Current Build - Falcate Braced Multiscale OM cutaway

[kiwigeo]

I opted to make up a whole new top rather than modify existing bracing on the old top. The old top centre joins closed up after a day or two and can be fixed with a bit of hide glue and a centre seam patch or two.

A new swiss spruce top (from same log by the look of the wood and serial no) was thicknessed to around 2.8mm (2.7mm final target) and braced up using red spruce for the bracing. Bracing will be 9mm high over the bridge. A new rosette was made up...IMO it turned out a bit better than the first one. The lower back brace has been modified to stiffen it up a bit.

[kiwigeo]

Bracing all done and topped with CF tow. UTB has been slotted and is ready to glue in and the top is finished.

Also managed to get the top of a falcate braced classical started...this guitar has been on the bench for 2 years. First neck wasn't quite right so made another one. The top is Englemann and was furry as hell even after several egg white sizing and sanding back sessions. The sheallc seal coat raised enough grain that the fibres were breaking through the shellac after a few body sessions. I gave it a good level with 800 grit wet and dry and walnut oil and it seems to have got rid of most of the nibs. In the background is a parlour guitar (falcate braced) waiting pore filling and french polishing.

[dshaker]

The top is Englemann and was furry as hell even after several egg white sizing and sanding back sessions. The sheallc seal coat raised enough grain that the fibres were breaking through the shellac after a few body sessions.

I haven't ever done this with a guitar, but I learned something from my furniture projects that might be worth mentioning. Someone told me that the fibers breaking through the finish was because sanding wore away at the hard grain lines, but pushed the soft wood, in between the harder grain lines, down into the cavity between the grain lines. Then, later, atmospheric moisture would enter the wood and expand the soft wood. The soft wood would then break through the finish.

The technique I was taught to deal with this was to sand with sandpaper down to about 400 grit, then, believe it or not, wet the wood slightly with water and pass a propane torch LIGHTLY over the wood to dry the wood. This caused the soft wood to expand significantly. Then I took relatively fine steel wool and rubbed the wood lightly with it until the wood was smooth again. This was explained to me as using the loops in the steel wool to catch the soft wood where it stuck up and tearing those fibers out, rather than pressing them down. Now the soft wood is no longer available to push up through the finish. I applied finish after the steel wool procedure, with no other intervening steps.

I can't say what would happen with Englemann spruce, but I used this technique on a tiger-stripe maple chair 25 years ago and then finished it with tung oil. The wood fibers of that chair haven't ever come through the finish, even though tung oil is almost certainly a thinner finish than shellac and 25 years is a long time.

[kiwigeo]

Got the new top on last night and this morning did some tap testing. Results as follows:

T(1,1)1: 103Hz
T(1,1)2: 197Hz
T(1,1)3: 224Hz

[kiwigeo]

I haven't ever done this with a guitar, but I learned something from my furniture projects that might be worth mentioning. Someone told me that the fibers breaking through the finish was because sanding wore away at the hard grain lines, but pushed the soft wood, in between the harder grain lines, down into the cavity between the grain lines. Then, later, atmospheric moisture would enter the wood and expand the soft wood. The soft wood would then break through the finish.

The technique I was taught to deal with this was to sand with sandpaper down to about 400 grit, then, believe it or not, wet the wood slightly with water and pass a propane torch LIGHTLY over the wood to dry the wood. This caused the soft wood to expand significantly. Then I took relatively fine steel wool and rubbed the wood lightly with it until the wood was smooth again. This was explained to me as using the loops in the steel wool to catch the soft wood where it stuck up and tearing those fibers out, rather than pressing them down. Now the soft wood is no longer available to push up through the finish. I applied finish after the steel wool procedure, with no other intervening steps.

I can't say what would happen with Englemann spruce, but I used this technique on a tiger-stripe maple chair 25 years ago and then finished it with tung oil. The wood fibers of that chair haven't ever come through the finish, even though tung oil is almost certainly a thinner finish than shellac and 25 years is a long time.

Thanks for the info. The Englemann Im using is from Graham Hein. Its as stiff as anything but sometimes really furry. Its not a huge issue as the first leveling session usually knocks back the nibs and the french polishing pretty much goes smoothly from there.

[kiwigeo]

Pics of the modified lower back brace. The centre section of the brace was taken from 21mm down to 15mm.

[Trevor Gore]

That looks a bit more normal, but the back still seems low in frequency for a brace that big.

What produces the odd harmonics on the mains frequency?

[kiwigeo]

That looks a bit more normal, but the back still seems low in frequency for a brace that big.

What produces the odd harmonics on the mains frequency?

The odd harmonics are from the laptop power pack. I normally run on the battery when doing testing but this was just a quick run. Theres also a power pack for the pre-amp which sometimes puts out a bit of noise. I also usually run mic and preamp cables more carefully but this time the mic cable was probably closer than usual to the pre-amp power pack.

[Lex]

Some very nice work going on there Marty

Im sold on the falcate bracing with live backs, I have managed to produce a couple of very powerful Instruments using Trevors techniques and Im sure this one will be also. Im impressed with your carbon fibre laying very neat indeed.

Cheers Tod G

[kiwigeo]

Some very nice work going on there Marty

Im sold on the falcate bracing with live backs, I have managed to produce a couple of very powerful Instruments using Trevors techniques and Im sure this one will be also. Im impressed with your carbon fibre laying very neat indeed.

Cheers Tod G

Yeah getting better with the laying down of the CF tow.....it's just practise and getting familiar with how much resin to lay on....just enough to get a bond but not too much to cause the tow to "float" and stick out from under the brace like gruns stick out your shorts leg when the elastic goes

[kiwigeo]

The tentative forward plan:

1. Targets are 95/180/226 for air, main top and back frequencies.
2. Allowance for effect on T(1,1)2 once the bridge goes on is one area of uncertainty. Assuming 0.6Hz/gram drop as per the book and assuming a max bridge weight of 25gram ....I need to allow for a drop as high as 15Hz. T(1,1)2 is currently at 197Hz so Ive only really got 2Hz to play with if I thin lower bout periphery. Should I thin at all?
3. With a Gore style CF/wood bridge will mass still have more effect than increased stiffness on resonances?
4. Back frequency is a tad low but there is provision to trim it up by adding mass to lower back brace. I actually tap tested the back with the top off and got peaks of 130Hz and 224Hz before carving out the centre of the brace...ie a 6Hz drop.

All comments and advice welcome.

[johnparchem]

The tentative forward plan:

1. Targets are 95/180/226 for air, main top and back frequencies.
2. Allowance for effect on T(1,1)2 once the bridge goes on is one area of uncertainty. Assuming 0.6Hz/gram drop as per the book and assuming a max bridge weight of 25gram ....I need to allow for a drop as high as 15Hz. T(1,1)2 is currently at 197Hz so Ive only really got 2Hz to play with if I thin lower bout periphery. Should I thin at all?
3. With a Gore style CF/wood bridge will mass still have more effect than increased stiffness on resonances?
4. Back frequency is a tad low but there is provision to trim it up by adding mass to lower back brace. I actually tap tested the back with the top off and got peaks of 130Hz and 224Hz before carving out the centre of the brace...ie a 6Hz drop.

All comments and advice welcome.

I got quite a drop stinging up my two SS falcate guitars of 7-10 Hz even after I put the bridge on.
On my two SS the T(1,1)2 went down after gluing on the bridge on two of my classical guitars T(1,1)2 went up about 8 Hz and on one the T(1,1)2 stayed about the same

[kiwigeo]

I got quite a drop stinging up my two SS falcate guitars of 7-10 Hz even after I put the bridge on.
On my two SS the T(1,1)2 went down after gluing on the bridge on two of my classical guitars T(1,1)2 went up about 8 Hz and on one the T(1,1)2 stayed about the same

Thanks John.

At this stage I think it's important to work out a strategy that leaves me with T(1,1)2 high side so I then have the option of trimming my adding side mass. Today Ill be mulling over the tap test data and revisiting the books before making a decision.

[blackalex1952]

Following this thread, with all its drama and jeopardy, its emotion, its beauty! I am inspired to take on a falcate build as soon as possible! It's like building one my self now, following all this. Can't wait till it's strung up! The tension is killing me! It's a cliff hanger!!! Better than SBS late at night! Where WILL those final resonances end up???? Will the side mass need to be adjusted, or will the bridge end up light and strong and yet, somehow, the top main will hit the target anyway, perhaps in combination of some fine back brace work?? Will the top and the back live happily ever after in a perfect relationship? Will there be a twist at the end? When it's finished, please post some audio recordings!
ps: NICE WORKSHOP!

[kiwigeo]

Will there be a twist at the end?

Not at the end....in the middle.

The back is off and the patient is undergoing surgery:

1. beefing up primary top bracing to get T(1,1)2 up over 200Hz.
2. Replacing lower back brace with a new one....slightly higher to get T(1,1)3 up a bit.

Am I crazy? No...just completely anal.

Shaving CF tow off top of primary braces

Tantelone guides for the brace extensions.

Brace extensions glued in

Off with the old back brace

And on with the new one

[blackalex1952]

To be continued...

[Trevor Gore]

So, Martin, when did you apprentice in violin making?

[kiwigeo]

So, Martin, when did you apprentice in violin making?

A violin is on the list of things to build.......might as well get a bit of practise in now .

[kiwigeo]

Got the back on and did a quick tap test:

T(1,1)1 - 104Hz
T(1,1)2 - 199Hz
T(1,1)3 - 239Hz taping and micing back. The peak is not coming through when tapping the top. The back brace is 23mm high and I didnt take any meat out of the middle so there's room for trimming this peak down to 226Hz

[kiwigeo]

Forward plan:

1. I still don't have a lot of between the T(1,1)2 of 199Hz and target of 180Hz so I'm not going to thin the edges of the lower bout.
2. Ill take a bit of meat off the lower back brace top bring T(1,1)3 down to around 226Hz.

I was hoping to get T(1,1)2 up above 200Hz but obviously the added height on the primary and secondary braces (+3mm) wasn't enough.

[kiwigeo]

Did some more thorough Tap testing today (average of ten runs) and got some better results:

T(1,1)1 - 104Hz
T(1,1)2 - 202Hz
T(1,1)3 - 240Hz (from testing on back - peak not visible on top spectrum)

Plan now is to drop T(1,1)2 by a maximum of 5Hz with thinning of the periphery of the lower bout.
Do the binding and then address trimming of the back resonance by trimming the lower back brace.

[kiwigeo]

Back's off again......was a bit "humpy" around the edges in two spots. Good enough for most but not good enough for me.

While the backs off I replaced the back linings, laid some extra CF tow on the primary and secondary braces to add a bit more stiffness and took a bit of mass off the side mass anchor splints.

[Nick]

This guitars been apart more times than Richard Burton & Elizabeth Taylor and had more work done than Joan Rivers!
I'm enjoying this build though Martin, warts and all, it's a great learning tool for beginners and older hands alike.

[kiwigeo]

This guitars been apart more times than Richard Burton & Elizabeth Taylor and had more work done than Joan Rivers!
I'm enjoying this build though Martin, warts and all, it's a great learning tool for beginners and older hands alike.

The "Grandpa's axe" build.

Back about to go back on and hopefully I'll be back on track. Bending binding around the cutaway is the next challenge. Need to empty the swear jar first.

[kiwigeo]

Got the back on the instrument and have done some Tap testing.

T(1,1)1 - 104.5Hz
T(1,1)2 - 200Hz the extra CF on the top braces doesnt seem to have added much stiffness.
T(1,1)3 - 235Hz. Another strong peak at 288.9Hz

Top

Back

I tried sticking some dummy bridges to the top and noted drops in T(1,1)2. Frequency drops worked out at 0.6Hz/gm pretty much as in the books. Assuming a bridge weight of 27gms Im expecting the bridge to drop T(1,1)2 by about 16Hz. This means I can only afford to drop the main top resonance by around 4Hz.

With the above in mind I plan to do some minimal thinning of top periphery keeping a careful eye on frequencies.
Back does not appear to be coupling with the top at present. Ill address any modifications to the lower back brace once bindings are on.

As usual any comments/advice welcome.