Step 13: Sanding, finishing & polishing

At this point, you should have a nearly functional guitar. Make the frets, put some strings on and it'll be ready to play. Trouble is, all the cutting, sanding and scraping can make the body look awful looking. And residual stickiness from the epoxy will attract all kinds of dust, lint, trash and stray carbon fibers. One person in the workshop called his guitar "Urban Blight" at this stage.

But, with some sanding and polishing, you can turn that all right around. Here's what I did to make my guitar look pretty again. You may notice some blemishes in the final photo - I think something touched the final coat of epoxy while it was still wet. I could have added yet another coat to fix these spots - but at this point I just wanted to finish, and it wasn't worth another day of drying. I can always fix it layer if I want.

Protect wood components

My method of finishing uses wet sanding - this can damage un-finished wood components. I suggest finish coating the wood top and protecting the other components - I kept my bridge and fretboard covered with painters tape for this step.

Level sanding

I had some big ridges of un-evenly dried epoxy on the bottom of my guitar, as well as many small drips and runs. I sanded these down with a sanding block and 80 grit sandpaper.

Use this corse sandpaper sparingly - epoxy isn't easy to break, but it can easily be scratched away. I only used this for the highest of high spots, and frankly 120 or 180 grit might be a safer choice. Once you get everything mostly even, move up to a higher grit and start wet sanding.

Wet sanding

Wet sanding is exactly what it sounds like, you use waterproof sandpaper (black or grey, as opposed to brown or red) and frequently rinse the area being sanded with water.

Wet sanding is good for hard clear-coats like epoxy because it keeps dust from settling into the surface and makes the sandpaper more efficient.
  • Using waterproof sandpaper, I started with 180 grit, then moved up through 220, 320 and 400 grit papers
  • The surface always looks PERFECT when wet (very deceptive). So between grits I wiped away the muddy dust with a damp rag and let it dry a minute.
  • Once dry, I wiped away any remaining dust with a tack cloth and looked at the surface. I was looking for the scratch pattern - a uniform grey with evenly spaced and sized scratch marks.
    • Larger, deeper scratches remaining after a thorough sanding, they are left over from a lower grit of sandpaper. You may have to drop down to a lower grit to remove these before continuing
    • Shiny spots are areas that have not been sanded. You want to sand everything evenly before moving to higher grits.

Hopefully the surface is starting to look good at this point, but there are probably some flaws. In my case, I had tiny tiny air bubbles trapped in my finish - millions of them. This made the finish beautiful in some places, but very cloudy in others. To fix this I thoroughly cleaned the surface of the guitar, then added one final gloss-coat of epoxy. I carefully measured out the epoxy with a kitchen scale, then brushed it on with a foam brush, and I let it cure one whole day in a warm room.

In addition to epoxy, you can also use other finishes I saw one person use polyurethane, and another use black tinted epoxy for a matte-black finish. But I wanted the carbon fiber weave to show through on mine, so I just used the same marine epoxy I had used to form the body.

Continue wet sanding

After the new layer of epoxy dried, I started sanding again with 400 grit paper, then 600 and 1000 grit. At this point, it had a semi-gloss appearance, which is all I needed. For a glossier look, keep using higher grit papers, then polish.


After sanding I used some auto-body rubbing compound (Turtle Wax). I rubbed it on thoroughly with a buffing pad, then gave the guitar a wipe-down with a damp rag.

The last thing I did was rub on a little paste wax, let it dry, then hand-buffed the body to a semi-gloss shine. I don't even know if this is appropriate, but it's what I've done with lacquer finishes on wood, and I like the look, feel and smell of the wax, so I'm glad I did it.
Not familiar with the 123Make software, but if there's a tool or way to slice the guitar vertically vs. Horizontally you might have a better resolution as far as your mold goes…Also by using slices tht equal the thickness of Cardboard you used i.e 1/8", 5/32nd" ect then simply Glue & stack them in order and fill in the void w/Bondo to make your mold.
Yeah, you can slice it up any way you want. I hadn't thought about playing around with the orientation like that, but perhaps I'll try and see if it makes a difference next time I try to make a mold.
Another note for you to keep in mind is I see you used Elmers type Glue on CardBoard which probably caused the paper on CardBoard to expand due to the water content in the Glue, It might be better to use a contact cement though alittle more costly but IMO would have been better to keep the cardBoard from expanding from Water Content.
It did expand a bit - and on top of that I did nothing to clamp it down. In this case, I wasn't too concerned about the exact final dimensions - I made the body first and everything else was designed around it. I mostly do simple woodwork, so glue is my go-to solution. But that's a good tip for future projects, I'll keep it in mind.
Don't wanna sound like I'm picking your work apart here but I hope you take in a Constructive manner. Instead of using CardBoard wouldn't it not have been better to use say Balsa wood for the rib construction vs. CardBoard material just form the standpoint of strength ?
No worries, I love criticism of this type. <br> <br>I used balsa because this was part of a prepared workshop, and they were using cardboard, so I just followed along - if I do this again I'll do my own research and definitely alter some of the methods - for instance I'm very interested in vacuum forming the CF instead of just laying it up. <br> <br>That said, I'm curious what advantage balsa would provide in this application over the cardboard? It seems it served its purpose by providing the shape for the mold - unless one is making a reusable mold it doesn't need to be that strong, from my understanding.
Actually not too bad for your 1st attempt, I bet after you sleep on all the steps involved you could refine yoru work and make a guitar just as good as some of those &quot;Pro's&quot; Look's Good !!
Thanks. I mostly do woodwork, and this was my first time trying composites. I'll definitely be returning to this type of thing in the future, maybe even another instrument - but taking it slow for now
What kind of carbon fiber cloth did you use? You mentioned that you used some inexpensive cloth - would you advise someone to use a different kind? <br>
<a href="http://www.tapplastics.com/product/fiberglass/carbon_specialty_fabrics/graphite_carbon_in_stock/97" rel="nofollow">This is the specific carbon fiber </a>I used, straight weave. It worked fine, but it was a bit hard going around tight corners. <a href="http://www.tapplastics.com/product/fiberglass/carbon_specialty_fabrics/standard_carbon_twill/98" rel="nofollow">This twill-weave carbon fiber</a> is supposed to be better than straight weave for wrapping 3D objects, but I can't say anything from personal experience.<br> <br> <a href="http://www.tapplastics.com/product/fiberglass/fiberglass_fabrics/s_2_glass_4522/88" rel="nofollow">This is the other material</a> I used, called S-glass. It's a type of fiberglass. The only reason I used it was to add bulk and stiffness to the shell inexpensively. Fiberglass is pretty strong, but not as strong as carbon fiber, and it also looks strange with epoxy - the moment it soaks up the epoxy it becomes translucent, and you can't see the pattern anymore.<br> <br> I did this as part of a workshop, and it was my introduction to composite materials - so I can't say a lot about the different options.
Impressive! Would be nice to hear a few chords played on it so we can hear how it resonates.
I've had some experience in building lightweight boats using carbon fiber (CF) and I notice some flaws in your construction that will almost certainly result in less than perfect harmony in the tone. It is almost essential to cure CF in a vacuum. Imagine a plastic bag 23 feet long with a sailing boat hull in it having a vacuum pump draw all the air out and You'll get an idea of what I've worked on. You can buy vacuum bags at hardware and department stores. They use them for compacting clothing into small bundles for storage, evacuating the air with a domestic vacuum cleaner. <br> <br>Think now about assembling your guitar over a concrete form. Yes, concrete! and putting the whole lot into a plastic bag after you've saturated it with resin. Use a vacuum cleaner to evacuate the air and the flaws I see in this example will not be there. If you can't find a ready made bag large enough for your guitar, try making one using sheet plastic and swimming pool liner repair glue with the valve from a cheap storage bag. <br> <br>I applaude your enthusiasm in experimenting and hope you continue to develop a technique that will suit this product. I think myself that harmony in a box depends 60% on the shape, 20% on the material used for construction and the remainder split up between how you hold it and the design of those pieces of material that support the strings. I think this shape is most likely to work but if the CF has pockets in it that prevent continuous sound reflection at the same energy, the overall tone of the instrument will suffer. Excellent try. I'll be very impressed if you keep developing your molding techniques and actually produce an excellent guitar.
No pic of the completed guitar? Oh, come on!
Haha, i did all the parts as separate instructables. Didnt think to add finished pics here. But thats a good idea, ill add them later.
looks like a good job...waiting to hear it also.
just wonder how does it sound?
Beautiful work! Congratulations
This is fantastic. Better than an Ovation to me. How does it sit against your body? I always found Ovations sat oddly or rolled away from me when I didn't want them too.
Very cool. Carbon fiber and traditional fiberglass can be a messy frustrating experience. Good on you for giving it a go on a complex build like a guitar.
I was unaware that Gibson ever made a round back guitar. The diagrams don't show it, either.
Sorry if it wasn't clear - first the dimensions were taken from the plans, then later the computer model sides were rounded over. This is because the type of fiber being used doesn't tolerate sharp corners. <br><br>I could have made the back and sides as two pieces, but since I was doing this as part of a group build workshop I didn't want to go too far in my own direction - I'll leave that for my next project.
Looks like an Ovation
Is this a heavy guitar compared to the wood original?
Good question, I haven't compared them side by side, but I'm not sure - but I think they are probably comparable. In general I think carbon fiber guitars are lighter, but the method I used requires more carbon and more epoxy to set strong, so it balances out. A properly vacuum formed one is probably lighter.
Very, very nice!
Thank you!
<strong>RESPIRATOR!!!</strong><br> carbon filings will give you just as nasty <strong>Permanent</strong> lung infections as fiber glass will!!&nbsp;<br> even small particles from a hand file or saw can lead to alot of pain!&nbsp;<br> of course dremel and other powertool cutting of carbon and fiber are far more dangerous<br> but if you dont want to be on a ventilator in later life wear a&nbsp;proper&nbsp;mask whenever using tools on composite materials<br> and no a paper one will not do!!&nbsp;<br> <br> other than that its an awesome project!&nbsp;<br> personal&nbsp;id of made a mould of the guitar body and&nbsp;vacuum&nbsp;infused the resin for a cleaner stronger finish! but thats alot more work!<br> i seriously love the inlay work wow that is something i need to practice<br> <br> finally&nbsp;.. how does it sound? alot of people say that carbon has unique acoustic&nbsp;propertys!?
You're right, I wrote respirator once, but it bears repeating. The first time I cut it I just had a paper mask, and quickly stopped and ran for my respirator. The guy pictured cutting it is an experienced shop guy who just doesn't always take those precautions - but maybe I'll add a safety warning there. <br> <br>I love the idea of vacuum infusion, but felt it was too much to take on for my first project. I'm looking into it for the future, though. <br> <br>I'll let you know how it sounds soon. My first tests were promising, but I got too excited and did a poor job mounting the bridge and it started to separate, today or tomorrow I'm going to do a proper job of clamping it down.
Great job! <br>I started making carbon fiber ukuleles about four years ago...it's a hobby. Mine look very similar to your design with rounded body /bottom/back with concave neck back so my thumb stays back. <br> I've completed 7. I vac bag them in a female mold so the outside looks almost perfect when it comes out. <br>I'm now working on steam pressed arch top for them. <br>
Very cool! Looks beautiful. I was actually thinking about a ukulele - I have a bunch of smaller carbon pieces from my own project and abandoned by others at the end of the build. Maybe I'll try your method.
Do you make them for sale
Now that's the approach! A female mold is the way to go!
yeah, I concur with tridrles, using a vac bag is essential for a strong finished result. stops redues the formation voids, bumps and the like. cool job over all wood work makes a nice contrast to the fiber <br> <br>Why didn't do a carbon top and neck ?
This was my first time ever working with carbon fiber, and it was part of a workshop that only covered this method. I'd like to try this again in the future, and if I do then I will definitely look into vacuum bagging. <br> <br>Two people in the group went for the full carbon instrument. I haven't seen either completed yet, but one of them seemed promising.
You could also use my old method for making fiberglass and carbon fiber OOAK RC airplane fuselages. Sculpt the form in Styrofoam then completely cover in the glass mat or carbon mat. I use epoxy resin (reason will be clear by the next sentence) to impregnate the mat. Then when the resin is dry and set, I drill a hole where needed, then I pour a solvent that will melt the Styrofoam (gasoline works fine, but I use Acetone in a well ventilated area) and not the epoxy.
Interesting. I imagine that generates quite a lot of fumes. That won't do for my current workspace, but I like the idea.

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Bio: I'm a long time tinkerer and lover of Instructables, but recently I joined Techshop in San Francisco, and decided to really get creative. Right ... More »
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