Build Thread, Osthoff Prototype

[Kevin A]

Originally Posted by Ruble

John and I are talking tops now... He is doing all kinds of mad scientist testing to pick the top... I hope to see some photos of it soon... It looks like it will be some kind of Euro Spruce but specifics are still being nailed down.

Thanks for following this tread.

Chris

Have you guys discussed any inlays yet?

[Ruble]

Originally Posted by Kevin A

Have you guys discussed any inlays yet?

I didn't know he was sending around pictures of my fretboard...

Actually I like blank fretboards...

Chris

[Kevin A]

Originally Posted by Ruble

Actually I like blank fretboards...

Chris

I like the same....less is more, sometimes. Most of my guitars are either blank or have minimal inlay.
Although I'm not opposed to a tasteful 12th-fret like the one John O did here on my 12-string. Rest of the fretboard is blank. ("Heb 13:8")

[joe white]

I like bloodwood bindings on dark guitars. Bloodwood seems to have a "sparkle" to the grain that is quite attractive.

[Ruble]

Originally Posted by getgo

I like bloodwood bindings on dark guitars. Bloodwood seems to have a "sparkle" to the grain that is quite attractive.

I agree very much... I have Bloodwood on my Osthoff AS...Redwood/Koa and had it on both of the Mustapicks that I had.

Chris

[John Osthoff]

Ok, I don't have a lot of progress photos right now. I have been working on the guitar and I do have 3 tops that I am working with. Right now I am leaning toward the Italian Spruce but the Carpathian and Caucasian tops are really nice too. Actually they are all really close in “value.”



I run a series of tests on all my tops (see my research page) and come up with a set a values for stiffness, along the grain and across the grain, but then apply these numbers to the density. The ratio of the x-grain vs the along grain stiffness is something that I really “pay attention too.” I will do some dynamic testing of the these tops once I get them cut to guitar shape. It is then we will decide which one to use on Chris’s guitar. One thing about this prototype that Chris has been really great about is allowing me to "explore" yet come up with standard to create a guitar that all subsequent versions of this model can be compared to.

By the way, even with all this scientific stuff, I do a lot of flexing, sniffing, scratching, looking, feeling, tapping to become more “in touch”with the top. I do spend an inordinate amount of time with them. All three of these contenders sound like a gong when tapped, I know anyone of them would work great so I will reserve those tops that don't end up on this guitar to go on some other version of this model (unless the dynamic testing disqualifies them, which is unlikely.)

I have also become a little intrigued with the upper traverse brace (the big brace under the fretboard that you can see through the soundhole. I have seen a lot of different treatments of this brace and I am in the camp of this brace is more about structure, not as much about tone. Still all these details seem to add up, so I think there is some balance that needs to be met. Anyway, I have been doing some modulus testing on this brace to give me a little more insight to this area of the upper bout.



While the test set-up is a little crude it actually gave me numbers I expected, but more importantly a comparison to work with. In the above setup, I found the spruce to have a Modulus of Elasticity of about 1.75Mpsi which is not an unreasonable number for Adirondack spruce. Before the scientific guys jump all over me, I know this system is not “Calibrated” and I should be using a longer span but it is a good comparison “indicator.” Also I wanted to keep the span close to the upper bout width of the guitar. (I am however a lot more careful with my top measurements.) When I bonded a .020” prepreg carbon fiber E ~10Mpsi strip on one side of the beam (ala AGF sponsor, Howard Kleeper) creating a composite beam the E (modulus of elasticity) increased to about 2.6Mpsi. What was interesting to me is that the beam deflection was the same (based on the resolution of my set-up) regardless if the carbon fiber was on the top of the bottom (compression vs. tension.) Putting the carbon fiber on both the top and the bottom (think I-beam) the E value was 4.4Mpsi. Once again with this area being “mostly” about strength, one might just jump to the last configuration, but I feel there is a balance that needs to be met. I have some other ideas for this brace that are in the process of testing, and while this stuff is a little boring for a build thread”it is part of what goes into the development process. Hopefully soon I can take some more pictures of fun stuff (rosette etc) soon.

[Ruble]

I have no idea what he is talking about...

When I was looking at Bluegrass monsters they called it a popsicle or tongue brace and they were better left out... Now it looks like we torture the tiny piece of wood before installing...

Prototypes are fun.

Chris

[Kevin A]

John is an engineer so he sometimes slips into the language of his peers leaving us non-scientific types struggling to comprehend the description.

I like pretty pictures myself.....

[Ruble]

Originally Posted by Kevin A

I like pretty pictures myself.....

Me too... I'm sure those are coming.

Chris

[GGJaguar]

Are those dumbbells National Bureau of Standards certified?

I don't know what the stiffness ratio is on the Adi top of my SD, but whatever you figured, it sure sounds great!

GG

P.S. F = mA

[gitnoob]

Originally Posted by John Osthoff

I have also become a little intrigued with the upper traverse brace (the big brace under the fretboard that you can see through the soundhole. I have seen a lot of different treatments of this brace and I am in the camp of this brace is more about structure, not as much about tone.

I recall that Somogyi discusses that in his book. He seems baffled that many builders taper the ends of that brace, and he seems to build his very robustly all the way to the rims.

[John Osthoff]

I have a couple of guitars also keeping me busy but I have managed to work in a little time on this prototype. Still doing some evaluation testing too (more later on that.)

Originally Posted by Kevin A

John is an engineer so he sometimes slips into the language of his peers leaving us non-scientific types struggling to comprehend the description.

There is another thread where a guy dismisses a lot of this measurement stuff as "nonsense." To each their own I guess. To me having an understanding of the some of the numbers, patterns and analysis can "guide" me a little bit better in making decisions that are still based on intuition and experience. I won't argue with anybody that there is no substitute for time in the shop, but these numbers mean something to me. I don't build to a formula but rather I use the parameters in a way that helps me to make (better) decisions during the build process. People seem to think my guitars sound pretty good, what I call successful, so for now, I will keep using these processes to help me in my builds.

Originally Posted by Kevin A

I like pretty pictures myself.....

Ok well, I don't have much "pretty" stuff at the moment but here are a few recent shots from the shop.

In this shot, I am using a forming fixture to rough in the “right” curvature on the heel-block. I will clean it up along the grain (as needed) but this fixture really gets things close.



Here the heel-block is being glued to the sides




Here is a shot of a fixture I use to get the neckblock to fit in “just right.” In this shot, I am roughing it in with some fairly aggressive fre-cut paper. I will clean it with a finer garnet paper before gluing.



Just another shot, working on the other surface. (I switch back and forth) until it is good. (In the background is a little fixture I use to drill the neck block of the carbon fiber reinforcement and location pins.)




In these next couple of shots the neckblock is getting glued in place





From this shot, we can see everything fit together quite nicely.



I got some more work done on the rim today, including the soundport, but I don’t have any photo’s processed.

[nacluth]

Nice stuff John. Is your heel block laminated for structural significance or aesthetics for those who peer into the body? If structure, is there a reason why 3-ply or is it just what came up?

[John Osthoff]

Originally Posted by nacluth

Nice stuff John. Is your heel block laminated for structural significance or aesthetics for those who peer into the body? If structure, is there a reason why 3-ply or is it just what came up?

It is actually 4-ply as there is also some carbon fiber in there ... go back in the the thread a little bit and you can see how I made it. I am sure it is over-engineered, but the heelblock can crack when made out of a single piece. I have always used at least a some sort of opposite grain running spline to help with possible failure. So yea is about structure but also as I explained earlier the glue joint with the top and back will be the same width as the kerfed lining. Once again something I have always done by hand caving the heel block after it is installed.

[Kevin A]

I still like pretty 'final' guitar pictures, but I'm also fascinated by both the science (engineering) & art that goes into the building of one of these bad boys.
Pics of jigs/etc. & how they're utilized I still find quite fascinating and enjoyable to follow through the whole build process! Thanks for posting those.....



One observation: In your photo, I see you're using a timer by Taylor. I know Taylor is an established company that has been making timers for a long time, but it looks rather 'old school' versus the more modern styling of say, the contemporary hip Martin model shown below it.