For example, I once made a lot of jewelry boxes with 3/8' thick sides. Bearing in mind that I had to sand all of the sides flat and smooth, I discovered that I could barely get 2 slices out of a 1' thick board or 3 slices out of a 1 1/2' board or 4 slices out of a 2' thick board. You need to allow 1/16' kerf waste for most band saw blades plus more if your blade wanders, which all blades do to a certain extent. Then all unevenness has to be sanded away in a drum sander or wide belt sander. In the final analysis, you can't realistically expect to get two finished 3/8' box sides out of a board that is only 3/8'+3/8' +1/6' = 13/16' thick. You will need not much less than a full 1' thickness in your original board. Since most hardwood lumber is sold milled down to 7/8' for a so-called 1' board, you are faced with only getting one, 3/8' slice, not two. On the other hand, most 2' lumber comes milled down to 1 7/8', which allows you to get three 3/8' pieces out, saving you money.
The more your band saw blade deviates from a straight line, the more thickness you will need. The important thing is to diminish this wandering and there are five ways to do this: (1) blade tension (maximum recommended to keep the blade from flexing), (2) blade width (the wider, the better for rigidity), (3) blade type (designed specifically for resawing), (4) motor power (to push the blade through the wood without slowing down) and (5) blade guides (the more blade control, the better).
If you plan on doing a lot of resawing, look at the specifications of band saws you are considering for purchase, in light of what has been said above. If resawing doesn't seem like it will play a large part in your future, then you are probably more interested in cutting curves in thinner material. In this case, the throat depth of your band saw becomes a very important factor because, on a little band saw, you will be constantly bumping into the back of the throat and you may not be able to finish the curved cut lines you have marked out.
Any 14-inch band saw will severely limit the width of cuts you can make to the left of the blade, so think about if this will present a problem for you. If you are planning on just cutting out tiny parts, fine. Alternatively, if you want to make larger parts for furniture, then a tiny band saw just won't do. Of course, there is no restriction to the right of the blade, on a 14' (or any other) band saw, except that you will have to furnish auxiliary support for your work piece if it extends very far off the edge of the table. Throat depth is not so much of an obstacle when you are using the band saw for resawing, although, for resawing, you will need to ponder the maximum distance between the table top and the upper blade guide. That distance determines how wide a board you can resaw on your band saw.
When buying a band saw, realize that an 18' band saw will allow a full 18' between the blade and the back of the throat. Band saws are dimensioned by the outside diameter of their wheels. These wheels are mounted inside the cabinet, one above the table and the other, below. Actually, there is a top cabinet and a bottom cabinet connected by a 'column'. The blade travels upwards from the bottom (powered) wheel through and inside the column to the top (idler) wheel before reversing direction and going downwards through the top blade guide, then the table, then the bottom blade guide before returning to the bottom wheel.
Because the column takes up a certain amount of room, an 18' band saw will not usually have a full 18' throat. It will be something less than that, perhaps 17 1/2' (if you are lucky) or even 17'. So, if you require a full 18' of clearance, you will have to have a 20' band saw. Prices increase with throat depth simply because as throat depth gets larger, the wheels and the cabinets must grow accordingly. In short, the whole machine gets larger.
Small band saws with small wheels may not be high enough to sit on the floor like bigger ones. With small band saws, you must either attach them to a bench top or buy or construct a stand. Usually the stand is part of the price of the smaller saws. Conversely, when working on a very large, industrial band saw, realize that the tale top will be quite high off the floor to allow for the lower wheel and its cabinet.
When you order blades for your band saw, do so in quantity. There are only a few sure things in life and blade breakage is one of them. Always have additional band saw blades on hand so you don't risk breaking your only blade right in the middle of a job. When you do order blades, you can usually find the lowest prices online but you will need to allow for delivery time and freight costs. You can buy blades directly from the saw maker but it is usually more reasonable to purchase them from a vendor who specializes in band saw blades. If you can't find the precise size your band saw needs, you can ordinarily have your blades custom-welded to any length you specify.
There are times when you want a particular band saw blade for a certain use like resawing. Here, the challenge is to get a moderately smooth cut but not to have so many teeth that it causes an excessive amount of friction, heat and wandering. In a case like that, you might want to buy directly from the maker of your band saw. Band saw blades designed to cut tight curves are as narrow as 1/8'. For most curves, I have found 1/4' blades to be satisfactorily narrow. The narrower the blade, the more likely it will be to break quickly but it can track tighter curves than wider blades. For really tight curves, a scroll saw may be a better tool than a band saw. Resaw blades should always be as wide as your band saw can fit.
There are two basic kinds of blade guides on band saws: 'blocks' and 'ball bearing guides'. Blocks can be made out of smooth metal, non-metallic composite or ceramic material. Ball bearing guides are more costly but are much easier on blades in that there is negligible friction and, therefore, less heat. There are side guides in any band saw to prevent the blade from moving left or right and a single block or bearing behind the band saw blade to prevent it from moving backward when pressure is applied to the front of the blade by the work piece. After-market ball bearing guides with full installation instructions can be ordered from manufacturers such as Carter. The more costly band saws come already equipped with ball bearing guides.
Like other stationary power tools, industrial-sized band saws usually have three-phase motors. You should not consider purchasing one of these unless you have three-phase power available at the location where you will be locating the saw. Three-phase power is usually only obtainable from the power company in manufacturing or commercial areas and cannot be found in residential areas. The only way to have three-phase power in a residential woodworking shop is to use a phase converter that is large enough for the power requirement of your largest three-phase motor. If you plan on running more than one three-phase motor at a time, you will need a correspondingly larger phase converter. There are two types of phase converters: Rotary (looks like a big electric motor) and electronic. Rotary is better if you can find it. Search for phase converters online.
A two-speed band saw is advantageous if you are planning on cutting metal or very dense hardwoods. Running the band saw on the slow setting will mean that while it will take longer to make cuts, it will reduce heat from friction and extend blade life. Metal cutting band saw blades are widely available for cutting mild steel and non-ferrous metals. Never use a metal cutting band saw blade to cut wood. Never use a wood-cutting band saw blade to cut metal.
Some band saw wheels are bare metal. If you want to use narrow blades, your band saw wheels should have rubber 'tires' that are glued onto or inserted into grooves in the metal band saw wheels. These tires are usually crowned. By adjusting the blade tracking device, you can get the blade to stay in one position on the tires or metal wheels.
Another adjustment moves the upper band saw wheel vertically to increase or decrease blade tension. You will need to remove this tension to change band saw blades and, on the newer band saws, you can usually find a lever that does this for you. If not, you will have to loosen the tension control enough to install a new blade on the wheels. Then re-apply the tension, using the blade tension scale, appropriate to the blade width you are using. Wide blades will need more tension than narrow blades. Narrow blades can break if too much tension is applied. Large band saw blades can wander off the band saw wheels if less than sufficient tension is used. Always refer to the tension scale on your band saw. Don't estimate.
After the band saw blade is tensioned properly, shut off power to the motor and turn the top wheel by hand to verify that the band saw blade is tracking properly. If not, make slow tilt adjustments to the upper wheel until the band saw blade stays in the approximate center of both wheels. A hand wheel or knob is provided on any band saw for this function. If the wheels are slightly out of alignment with respect to each other, you can still track a band saw blade. In this case, the band saw blade will be more to the back of one wheel while being more to the front of the other wheel. This discrepancy should eventually be adjusted or 'tuned' out of your band saw, but, for now, it's OK as long as the band saw blade stays on the wheels while cutting. Once you have the band saw blade tracking properly, reconnect the power and start cutting.