OM size Nylon String Crossover

[David Stiles]

Hi, It's been a while since I made a guitar. I have been having too much fun making violins & bows.

I am however about to start a falcate crossover guitar and am planning to use my body mold which is a Gore mid- size SS. I believe that I would need to reduce the body depth and sound hole size from the normal SS dimensions. I am also designing a heelless bolt-on neck with elevated fingerboard.

Is this OM/OOO size going to work for a crossover? I am not keen to make a new mold but have niggling concerns as to whether I should.

[Mark McLean]

Hi David
A OM/000 would work OK for a nylon string. I made one using a Gibson L-OO mold and it was fine. That is slightly smaller than a OM, but similar. If you go too big (to D or J size) the nylon strings struggle to drive the big top. Mine was also falcate braced. You can certainly afford to have the top a bit thinner and lighter braced than you would for a steel-string. One other difference, assuming that you are planning to use a classical-style pinless bridge, is that you don't need to do that fiddly thing with fitting the primary falcate braces between the pin holes. You could also opt not to have a bridge plate. Easy!

it doesn't necessarily need to be a thinner body. Most classicals do have a smaller sound hole, but I think mine was about the same as a Steel-string (a bit hard to say as I did an oval for this one, just to be different). Make sure it is big enough for you to stick your hand in to do the neck bolts if they are going to be internal.

[kiwigeo]

Most classicals do have a smaller sound hole, but I think mine was about the same as a Steel-string (a bit hard to say as I did an oval for this one, just to be different). Make sure it is big enough for you to stick your hand in to do the neck bolts if they are going to be internal.

If there's any of the fretboard overhanging the soundhole then make allowance for that as well.

[David Stiles]

I have left this thread hanging for a while!

Thanks to Mark & Martin for your replies. Good point regarding bolt access.

My thinking about sizes went like this:

1. OM has larger outline than a typical classical so, make it thinner to compensate.
2. Smaller volume will make for higher air resonance so, make the sound hole smaller to compensate.

I now realise that this probably doesn't matter as I am not trying to make a true classical anyway. I also note that classicals typically have higher air resonance than SS anyway so a small reduction in body volume from SS design will achieve this with standard SS sound hole size.

[David Stiles]

After a few distractions, I have made some progress on this guitar. As I mentioned, I am going heel less neck with elevated fingerboard. Here is my neck block. I plan to use 4 x M6 bolts, sort of like a telecaster. I should be able to put the bolts in through the sound hole.

[David Stiles]

Here is my rosette, made using off-cuts from Black Bean back:

[David Stiles]

Back, Top and sides ready to assemble:

[kiwigeo]

Some neat work there David....puts my efforts to shame.

[Dave M]

That's just what I was going to say. The carbon fibre and epoxy work is very tidy.

When you say crossover does that mean you will be putting pickups in?

[David Stiles]

Thanks guys.

'Crossover' is nylon strings with some features that would not be usual on a steel string. A narrower fretboard with a radius. It does have a pickup now.

[Bob_H]

Nice, and interesting. Will be keen to see the neck joint progress. Would it be fine on a steel string as well?

[David Stiles]

I spent a lot of time thinking about the neck joint.

I fitted the sides of the neck to the neck pocket before glueing the top on. It was easier that way as I could work with the taper of the pocket to gradually bring the neck into the correct position. The neck was aligned with the body centerline and the 12th fret was lined up at that stage. After glueing the top, I only had to plane a slight chamfer on the underside of the neck to get the pitch correct (2mm below the top at the saddle).

There has been discussion on ANZLF about heelless necks and my takeaway was that they can be plenty strong enough for steel string but 'don't look right'. This might change with Martin now doing a heelless model. My motivation for going heelless is nostalgia. My very first guitar back in the day was a Maton F10 Classical; I still have it.

Elevated fingerboard is a classical guitar trend, as far as I know not used for SS. For me, it gives more room for the neck bolts as well as making access to higher frets easier.

Here is complete neck set:

[Mark McLean]

That should work well. Graham McDonald's bouzouki designs include one with a bolts-through-the-back set-up like that and it is very solid, and nicely adjustable for neck angle. I like the idea of the elevated fingerboard too. This is a very interesting build!

[Duct Tape]

Do you mind sharing what your widths were at the nut snd 12th fret? I’m thinking of a similar build.

Thanks

Jon

[asgilbert]

Hi David, Love your work. Sorry for the what might be a dumb question to all in the know... Being wood, do you leave time for the joint to settle and redo the bolts before final glue up of the fretboard?

[David Stiles]

Jon, I went for 48mm nut width and 58mm neck width at12th fret.

asgilbert, all the wood is well seasoned and the neck was cut to rough size at least six months ago so everything should be fairly stable now .
Changes in humidity will always cause some variance of the neck angle (height projected to bridge position). It is important to acclimatise the guitar body at 50% humidity when setting this up. If necessary, I should be able to shave the underside of the neck to adjust this angle right up to final assembly after varnish, & beyond. There is a double acting truss rod as well.

[Taffy Evans]

Hi, interesting build, thanks for sharing the process and thinking behind it.
Taff

[asgilbert]

Hi, interesting build, thanks for sharing the process and thinking behind it.
Taff

Thanks

[David Stiles]

I have had made some progress. Completed the binding using off the shelf Indian Rosewood/Maple from guitarwoods.com.au
I thought the colour looks good against the Blackbean. I used double black/white purfling which matched the rosette purfling pretty well.

[David Stiles]

While I am waiting for some veneer for the headstock so I can finish the neck, I made my bridge. It's Blackwood with Carbon Fibre to the Gore/Gillet book design. It weighs 14g.
Rather than making it 12-hole, it has 18 holes but six of them are only a few millimeters deep. So, tying strings will be like a 12-hole bridge but the bitter end of strings will anchor in the half holes. There are pros and cons but it seems to me that this be the least fiddly way to tie when changing strings. At least, this guy makes it look easy in his video: https://www.youtube.com/watch?v=-oDlPbqQ2-Q

[kiwigeo]

Coming along nicely David..

[David Stiles]

I have finished french polishing and fitted the bridge. There are some visible bending cracks on the top bout. I thought about getting some new sides but did a bit of epoxy work and I quite like the look of them now.
Here is the crack when it happened:

And here is the result:

The Black Bean is fairly gnarly so a few the cracks and other marks kind of work.

Bridge on:

Neck Joint:

[David Stiles]

Just been looking at resonances. The main body resonances when the box was first closed were: 88,176 & 237

Now after binding, shellac and bridge, I get: 97,188 & 231.

The top went up because of the bracing added by the bridge; a bit more than I would have expected really. I guess the back went down due to the weight of finish. Can't explain the large increase in the air resonance; 88 to 97? Anyway, my target top resonance of 190 is not going to happen, but it should be all workable. If I end up with a problem resonance, I have scope to drop frequencies by tuning the back down.

[Mark McLean]

It is looking great David. I like the neck joint. It looks very elegant with the bolts all internal, and the absence of the heel plus the elevated fingerboard should make for good playability up the neck. Did you taper the body width at the neck end when you decided to elevate the fb?

[David Stiles]

Thanks Mark, the top is domed at 10m radius but the dome is tilted down toward the neck. When I was shaping the dome I took 5mm off the neck block and virtually nothing if the tail block. This way the neck meets the sides at closer to a right angle than it would have otherwise. Neck doesn't appear to be at a weird angle to the body.

On the subject of neck joint, I just finished putting a shim in the neck joint. When the guitar came together, I hit target classical string height but I realized that I would prefer a lower action in a crossover. I could have planed the heel however I went the reversible option and made a tapered shim out of maple veneer. That got the action down to 3mm/2.25mm at the 12th fret which plays nicely with no buzzing.