Saturday, March 14, 2009

The top is braced

This weekend I had some time to brace the top.  Here are a couple of shots:

this is a small deviation from how I normally brace the tops, namely that I added a cross grain brace to help support the dome in the top. That brace is capped with carbon fiber to give it additional strength because it's so short.  The height of the brace is such because there are additional structural braces inside the bandura that run vertically to resist the pull of the strings.  A tall brace will interfere with these braces.  I recently posted some questions to the OLF regarding some bracing ideas and that discussion can be found here.

Some specs from this top:

Weight before bracing: 278g
Weight after bracing (not final): 368g
Thickness: ~0.128"

Guitar makers will notice that this top is almost double what a guitar top weighs.  Considering the additional load that a bandura top takes it's not surprising.  Tapping produces a decent tone but nothing like what you hear when tapping a guitar top.  Unfortunately, I'm not sure that anything can be done about this because of the huge load on the bridge from all of the strings.  The good news is that this won't necessarily mean that the sound will be bad.  My prior instruments have bracing that's just as heavy or heavier than this one and sound pretty good.

Sunday, March 8, 2009

A busy day in Banduristan

It's been a while since I've posted because I haven't had a chance to work on anything for quite a while.  Fortunately, this weekend I managed to get a lot done.


Doing the rosette was basically holding up the rest of the build.  The pattern is rather complicated to do and took me almost all day Saturday.  There are a few flubs in the fine lines around the abalone but the materials are so expensive I decided to try and fix it as best I could and move on.  As it is, the mistakes are visible under close inspection but it looks fine from two or three feet away.

I used a precision adjustable router base to cut the ring-slots. 

The wood ring is a piece of koa I brought back from Hawaii back in 2000.  A tip I got from the OLF was to inlay the wooden ring first, then cut the slots for the purfling and abalone.  For the abalone, I used a new product called Zip-Flex which made life much easier.

As it was, inlaying the black-white-black was very difficult and is where the flubs are.  I tried to use a scarf joint:

to make it look seamless but it didn't work out so well.  The problem was that I only cut the angle on one end and tried to bend the other end up along the angle but it didn't follow closely enough.  Next time I'll do a true scarf joint which should work better - it worked perfectly on the abalone strips!


With the rosette done, I could move on to the braces.  Here you can see the four almost finished braces.  Because the braces are so big, I cut out the centers to form sort of an 'I' beam to lighten them up a bit.  I dropped the weight by about 25% by doing so.  You can also see the 'secret weapon' which is the small brace with the black top.  The black stuff is a strip of carbon fiber glued to the brace to help strengthen it. This short brace will be glued at 90 degrees to the grain of the wood and I'm hoping that this will hold the dome and keep the string tension from collapsing the top.  I'm a little concerned that this brace will make the top too stiff but I'm hoping that the top not collapsing will make up for the extra weight.  When checking tap tones of guitar tops vs. bandura tops, the guitar top has a much higher pitch which implies that guitar tops are much stiffer than bandura tops yet guitars have a much better bass response.
In this shot, you can see the dome shaped into the braces.  

Here you can see the layout of the braces.  The 'I' beam braces go up and down and the carbon capped brace goes diagonally.
Finally, I also managed to complete most of the body and glued up the шемсток or 'upper bridge'.