Lattice Braced Concert Uke

[Allen]

Thanks for that picture David.

Can you explain your process here David. I don't know what CF Tow is, and I'm guessing a bunch of others are in the same boat.

Some pictures of the process would be really appreciated.

Cheers Mate.

[schrammguitars]

I use this one from Joe http://www.veneersupplies.com/product_i ... cts_id=683

[schrammguitars]

CF tow is like yarn on a spool. 6k means there are 6,000 fibers like hair. 6K tow is about 1/8" or 3mm wide. I don't know where you guys in Australia purchase it. I'd be curious to know. Here is the best price I've found in the states http://www.aircraftspruce.com/catalog/c ... onYarn.php
You can also get great deals on Ebay.

In small quantities you can get it at https://www.acp-composites.com/home.php?cat=251 but it is much cheaper if you get the spool found in the first link above. Get some guys to chip in.

I have a special jig that I made that has nails spaced about a foot a part and I wrap the tow around. There is wax paper under it. Epoxy is brushed on the tow and worked into it with a stiff piece of rubber or plastic. I then cut the tow with a knife or chisle to the lengths that I want. I wear rubber gloves and pick up the tow and squeeze out the excess epoxy. I then lay the tow on top of the brace. To slow down the cure prior to brushing the epoxy I have a small bowl of ice and place my cup of epoxy in it. This slows it down so I have more open time. Next I slip the lattice in my vacuum bag over night and in the morning I remove it. I cover the lattice with plastic sheeting so it doesn't stick to the bag. If you use the shiney clear stuff it makes a nice gloss finish on your tow.

[Kim]

Carbon Fibre Tow is raw carbon fibre stands Allen. You cut the dry stands to length and lay up as required with epoxy.

http://www.flyelectric.com/carbonfibre.html

That said it would be great if David could share a few images of his process Cool

Dang! beat me by that much. Very Happy

Cheers

Kim

[Allen]

So, let me get this straight.

First off you have your lattice that you lay the epoxy saturated cf tow on with some kitchen film over so it doesn't stick. Vacuum bag this presumably in the form so that it conforms to the shape of the top.

Once cured, you then lay this on the soundboard and vacuum back it to the top. Again in the form.

Once cured you then shape the lattice and finally lay another layer of cf tow on top of the lattice. Giving you cf tow separated by balsa.

Did I get that right?

What epoxy resin are you using for this David?

[schrammguitars]

Thats it Allen.

I use System Three Epoxy, but I'm looking into another brand called Poly Epoxy.

[Allen]

Do you find that you can make a nice and neat lay up and get it all glued to the sound board without epoxy spreading out everywhere?

[schrammguitars]

Yes.

[Allen]

What dimensions do you start off with on the lattice pieces David. Looks like about 3 mm x 5 mm tall?

[schrammguitars]

3mm wide and 8mm tall. Same as the Smallman lattice. A lot of it is removed as you go out from the center. Close to 40% of the lattice is removed. The outer diamonds are actually down to the top but have a layer of tow on them. I don't have any good photos of how much is removed.

It is easy to over brace using the lattice. It takes some guts to start chopping at it and removing a lot more than you think you should but that is how you have to do it. You think it wouldn't work but it does. It takes some time to master this design. I wouldn't say I'm a "master" yet...but I'm getting real close. Like Greg said on his radio interview "You can't see light weight." That is the key. My recent experiments with balsa testing has revealed a lot and opened my eyes regarding its use. I'm excited about the future of this design in my workshop.

Anyhow, I'd love to see what you can do with the Uke.

[Allen]

Thanks David. As you said, it's amazing how stiff the structure gets. From the profile of the top under the vacuum bag, it looks like you make the entire top a uniform thickness similar to the way Greg Smallman does rather than my attempt.

Another thought that comes to mind is how do you decide on how much of the Balsa lattice to remove, is presumably the next layer of CF Tow is going to stiffen it up significantly one more?

I'm thinking that this method must involve a considerable amount of trial and error to get the mix just right.

[schrammguitars]

>>>I'm thinking that this method must involve a considerable amount of trial and error to get the mix just right.<<<

That is correct.

I like what you have done. I hope to hear some sound samples. I encourage you to make more and experiment. Shape the lattice like a mountain. Don't taper the brace ends like you do fan bracing, you'll have too much stiffness along the whole brace. You want it stiff in the middle and looser as you go away from the bridge.

[Kim]

This is all extremely helpful stuff David that will save those of us who will head this direction with their building an enormous amount of T&E. So very generous of you to share your knowledge with us.

Thank you

Kim

[Allen]

Have a lot more done with lots of boring stuff in between that I didn't bother getting pictures of. The neck is Qld. Maple. Spanish Heel style and I made 2 at the same time, as it was not a hell of a lot more work while I was at it.

I cut the slots in the neck for the sides to fin it on my table saw. I have one of those ultra thin kerfed 6 " blades that are sold as ones to go on battery powered skill saws. Mostly used by trim carpenters. Works on the table saw a treat, and doesn't waist a lot of expensive tone wood in the process.

Anyway, to get to the point, the kerf on this blade is 1.8 mm wide, so it just so happens that this is what the sides on the uke are. Cool Nice slip fit with a bit of hide glue and they are rock solid.

Mahogany kerfed linings as I had some and wanted to keep the look consistent inside.

img~

I wanted to go with a very stiff back on this build, so it's at 2 mm thick and the bracing is fairly substantial with some Ebony capping. Has radiused bracing at 15".

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I drilled the holes for no other reason than to have a bit of visual interest on the inside and to tie it in with the UTB on the top.

Now, many of you have probably tapped a top once it was attached to the rims, but without a back on yet. On most of mine the tap tone is rather lack lustre at this point. Nothing to bounce the sound back. It just seems to die.

This one astounded me. It's got a percussive response a bit like a snare drum but without the rattle. I can actually feel the top want to bounce my finger off it when I give it a tap.

And It has sustain.....Hard to describe it, but the sound starts abruptly, has a very slight decay, but then comes at you again. I'm really hopeful that this continues right through to the strings being on.

[DarwinStrings]

Well done for just diving in Allen, it's a bummer you don't get to see that translucent look in the finished product. There is something about making those lattices that I really enjoy as well.

[Lillian]

Allen, ya know you're gonna have to get a sound clip on this one. I know I'm not the only one totally intrigued by this build. And dropping by to have a listen isn't going to happen any time soon. So... please.

[Allen]

Got the back glued on overnight and tapped it again this morning.

Nothing,,,dead. I think it's because there isn't enough venting of the box with just those tiny decorations in the top and it's being "throttled". Good thing I was planning on the sound port, as it is going to need one.

[jeffhigh]

So Allen, did you end up capping the lattice on this at all?

[Allen]

The lattice is not capped Jeff, and right now I'm assessing the top to see if it's viable now that the box is closed up. I'm of a mind that it may be too lightly built and will be destined to failure. Not something that I'm keen on having happen.

The problem as I see it is the waist. Without that transverse brace that is typically straight across there, and how lightly braced and thin I made the top, the waist seems rather weak, and I'm thinking that the top is just going to sink away into it from string tension.

And while it's not my favourite thing to do I might just pull the top off of this one and try again. Fairly easy to do now, not much fun at all after the instrument is finished.

I've just sat it aside for the moment and having a think about it. I've got some CF Tow coming from the place that David Schram recommended. I just might be going into CF lattice bracing sooner rather than later.

Live and learn, and I'm taking you all along with me.

[Kim]

Forget the finish Allen, just string it up so even if it does fail you gain the most from the experience in seeing exactly 'how' it failed, how it sounded before it failed and get 'some' idea of how much you may need to do, or not do, next time in order to have the top still very light, but strong enough. If you scrap it now you would have gained little from the work to this point except for may be more caution than is good for achieving what you initially set out to do.

Just my thought anyhow.

Cheers

Kim

[liam_fnq]

Forget the finish Allen, just string it up so even if it does fail you gain the most from the experience in seeing exactly 'how' it failed, how it sounded before it failed and get 'some' idea of how much you may need to do, or not do, next time in order to have the top still very light, but strong enough. If you scrap it now you would have gained little from the work to this point except for may be more caution than is good for achieving what you initially set out to do.

Just my thought anyhow.

Cheers

Kim

[J.F. Custom]

Allen,

Just looking back at this thread as I thought I remembered you had drilled some holes in the braces much as I had recently done and just posted about in Nick's "Bracing Question" thread; though possibly for different reasons.

Am curious after your last couple of posts where you ended up with this one? Had you progressed any further yet? Did you test in the white with strings? I'd be interested to know where you are at with it and what your thoughts are now...

Jeremy.

[Allen]

Just put some strings on it yesterday afternoon while still in the white. Top started to deform in the waist as soon as strings came up to tension. Just as I suspected it would after having the box closed up. It did have really good volume and snappy response from each note.

So a few minutes later I had the bridge and fingerboard off. Oh I love hide glue for stuff like that. I'll get another top built and continue on with this thread.

[Allen]

Ok, it's been a while since I done anything on this project as I had a lot of other stuff on my plate to get done first. I find that if I let a project sit idle for too long then I loose interest, so have to force myself to finish off things before it gets to that point. As well I had to get some things in place before continuing with this.

So now I've got my vacuum pump/reservoir built. A Vacuum press and a new workbench at a more comfortable hight for my 6'1" stature with a melamine top so the vacuum press works directly on it.

Now back to that lattice bracing.

Micheal Connor sent me some Paulownia off cuts from his surf board building enterprise, and I got a 1 pound spool of CF TOW from the US. The Paulownia is very light. Much like Balsa. I just read on Wikkipedia that it's also use for sound board material on instruments in Korea and China.

I cut the lattice as per David Schramms at 3 mm X 8 mm with a 30 mm spacing and built up the lattice on a work board that I've put a small radius into the lower bout. At it's deepest it's 2 mm.

I wet the CF TOW out with some WEST Systems epoxy with the 206 slow hardener, then carefully cut the stuff to the appropriate length and did my best to lay it out on the lattice. No easy feat I can tell you.

Then flipped it over and laid it on the workboard that had previously been wrapped with some kitchen cling film so the lattice didn't adhear to the workboard. Another piece of clingfilm over the lattice so I didn't get glue on the new vacuum press, Then laid the press on top and hit the valve for the vacuum.

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[DarwinStrings]

Nice to see you back on to it Allen, I am assuming you will add tow to both sides of the lattice but that has left me wondering how you will glue the lattice to the soundboard. Also why did you chose paulownia instead of balsa, was it just availability?