scalloping braces after the fact

springer · #1 12-31-2016, 04:44 PM

Got a nice vintage Yairi Alvarez. The top seems a little glossy and thick for my taste (partly as a result of some repair being done and more finish applied). I think reducing some of the finish via scraper and maybe fine paper could be a good thing. Did a little test and it scrapes off easily so it must be nitro thankfully. It's had plenty of time to cure.
I'd also like to put some scallop in the X bracing, tone bars. Some of you done this in an already built guitar right? Tiny planes, sand paper? I think these two things might transform a pretty good sounding to even better. Any thoughts, advice appreciated.

dekutree64 · #2 12-31-2016, 05:58 PM

Yep, finger plane and coarse sandpaper will do the trick.

Measure how much the bridge rotates under string tension compared to all strings loose. Don't go over 2 degrees.

Don't dig deep scallops that cause localized high curvature. Try to spread the stress evenly over the whole soundboard.

Being vintage, the neck angle may be off. Take a ruler just in front of the bridge and see how high the strings are above the soundboard. 1/2" is the general standard. If it's below 7/16" with the action where you want it, then I'd recommend fixing that and seeing how it sounds before altering bracing.

springer · #3 12-31-2016, 10:58 PM

I'll string it up and check the string height, but I'm pretty sure everything in good shape with the neck, no issues. I'm calling a mid seventy "vintage" but it's not that ancient.

"Measure how much the bridge rotates under string tension compared to all strings loose. Don't go over 2 degrees."

Are you saying... as I reshape/remove material from braces that the bridge on the strung guitar will begin to rotate more and more so dont go over 2 degrees?

printer2 · #4 01-01-2017, 09:21 AM

Quote:

Originally Posted by springer

I'll string it up and check the string height, but I'm pretty sure everything in good shape with the neck, no issues. I'm calling a mid seventy "vintage" but it's not that ancient.

"Measure how much the bridge rotates under string tension compared to all strings loose. Don't go over 2 degrees."

Are you saying... as I reshape/remove material from braces that the bridge on the strung guitar will begin to rotate more and more so don't go over 2 degrees?

You got it.

Truckjohn · #5 01-01-2017, 10:59 AM

A few tips.

This is mostly flying blind work. Most people who do this end up destroying the guitar.... It's very easy to put the top into a situation where the bridge pulls loose, the action rises huge, it caves in across the sound hole, or it's just loose and flabby sounding.

Often - gently shaving the back braces has a larger effect on tone and also doesn't put the guitar at risk of caving in or the bridge from tearing off.

If you have large or inflexible arms and hands - this is not the sort of thing you want to try.

Going too far on the top will end up leaving you with a lumpy, flabby, unfocused, woofy sounding or broken guitar. It will take a couple weeks of good playing for the guitar to react..... And by then - it's too late if you overdo it.

If you are still determined to muck around with the top bracing even though we told you not to....

Do not touch the X brace from about the middle of the bridge plate north.
Do not touch the upper transversal or any braces that support the sound hold.
Do not be aggressive in one spot. That will cause humps and cracks.

Start with coarse 60 or 80 grit sandpaper instead of a blade. This will slow things down and also prevent cutting too deep or slicing off the end of your finger.

Sand a little then restring and play. Stop when the sound just begins to open up a little. That's it.

Remember - it's really easy to destroy a guitar... Very hard to undo the mess.

raggedymike · #6 01-01-2017, 11:05 AM

I bought a Martin D18 circa 1966. Around 1970 I had the braces shaved by Matt Umanov (it was all the rage back then). Didn't really do anything for my guitar except void the warranty and maybe give it a belly sooner than otherwise. Is this still a thing?

springer · #7 01-01-2017, 12:06 PM

advice well taken. I considered the possibility of mucking things up. Glad I asked. IF I decide to mess with it, i'll definitely take the conservative approach using points mentioned above. Thanks a bunch

tadol · #8 01-01-2017, 12:53 PM

If its got a really thick finish on the top, and you've already started scraping, I'd just take it all off and spray a shellac sealer coat on it to keep it clean and play it like that a bit. Without a specific tonal goal, mucking around with the interior semi-randomly is a huge risk - you did say its a pretty good sounding guitar already, right?

Alan Carruth · #9 01-01-2017, 03:17 PM

It's already a pretty good guitar, so how do you want to change it?

For the most part, it's easier to get more bass than more treble. Shaving braces, whether on the top or the back, will usually tend to bring up the bass. So will thinning the top, and that's almost inevitable when you scrape or sand off finish. If the guitar already has enough bass, than I'd leave it alone.

Treble is harder to get. You can raise the pitch of the 'main air' resonance either by adding a side port, or enlarging the main sound hole. The port acts as a monitor in noisy or dead spaces, so that can be a benefit in itself. Enlarging the hole often gives a more 'open', 'forward' or 'projecting' sound, depending on who's talking about it.

If what you want is more 'clarity' or 'sparkle' it's harder to say just what you should do to get it. In part that's because it's hard to say where it comes from, and in part, again, the terms differ depending on who's using them. It's pretty certain that one thing that makes a guitar sound 'flat' or 'boring' is high damping: something is dissipating the string energy before the box can turn it into sound. The problem is that there are lots of things that can do that, from the wood used to poor construction to the finish, and, again, there's a lot of disagreement about what the terms mean.

At any rate, without knowing what difference you're trying to make, and where the instrument is to begin with, it's hard to say how to get what you want. Shaving the top braces will certainly alter the tone. Whether you'll like the change, or the things that go along with it, is another matter.

springer · #10 01-05-2017, 04:33 PM

ok I think you guys have cured me of the compulsion to mess with the insides, except to repair a finger brace which came completely loose and one partly separated, and some old glue cleanup. There actually does seem to be some mild scallop going on so... and since this could be hand made by Yairi himself (his autograph on label) ... etc. I wanted to post pics but ran into complications getting set-up with PictureBucket. Maybe another time.
I'll go ahead with the top finish removal and see how that goes.
Thanks for the wise advise.

My desire to 'mess' with this guitar stems from missing my old law-suit Takamini (stolen)which had a nice lively mid-range growl. Nothing wrong with the tonal spectrum of this Alvarez in terms of low and upper end really, it's just a little muted in comparison. Was hoping to enliven it up a bit.