One-piece necks vs. more-piece necks

[Tim McKnight]

Originally Posted by Laurent Brondel

Paul, it may be be true in theory, particularly if you build T or H beams. But in luthiery practice, when you're laminating 3 or more pieces of mahogany with the same grain direction parallel to each other, you do not gain in stiffness. As I wrote before, if you use other denser/stiffer woods along mahogany, this is another story. It is not the laminations that make the neck stiffer in this case, but the addition of stiffer components.

Truss-rod adjustments remain the same, with the same feel, and I always use the same rods. I also tend to bend the neck when I play, and the laminated necks do not feel stiffer. Now maple and wenge necks do feel stiffer and barely need a rod adjustment (the rod is much stiffer to adjust).

Laurent,
I beg to differ and agree with Paul that a beam of the same species of laminations are measurably stiffer than a solid piece of the same dimension, regardless of grain orientation. Its been proven numerous times. I actually posted a thread here a few years ago of an experiment that I did and documented the deflection of several laminates as compared to the deflection (stiffness) of the same size solid woods.

Just found the thread though the pictures have been removed, the data still remains which proves that lamination's of the same species are at least 2x the strength of the same dimensioned solid piece of the same thickness with the same grain orientations!

http://69.41.173.82/forums/showthread.php?t=116679

And yet another thread that lends support - http://69.41.173.82/forums/showthread.php?t=116348

[Thomas Rein]

From the USDA Wood Handbook:
"Aside from the beneficial effect of dispersing imperfections, available test data do not indicate that laminating improves strength properties over those of a comparable solid piece. That is, gluing pieces of wood does not, of itself, improve strength properties, unless the laminations are so thin that the glue bonds significantly affect the strength of the member. In laminating material of lumber thickness, that would not occur."

I take the thin laminations qualifier to mean if the glue is absorbed into the lamination to the point that the thin lamination itself then becomes stronger. If a beam is made of very thin members that are nearly saturated with a somewhat rigid adhesive, then the resulting piece would be stronger. I picture the funky old wood veneer salad bowls that were saturated with epoxy and formed into a mold using heat and pressure. Some of the younger members here probably have no idea what I am talking about.

A central lamination of 1/2" thick maple with outer wings of mahogany would probably be stiffer than a solid piece of mahogany, just by virtue of the maple being stiffer. That would be an easy test to conduct. Personally, I am not interested in laminating the central neck shaft of necks. I can't think of a glue that has better strength properties than the natural internal mechanism that is holding wood together.

One other interpretation of multi-piece necks is the scarf joint already mentioned and gluing on the heel. If carefully done the results are nearly invisible and saves a tremendous amount of valuable material, namely mahogany, which is getting more scarce by the week. Bandsawing a 1-piece neck out of huge chunks of mahogany is from the era of boundless resouces. Back in the day you could get rail cars full of pattern grade mahogany 2 feet wide, 3 inches thick, and 20 feet long. Put a marginally skilled worker next to a big bandsaw and some patterns and he could reduce that timber into necks in very short order. It didn't matter that 40% of the wood was waste because mahogany was dirt cheap and plentiful.

[Tim McKnight]

I would like the see the USDA data that they are citing. Any 1st year engineering student could shoot holes in this hypothesis. Any time you join two or more substrates with a bonding film or mechanical fasteners you linearly and exponentially reduce the compression, tension and shear in the entire engineered structure.

Its quite easy to prove as well, as I did, by gluing some thin pieces of scrap together then measure the pre and post deflection of the material. The data quickly separates opinion from fact.

[Howard Klepper]

Tom and Laurent have it right. A laminated beam of wood with laminates of typical lumber dimensions is both in theory and practice no stiffer than a solid beam of the same material and dimensions. Tim's test of laminated sides is exactly what the Forest Products lab refers to about thin pieces, where the amount of wood saturated and thereby stiffened by the glue becomes significant.

Basic physics and engineering principles say multiple layers of the same material glued together are not stiffer than the same size and shape solid of that material. Where would that added stiffness come from (unless the glue saturated wood is a significant thickness relative to the rest)? Engineers calculate beam stiffness by material and dimensions; they do not add a stiffness factor for being a laminate if the materials are not changed (such as by putting denser, stiffer material further from the beam's neutral axis). Sometimes people have the idea that increased stiffness comes from the rigidity (in the sense of no creep) of the glue layer. But a rigid glue layer (or mechanical means of laminating) just makes the lamination equal to a solid beam.

If it has been "proved" over and over that the lam beam is stiffer, can someone please cite a reference that isn't another forum discussion thread? I'd say that the Forest Products Lab reference puts the ball in your court. Show some engineering text that adds a stiffness factor for a beam just because it is laminated, without a change in material. [You won't find it.]

Wood lam beams have advantage in resistance to failure because the fracture planes of the different layers don't align. They also are more resistant to distortion because stresses will tend to be in various directions. That is not the same thing as stiffness.

[Kent Chasson]

Tim, that is very convincing for sides. Makes me want to try it. A friend of mine who is a very traditional builder has been doing a lot of builds with laminated backs lately and liking the results. Lighter but the same stiffness. But...

I'm not sure how well it translates to necks.

First, with wood that thin, the glue saturates a much greater portion of the wood (which is why I clarified in my first post that we weren't talking about true plywood necks).

Second, it appears you are measuring in the opposite axis that I am most concerned with for necks. I'm not proposing it doesn't help with necks, just that your tests are for something fairly different.

Anyway, my only beef is with people who that say laminated necks are by definition more stable and superior to solid wood. Fine necks can be built with any number of methods and in my opinion, wood selection and care in construction are much bigger variables than whether a neck is laminated or not.

[Kent Chasson]

Originally Posted by PWoolson

...
Kent, ALL wood has internal stresses of one sort or another. No, I don't grab pieces with radically uneven grain and runout. But no matter how perfect the piece appears, it will have some internal stress.
...

Maybe on a theoretical level but not on a practical level. The wood I use for my solid necks comes from large planks so I can get necks with matching heel blocks from that same board. I often rip 6-12 neck blanks form one 2-foot chunk. Often, every board will come off the saw almost perfectly straight. If I cut the blanks into smaller pieces, they would stay straight too. If it bows or twists coming off the saw, I don't use it for necks.

[silvereagle48]

Boy this post got alot of the builders knickers in a wad

[Jimmy Caldwell]

Here's a link to some interesting information.

http://www.fpl.fs.fed.us/documnts/pdf1996/ramme96a.pdf

The question of laminated timber vs. solid timber comes up quite often in my profession (The one I pursue so that I can continue to build guitars). The answer really depends on the frame of reference in which the question is being ask. First you have to define what you mean by "laminated" as it pertains to the intended use. Laminated or structural beams, to most people are thought of in the context of spanning great distances and/or holding up heavy objects. These beams are engineered to suit their intended purpose and built to very exacting specifications and do indeed outperform solid timbers of equal size. But, there is a caveat.

The increased performance lies not in the lamination, but in the engineering. There is specific criteria associated with each member of these beams depending on their placement in the beam. If you could find a solid timber that met the design criteria needed, then it would indeed be just as strong as the engineered timber. But in most real world situations, that's not possible. If it were, the engineered wood industry wouldn't exist. What engineering does is allows the use of mixed grades of solid timbers to met the design criteria. This is an oversimplification, of course, but these are the basics.

In the context of building guitars, we're working with such small pieces of wood that we can indeed find solid wood with properties that meet the design criteria. What laminating necks does, at least IMO, is allow the use of multiple species for either their visual or stiffness properties, and is certainly a more efficient use of our dwindling supply of suitable woods. Either way works, both are sufficiently strong, just two different methods.

[Kent Chasson]

Originally Posted by Jimmy Caldwell

Here's a link to some interesting information.

http://www.fpl.fs.fed.us/documnts/pdf1996/ramme96a.pdf

The question of laminated timber vs. solid timber comes up quite often in my profession (The one I pursue so that I can continue to build guitars). The answer really depends on the frame of reference in which the question is being ask. First you have to define what you mean by "laminated" as it pertains to the intended use. Laminated or structural beams, to most people are thought of in the context of spanning great distances and/or holding up heavy objects. These beams are engineered to suit their intended purpose and built to very exacting specifications and do indeed outperform solid timbers of equal size. But, there is a caveat.

The increased performance lies not in the lamination, but in the engineering. There is specific criteria associated with each member of these beam depending on their placement in the beam. If you could find a solid timber that met the design criteria needed, then it would indeed be just as strong as the engineered timber. But in most real world situations, that's not possible. If it were, the engineered wood industry wouldn't exist. What engineering does is allows the use of mixed grades of solid timbers to met the design criteria. This is an oversimplification, of course, but these are the basics.

In the context of building guitars, we're working with such small pieces of wood that we can indeed find solid wood with properties that meet the design criteria. What laminating necks does, at least IMO, is allow the use of multiple species for either their visual or stiffness properties, and is certainly a more efficient use of our dwindling supply of suitable woods. Either way works, both are sufficiently strong, just two different methods.

Jimmy, I totally agree except the part about efficient use of materials. I tend to have a lot more unusable waste building with laminated necks. But it is difficult to find wood of the size I need, particularly in species that are relatively sustainable. There is a good case to be made for using laminates as a way to use more sustainable material but talk about a topic that gets people's knickers in a wad...

[Torch]

Only been on the forum a few months, but this, by far, is the most interesting discussion yet. I appreciate the information and the efforts to rationally discuss this topic.

[Aaron Smith]

For the builders who make laminated necks- do you change the grain orientation with each lamination? My understanding of the stability argument has always been that it's the different grain directions that add stability; not any net stiffness effect. Wood is not an isotropic material, and even the best piece of wood has different stiffnesses in different directions of stress. Also humidity changes affect the wood in dramatically different ways according to grain orientation.

I'm not a guitar builder but I am a woodworker. In other woodworking fields, when people laminate woods it's almost always so they can mix up the grain directions and make a more dimensionally stable piece.

[Laurent Brondel]

Aaron, for neck stock I assume every builder would want maximum longitudinal strength and reversing grain direction for one lamination or more would only weaken the neck in that respect.

[Matt Mustapick]

Originally Posted by Ivob

i've checked some builders' website, e.g. all the lakewood guitars have one-piece necks, and the guitars are quite expensive and are considered to be high-quality instruments... even one custom builder here in our country makes one-piece neck guitars for his high-ends. but the term "high-quliaty guitars" is evidently a relative term...

The important thing to remember is that top-shelf instruments can be built with one-piece necks or 100-piece necks. For what it may be worth, I use three, and I don't say that that number is better than one, two, or four.

[Howard Klepper]

Originally Posted by Aaron Smith

For the builders who make laminated necks- do you change the grain orientation with each lamination? My understanding of the stability argument has always been that it's the different grain directions that add stability; not any net stiffness effect. Wood is not an isotropic material, and even the best piece of wood has different stiffnesses in different directions of stress. Also humidity changes affect the wood in dramatically different ways according to grain orientation.

I'm not a guitar builder but I am a woodworker. In other woodworking fields, when people laminate woods it's almost always so they can mix up the grain directions and make a more dimensionally stable piece.

I think Aaron is not talking about making plywood with alternate lams at 90º, but the typical table top laminations that reverse the way the growth rings curve with each lam, so that tendency to cup will likewise reverse with each piece.

I always have my two major pieces, the outer laminates, with their growth rings facing opposite directions. For thin inner laminations, it is much less critical, but I will do this if it is feasible. That depends on what kind of board they are cut from--flatsawn or quartersawn.

[Aaron Smith]

Originally Posted by Howard Klepper

I think Aaron is not talking about making plywood with alternate lams at 90º, but the typical table top laminations that reverse the way the growth rings curve with each lam, so that tendency to cup will likewise reverse with each piece.

I always have my two major pieces, the outer laminates, with their growth rings facing opposite directions. For thin inner laminations, it is much less critical, but I will do this if it is feasible. That depends on what kind of board they are cut from--flatsawn or quartersawn.

Yes Howard- that's what I was talking about. I just wanted to say thank you to you and all the other builders for adding to this thread! Best AGF thread I've seen in some time.