- 1 Band Saws
- 1.1 Specifications:
- 1.2 Blade Selection
Bandsaws are typically rated by throat depth. This is the measurement of how much material can be fed between the left hand side of the blade and the backbone, or upright member, of the saw.
Resaw capacity is the maximum thickness of material that can be sawn, with the upper guides adjusted to the fully raised position.This typically has little relevance to pen making. However, resaw depth can determine how "deep" a bowl blank can be cut with the saw. Or, how large a piece of wood can be processed into pen blanks.
The horsepower rating of the drive motor.This can be important for those who process their own pen or bowl blanks.
The length of the blade if it were cut at one point, pulled straight, and measured with a tape measure.This information is required to purchase optional or replacement blades for the saw.
Blade / tooth type:
See Blade Selection (below)
The bandsaw should come equipped with upper and lower blade guides. The upper guides can usually be raised and lowered to match the thickness of the material. The lower guides are under the table.
Blade guides can be roller type or rub blocks. The roller type are often simple ball bearings and the blade runs directly against the outer race of the bearing. Rub blocks are a solid material. The guides keep the blade straight as the material is fed through it.
Precision woodworkers will often customize their bandsaws to put aftermarket blade guide on their saws. For the pen turner, the standard guides are usually sufficient, if they are adjusted correctly and in are in good working order. NOTE: Rub blocks are perfectly acceptable guides for most applications.
One of the guides runs against the back of the blade to prevent deflection as material is fed into the saw. This is usually a roller bearing. In some configurations the bearing is mounted at right angles to the blade, and the blade runs against the outer race of the bearing. In other configurations, the bearing is mounted in line with the blade
Cast iron or aluminum (or other light metal). Cast iron is better, although it required some maintenance to keep it from rusting in a humid environment.
Fences and angle guides:
The saw may or may not come with a fence to control cutting width. For precision resawing (example: cutting verneer), a custom fence is often made or purchased.
There should be grooves in the table for an angle guide. However, the angle guide will likely not be furnished with the saw. The grooves can also be used to guide a bandsaw sled.
Blades are purchased by the length of the blade. The operators manual will tell you which length blade to purchase for your saw. If you cannot find the specification, run a string around the top wheel, through the upper and lower guides, around the bottom wheel until you have reach the other end of the string. Mark both ends of the string at a point where they overlap, and measure the length of the string between the two marks. Round up to the next 1/2-inch. That should tell you how long a blade you need. Blades are sold in several standard lengths, but can be custom ordered in any length.
Teeth per Inch (TPI)
Bandsaw blades should be selected for the type of work that is to be done with the saw. The blades come in many tooth patterns and widths, and even in a few thicknesses. When considered together, the possibilities are almost limitless.
Let's begin by considering the number of teeth per inch (TPI). The rule of thumb is that at least three teeth should be in the material at any given time. Therefore, as an example, to cut a 3/4-inch pen blank in two, the coarsest blade to consider for this application is 4 TPI. Anything finer than 4 TPI should only serve to make a finer cut that may need less sanding to clean up.
Is is possible to have too fine a blade - for bowl blank preparation in wet wood,, for instance, a blade with 6 TPI or more will likely clog with sawdust and become difficult to manage in the cut. For these types of applications a 3 TPI blade works quite well.
The more TPI on the blade, the slower the cut will be, and the better cut quality will result. Fewer TPI will result in a faster feed rate, but will leave a rougher finish on the cut.
Tooth Set and Pattern
'Set' refers to the bend in some or all of the teeth. For home shop bandsaw blades this is almost never done by the owner. However, understanding what set is and how it affects the action of the blade can be helpful.
In some blades, all teeth are set, either right or left. Typically, every other tooth is set right, and the alternate teeth are set left. The total set is what determines the width of the kerf, or the width of cut. Set, along with blade width, is what determines the minimum radius of a curved cut. The curve can only be as tight as the width of the blade, with the back riding against the side of the cut, allows. The wider the cut, the sharper the curve can be with a given blade width.
For some applications, not every tooth on a bandsaw blade is set. Teeth that are not set serve as 'rakers' - they remove material from the cut with adding much to the cutting action. Some blades have modified rakers where some teeth are set, but not to the full width of the cut.
In general, the width of the blade (from front to back when mounted in the saw) will be chosen based on the desire to be able to cut curves. The narrower the blade, the tighter the curve it can cut.
Blade thickness for home shop bandsaws will range in the 0.020 to 0.035 inch range. Thickness is determined mostly by the radius of the bandsaw wheels - in general terms the smaller the wheel, the thinner the blade should be so that the blade does not fatigue and break too quickly.
For processing green wood, when given an opportunity, purchase the thickest blade available - the blade will pay for itself with longer life.
Much could be written about blade material, and probably will be.
A 6 TPI blade in 1/4 or 3/8-inch width is a good blade for general cutting applications.
For processing green wood, a 3/8 or 1/2 inch blade in 3 TPI is recommended. If your saw has 14 inches or greater throat depth and is a two-wheel saw, the 0.035 inch thickness is a better choice for this appliction.