the shape, radius I want.

    I am also thinking the neck should be 2 parts, 1 part being the bottom U shaped neck, and then affixing the 2nd part fretboard that will also be a composite.

    Now what did you say about needing a truss rod? or not needing one? I'll look into other posts about incoporating that into the design. I have to give a presentation thursday about my project.

    Thanks again!
     
  12. Leave the foam....

    Cheers ROdy
     
  13. So go foam core over hollow?

    I was thinking hollow would be more "sound resonant" as Modulus claims anway. But I think with a foam core it would be more structurally sound and would probably make adding a fingerboard and truss rod easier.
     
  14. pilotjones

    pilotjones Supporting Member

    Nov 8, 2001
    US-NY-NYC
    Only to the extent that the foam has some actual structural strength, and MOE. These are likely very low with respect to the other materials (as in one or two orders of magnintude); plus, the foam is at the core, which is surrounding the neutral axis/plane for any conventional bending analysis, therefor further minimizing its contribution.
     

  15. Good point. I guess I was going on the idea that the foam would improve impact strength, but I don't think my fingers are going to be punching through carbon fiber/epoxy PMC. Thus I would remove the foam only for the purpose of improving sound resonance.

    The foam initially is necessary though because it will provide the plug and basis which I will wrap and hand lay up the expoxy carbon fiber. I am unsure whether I will make a separate fingerboard to place on top of the board or just make the fingerboard part of the mold.

    My professor suggested that I make the neck U shaped so that the strings are laying on an open surface to allow for slide gui**ring. I don't think I will go with that considering who would want a bass exclusive to sliding.

    I believe making a fretless will be easier than trying to add frets to the composite fingerboard. I could always buy a soft wood material fretboard and lay it on.

    Now my question is how am I going to attach the neck to the body of my bass? heh.
     
  16. zac2944

    zac2944

    Dec 28, 2004
    Rochester, NY
    KF, sweet project! I'm an RIT ME too. I graduated back in '02.

    Like Angus has been saying, I would recommend keeping your project as simple as you can. I'm assuming that you'll only have 7 weeks left after break and you've got other class work as well. Time flies when you're working hard, and projects you are passionate about always seem easier at the beginning.

    If you need a cheap neck for your mold you might want to get a used one off the bay, or get a cheap one from rondomusic.net. They sell a $40 bass neck.

    I think that a truss rod is a good idea for your neck. That way you'll have some adjustability. Until you've tested your design it will be thought to know just how much the neck will flex when it is strung. If you go without one and it flexes too much there isn't much you can do. Unfortunately, fixing the truss rod into the hallow carbon neck sounds like a lot of work too. It's not like wood where you can just take a router/mill and create a slot for the truss rod. I imagine you'll have to mold that in.

    This sounds to me like a really challenging and fun project. Let me know if you have any machining or mold building questions. (Unless you're on the F1 team, because then you'll already know everything ;) ) I worked in Rochester for a while (with Rob Kraynik's brother) in that industry and still have many good contacts. Please keep us posted.
     
  17. Aww man, you're lucky KF, I'm doing MET up here in Ontario and we didnt get any project like that for our materials class. But good luck to you and hope it turns out awesome!:hyper:
     
  18. OK, I am ready to buy one!!! :)

    You could also go with a solid one-piece, graphite composite moulding concept like the AWESOME design that is featured on my Status Stealth bass.

    I would perhaps go fretless on your first test build, just to keep your costs down. The last thing you want is a great "shell", potentially ruined by a tricky fret installation. But, kudos to you if you come up with a way to put in STAINLESS STEEL frets!! :)

    Good luck and keep up the hard work!

    Cheers,

    Jay

     
  19. I agree.....and I disagree. You are correct in saying that the foam has no bending stiffness to speak of. But that does not mean that it has no significant contribution. Sandwich contructions, especiall using fiber composites as a skin, work mainly on the principle that the load-bearing members are placed at a distance from the neutral plane where they are used in tensile mode which is the mode in which they are most effective, and where, due to Steiner's parallel axis theorem, they produce a moment of inertia proportional to the square of the distance to the neutral line (assuming this coinsides with the center of rotation). In order to maintain both these conditions, this distance must be maintained and no buckling must take place. The way to do this is to place the skins on top of a highly incompressible core. This is the reason why balsa wood is not to be scoffed at. Balsa wood, especially used with its fibers perpendicular to the neutral plane (iow, the compression forces act along the fibers, not across it) can make a very effective core material for sandwich constructions as it is very incompressible and lightweight.

    Think of an I-beam, but taking out the | part...

    In other words, leave the foam.

    Cheers Rody
     
  20. pilotjones

    pilotjones Supporting Member

    Nov 8, 2001
    US-NY-NYC
    Rody

    The theory is correct, and it does apply to the laminate sheet situation you describe. (They are fantastic materials to use!) But I don't think it is as appropriate to this application as straightforwardly (word?) as you suggest.

    Specifically, this application does not so much resemble the laminate sheet construction as it does a tube, specifically in the neck. The side walls would take virtually all the compression and neutral axis shear stress resulting from beam loading, and the core would not enter into it -- just like a square or rectangular structural steel application.

    The body may possibly present as situation where, due to the wide face size moving the walls significantly outward in comparison to the thickness, the core could be of some use.


    Empirically, BassLab instruments have always been noted to be extremely stiff all over, despite being hollow. Curved body faces do help in this respect.
     

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