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Australian blackwod thickness?
http://www.luthiersforum.com/forum/viewtopic.php?f=10101&t=47563		 Page 1 of 1
Author:  dertien616 [ Sat Apr 02, 2016 7:01 pm ]
Post subject:  Australian blackwod thickness?
I'm starting on my second guitar next week. Just ordered all the wood from lmii. I'm doing back sides and top all australian blackwood. Just wondering what thickeness I should be around for everything. Also I've read a little about deflection testing. Is that something I should do for getting the top thicknessed?
Author:  dertien616 [ Sat Apr 02, 2016 7:10 pm ]
Post subject:  Re: Australian blackwod thickness?
Also does anyone have experience bending this with a bending machine. What temps should i bend with? I've only bent Indian rosewood
Author:  johnparchem [ Sat Apr 02, 2016 7:53 pm ]
Post subject:  Re: Australian blackwod thickness?
I use it a lot for back and sides not for tops. You can treat it like Koa. I bend the sides at about the .080", I will thin the area affected by a Venetian cutaway to about .070". I do active backs and I get the thickness from formulas I got out of the Gore\Gilet books. I find that Koa and Australian backs are around 2.4-2.6 mm for a 000 size.

I bend hot 275-300F; unfigured Koa and Australian Blackwood bend easy but highly figured wood can always cause a bit of a problem.
Author:  Hesh [ Sun Apr 03, 2016 6:22 am ]
Post subject:  Re: Australian blackwod thickness?
Hey Thomey - Treat Blackwood just as we would treat Koa since the two are related and in the same family. What John said works for me too.

What I wanted to add is that both Koa and I believe blackwood can show or develop during the bending process a greenish cast that many on the this forum though the years have had the non-opportunity to have to deal with.... gaah :D Turns out that these woods may react with metal, the metal slats, tin foil, etc. As such the wood should be wrapped in craft paper and not directly in contact with metal slats or tin foil wrap.

Regarding deflection testing the goal is to develop a knowledge/data base of your very own that you can reference when you are building more guitars telling you what worked well and what worked not so well for you.

At this point when we are new builders we build according to thicknesses that are deemed suitable but we also deflection test and record the data so that when all is said and done you have a shot at replicating previous results if it worked out well for you. You will find lots of threads on deflection testing here on the OLF if you search for them. The jig and method that you adopt should be recorded and replicated as well so that all things in your testing are static except the wood sample.

Do you need to deflection test to build a killer sounding guitar? Nope. Is deflection testing and recording your results a good idea anyway? Yep :) Then one day when you are about to post pictures of number 100 your data base and experience will permit you to have somewhat repeatable results much of the time.

As a new builder don't forget to tap things and flex things often to start to get that feel for the wood. When I started out I understood the value of a more scientific approach but very much wanted to be an old school Luthier who also had not only an appreciation for our materials but a keen sense of understanding of them developed by time, experience, and handling the materials as often as possible.

One very fine pro builder, Mario P. used make and carry around small blocks of certain woods in his pocket. When I read this I started doing it too and carried some 1/2" X 1/2" X 1/2" BRW in my pocket for about three years...:) Got some strange looks from the TSA back then especially when returning from overseas with lots of exotic wood in my bags...:)
Author:  dertien616 [ Sun Apr 03, 2016 7:37 am ]
Post subject:  Re: Australian blackwod thickness?
So what should my thickness be around for the top. This is a grand auditorium guitar. I've read some people say no less than .120 and some say you can go as low as .90 with black acacia.
Author:  Hesh [ Sun Apr 03, 2016 7:59 am ]
Post subject:  Re: Australian blackwod thickness?
I never topped a guitar with blackwood but if I did for the size that you are doing I would likely be closer to the 90 area than the 120 area. Remember too that a guitar top is a "system" including bracing, bridge plates, bracing height, stiffness, width, AND material. The guitar may be rabbeted or thinned around the perimeter of the underside of the top too. All these things and more contribute to how the final system will function.

Backs have two schools of thought, or at least two.... Some are into "reflective" thicker backs some are into "reactive" thinner backs and want the guitar to function like a bellows pumping out tone and sound.

If you are looking for magic numbers good luck and tell me please when you find them...:) If you want a safe bet for building something that will work fine I'd go 90 and brace accordingly. Just trying to convey that top stiffness can be achieved two ways and more when considering the top and braces as a system.

My preference for the thinner hardwood top is based on wanting something less massive knowing that I can increase stiffness if necessary with less massive spruce bracing.
Author:  dertien616 [ Sun Apr 03, 2016 8:21 am ]
Post subject:  Re: Australian blackwod thickness?
Ok I am definitely going to start recording deflection like you said so if it works out I have something to refer back to. What size weight should I use? I watched a YouTube video with Chris paulick. I think he said use 5lb 4.4oz and it should deflect 1/4".
Author:  rlrhett [ Sun Apr 03, 2016 11:08 am ]
Post subject:  Re: Australian blackwod thickness?
I LOVE black acacia (Australian blackwood). We can have it as urban lumber around here. It is as beautiful as Koa. Whenever it is available there is always a scramble at the school to get some. HOWEVER, it LOVES to split and splinter. Side reinforcements are not a bad idea, and be sure to cut your binding channel in at least two passes.
Author:  Hesh [ Sun Apr 03, 2016 1:19 pm ]
Post subject:  Re: Australian blackwod thickness?
Rirhett hope you are well my friend.

I love the stuff too and have built with it 5 - 6 times now. To me it can be just as pretty as Koa and even more so since I'm not a fan of the reds that are often in Koa. The chatoyance of a highly flamed piece of blackwood can be absolutely stunning!

Thomey the weight that you use is not as important as using the same weight every single time. Something else that's key is how far the boards or what ever you use to prop the wood are from each other not so much in what the number is but again in how consistently you set-up your tests every time.

Searching the archives will get you some of the jigs and specs that the good folks here use.

Lots of us use different weights and spreads on the boards or again what ever used to prop up the wood. You can really do anything that you want here within reason just be consistent AND do the tests at a consistent thickness every time so you are eliminating variables. Again thickness can vary too just use the same thickness every time as you build your data base. I used .140".
Author:  Mike_P [ Sun Apr 03, 2016 1:57 pm ]
Post subject:  Re: Australian blackwod thickness?
I love the stuff, and yeah it can blow the socks off of Koa...

have hold of a 6 pc. set where the top/back stuff taps far more like spruce than blackwood...most likely sides will become binding and the other used for tops only (highly figured, very light in color with some weird black inkline separating sapwood to heartwood...yummy)
Author:  Trevor Gore [ Sun Apr 03, 2016 5:14 pm ]
Post subject:  Re: Australian blackwod thickness?
dertien616 wrote:
... I'm doing back sides and top all australian blackwood. Just wondering what thickeness I should be around for everything. Also I've read a little about deflection testing. Is that something I should do for getting the top thicknessed?

There's a wide variety of thickness you can use, provided you adjust the bracing to suit.

You might be interested in the approach I used on this all-koa guitar (sort of similar to Aus blackwood), which was to get the top mass down to what a spruce top would weigh on the same guitar. I'd use a similar approach on any highly figured hardwood topped guitar.
Mike_P wrote:
I love the stuff, and yeah it can blow the socks off of Koa...

I use blackwood quite frequently. The plain stuff is very easy to bend; the highly figured stuff less so, but it will still bend around a Venetian cutaway without too much trouble. Some blackwood in this guitar for those who like the stuff...
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Author:  Rod True [ Mon Apr 04, 2016 12:30 am ]
Post subject:  Re: Australian blackwod thickness?
Beautiful as always Trevor.

I'm currently working on my 3rd Aus Blackwood guitar. I've never had an issue bending it, note Hesh's comment about it staining green (it's just on the surface though so sands out easily).

Don't know what you'd want to set your top thickness to. Listen to Trevor. Being your second guitar and all make sure you set your expectations at a proper level for yourself...

Blackwood makes a great neck too as shown in Trevor's photo.
Author:  dertien616 [ Mon Apr 04, 2016 7:16 am ]
Post subject:  Re: Australian blackwod thickness?
I looked at Trevor's guitar and that bracing is completely different than what I planned. I was planning on building it like I did my last guitar which was spruce top and I did a standard x bracing. I'm a little confused now on how I should brace it.
Author:  Trevor Gore [ Mon Apr 04, 2016 9:42 pm ]
Post subject:  Re: Australian blackwod thickness?
Rod True wrote:
Beautiful as always Trevor.
Thanks, Rod.
Rod True wrote:
I've never had an issue bending it, note Hesh's comment about it staining green (it's just on the surface though so sands out easily).
I know people who have had quite a bit of staining happen, but it's never been a problem for me. I use little water (and what I do use is filtered rain water, which is all I have here) and stainless steel slats direct to the wood on my bender. I think staining is exacerbated by alkaline (hard) water, iron contaminants (either in the water or from tools) and maybe some body chemistry if you handle the surfaces a lot.
Rod True wrote:
Blackwood makes a great neck too as shown in Trevor's photo.
Neck wood on both guitars is Pterocarpus indicus
dertien616 wrote:
...I'm a little confused now on how I should brace it.

There are many more ways to brace a guitar than standard X-bracing, but it largely depends on what you are wanting to achieve with this guitar. Hardwood tops with standard X bracing will always have a heavier soundboard than spruce topped instruments. Put simply, responsiveness (sound output) is inversely proportional to the top mass; the heavier the quieter (which tells you why spruce and cedar are popular soundboard woods). However, if you want a stage guitar, for example, building a responsive guitar may not be your best choice, because you'll be fighting feedback all the time. So standard X bracing may be your better bet.

The blackwood guitar in the pics above is falcate braced, which suits finger picking styles because it's highly responsive.

Horses for courses.
Author:  dertien616 [ Mon Apr 04, 2016 10:11 pm ]
Post subject:  Re: Australian blackwod thickness?
Ok that makes sence. One more question about the rabbeting the bottom of the top around the edges. I know Taylor does that with a few models. How do you do that and how deep and wide should the rabbet be also how far away from the kerfing should it be. I'm thinking about trying that on this guitar but can't find any info on it. How does that affect the sound?
Author:  Trevor Gore [ Mon Apr 04, 2016 11:08 pm ]
Post subject:  Re: Australian blackwod thickness?
dertien616 wrote:
One more question about the rabbeting the bottom of the top around the edges...

Personally, I've never thought that was a particularly good idea. Better to thin the top from the outside in a horseshoe around the lower bout, starting about 50mm in from the edge. Tap as you go and stop thinning when you have the result you want. Taylor does the rabbet thing because he can CNC it and because he doesn't want people messing with his process. The rabbet is just an approximation to real edge thinning.
Author:  dertien616 [ Tue Apr 05, 2016 6:48 am ]
Post subject:  Re: Australian blackwod thickness?
Ok so I'm assuming you wait until the body is built to start thinning the edges?
Author:  Trevor Gore [ Tue Apr 05, 2016 7:36 am ]
Post subject:  Re: Australian blackwod thickness?
Correct.
Author:  James Orr [ Tue Apr 05, 2016 9:45 am ]
Post subject:  Re: Australian blackwod thickness?
Regarding deflection testing, .25" is the number I saw recommended quite a bit, too. However, I did a test with six sitka tops last November comparing the results I got from using the method from Trevor's book to deflection testing across a 20" span with a 5 lb. weight. I also took into consideration that my best guitars have had spruce tops in the mid to low .09" range, and realized .25" would have leave things too stiff for my liking.

I'd recommend at least .3" for an all-around, general purpose guitar. I think that would give you a lot of flexibility (no pun intended) not knowing anything else about how you construct the guitar.

I've had the opportunity to talk with guitarmakers whom I highly admire and who's work I would love to emulate. I assumed they'd use something repeatable like deflection testing. As it turns out, some do and some don't. Those who don't employ a much more tactile approach, using their hands to flex the wood and make their decisions. That's a sense I'm working to develop. I have my six test tops, and I flex them from time to time to help develop that sense. It's more difficult to do when you build one guitar a year, so having those references to grab and flex has been nice.
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