Kari Topped 12 String Dreadnought

[bdunne]

This is my second 12 string build and it took a long time from start to finish with the day job interfering more than I had hoped. I bent the sides on this with my new sidebender and following the recommended temperatures and times managed to scorch the waist area of the sides. I've scorched sides before when bending by hand and it has always scraped and/or sanded out quite readily so I didn't really worry about the scorching on these sides, until I couldn't remove it and determined that the scorching or discolouration went all the way through. As I had already built the box by the time I realised it I decided to salvage it by dying the sides black to hide the discolouration. It was pretty effective, as long as you like a guitar with black sides. I thought it came out quite nice.

This has a fully compensated nut and saddle and the difference it makes on a 12 string is enormous. This guitar sounds spectacular. I used black Tusq for the nut and saddle and although the end result seems to work pretty well I wasn't happy with the stuff to work with. Both blanks had voids that were exposed when machining in the compensation which was disappointing.

Top - X braced Kauri Pine,
Back and sides - Tassie Blackwood.
Fret board - Mulga, bound with WA Sheoak
Head Stock and bindings - "Forrest Red" sourced from Bunnings flooring boards. (absolute bugger to bend)
Bridge - Tassie Blackwood
Neck - Sipo Mahogany

[GregL]

Hi Brian,

That looks great!
How did you determine the nut and saddle compensation?
How did you "machine" the exact compensation into the nut and saddle?

Thanks,
GregL.

[Kamusur]

Even down to the string spacing over and across the headstock that looks really good Brian.

Steve

[bdunne]

Hi Greg,
I used a method similar to that described in Trevor Gore and Gerard Gilet's design book. In this instance I made a quick rig of the same scale length (25") with frets at 1 and 12 and an adjustable nut and saddle. I measured each of the strings and measured the amount of compensation for each from the theoretical 0 fret and saddle position. I'm in the process of building a rig I can use to measure the string stiffness so I can apply the same measurements to other scale lengths ( also described in Trevor and Gerard's design book). As to machining I couldn't really afford a CNC but I did pick up a mini milling machine from Proxxon world in Tuggerah. German made and capable of machining within about 0.1 mm which seems to be more than adequate for my Lutherie work.

Brian.

[ckngumbo]

Everything about that guitar is really, really sweet!
Congrats
Bob

[GregL]

Hi Brian,

Thanks for the info.
I've made an adjustable jig for intonation (see here: viewtopic.php?f=24&t=6406&p=72363) to do exactly as you have done - I still haven't used it, but I hope it'll work.
Which mini milling machine from Proxxon did you get (if you don't mind me asking)? Is it the MF70?

Thanks,
GregL.

[bdunne]

Hi Greg,
I built my rig on the same principles as yours, just a lot simpler. Only one string at a time and I only really intended it as a single use for this 12 string. I want to set one up where the measurements allow string stiffness to be calculated and thus allow intonation to be calculated for any scale length as per Trevor and Gerard's book. That way I only have to make the measurements once for a given set of strings. I am going to retrofit/apply it to my earlier 12 string, it worked so well.

Yep, I have the MF70, plus a pile of other Proxxon gear, it's very well made and does a great job. As long as you don't over stress them.

Brian.

[Trevor Gore]

Nice guitar, Brian. And a nice job on the intonation, too.

[kiwigeo]

The side save alone makes this guitar a first class effort. Nice work Brian.