The Best Cuts of Wood for Guitar building
The best cuts of wood for guitar building are typically quarter-sawn cuts. The easiest way to buy your wood for guitar making is to get it from a tone-wood dealer or luthier supply company. The wood is pre-cut to dimensions close to the sizes needed. Each piece has already been milled from the right cut – hopefully. You will have to dimension it the rest of the way yourself by hand. However, this is not always going to get you the best wood available and it is expensive. You will pay more because for the milling.
The best way to get your wood for guitar making is to buy large pieces and mill it yourself. To get the best cuts of wood for guitar building you need to know something about where exactly in the tree the wood came from. To mill your own wood you will need some equipment and some wood knowledge. The initial cost of the equipment is high but milling your own wood for guitar building can save you a bundle of money over the long haul. To mill your own wood you will need a re-saw band saw at minimum. You need to know what cuts of wood to look for and what to do with it when you find it. If you have selected a good cut of wood you can then slice it up to get exactly what you want.
Some of the traditional wood used for guitar building is difficult if not impossible to find in planks or logs. As this wood becomes harder and harder to find, luthiers are using non-traditional wood out of necessity. Some non-traditional wood has produced some really nice instruments. Therefore it is possible.
Cuts of Wood
On the right is a drawing from my book, “Classical Guitar Making: A Modern Approach to a Traditional Design”. It shows the three main types of cuts and where they come from in a tree.
The types of cuts are determined by the orientation of the growth rings with respect to the face of the board being cut. The dotted lines are the cut lines for flitch cutting a log. More on this below.
The best cut of wood for guitar building is quarter-sawn. Wood is considered quarter sawn when the growth rings seen in the end grain of the board are between 90 and 60 degrees to the surface of the board. This is the ideal cut for guitar wood.
Quarter sawn wood comes from cutting the log in half at the center along its length then cutting each half into halves again, hence the term quarter sawn. In this way both faces of all four pieces are quarter-sawn.
When at tree is flitch cut (see below), which is where you just slice it from top to bottom, the middle pieces will be quarter-sawn near the center (see a video of a log being flitch cut). How much of it is quarter-sawn as you move away from the center depends on the diameter of the tree. How many quarter-sawn boards you can get out of a log generally depends on its diameter. The trees diameter depends on how old the tree is. The older the tree the tighter the grain. This is typically calculated in lines per inch. Guitar tops typically have very tight grain but it is questionable that tighter grain produces better sounding instruments. Old trees generally yield the best wood for guitar building
Wood is considered rift sawn when the growth rings are between 60 and 45 degrees to the surface of the board. Rift sawn pieces are come from planks that are cut above and below the center of a flitch cut log. On a quarter-sawn log the rift pieces are closer to the bark on each of the four pieces.
This cut is fairly stable and can have straight grain lines on all four surfaces. It is identified by the end grain in the photo on the right. Rift sawn wood that is 45 degrees to the surface is sought after for parts where it is important that the grain follows its shape such as chair legs. Rift cut wood is often a good cut of wood for guitar building on just about anything but the top.
Wood is considered flat sawn if the growth rings are 45 degrees or less to the surface of the board. Flat sawn wood can be easily identified by the flame pattern in the grain on the surface of the board. The end grain can be seen in the photo on the right.
Flat sawn wood comes comes from planks that are cut on farthest away from the center of the log near the bark. Flat sawn wood is the least stable and most likely to cup even under ideal conditions due to the shape of the end grain. This is typically not good wood for guitar building especially on tops and backs. Although it can be tempting because of the beautiful flame grain patters in flat sawn wood it should be avoided because of its instability. It is most likely to develop problems and crack down the road. Every time I see a flat cut Brazilian rosewood back I cringe. This may be beautiful but it is an accident waiting to happen.
Flitch Cutting a Tree
On the right is a photo of a flitch cut tree in my garage. If you have the whole tree cut like this you have your choice of cuts when using it. This is ideal for furniture making becuase you can get any desired grain effect to match the shape or style of your piece.
Flitch cutting is when you cut up the entire log by slicing along its length starting from top to bottom. You can make each slice as thick as you like. This is good if you know what you will be using it for. This is the best way to purchase wood as you have your choice of cut and will be able to get every type of grain and graphic available to you to use in your projects. Wood is typically flitch cut into 2-3 inch slabs as described, stickered and left to dry. Teh general rule of thumb is one year of drying per inch of thickness. There is more about wood and moisture below.
Characteristics of Quarter Sawn Wood for Guitar Building
The best cuts of wood for guitar building are quarter-sawn wood. Quarter-sawn wood possesses two characteristics that are a desirable in guitar making – strength and stability. If the wood you are using lacks either of these there will be problems down the right if not right away.
The ideal quarter-sawn piece of wood for guitar building is one that has its end grain lines at 90 degrees to its face has no run-out along its length (see run-out below). Ideal cuts like this are rare if you are buying your wood pre-cut from a luthier supply company, especially these days. It is easier to get if you are milling your own wood since you can cut it along the grain lines to minimize run-out.
The piece of quarter sawn mahogany on the right is quarter-sawn with end grain that is less than ideal but is still acceptable. To look for run-out you must sight down the edge of the board (see below).
The width of a guitar body is about 14-15″ or so at the lower bout. Wood changes dimension with humidity. It changes most across its width. It swells and stretches when it is humid and shrinks when it is dry. This change in dimension can be significant for a piece of wood 14-15″ wide. The wider the piece the more the change. It is a linear progression. The general rule is for anything under two and a half inches changes due to humidity can be neglected. Of the three different cuts of wood quarter-sawn wood will expand and contract the least. This makes it the best choice for tops, backs, sides and necks.
The wood used on the body of the guitar is quite thin. The wood used for the top must be very strong to resist the tension of the strings without deforming. It must also be light for acoustic purposes. Spruce and cedar have a good strength to weight ratio making them ideal for soundboards. The soundboard is also braced underneath to add more strength and keep it from deforming. Quarter-sawn wood is the strongest along its length of all the cuts. Since the soundboard and the neck are having forces applied along their lengths quarter -awn wood is the best choice. For these two parts of the guitar the closer to perfectly quarter-sawn the better.
What is runout? Runout has to do with the side grain of the wood. The tree is both round and tapered. It gets narrower as you move up from the ground.
The middle of the bottom section of a large diameter tree will often yield perfectly quarter-sawn wood with little or no runout because the taper over say an eight foot length is minimal and can be neglected. When looked at from the side the grain lines would run pretty much parallel to the face along the entire length.
If you take a quarter sawn piece from the top section of the tree where the taper is ore pronounced the grain lines will run at some angle to the face. They will intersect the top face at some point and the bottom at another. The distance between these two points on any give grain line is referred to as runout. This can also happen if the tree is improperly milled.
Quarter sawn wood has the greatest strength along its length when run out is minimal(more on this in the section on neck wood). Hands down a quarter sawn piece of wood with little to no runout is the best cut of wood for guitar building. This cut will work for any part of the guitar.
Grain Lines per Inch
There is some debate among luthiers as to whether tighter grain produces better sounding instruments. I have heard many great sounding instruments with tops that have what some would consider widely spaced. So I don’t really feel this is the case.
The misconception comes in thinking that wider spaced grain lines mean that the tree is younger that one with tighter spaced grain lines and this is simply not true. The early wood or the most recent growth rings on some trees is wider that the late wood.