While the table saw is useful for cutting sheet goods and ripping boards, it's limited in ability. There is no problem ripping a board to make it thinner if you want to cut down the width of the board, but if you want to rip the board to reduce its thickness, you need a band saw.
The way a bandsaw works is it has an upper and lower wheel that the blade goes around. The wheels are generally cast and balanced with the edge covered with rubber to grip the blade. The lower wheel is driven by a motor and the upper is the adjustable tension wheel. A table provides a place for the workpiece, with the blade passing through the middle of the table and traveling downwards. Band saws come in a variety of sizes, with prices up to several thousand dollars. Industrial ones are typically multi-speed for cutting metals as well as wood.
Band Saw Uses
Band saws are very versatile and can be used in a wide variety of applications. They are also one of the few power tools suitable for both woodworking and metal cutting. While band saws intended for cutting metal are slightly different than those designed for cutting wood, the basic tool remains the same. The major difference between the two is the machines designed for cutting metal are variable speed, as a slower blade speed is needed for said materials.
Cutting Curves
Band saws are also useful for cutting curves, although they won't cut as tight a curve as a scroll saw will. On the flip side of the coin, they will usually cut a smoother curve than a scroll saw. Blade width makes a big difference in this regard, as even the narrowest band saw blades are wider than those used on scroll saws. From there, they vary up to 1/2" in width.
Resawing
The blades used on band saws are the thinnest around, rivaling those used for a scroll saw. This makes them ideal for resawing boards (ripping then to split the thickness). Little material is used as the saw kerf is minimal.
Types of Band Saws
Band saws break down into four basic categories, more based upon their use than anything else. Although we're only looking at band saws for woodworking and portable band saws, even within the realm of woodworking, there is quite a variety in size and cost.
Wood-cutting
These are units that are designed for woodworking. They are typically single-speed units used for resawing boards and cutting curves.
Metal-cutting
These units are larger than those used for wood cutting, have larger motors, and are variable speed. The harder the metal is cut, the slower the saw's speed needs to be.
Horizontal
Horizontal band saws aren't as common as vertical ones areas they're used solely for cutting metal pipe and tubing as well as extrusions. These band saws are typically variable speed with a clamp to hold the workpiece in place. The weight of the saw itself provides the pressure to move the blade through the material as it is being cut.
Portable
Like the horizontal band saws, these too are used for cutting metal pipe, tubing, and extrusions as well as cutting rebar for concrete work. Mostly they're used by welders, electricians, masons, and plumbers.
Choosing a Band Saw
Before looking for a band saw, you have to have an idea of what you are going to use it for. Specifically, you need to know the largest material size that you will use in the saw. That will determine the size saw that you need which establishes a starting point for your search.
Throat depth
The saw's stated size is the diameter of the saw's drive wheels. The throat depth is generally about 1/2 inch less than the wheel diameter which limits the width of the boards that can be cut on the saw. For most users, throat depth isn't a major consideration. Although, if you are cutting shapes out of the middle of a board, it can be a problem.
Motor
If the saw is going to be used for resawing boards, it will need a larger motor than one that is only going to be used for cutting curves. The act of resawing creates a lot of friction, which is why a larger motor size is required.
Resaw capacity
The limiting factor for resawing is the space between the saw’s table and the highest point the blade guide can be adjusted to. For a 14” saw, this means the maximum size which can be resawn is usually a 1”x6” board. By comparison, a 20” saw can resaw a 1”x12” board. However, this made for a much more expensive saw.
Fence
A fence is usually needed for resawing, although very few band saws come with a fence and most woodworkers make their own before clamping it to the table. The saws which provide a fence typically have the same style fence found on a table saw. For resawing anything over a 1"x 4" board, it's recommended to attach a piece permanently to the fence to make it higher.
Bearings
The other important factor is the bearings, especially the bearings used for blade guides. Quality band saws will have ball bearings for the wheels and the blade guides, while cheaper units may not. If the saw only has sleeve bearings for the wheels, make sure they're replaceable and you lube them regularly. The bearings on the blade guides are important for ensuring the blade stays straight, especially for resawing operations.
Other Features to Consider
Table size
While all band saws come with a table, the size of the table can vary considerably. Like with any other power tool that uses a table, the size and smoothness of the table will affect your work. Most band saws only come with small tables which increases the chance of you wobbling the workpiece while cutting.
T-slot
A few of the band saws I've looked at have a T-slot cut into the table for using a miter gauge. If you're going to use the band saw for cutting pipe and tubing, this can assist you in keeping the blade perpendicular to the workpiece and make your cut cleaner.
Blade teeth
The larger the teeth on the blade, the faster it will cut. However, you should always ensure you have enough teeth on the blade so there will be at least three teeth for the thickness of the material you're cutting. Any less than this risks having the teeth catch on the edge of the workpiece and jam the saw.
Work light
A work light to illuminate the cut line can be very useful, especially on portable bandsaws. Often, workshops don't have enough overhead light or there might be something shadowing your cut. The light can make it much easier to see where you're cutting, ensuring an accurate cut.