Australian/New Zealand Luthiers Forum

John, Trevor-- I was unclear on what the difference is between elastic modulus and flexural modulus, so I looked it up on wikipedia. Elastic Modulus Flexural Modulus According to the above, elastic modulus is a more general term, defined as stress/strain, which in an anisotropic material such as woo...

I've never done it myself, but here's a few threads on using deflection: Plate target thickness of non rectangular plates using deflection testing Re: Top thicknesses :) I think the results from deflection testing will depend a lot on how flat the board is. It might make sense to measure both sides ...

I hate to revive this thread after nine years, but... Does anyone have values for k and μ for a set of nylon strings? It would help me test my spreadsheet. In the case of steel strings, I can get a reasonable approximation for compensation using the D'Addario tensions, masses, and E for steel of 207...

Trevor, thanks for the links. I'll take a look. I'm definitely out of my depth. I took some of this in freshman engineering 45 years ago, before switching to computer science. Unfortunately, I did not do well in those engineering classes (too much beer, I guess!). I've been working from this source:...

Trying to answer my own question, could the shear force be the moment (torque) at the saddle divided by the length of the beam? F = M/l So if I had a string tension of 709 N and a saddle height of 14 mm, then the moment M = 709*0.014 = 9.9 N·m. I could say that the length of the "beam" (i.e. the top...

Page 4-45 talks about shear stress in braces, and warns that it can be exceeded in some species, especially balsa. But it doesn't explain how to calculate the shear stress in a brace or the maximum shear stress in a given material. It defines the shear modulus, but doesn't tell us how to get it or h...

The 4DOF model requires values for the damping, R, of the air, top, sides, and back. How can I measure these values? I know how R is related to Q or δ. R = √(Km)/Q = δ√(Km)/π In section 4.3.3 we see how to measure Q or δ of a rectangular panel. For various species commonly used for top panels, we ge...

Here's how I understand his system. You start with a certain target thickness for the panel, which you calculate from the seven measurements you take of the rectangular, raw panel (length, width, initial thickness, mass, and three frequencies) using the formula in Equ. 4.5-7. Once thicknessed to tha...

Someone, I think Al Caruth, suggested the use of a light pointer such as a lecturer might use. This could be shone on a wall some distance from the guitar giving greater precision. This reminds me of an experiment I saw at NIST, the US government agency that defines measurement standards. My brothe...

I suppose you could get them wet, wrap them up in foil, and put them in the oven at 150 °C too.

Jani, what temperature did you use to bend the spruce?

I reckon that Ibanez would be built like a brick shit house.... It sure is. Despite being fully hollow, it's not really an acoustic instrument. Although it's louder than a solid body guitar. I put 4.7 kg on the rig and only got 0.11 mm of deflection. So K is somewhere around 420,000 N/m and the top...

OK, the last one I showed was a bit crude. But I learned a lot, and have tried to improve it. https://lh3.googleusercontent.com/pw/AP1GczPgKTmesWJYfT_IeOUUHSWjK0mOsNxOQfopCSvOUlIDckBtnpkhRvoXVTyJLl6NPya30NeIOchCqEfptYJqKKrzD-mgrabQ9_CWsXH66Wdds8B9_qMlmOcxr2xFnU_YRdE01UgtMM7lx-KBTXVvAlxG6g=w1234-h929...

So here's a fun experiment. I modeled a Gore Medium steel-string in CAD. Well, just the body so far. Here's how I did it. First, I used R.M. Mottola's very useful "G" Thang tool to draw the outline. I used the printed Drawing No. 4 from the book, and visually tried to find the radii and centers of t...

That's great, Jani. It makes me happy that someone finds it useful. I'm curious which method you used. Measure the action of every fret, every string Fit polynomials to the measured data Model the neck as a line + ellipse + circle Model the neck as a line + parabola The spreadsheet is set up to do t...

Unfortunately, I have no further explanations, just further information. A little googling, and I found that steel strings on guitars are made of the same material as piano wire . Which is spring steel . Specifically, SAE grade 1080 ( ASTM A228 ), which has an elastic modulus of 190 GPa. Or maybe 21...

Jurgen-- I know it's been four years since you posted this, but did you ever figure this out? I got the same results you did. I got a value for E that was nearly twice the usual value (411 vs. 210 GPa). Using your numbers for the E string: T = 8.07 * 9.80665 = 79.14 N ΔT = 79.14 * ((((135.7*325.25) ...

I have posted several spreadsheets here before. Panel thickness, fret positions, fretboard radius/width, neck shape, intonation compensation, 4DOF model, brace stress/sizing. I decided to combine these into one big spreadsheet file with 20 worksheets, and create connections between them, so when you...

edvinguitars.fi wrote: ↑

Tue Mar 05, 2024 6:04 am

Without weights ( except my weighty double laminated sides using purple heart in inner) I hit 96/178/226, by shawing off the back brace briefly, maybe 2-3mm

I think that's right on target. 95/180/227. In any case, it sounds great!

Thanks for sharing.

Greg

Well, with the caveat that I've never built a 12-string, I have these observations, based on my calculations: The panel is 60 to 70 % of the mass of the active area of the sound board. Mass is the #1 priority in a good sound board (other than not breaking, of course). Braces are 75% of the rigidity ...

Wow. Gorgeous. Amazing work. Did you have any trouble obtaining North American woods (Walnut, Sitka) in Finland? And Spanish Cedar comes from Central and South America, I think? Usually used on nylon-string guitars, its flexural modulus is a little on the low side, at 9.12 GPa. Have you found much d...

This forum (on "the book") used to be a lively place. Now it can be weeks between posts. I've posted some things that should be of interest to those who have the book, and, save for Trevor (thanks, Trevor!), I haven't gotten a single comment. So where have the "left-brained" people gone? Where can o...

Google Sheets is a bit slow on the 4DOF model (it's plenty fast for everything else). In the spreadsheet linked above, I only calculated every 1 Hz, 60 to 500, so 440 rows. This takes 9 seconds to recalc, so about 50 rows/sec, if for example, you change Kt. In a copy of this sheet I tried every 0.1 ...

I couldn't find any threads about this section--I guess no one has implemented these formulas? Here's a Google Sheet for neck cross sectional shape , as in section 4.6.7. Look at the sheet labeled "back". You may make a copy and modify it for your purposes. I wasn't sure how to smooth over the trans...

Can Google Sheets implement the 4DOF model? Yes, it can. It works pretty well, too. The graph appears to exactly match the output from Jim's Octave script (graph I posted earlier in this thread), and is pretty close to the book, Fig. 2.4-4. The differences appear to be in the dB values, but the freq...