Bunya/Blackwood OM

[Tod Gilding]

I built this guitar for my son, but it was also an experiment in the use of Bunya as a soundboard.I hadn't heard many bunya topped guitars that I liked,most lacked volume and projection.with this one I took the top down to 2.2mm and X braced it as I would with a more traditional top, it has worked, great tone, even response and volume across all strings and good projection. If I have learnt anything from this, it is that bunya tops need to be taken down a little more than most species,but I need to get a setup to check accurately the deflection,before making any conclusions.
And improving my joinery skills

Specs

Tasmanian Blackwood Back and Sides
Bunya Soundboard
Braces and neck Australian Red Cedar
Fretboard and headplate Sally Wattle
Machines Grover Rotomatics
Scale length 25.4"

[charangohabsburg]

This top surely is an eye-catcher!
Nice background too, great colour-match with the guitar.

[christian]

Nice One Tod !!!!
has a real warm earthy look to it, man that Bunya looks so similar to Macrocarpa.
I don't suppose you know the properties of bunya ? weight and MOE?

Cheers,

Christian.

[Tod Gilding]

Thanks Marcus and Christian.

Christian I have never seen bunya like this,it was given to me as a billet just large enough for 2 bookmatched tops,the person I got it from salvaged it from tree that he played in as a kid,and wanted a momento that he intended to carve a picture into, but after 40yrs of having it laying around he decided that I may as well make a guitar with it.

Bunya Properties:
Density. 530 kg/m3 at 12% moisture content; approximately 1.7 m3 of seasoned sawn timber per tonne.
Strength groups. S6 unseasoned; SD5 seasoned.
Stress grades. F4, F5, F7, F8 (unseasoned), F7, F8, F11, F14, F17 (seasoned), when visually stress graded in accordance with AS2858-2000, Visually stress-graded softwoods for structural purposes.
Joint groups. J4 unseasoned; JD4 seasoned.
Shrinkage to 12% MC. 4% tangential; 2% radial.
Unit shrinkage. 0.23% (tangential); 0.11% (radial). These values apply to timber reconditioned after seasoning.
Durability above-ground. Class 4 - life expectancy less than 7 years.
Durability in-ground. Class 4 - life expectancy less than 5 years.
Lyctine susceptibility. Not susceptible.
Termite resistance. Not resistant.
Preservation. Heartwood is relatively easy to impregnate with preservatives.
Seasoning. Dries rapidly but precautions against bluestain are necessary.
Hardness. 1.7 kN green, 2.3 kN dry (Janka hardness).
Machining. Easy to work.
Gluing. Glues well.

[christian]

Hey thanks for the info Tod !!! I never used to be one for the numbers but I find it very interesting now especially when comparing it to timbers I use.
at 530Kgm3 its got a bit of weight to it and no doubt good stiffness, no wonder you could afford to thin it out to 2mm.
again great guitar mate !!!
Cheers,

Christian.

[Trevor Gore]

Amazing effort! Takes a lot of "bottle" (as we used to say in the olde country) to use a top like that.

Regarding bunya's properties, Bootle gives its Young's Modulus as 13GPa, but I've never found any that stiff, more like 9-10GPa. It varies a lot in density too (not unusual), ~450kg/m^3 to ~540Kg/m^3.

[Tod Gilding]

Thats One way of putting Trevor

I have heard a whisper that I may get your books for christmas, that could be a good way to spend Chrissy day,a cold one and Contemporary Acoustic Guitar Design and Build

[ozziebluesman]

G'day Tod,

Nice guitar mate! Congratulations.

I have a set of silver wattle that has that same arrow figure through the back like your guitar back. I've used bunya as a top on a parlor sized guitar I built and liked the volume and projection from the guitar. I went just a tad under 3mm on my top and I was happy with the outcome.

Thanks for posting

Cheers

Alan

[Tod Gilding]

Thanks Alan ,It's very Rustic and the bunya , as Trevor pointed out, does vary a lot,this top that I have used was very stiff,I had it at 2.5mm and it felt like you could drive a truck on it.

[christian]

Wow 13Gpa at 450kgm3 thats up around the best spruce !! amazing how much variance you can get from the same timber eh?
maybe the piece you used Tod had in actual fact been run over by a truck a few times and compressed the fibres!!! hahaha
its still a testament to some bloody good bracing on your part.

Cheers,

Chtristian.