Lutz Top Tap test Results

[kiwigeo]

Today I did some tap testing on a Lutz top set. The Frequencies I picked were above high end values for ranges quoted for Engleman and Sitka Spruce in The Books. There also seems to be a significant variation in properties for two halves of what is supposed to be a set. Calculated Youngs Modulus values seem reasonable as does VL/Vc ratio. VA plots attached. If someone could verify that Im picking the right frequencies from the plots it would be appreciated.

Side A Flong = 82.3Hz

A Flong.jpg (30.37 KiB) Viewed 13236 times

Side A Fcross = 172Hz

A Fcross.jpg (28.19 KiB) Viewed 13236 times

Side A Fdiag = 56.5Hz

A Fdiag.jpg (30.07 KiB) Viewed 13236 times

EL = 11.07Gpa
EC = 0.92Gpa
GLC = 0.83Gpa
Elong/Ecross = 11.98
Density = 400.9Kg/m3
Thickness = 5.0mm
Dimension = 541 x 213mm

Side B Flong = 105Hz

B Flong.jpg (29.7 KiB) Viewed 13236 times

Side B Fcross = 196Hz

B Fcross.jpg (30.85 KiB) Viewed 13236 times

Side B Fdiag = 62.6Hz

B Fdiag.jpg (30.1 KiB) Viewed 13236 times

EL = 21.16Gpa
EC = 1.59Gpa
GLC = 1.42Gpa
Elong/Ecross = 13.32
Density = 468.91Kg/m3
Thickness = 4.7mm
Dimensions = 556 x 213mm

[Trevor Gore]

Check that you've got the board dimensions and mass punched in correctly. A set where the boards are different lengths seems odd...

[kiwigeo]

Rechecked all figures. Changes in dimensions but all other data remains same. Still significant differences between the two halves of supposedly a set:

Side A

Dim: 557 x 212.5mm
h: 5.0mm
Wt: 231gm

Flong - 92.5
Fcross - 174
Fdiag - 57.0

EL - 12.17Gpa
EC - 0.91Gpa
GLC - 0.86GPa
EL/EC - 13.34

Side B

Dim: 557 x 213mm
h: 5.0mm
Wt: 261gm

Flong - 106
Fcross - 198
Fdiag - 65

EL - 18.01Gpa
EC - 1.34Gpa
GLC - 1.27GPa
EL/EC - 13.40

[Trevor Gore]

Using your figures, I get much the same numbers for the elastic constants.

A few things come to mind:

1) Not a set. Check face grain and end grain and see if they match up
2) 18 GPa is tough to digest. Check with a static test (3 point bending)
3) One piece is significantly curved/bowed (both should be flat)
4) They're both the same thickness (5.00mm); one is 50% stiffer. You should be able to easily feel that. Can you?
5) Wood is weird and your results are correct!

[kiwigeo]

Using your figures, I get much the same numbers for the elastic constants.

A few things come to mind:

1) Not a set. Check face grain and end grain and see if they match up
2) 18 GPa is tough to digest. Check with a static test (3 point bending)
3) One piece is significantly curved/bowed (both should be flat)
4) They're both the same thickness (5.00mm); one is 50% stiffer. You should be able to easily feel that. Can you?
5) Wood is weird and your results are correct!

1. It's one Shane Neiffer's sets......the halves seem to match up visually but Ill have a closer look with my Stewmac magnifying glasses on....
2. Will do a static test.
3. Both pieces are flat.
4. I ran the pieces through the drum sander and checked thickness...theyre the same.
5. Wood can be weird.....and interesting.

[garryalb]

Hi Martin,

Your dimensions are only half a mm different in width but the weight is 30g different. Typo?

Garry.

[kiwigeo]

Hi Martin,

Your dimensions are only half a mm different in width but the weight is 30g different. Typo?

Garry.

The weights are correct...and yes there's 30grams difference.

Ive got at least 100 of Shanes top sets on my shelves so over the next few days Ill be tap testing as many of them as I can to build up a better picture of variability in tap data. Ill compile the data and post here on the forum.

[Craig Bumgarner]

I've been using Lutz from the same source on a half dozen guitars over the last year. I've tapped each set, but mostly just one half. I'd comment on the FRC shots if I could see them. I can't seem to bring the JPG up separately, how is that done?

[Trevor Gore]

4) They're both the same thickness (5.00mm); one is 50% stiffer. You should be able to easily feel that. Can you?

4. I ran the pieces through the drum sander and checked thickness...theyre the same.

Sorry, I meant you should be able to feel the difference in stiffness (and as the thickness is the same, it would be due to the difference in modulus)

[kiwigeo]

I've been using Lutz from the same source on a half dozen guitars over the last year. I've tapped each set, but mostly just one half. I'd comment on the FRC shots if I could see them. I can't seem to bring the JPG up separately, how is that done?

Save the image and then open with a photo viewing program. On my Mac, right click - save image - and then open with Preview. Sorry I do my testing on a Windows machine and the pics are saved screen shots. The VA image capture facility seems to crash VA when I try and use it. After doing a few more tests yesterday Imm confident my picks of the peaks are correct and consistent.

[Craig Bumgarner]

Martin, sorry, but when I save the image and view, they are too fuzzy to read. The pictures (attachments), unlike others on the forum, have no links that I can find associated with them. Normally, when I hover the mouse over an attachment, the cursor changes to a finger pointing hand that indicates an active link. Click the link, see the big version. Nothing like that on your FRC pics. The by line indicates the number views, 110 for the first one currently and I think this only happens when the picture is clicked and viewed, so I gather it is working for some.

[kiwigeo]

Martin, sorry, but when I save the image and view, they are too fuzzy to read. The pictures (attachments), unlike others on the forum, have no links that I can find associated with them. Normally, when I hover the mouse over an attachment, the cursor changes to a finger pointing hand that indicates an active link. Click the link, see the big version. Nothing like that on your FRC pics. The by line indicates the number views, 110 for the first one currently and I think this only happens when the picture is clicked and viewed, so I gather it is working for some.

Craig, Ill take some pics with the iPhone and post up later on today.