Shuen-git rl 周旋捷; Swann Jie sl/, 2011:
N°2 好奇藝術::舊+新 Kunstkammer :: Old+New & Film Reviews
N°3 Digital Guqin Museum 數碼古琴互動藝術研究創作室
HandScroll Guqin; HuaKui cubes;
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I put the last coat of latex on yesterday, so it's time to peel the sucker off. If you look closely the tip of the headstock is still wet where it runs down to and gets thick (and also has no airflow down there in the headstock well) - but it's dry enough to remove. Notice it's the same colour as a rubber band - because it is, really.
Now it needs a bit of attention and the mold needs a good inspection to make sure there's no crud anywhere on it - and a nice new layer of mold-release wax - because we really, really don't want stuff sticking to molds that makes hours of extra work, hours and hours.
The bag is lined and the valves installed and the mold has double-side tape, so it can all hold a vacuum. When there's carbon and epoxy in the middle of the latex and the mold ... there bloody better not be any air. With the vacuum pump we can get about 12 pounds on each square inch of the mold, or a few thousand pounds of even pressure over the whole back/neck. Atmospheric pressure is our friend.
Better make a vacuum bag for the front plate. Same deal - paint on the latex...
You may notice that it's a leftie, remember you're seeing the guitar from the inside .
Buckets of latex later:
And I did some preliminary sketching of the outline and placement of the cone on a similar "lab rat" guitar. The cone will be about 3/4" deep I think, about 11" wide and about 9" long.
There needs to be enough space for a front humbucker. This one below has 22 frets and is a 25.5" scale, so that's why the cone goes past the HB route. At 25" scale we've got nearly 1/2" closer to the nut for the 22nd fret, so where the 21st fret is on this guitar, the 22nd will be.
Oh and BTW - it'll be a National-style biscuit bridge cone facing downward.
Here's a roll of 220g twill (the "twill" bit means that each warp goes over two wefts and then under two, that's why you see diagonal lines on carbon things like denim jeans). I think that's about 7.5oz.
I'm using this stuff for the "cosmetic" layer on the outside - the bulk of the carbon behind this layer (structural) is a 400g double-bias (which isn't woven cloth but a 45/45 degree sewed together material - it's the stuff in the very first photo of this thread).
The next part is a lot of cutting out to pre-prepared patterns very much like a tailor making a suit, so it all fits the mold nicely. We want Armani, not MiC WalMart .
I'm afraid the next bit is not going to be photographed because epoxy has a bad habit of wrecking cameras! I'll see if I can get a few pictures here and there (each time I will have to don a fresh pair of gloves) - but since I only have 20 minutes (epoxy starts to gel) to get the whole back/neck done ... we'll see how it goes. It's a panicky task .
When all the carbon is wetted out with epoxy a layer of "perforated release film" goes on top. This allows any excess resin to be squeezed out of the carbon and into the breather fabric above it, giving a good fiber:resin ratio. The breather fabric also spreads the vacuum pressure.
Last edited by Nick JD; June 2nd, 2010 at 02:42 AM.
So, all those hours of preparation come down to a 20 minute rush. Making composite things (and making most things, actually) boils down to having everything lined up and ready to go - in order. You've got to be a bit like a surgeon here ... "Scalpal! Retracter!" because there simply isn't time to go looking for that tool when the resin is sitting there in the pot getting warmer and warmer and you've already wetted out a gazillion dollars worth of carbon...
I took the gloves off and got one photo of the first layer going down on the neck. It's a modern "C" shape.
The rest of the guitar is the same. Successively adding layers and wetting them out with epoxy - and then coaxing out the air bubbles.
Then the release and breather layers are added and the vacuum pump attached. The thing to watch out for here is "bridging", where the cloth is caught between two things and doesn't conform to the mold shape. It's a pain - but you get to know the bad spots in the mold after a few times.
This is about how much resin you want to see bleeding out through the perforated release film.
The neck got a little too much resin ... but it's coming out into the breather fabric and will be thrown away.
All good! This epoxy doesn't require an autoclave - which is nice. If we were making a wing for an Indy Car we'd be a bit more concerned about total strength - because this guitar isn't going to hold 1200 pounds of downforce at 200mph ... we'll be fine.
The mold will last as long as you care for it. It's critical that it's stored well, because you can imagine that a warped mold will make a warped guitar. Before I first use a mold it gets 12 layers of release wax polished into it. That takes about two days - leaving 30 minutes between each layer - but it's an insurance policy against moldings sticking to molds. Epoxy will rapidly become your enemy if you are not a nutter with the release wax.
The latex bags last for quite a few guitars. Sunlight and moisture are not good for them; age is the problem rather than usage if they are well-cared for. If they get a hole or two they are still good - when you hear a vacuum leak a small piece of masking tape takes care of it instantly. That's the beauty of a vacuum ... it sucks the patch down.
I'll probably move to silicon bags soon.
1400g per square meter. Ends up about 2mm thick.
You get a big piece of paper and push it into the complex 3D shape - and through trial and error develop a pattern that you can then use to cut out your carbon to fit nicely and cleanly.
A good way to think of it is the panels of a tent. They all came off a flat roll and yet they are the right shape to come together into a complex 3D object. Same thing.
Here's the top plate mold getting vacuumed. You'll probably notice all the little bits of masking tape on the bag -someone forgot to do the final two layers of latex and the bag was very thin in some places - still works, just looks old when it's new.
And this doesn't really need any explaination .
I forgot to mention that this guitar is getting a white:black:white binding on the body (top), fretboard and headstock. It'll be 0.35mm white, 0.75mm black and 1.0mm white.
I'm think it's a rotary vane pump, but to be honest I'm not too sure what's inside it. Looks like a piston pump to me. Dunno!
It runs permenantly, until the resin has hardened - which is usually about 3-5 hours. 25.5"Hg.
Here's the fretboard under vacuum.
I popped the back/neck molding out of the mold so here's some pictures.
The next step is to cut it out so all those frilly edges are gone and we have a nice, clean glue edge. The white cloth you can see on the edges is patches of 2oz (super thin) glass to hold the edges of the cosmetic layer in place so they don't slip when the structural layers are going on behind them. The reason I use a fine glass is it's see-though and movement can be noticed. It gets cut off with the excess.
The headstock is a difficult part to cut out requiring a special-made tool. I never look forward to that part.
I think it's going to look quite nice with the white binding.
And here's the inside. You can see where the neck carbon strips meet the body. The layers are layed alternately and overlapping so the joint is solid and the guitar becomes one piece.
If you're wondering why it appears the fibers are going the wrong way on the inside of the body it's because those white pinstripes you can see are actually white sewing that connects the carbon layers together in the "double bias" cloth. Half the fibers run at 45 degrees, the other at 45 degrees. This makes for a very strong cloth that doesn't need much resin because the spaces between the weave don't need filling and the fibers are straight, not curly.
Weight for weight there's not much on this earth with a higher tensile strength than those little black fibers.
Here's the top plate. Just needs to be trimmed and to have the cone well cut out of the middle.
Jammed in there somewhere is a headstock face plate.