Search found 1364 matches

by Trevor Gore
Mon Nov 19, 2018 9:32 am
Forum: Contemporary Acoustic Guitar Design and Build - Trevor Gore
Topic: Calculation of brace Young's Modulus (eq. 4.4-4)
Replies: 7
Views: 160

Re: Calculation of brace Young's Modulus (eq. 4.4-4)

You have too many zero in your first row of data, column E.

Flexural rigidity is a pretty straightforward calc. You need to develop some confidence in your results, best done by "triangulation". i.e. calculate three different ways and if you get the same answer three times it might be right! :D
by Trevor Gore
Mon Nov 19, 2018 9:21 am
Forum: Contemporary Acoustic Guitar Design and Build - Trevor Gore
Topic: Predicting Panel Mass SS - Lookover
Replies: 4
Views: 96

Re: Predicting Panel Mass SS - Lookover

The answers can be slightly different due to Excel, but it's most likely that slight differences are due to rounding errors. If you hand transfer data from an elastic constants spreadsheet to a panel mass spreadsheet it is unlikely that you will be transferring all 15 significant figures that Excel ...
by Trevor Gore
Sun Nov 18, 2018 3:01 pm
Forum: Contemporary Acoustic Guitar Design and Build - Trevor Gore
Topic: Measuring Elastic Constraints - Lookover
Replies: 9
Views: 222

Re: Measuring Elastic Constraints - Lookover

That looks about right, John. You seem to have replicated the Table 4.5-3 results.

Feeling good? :D

Well done!
by Trevor Gore
Wed Nov 14, 2018 9:49 am
Forum: Contemporary Acoustic Guitar Design and Build - Trevor Gore
Topic: Calculation of brace Young's Modulus (eq. 4.4-4)
Replies: 7
Views: 160

Re: Calculation of brace Young's Modulus (eq. 4.4-4)

Density is mass/unit volume, so you need what the scales say, namely 0.172 Kg. If I change 1.687 to 0.172 in your formula I get 10.5 GPa, which is about right. Straight off the spreadsheet: =(((414.6 * 0.5085^2) / (1.0279 * 0.019)) ^2) * (0.172 / (0.5085 * 0.051 * 0.019)) I can't see where you're go...
by Trevor Gore
Tue Nov 13, 2018 10:23 pm
Forum: Contemporary Acoustic Guitar Design and Build - Trevor Gore
Topic: Starting out on J45
Replies: 14
Views: 1769

Re: Starting out on J45

Definitely need 3/8" or 10mm, preferably 10mm for the mortise chisel. Often, 3/8" is sold as 10mm, so be sure you know what you're getting. 1/2" is too big and 1/4" is too small! The bar size is typically 3/8" for brass (which needs filing to fit in the 3/8" hole, hence a preference for 10mm) or 10m...
by Trevor Gore
Tue Nov 13, 2018 10:06 am
Forum: Contemporary Acoustic Guitar Design and Build - Trevor Gore
Topic: Calculation of brace Young's Modulus (eq. 4.4-4)
Replies: 7
Views: 160

Re: Calculation of brace Young's Modulus (eq. 4.4-4)

So, I’m a bit confused how to get that into GigaPascals (N/m^2). Pascals are a measure of pressure, units of newtons per square meter. A newton is defined here . Young's modulus, E, is stress/strain. Stress has units of pressure as above, strain is meters/meter, so the units cancel and strain is di...
by Trevor Gore
Tue Nov 13, 2018 9:05 am
Forum: Contemporary Acoustic Guitar Design and Build - Trevor Gore
Topic: Measuring Elastic Constraints - Lookover
Replies: 9
Views: 222

Re: Measuring Elastic Constraints - Lookover

John, Carefully check Table 4.5-3 in the black book, especially the density numbers. You're showing 0.395 Kg/m^3. Should be 1000 times that. Also check out these threads: http://www.anzlf.com/viewtopic.php?f=33&t=4019 http://www.anzlf.com/viewtopic.php?f=33&t=3626 The 2nd edition of the books has ev...
by Trevor Gore
Mon Nov 12, 2018 10:39 am
Forum: Instrument Builders Forum
Topic: Removing old shellac?
Replies: 8
Views: 242

Re: Removing old shellac?

How old is old? Old, fully hardened hard shellac is pretty well impervious to anything, including methyl chloride based strippers. Sanding works best on that stuff. Recently applied shellac will mostly wash off with IMS, even if you used hard shellac. I've had cases where I've tried to FP WRC and on...
by Trevor Gore
Sun Nov 11, 2018 10:58 pm
Forum: Contemporary Acoustic Guitar Design and Build - Trevor Gore
Topic: Measuring Elastic Constraints - Lookover
Replies: 9
Views: 222

Re: Measuring Elastic Constraints - Lookover

John, Your frequency measurements look about right. Check out Table 6.1 in the white book. Mahogany will fall between spruce and rosewood. Your elastic constants are incorrect, though. Your numbers for E long (for example) should be ~ 10 GPa, which is 1.0E+10, not 1.xxE+16 as you have. Check your ze...
by Trevor Gore
Sun Nov 11, 2018 10:37 pm
Forum: Contemporary Acoustic Guitar Design and Build - Trevor Gore
Topic: Predicting Panel Mass SS - Lookover
Replies: 4
Views: 96

Re: Predicting Panel Mass SS - Lookover

Your panel mass is about double what I'd expect. I think you may have omitted a factor of 2 (remember you're using a half template).
by Trevor Gore
Sun Nov 11, 2018 10:27 pm
Forum: Contemporary Acoustic Guitar Design and Build - Trevor Gore
Topic: Main Air is at 110 Hz, aka the A note
Replies: 4
Views: 118

Re: Main Air is at 110 Hz, aka the A note

Kevin, Adding side mass to reduce the frequency of the T(1,1)2 mode has very little effect on on the T(1,1)1. Check out Fig. 2.4-2 in the black book. Shaving the back braces can reduce the T(1, 1)1 (and the T(1,1)3 of course), but you don't want to reduce the T(1,1)3 any lower than it is now. The "a...
by Trevor Gore
Sat Nov 10, 2018 3:29 pm
Forum: Contemporary Acoustic Guitar Design and Build - Trevor Gore
Topic: Main Air is at 110 Hz, aka the A note
Replies: 4
Views: 118

Re: Main Air is at 110 Hz, aka the A note

First, I need a little more information:

1) Is this guitar complete and if not what stage of build?

2) Do you know what mode the 239Hz peak is?
by Trevor Gore
Sat Nov 10, 2018 11:26 am
Forum: Contemporary Acoustic Guitar Design and Build - Trevor Gore
Topic: Falcate #2 Tapping Results
Replies: 5
Views: 139

Re: Falcate #2 Tapping Results

... I think my main focus with this guitar is that the back be as "live" and resonant as I can make it. What are some hallmarks of a truly live back? Higher dB on the T(1,1)3? Thanks again for all the help! Chris To me it is the way it couples with the top also I get a much more complex final tap s...
by Trevor Gore
Mon Oct 15, 2018 10:22 pm
Forum: Contemporary Acoustic Guitar Design and Build - Trevor Gore
Topic: 3 piece pernambuco back
Replies: 6
Views: 936

Re: 3 piece pernambuco back

John, I am assuming you're going for a live back because you're computing a target panel thickness. Check what the back panel mass will turn out to be and then compare that with other live back guitars you have made. I'm suspecting that the pernambuco might be too dense and therefore have too low a ...
by Trevor Gore
Wed Oct 10, 2018 10:10 pm
Forum: Instrument Builders Forum
Topic: Louro Faia for binding .. a complete failure
Replies: 25
Views: 1188

Re: Louro Faia for binding .. a complete failure

kiwigeo wrote:
Wed Oct 10, 2018 10:53 am
Ok Trevor what's going on?? Time to come clean. :evil:
Well, I thought all luthiers could grow (and resorb) a third hand at will.

Are you saying you can't?

You'd better get down to the vet and see what he can do for you, or you might be permanently stuck with those four feet. :shock:
by Trevor Gore
Tue Oct 09, 2018 10:16 pm
Forum: Instrument Builders Forum
Topic: Louro Faia for binding .. a complete failure
Replies: 25
Views: 1188

Re: Louro Faia for binding .. a complete failure

Trevor, you look pretty close to burning your fingers... Well, that shot was posed for the book. I was operating the camera at the same time as posing for the shot. But I don't wear gloves when bending wood anyway. I haven't burnt my fingers yet, but that's perhaps not a recommendation for others! ...
by Trevor Gore
Tue Oct 09, 2018 9:17 am
Forum: Instrument Builders Forum
Topic: Louro Faia for binding .. a complete failure
Replies: 25
Views: 1188

Re: Louro Faia for binding .. a complete failure

Yes Trevor has caused a fair bit of grief pretty much round the world with that cutaway! :D I must have done dozens of those cutaways and never really had a problem. In terms of binding, the figured blackwood and figured sycamore/maple are the easy ones, because the wood is pretty floppy. The tough...
by Trevor Gore
Mon Oct 08, 2018 10:14 pm
Forum: Instrument Builders Forum
Topic: Louro Faia for binding .. a complete failure
Replies: 25
Views: 1188

Re: Louro Faia for binding .. a complete failure

kiwigeo wrote:
Mon Oct 08, 2018 9:31 pm
It was you who designed that bldi cutaway OM with that cutaway horn with a radius so tight that the blackwood bindings started trembling in fear whenever I got them close to the mold!!
Yep, and they just submit to their fate as soon as I point a bending iron at them!

Show 'em who's boss! :D
by Trevor Gore
Mon Oct 08, 2018 9:07 pm
Forum: Instrument Builders Forum
Topic: Louro Faia for binding .. a complete failure
Replies: 25
Views: 1188

Re: Louro Faia for binding .. a complete failure

I recently spent a week trying to bend some blackwood bindings for a Gore style OM cutaway. I gave up in the end and used some Brazilian Rosewood bindings I found hidden on one of my shelves.....that stuff just bent like butter!! A week???!!! Probably works better if you do it quicker! :wink: :mrgr...
by Trevor Gore
Fri Oct 05, 2018 9:44 am
Forum: Contemporary Acoustic Guitar Design and Build - Trevor Gore
Topic: interpretation of data
Replies: 9
Views: 607

Re: interpretation of data

The new piece has typical density for its Young's modulus, whereas the original piece had rather high density for its Young's modulus, so at least you're now starting on a more level playing field. The best wood (in terms of making the lowest mass tops) is usually the lowest density wood, because ad...
by Trevor Gore
Thu Oct 04, 2018 1:39 pm
Forum: Contemporary Acoustic Guitar Design and Build - Trevor Gore
Topic: First Falcate underway! Plate Thickness question?
Replies: 10
Views: 816

Re: First Falcate underway! Plate Thickness question?

The small peak at 221Hz may not be the T(1,1)3. You have identified the B(1,1) at 230Hz. Usually the T(1,1)3 is a little higher in frequency than the B(1,1), so I would expect the T(1,1)3 to be around 233Hz. The peak at 221Hz may be either the result of a whole body mode (bending like the fundamenta...
by Trevor Gore
Thu Oct 04, 2018 8:54 am
Forum: Contemporary Acoustic Guitar Design and Build - Trevor Gore
Topic: First Falcate underway! Plate Thickness question?
Replies: 10
Views: 816

Re: First Falcate underway! Plate Thickness question?

The T(1,1)1 and the T(1,1)2 seem a little high, but the T(1,1)1 is likely a consequence of the T(1,1)2. The T(1,1)3 is in about the right place for a live back with a T(1,1)2 at 180Hz. What size top braces did you use and what Young's modulus were they? Also worth checking the T(1,1)2 frequency agai...
by Trevor Gore
Wed Oct 03, 2018 11:14 am
Forum: Contemporary Acoustic Guitar Design and Build - Trevor Gore
Topic: Three Random Questions
Replies: 3
Views: 261

Re: Three Random Questions

#1: Do these density, frequency and Gpascal values fall in line with others that use sitka? There's a saying that some of us are wont to use "Spruce is spruce", meaning that across all the various spruce species Young's modulus is proportional to density, irrespective of species. Your piece of Sitk...
by Trevor Gore
Fri Sep 28, 2018 9:15 am
Forum: Contemporary Acoustic Guitar Design and Build - Trevor Gore
Topic: interpretation of data
Replies: 9
Views: 607

Re: interpretation of data

Keeping count of the zeros is often a source of error. Everything should be in SI units (meters, kilograms, seconds). Stress/pressure is in Pascals, but we work in GPa (10^9 * Pascals). Your answer should come out in meters, which then need multiplying by 1000 to get millimetres. Applied loads (when...
by Trevor Gore
Thu Sep 27, 2018 10:51 pm
Forum: Contemporary Acoustic Guitar Design and Build - Trevor Gore
Topic: interpretation of data
Replies: 9
Views: 607

Re: interpretation of data

Would be great if you can check the calculations. I checked using the data in your first post. I get the same El, Ec, G and density as you, but for f=60 I get a target thickness of 2.52mm rather than the 2.83mm you got. You need to check your coding for equation 4.5-7. Check your results using the ...