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  #31  
Old 12-06-2018, 12:38 PM
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Rodger Knox Rodger Knox is offline
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Originally Posted by murrmac123 View Post
Not sure about that , Rodger.

If you compress a flexible steel bar, for example, you put the convex side into tension, and the concave side into compression, but there is no dimensional change.

Same with a guitar neck IMO.
"If you compress a flexible steel bar" implies (to an engineer) axial loading which means all of the cross section of the bar is in compression, and it will be shortened equal to the force time the modulus of elasticity. The rest of the quote seems to imply that you meant "bend" instead of "compress", which would put the convex side into tension, and the concave side into compression. The bend is a dimensional change, the convex side is stretched a bit by the tension and the concave side is squeezed a bit by the compression.

The concept I'm trying to get across is that any force applied to a material results in a deformation of that material, and that deformation is proportional to the force applied, and the modulus of elasticity of the material is the proportionality constant. All materials behave this way up to the elastic limit, which is the amount of force required for permanent deformation or failure.

This is basic mechanics of materials for an engineer, and there's a language that engineers use to discuss these concepts. Stress is a force per unit area, strain is the deformation caused by the stress. It's difficult for me to discuss these concepts without resorting to engineerspeak.

Sorry for the derail...
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  #32  
Old 12-06-2018, 08:08 PM
charles Tauber charles Tauber is offline
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Originally Posted by Rodger Knox View Post
It's difficult for me to discuss these concepts without resorting to engineerspeak.
A good summary.
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  #33  
Old Yesterday, 03:33 PM
Ned Milburn Ned Milburn is offline
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Originally Posted by packocrayons View Post
I just saw this and am concerned about my first build - Does the truss rod not go into a straight channel between the neck and the fingerboard? What's supposed to be curved?
Single action truss rods need a curved channel. They operate by tightening or loosening to increase pressure against the curve.

Double action truss rods have 2 metal pieces that are solidly fastened at one end, and the other end can be adjusted to slip one metal piece against the other, to adjust the bow in either direction.

There are many modern style double action truss rods that are quite compact and lightweight that out-perform the single action style in so many ways. You can even buy these on e-bay for about 6 or 7 bucks a piece, or you can buy USA made for 30 bucks to 50 bucks or more...
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  #34  
Old Yesterday, 04:20 PM
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Quote:
Originally Posted by Ned Milburn View Post
Single action truss rods need a curved channel. They operate by tightening or loosening to increase pressure against the curve.

Double action truss rods have 2 metal pieces that are solidly fastened at one end, and the other end can be adjusted to slip one metal piece against the other, to adjust the bow in either direction.

There are many modern style double action truss rods that are quite compact and lightweight that out-perform the single action style in so many ways. You can even buy these on e-bay for about 6 or 7 bucks a piece, or you can buy USA made for 30 bucks to 50 bucks or more...
As I define it, single action only work against the string tension, whereas double action can exert their force either way. The single action rod i use, LMI's TRST, uses two full length pieces of steel, and has the same weight/bulk as most double action systems. I like it because I do not ever expect to need to combat a back bent neck due to my construction technique, and the adjust-ability is smoother, more accurate, and more stable than any double action rod I've tried. Basically, I find double action rods too finicky initially, and too often require attention down the line.
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  #35  
Old Today, 11:59 AM
Monsoon1 Monsoon1 is offline
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My only experience with this was a couple of stunning acoustics on ebay, maybe 10 years ago.
They both were crazy gorgeous brw back and sides with what was possibly sitka tops. It was an estate sale, and the builder was unknown. And if I remember right, neither one got even $500. If I'd had the money I would have snapped both of them up.
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