Having trouble with target plate thickness calculations

You can ask questions here about Trevor and Gerard's exciting new book on Luthiery.

Moderators: kiwigeo, Jeremy D

Post Reply
d.pearcy@comcast.net
Gidgee
Posts: 5
Joined: Tue Mar 01, 2022 3:25 pm

Having trouble with target plate thickness calculations

Post by d.pearcy@comcast.net » Sun Mar 06, 2022 11:55 am

I have tried everything I can think of and my Excel spreadsheet is returning nonsensical values for target plate thickness (i.e. target thickness greater than starting thickness.
It appears to be returning correct values for E long, E cross and G.
I've attached a screenshot of the formula I'm using. Any guidance would be much appreciated.
Attachments
Plate Thickness Calc.pdf
(172.69 KiB) Downloaded 182 times

User avatar
lamanoditrento
Blackwood
Posts: 570
Joined: Thu May 05, 2016 9:50 am

Re: Having trouble with target plate thickness calculations

Post by lamanoditrento » Sun Mar 06, 2022 5:33 pm

Normally the issue with errant results is a wandering decimal place. I would start there to make sure your standard units are converted correctly.
Trent

User avatar
kiwigeo
Admin
Posts: 10365
Joined: Sat Sep 29, 2007 5:57 pm
Location: Adelaide, Sth Australia

Re: Having trouble with target plate thickness calculations

Post by kiwigeo » Sun Mar 06, 2022 8:15 pm

Keep track of your zeros..... 8)
Martin

GregHolmberg
Sassafras
Posts: 43
Joined: Mon May 17, 2021 5:05 am
Location: California, USA

Re: Having trouble with target plate thickness calculations

Post by GregHolmberg » Mon Mar 07, 2022 8:25 am

Hard to tell, since the PDF doesn't show your formulas.

Here's my spreadsheet (google sheets).

My answers match the book. Well, they did until I changed what I was using for Poisson's ratios (νLC and νCL, as shown in table 4.5-1). You can see what I'm using for those on the second worksheet, "Constants". I tried to use the actual numbers for Engelmann Spruce, which is the wood that I have. As Trevor pointed out in the book, it didn't make much of a difference.

Greg

GregHolmberg
Sassafras
Posts: 43
Joined: Mon May 17, 2021 5:05 am
Location: California, USA

Re: Having trouble with target plate thickness calculations

Post by GregHolmberg » Mon Mar 07, 2022 8:46 am

Some comments on my results.

I bought some inexpensive panels from stewmac--US$20 for a pair. Grade "A", whatever that means. They also sell more expensive grades.

These panels were fairly heavy for Engelmann Spruce--460kg/m^3. Gore's nicer pieces averaged 366, and the wood-database.com says 385. I guess I got what I paid for.

Still, they look nice, don't have too much grain run-out. 4 to 8 rings per cm. Stiffness was good at 13.6 GPa. However, the stiffness was not enough to make up for the high density, and I got an R (sound radiation coefficient) of ~ 12, versus 14 for Gore's pieces. At the target thickness, 2.6 mm, I got a mass of 174 g, versus Gore's 146.

In his commentary on Table 4.5-3, Gore implies that he rejects panels if the cross-grain stiffness is too low or the mass too high. From the examples he gives, I'd guess his limits are about Ecross >= 60 and mass < 160. Clearly my panels don't make the cut.

What kinds of requirements are you using for your panels? Ecross, mass, R, something else?


Greg

d.pearcy@comcast.net
Gidgee
Posts: 5
Joined: Tue Mar 01, 2022 3:25 pm

Re: Having trouble with target plate thickness calculations

Post by d.pearcy@comcast.net » Mon Mar 07, 2022 10:41 am

lamanoditrento wrote:
Sun Mar 06, 2022 5:33 pm
Normally the issue with errant results is a wandering decimal place. I would start there to make sure your standard units are converted correctly.
Thank you, I will have a closer look

d.pearcy@comcast.net
Gidgee
Posts: 5
Joined: Tue Mar 01, 2022 3:25 pm

Re: Having trouble with target plate thickness calculations

Post by d.pearcy@comcast.net » Mon Mar 07, 2022 10:43 am

kiwigeo wrote:
Sun Mar 06, 2022 8:15 pm
Keep track of your zeros..... 8)
Thank you. I will look again.

d.pearcy@comcast.net
Gidgee
Posts: 5
Joined: Tue Mar 01, 2022 3:25 pm

Re: Having trouble with target plate thickness calculations

Post by d.pearcy@comcast.net » Mon Mar 07, 2022 10:45 am

GregHolmberg wrote:
Mon Mar 07, 2022 8:25 am
Hard to tell, since the PDF doesn't show your formulas.

Here's my spreadsheet (google sheets).

My answers match the book. Well, they did until I changed what I was using for Poisson's ratios (νLC and νCL, as shown in table 4.5-1). You can see what I'm using for those on the second worksheet, "Constants". I tried to use the actual numbers for Engelmann Spruce, which is the wood that I have. As Trevor pointed out in the book, it didn't make much of a difference.

Greg
I appreciate your help. Your formulas have gotten me on the right track!

d.pearcy@comcast.net
Gidgee
Posts: 5
Joined: Tue Mar 01, 2022 3:25 pm

Re: Having trouble with target plate thickness calculations

Post by d.pearcy@comcast.net » Mon Mar 07, 2022 10:46 am

GregHolmberg wrote:
Mon Mar 07, 2022 8:46 am
Some comments on my results.

I bought some inexpensive panels from stewmac--US$20 for a pair. Grade "A", whatever that means. They also sell more expensive grades.

These panels were fairly heavy for Engelmann Spruce--460kg/m^3. Gore's nicer pieces averaged 366, and the wood-database.com says 385. I guess I got what I paid for.

Still, they look nice, don't have too much grain run-out. 4 to 8 rings per cm. Stiffness was good at 13.6 GPa. However, the stiffness was not enough to make up for the high density, and I got an R (sound radiation coefficient) of ~ 12, versus 14 for Gore's pieces. At the target thickness, 2.6 mm, I got a mass of 174 g, versus Gore's 146.

In his commentary on Table 4.5-3, Gore implies that he rejects panels if the cross-grain stiffness is too low or the mass too high. From the examples he gives, I'd guess his limits are about Ecross >= 60 and mass < 160. Clearly my panels don't make the cut.

What kinds of requirements are you using for your panels? Ecross, mass, R, something else?


Greg
I'm just trying to figure out the mechanics of taking the measurements and crunching the numbers. You are way beyond me!

WilliamDavidReynolds
Kauri
Posts: 30
Joined: Tue Jul 26, 2022 3:43 pm

Re: Having trouble with target plate thickness calculations

Post by WilliamDavidReynolds » Thu Dec 08, 2022 2:51 pm

Hello,

I’ve been building the spreadsheet in .xl and doing quite a bit by hand too.
I’m having a decimal issue with EL or equation 4.5-2, plugging in Trevor’s measurements I keep getting 1.184 can’t figure out how to get it to 11.84

I changed the decimal on the Mm and the density, about fifteen times and nothing works.

Until I get this working, nothing else will work

My decimal is off in next equation as well, 4.5-3
It’s pretty basic math as far as complicated goes and I’m stumped

GregHolmberg
Sassafras
Posts: 43
Joined: Mon May 17, 2021 5:05 am
Location: California, USA

Re: Having trouble with target plate thickness calculations

Post by GregHolmberg » Fri Dec 09, 2022 11:56 am

Well, we can't do much for you without seeing your spreadsheet.

I suggest you look at mine (linked above) and look for differences.

Greg

User avatar
lamanoditrento
Blackwood
Posts: 570
Joined: Thu May 05, 2016 9:50 am

Re: Having trouble with target plate thickness calculations

Post by lamanoditrento » Fri Dec 09, 2022 4:30 pm

My recommendation is to have one cell with the measurement you want to use and another cell that converts your measurement into SI. You can quickly check the conversion is ok as you create them with easy numbers e.g. 1000g coverts 1kg. And then have your formulas draw the data from SI cells.
units to si.JPG
units to si.JPG (24.39 KiB) Viewed 1747 times
Trent

WilliamDavidReynolds
Kauri
Posts: 30
Joined: Tue Jul 26, 2022 3:43 pm

Re: Having trouble with target plate thickness calculations

Post by WilliamDavidReynolds » Sat Dec 10, 2022 3:34 am

GregHolmberg wrote:
Fri Dec 09, 2022 11:56 am
Well, we can't do much for you without seeing your spreadsheet.

I suggest you look at mine (linked above) and look for differences.

Greg
I looked at your spreadsheet. Very detailed results and nice layout, though your formulas aren’t listed, I’m not worried about reading others results from their samples though, but it is a respectable amount of work you’ve put into your testing.
Especially the clamped tests, and now I believe I gotta come up with my own poison/hearmon ratios of my woods.
I decided I’m not building anymore guitars until I get the math done, I did some tinkering with my formulas construction in excel with minimal results,
Do you have Gores equ. 4.5-6 results in your spreadsheet? I couldn’t find anything that looked that way, my outcome for that equation is 4.89,,, and I’m believing it should be different

I could email you my spreadsheet if you like, would be great to get feedback.

GregHolmberg
Sassafras
Posts: 43
Joined: Mon May 17, 2021 5:05 am
Location: California, USA

Re: Having trouble with target plate thickness calculations

Post by GregHolmberg » Sat Dec 10, 2022 8:01 am

I don't understand why you say you can't see the formulas in the spreadsheet. Click on a cell, see the formula at the top?

Eq. 4.5-6 is for frequency, f. Not sure why you would want that, but no, it's not in the spreadsheet. f is the parameter you would choose, as in Table 4.5-2, not something you calculate.

4.5-7 is the inversion of that for thickness, h, which is what everyone wants. You can see that formula in column T.

By the way, the measurements in my table are not mine. They are averages for the species taken from wood-database.com

Greg

WilliamDavidReynolds
Kauri
Posts: 30
Joined: Tue Jul 26, 2022 3:43 pm

Re: Having trouble with target plate thickness calculations

Post by WilliamDavidReynolds » Sat Dec 10, 2022 1:32 pm

GregHolmberg wrote:
Sat Dec 10, 2022 8:01 am
I don't understand why you say you can't see the formulas in the spreadsheet. Click on a cell, see the formula at the top?

Eq. 4.5-6 is for frequency, f. Not sure why you would want that, but no, it's not in the spreadsheet. f is the parameter you would choose, as in Table 4.5-2, not something you calculate.

4.5-7 is the inversion of that for thickness, h, which is what everyone wants. You can see that formula in column T.




By the way, the measurements in my table are not mine. They are averages for the species taken from wood-database.com

Greg

I believe I can’t get a cell to react when I click on it is that your spreadsheet is an html.
I have 4.5-6 calculated because the sequence in the book shows this equation before 4.5-7 and 4.57 calls for F,
I’m overwhelmed haven spent days on spreadsheet trying to get his 2.72 target thickness using the measurements from table 4.5-3.
So you’re saying to use table 4.5-2 for F, steel string top is 75. So plugging 75 into 4.5-7 gave me 2.7153,, which is correct. Ok,,, so I’m baffled why I’m following along the equations and the book even says frequency is subjective ,,, I can barely write I’m so frustrated. Haha, ugh

WilliamDavidReynolds
Kauri
Posts: 30
Joined: Tue Jul 26, 2022 3:43 pm

Re: Having trouble with target plate thickness calculations

Post by WilliamDavidReynolds » Sat Dec 10, 2022 1:59 pm

GregHolmberg wrote:
Sat Dec 10, 2022 8:01 am
I don't understand why you say you can't see the formulas in the spreadsheet. Click on a cell, see the formula at the top?

Eq. 4.5-6 is for frequency, f. Not sure why you would want that, but no, it's not in the spreadsheet. f is the parameter you would choose, as in Table 4.5-2, not something you calculate.

4.5-7 is the inversion of that for thickness, h, which is what everyone wants. You can see that formula in column T

By the way, the measurements in my table are not mine. They are averages for the species taken from wood-database.com

Greg



So it’s working now.
Thank you for clarifying We don’t use 4.5-6,,,,,,,,,, ugh, and clarifying I do, indeed use Table 4.5-2 for F
This was it. The only thing that had me jacking around. My wife was doing her own spreadsheet version too, because she is a computer wiz. We both were changing our formulas layouts around and around in cells and over cells and etc.
guess I can thickness my Euro spruce top to 2.86mm now thanks to your help. I was going blind looking at the laptop.

When I decided to steer off the archtop path and do these flattops(34’ radius) I bought Gore/Gilets book because like you and the rest on here,,, want to be responsible and scientifically shoot for the highest quality guitars with consistent results.
I’m a hands guy,,, science/math I can do but just twists my rear into knots and makes my mind seize.
Thank you sir

WilliamDavidReynolds
Kauri
Posts: 30
Joined: Tue Jul 26, 2022 3:43 pm

Re: Having trouble with target plate thickness calculations

Post by WilliamDavidReynolds » Sat Dec 10, 2022 7:31 pm

GregHolmberg wrote:
Sat Dec 10, 2022 8:01 am
I don't understand why you say you can't see the formulas in the spreadsheet. Click on a cell, see the formula at the top?


Greg
Ok Greg, now that I’m not consumed in top and back thickness science which was just ridiculously easier than I was swinging my hammer,, I was looking at your spreadsheet on my phone and it asked me to install the app. Well I felt really dumb, because I didn’t look for the app myself. I can see your formulas now.
Once again thanks for the heads up on the frequency equation being null. I can’t believe we had everything correct and kept plugging in that equation.
Thank you.

AKEric
Sassafras
Posts: 47
Joined: Fri Sep 28, 2018 1:29 pm

Re: Having trouble with target plate thickness calculations

Post by AKEric » Sun Dec 11, 2022 3:26 am

"I’m overwhelmed haven spent days on spreadsheet trying to get his 2.72 target thickness using the measurements from table 4.5-3."

Keep at it. I'm far from a math wiz, with zero experience with spread sheets until now, and it took me a month of diligent work to get my spread sheet to work. Scouring this forums' previous posts helps a lot. I think I've read every one from the very beginning. Amazing range of topics.

Still haven't figured out how to put a box around someones quote, though.

Eric

User avatar
kiwigeo
Admin
Posts: 10365
Joined: Sat Sep 29, 2007 5:57 pm
Location: Adelaide, Sth Australia

Re: Having trouble with target plate thickness calculations

Post by kiwigeo » Sun Dec 11, 2022 5:58 pm

AKEric wrote:
Sun Dec 11, 2022 3:26 am

Still haven't figured out how to put a box around someones quote, though.

Eric
Top right of post window there's a row of buttons....the one at right with the quotation marks will bring up a reply window with the original post in quotes.
Martin

AKEric
Sassafras
Posts: 47
Joined: Fri Sep 28, 2018 1:29 pm

Re: Having trouble with target plate thickness calculations

Post by AKEric » Mon Dec 12, 2022 4:11 am

Thanks Martin. I should have seen that. Much appreciated.

Eric

GregHolmberg
Sassafras
Posts: 43
Joined: Mon May 17, 2021 5:05 am
Location: California, USA

Re: Having trouble with target plate thickness calculations

Post by GregHolmberg » Mon Dec 12, 2022 7:12 am

WilliamDavidReynolds wrote:
Sat Dec 10, 2022 7:31 pm
Ok Greg, now that I’m not consumed in top and back thickness science which was just ridiculously easier than I was swinging my hammer,, I was looking at your spreadsheet on my phone and it asked me to install the app. Well I felt really dumb, because I didn’t look for the app myself. I can see your formulas now.
Once again thanks for the heads up on the frequency equation being null. I can’t believe we had everything correct and kept plugging in that equation.
Thank you.
Ahh, looking at it on your phone. I see. If you look at it in a browser on a computer, there's no app to install. Google Sheets is a JavaScript app that runs in the browser, so nothing to install on a computer. I recommend the Google Chrome browser for Google Sheets.

Just FYI, there are many formulas in the book that you don't need to implement. Gore is just showing his work--how he got to the final equation. This is typical in academic papers--you have to prove what you're saying. 4.5-6 is just an intermediate step. But for practical purposes, you can just take his word for it and skip all the intermediate equations and go straight to the last one in a section.

Wait until you get to the 4DOF equations of section 2.4.1! Vectors of complex numbers! Some people say you can implement this in a spreadsheet. I haven't figured out how yet. I think it would require 5000 rows using complex numbers. Not sure. I just use the MATLAB script someone posted elsewhere on this forum. It would be nice to have these equations in a spreadsheet (I think Google sheets supports complex numbers), but it's beyond me at this point.

Calculating the brace stress as in table 4.4-2 is pretty tricky, since he doesn't actually show how to do it, and it's quite complicated. I did it in this spreadsheet if you want to see.

Another difficult one is Eq. 4.7-37, minimization of intonation errors. It requires an optimization feature in the spreadsheet software which takes two inputs. Google sheets optimization only takes one input, so I will have to move to LibreOffice for my spreadsheets.

Gore has said several times that he doesn't plan to publish his spreadsheets because he believes it's an important part of the learning process to implement them yourself. It's true, you do learn a lot, but it greatly limits the set of people who can take advantage of these formulas. I'd rather see many more people building better guitars, even if they aren't spreadsheet people. Therefore, I will publish all my spreadsheets once I figure out some of the above issues.


Greg

WilliamDavidReynolds
Kauri
Posts: 30
Joined: Tue Jul 26, 2022 3:43 pm

Re: Having trouble with target plate thickness calculations

Post by WilliamDavidReynolds » Mon Dec 12, 2022 9:52 am

GregHolmberg wrote:
Mon Dec 12, 2022 7:12 am
WilliamDavidReynolds wrote:
Sat Dec 10, 2022 7:31 pm
Ok Greg, now that I’m not consumed in top and back
Greg
I believe I like that Gore wants us to learn it, and I did learn 4.5-7,, and will do bracing calc soon, for the model Super Dread I just designed I’ll be using Gores 6.3/13mm bracing and im not calculating the stewmac brace wood I bought. Not for this anyway, soon though.
But I also believe using one’s own spreadsheets is liability free. Like I’d be scared to tell someone here is mine, what if it’s wrong by .1mm, what if I caused someone to waste time and money in materials.

Now I did like your layout and coding, and cross referenced what we were doing with yours, excel finally started spitting out proper numbers after I deleted the F frequency input from 4.5-6 equation and our spreadsheets were on track.

Post Reply

Who is online

Users browsing this forum: No registered users and 8 guests