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  #106  
Old 12-15-2018, 12:51 AM
GaultierRedon14 GaultierRedon14 is offline
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I've been quietly following along and learning from your posts, Tim. Thanks! One question that came to mind after reading your last post was, how does scale length affect your thicknessing and bracing, and/or voicing?
For example, a client orders two guitars, same model, same tone woods, same playing style and string gauge, etc., but wants one to a scale length of, say, 24.9 or 24.75, and the other to be 25.4 or 25.5.
So, how big of a difference might there be in the thickness of the top, or size of the braces between the two?
Is this essentially the same question you have to answer for a client who wants to build two identical guitars but one designed for medium gauge strings and the other for light gauge strings?
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  #107  
Old 12-15-2018, 07:06 AM
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Originally Posted by Knives&Guitars View Post
I will gratefully take, enjoy and even relish your long winded answers anytime! Great explanations!
I'm glad I was able to answer your questions.

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Originally Posted by pandaroo View Post
Thanks for the detailed response Tim, this is something I that would revisit with you for sure closer to time nearing my build
I'll look forward to our discussions.
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  #108  
Old 12-15-2018, 08:05 AM
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Originally Posted by GaultierRedon14 View Post
I've been quietly following along and learning from your posts, Tim. Thanks! One question that came to mind after reading your last post was, how does scale length affect your thicknessing and bracing, and/or voicing?
For example, a client orders two guitars, same model, same tone woods, same playing style and string gauge, etc., but wants one to a scale length of, say, 24.9 or 24.75, and the other to be 25.4 or 25.5.
So, how big of a difference might there be in the thickness of the top, or size of the braces between the two?
Is this essentially the same question you have to answer for a client who wants to build two identical guitars but one designed for medium gauge strings and the other for light gauge strings?
That's a great question GaultierRedon14. Scale length isn't as critical of a factor to apply to my voicing process as is string gauge. For example there is ~7 lbs of string tension difference between a 24.75" scale length and a 25.5" scale length. That ~7 lb difference is more likely to be felt by the player because fretting will be easier felt on the shorter scale since it takes less force to fret each string. Theoretically that ~7 lbs less string tension could make the guitar have slightly less volume but I think it would be difficult to prove since there has never been two EXACTLY identical guitars built, that I am aware of, to compare equally.

An 11/52 "light" set of strings has roughly 145 lbs of string tension verses a set of "medium" 13/56 strings that have 190 lbs of tension to apply to the top and neck. That 45 lbs of string tension difference is huge and should be taken into account in a lightly built and responsive guitar.

Brace placement is another critical factor to consider when laying out brace locations on 2 tops of different scale lengths. Since the bridge location is .75" lower on a 25.5" scale than on a 24.75" scale one must shift the sound hole, bridge plate, X brace intersection and all other braces to accommodate for the differences in scale length.
For example: If I mounted a "short scale" 24.75" braced top on a guitar body then glued the bridge at a ďlong scaleĒ 25.5" location then there would be way too much torque on the top bracing since the X intersection is .75" further away from the bridge then it should be. This top will likely not respond appropriately or would soon fail due to insufficient support for the torque applied to the bridge from the longer scale length. In this example itís not a matter of the scale length being the problem but rather mounting the bridge to an insufficiently supported area of the top.

Adjusting the top thickness for the differences in string gauges is a mathematical (cube root rule) process if using a deflection board, as we do. The stiffness of the top is measured by placing a heavy weight on the top and then measuring the amount of deflection or bend it has under that same applied weight. As we remove material from the top, by making it thinner, the top will bend or deflect more as it gets thinner. As the cube root rule defines stiffness is proportional to the height or thickness of the top and it only takes removal of a small amount of material to make a significant difference in the topís or braces stiffness. We have target deflection numbers that we use for different body sizes and string tensions. This assures me that each top will be sufficiently stiff enough for the string gauge the customer will be using. This is only a starting point because we then have to brace the top and voice the top after that. We continue to use the deflection board during each step of the process to monitor the changes in deflection and how this correlates to the tone and responsiveness we are targeting for each unique client.
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  #109  
Old 12-16-2018, 06:59 AM
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Meanwhile the FB surface gets its radius:




















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  #110  
Old 12-17-2018, 06:55 AM
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Marking the rim where to cut notches to accept the top's brace ends:










Sawing the edges of the notches using a straight edge as a guide:










Routing the notches between the previously ^ sawn edges:










Ready for a test fit:











Gluing the top to the rim:





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  #111  
Old 12-17-2018, 03:26 PM
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Nice progress since I last checked in, Tim! Nice to see you using a CNC as well!

Ken
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  #112  
Old 12-18-2018, 05:35 AM
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Nice progress since I last checked in, Tim! Nice to see you using a CNC as well!

Ken
Thanks for stopping by and checking in Kenneth.
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  #113  
Old 12-18-2018, 09:06 AM
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VERY INTERESTING! Another piece of the puzzle falls into place... I too am glad to know this stuff. Amazing amount of skill and knowledge go into these BOSS guitars.
Thanks Tim (and Mary too!)

Paul


QUOTE=Tim McKnight;5919730]That's a great question GaultierRedon14. Scale length isn't as critical of a factor to apply to my voicing process as is string gauge. For example there is ~7 lbs of string tension difference between a 24.75" scale length and a 25.5" scale length. That ~7 lb difference is more likely to be felt by the player because fretting will be easier felt on the shorter scale since it takes less force to fret each string. Theoretically that ~7 lbs less string tension could make the guitar have slightly less volume but I think it would be difficult to prove since there has never been two EXACTLY identical guitars built, that I am aware of, to compare equally.

An 11/52 "light" set of strings has roughly 145 lbs of string tension verses a set of "medium" 13/56 strings that have 190 lbs of tension to apply to the top and neck. That 45 lbs of string tension difference is huge and should be taken into account in a lightly built and responsive guitar.

Brace placement is another critical factor to consider when laying out brace locations on 2 tops of different scale lengths. Since the bridge location is .75" lower on a 25.5" scale than on a 24.75" scale one must shift the sound hole, bridge plate, X brace intersection and all other braces to accommodate for the differences in scale length.
For example: If I mounted a "short scale" 24.75" braced top on a guitar body then glued the bridge at a ďlong scaleĒ 25.5" location then there would be way too much torque on the top bracing since the X intersection is .75" further away from the bridge then it should be. This top will likely not respond appropriately or would soon fail due to insufficient support for the torque applied to the bridge from the longer scale length. In this example itís not a matter of the scale length being the problem but rather mounting the bridge to an insufficiently supported area of the top.

Adjusting the top thickness for the differences in string gauges is a mathematical (cube root rule) process if using a deflection board, as we do. The stiffness of the top is measured by placing a heavy weight on the top and then measuring the amount of deflection or bend it has under that same applied weight. As we remove material from the top, by making it thinner, the top will bend or deflect more as it gets thinner. As the cube root rule defines stiffness is proportional to the height or thickness of the top and it only takes removal of a small amount of material to make a significant difference in the topís or braces stiffness. We have target deflection numbers that we use for different body sizes and string tensions. This assures me that each top will be sufficiently stiff enough for the string gauge the customer will be using. This is only a starting point because we then have to brace the top and voice the top after that. We continue to use the deflection board during each step of the process to monitor the changes in deflection and how this correlates to the tone and responsiveness we are targeting for each unique client.[/QUOTE]
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  #114  
Old 12-20-2018, 08:36 AM
phade314 phade314 is offline
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McKnight,

I'm a closet physics geek, so I'm loving these "pour a cup of coffee" explanations. I'm sure the question I'm about to ask will cause some to shudder, but have you, or anyone else you know of, looked into carbon fiber bracing? I was into cycling when carbon fiber was becoming all the rage, the appeal being it was light and strong. You could control which plane it maintained rigidity and which plane allowed it to flex. To me it sounds like a great material for bracing. Also, I see that you offer a double top, how about a double back? or both?
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  #115  
Old 12-20-2018, 06:58 PM
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McKnight,

I'm a closet physics geek, so I'm loving these "pour a cup of coffee" explanations. I'm sure the question I'm about to ask will cause some to shudder, but have you, or anyone else you know of, looked into carbon fiber bracing? I was into cycling when carbon fiber was becoming all the rage, the appeal being it was light and strong. You could control which plane it maintained rigidity and which plane allowed it to flex. To me it sounds like a great material for bracing. Also, I see that you offer a double top, how about a double back? or both?
Hi Phade and welcome to the forum BTW. Several years ago a company, which I fail to recall their name, designed a hollow carbon fiber X brace and they sent me a couple prototypes to experiment with. I learned quite a bit and as you mentioned CF is very light and rigidity can be controlled depending on the plane itís oriencped in. The concept seems great on paper but in real life there are some difficulties to deal with when combining an inorganic CF material with an organic wood. Although CF can microscopically move, it certainly has far less movement than wood exhibits during humidity changes. CF resists movement so something has to give when itís joined to wood, either the wood or the CF to wood glue joint. Second problem I encountered was since the X brace was extremely stiff and also hollow there was no way to voice it, unless I ground material off itís height which totally compromised its structural integrity. Those two experimental guitar tops ultimately ended up as BTUs in my wood stove.

I still use CF in a few unseen areas of my builds, i.e. in specific places that I do not want to move.

I believe it was Rainsong that experimented with wood tops on CF bodies or CF tops on wood bodies? Those guitars didnít fare very well either.

We do offer a double top as an option and I have also built a few spec double backs using similarities shared with the double top. We do offer something very unique we call the ďHollow BackĒ.
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  #116  
Old 12-21-2018, 11:34 AM
Knives&Guitars Knives&Guitars is offline
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Once again I must express my sincere gratitude for all of your detailed explanations you have offered. String Gauge verses scale length, top deflection, bracing is now becoming much clearer.
Had fun tooling around your website last night. Read your explanation on the double top. Sounds like an acoustic dream.
*I would assume that specific Spruce Top species makes less of a difference in double tops? Or does the species of Spruce in Double tops still make a big enough tonal difference?
The one thing that I could not find on your website was an explanation of the construction of Hollow backs.
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  #117  
Old 12-22-2018, 06:50 AM
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Originally Posted by Knives&Guitars View Post
Once again I must express my sincere gratitude for all of your detailed explanations you have offered. String Gauge verses scale length, top deflection, bracing is now becoming much clearer.
Had fun tooling around your website last night. Read your explanation on the double top. Sounds like an acoustic dream.
*I would assume that specific Spruce Top species makes less of a difference in double tops? Or does the species of Spruce in Double tops still make a big enough tonal difference?
The one thing that I could not find on your website was an explanation of the construction of Hollow backs.
IME, The outer top species used in a double top has more contribution to the tone of the guitar than does the inner top, which sounds counter-intuitive. We have built all sorts of weird combinations of double tops with different wood species used on the inner top than what is used on the outer top and it seems whatever wood species the bridge is glued will sound more like that wood [in general] than the inner top.

You won't find any construction information of our "Hollow Backs" on our website and that is be design A guy has to keep a few secrets, ya know. As far as my patent research has shown it is a totally unique design that has never been used before. At the time I came up with it, I couldn't afford to patent my idea nor could I afford to defend the patent so we never pursued it. Looking back I probably should have found a way to patent the idea but hind sight is always 20/20.
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  #118  
Old 12-24-2018, 06:36 AM
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The top is on so next we start the binding process. End graph goes in:










While that dried we bent the purflings:










Our customer chose Herringbone for the top and Rope for the back:










Binding and purfling channels get cut in the sides and top:










... and back:
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  #119  
Old 12-24-2018, 08:51 AM
SJ VanSandt SJ VanSandt is offline
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Herringbone and rope combined - don't think I've seen that before. (I don't guess they'll be showing at the same time - maybe I've seen a dozen guitars like that and never noticed.) Fairly subdued colors in that purfling - did you make it yourself?
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  #120  
Old 12-26-2018, 06:34 AM
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Herringbone and rope combined - don't think I've seen that before. (I don't guess they'll be showing at the same time - maybe I've seen a dozen guitars like that and never noticed.) Fairly subdued colors in that purfling - did you make it yourself?
Its a first for us too Stan but we aim to please our clients requests. Can't wait to see it under a finish because I think it will look great.

No, I didn't make the purflings so the credit goes to Michael Gurian and company. They make some pretty awesome stuff. I believe the woods in the rope purflings are Maple, Walnut and ebony. The top Herringbone is Maple and Ebony.
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