Monday, March 15, 2010

How to Get the Most Out of Your Band Saw

          Any band saw can resaw. The question is: “How well and how thick?” The first thing you need to decide if resawing on your band saw is an activity in which you are likely to engage frequently, occasionally or never. For those of you who don’t know, resawing is the ability to cut thin slices or veneers out of a board standing on its edge on the band saw table, while being guided along a high fence. Where this pays off is when you are trying to get maximum mileage out of an especially fine, beautiful, expensive hardwood board.


          For example, I made a lot of jewelry boxes with 3/8” thick sides. Considering that I had to sand all of the sides flat and smooth, I found 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 end, 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 bet three 3/8" pieces out, saving you money.

          The more your band saw blade wanders, the more thickness you will need. The important thing is to minimize 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 stiffness), (3) blade type (designed specifically for resawing), (4) motor power (to drive the blade through the wood without bogging down) and (5) blade guides (the more blade control, the better).


          If you plan on doing a lot of resawing, pay close attention to the specifications of band saws you are considering for purchase, in light of what has been said above. If resawing doesn’t look 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, throat depth of your band saw becomes a very important consideration because, on a small band saw, you will be constantly bumping into the back of the throat and you may not be able to complete the curved cuts you have penciled out.

          Any 14-inch band saw will severely limit the width of cuts you can make to the left of the blade, so consider if this will present a problem for you. If you are planning on just cutting out small parts, fine. On the other hand, if you want to make large parts for furniture, then a small band saw just won't do. Of course, there is no limitation to the right of the blade, on a 14" (or any other) band saw, except that you will have to supply auxiliary support for your work piece if it extends very far off the edge of the table. Throat depth is not so much of a problem when you are using the band saw for resawing, although, for resawing, you will need to consider the maximum distance between the table top and the upper blade guide. That measurement determines how wide a board you can resaw on your band saw.


          When shopping for a band saw, don’t be fooled into thinking that an 18” band saw will give you a full 18” between the blade and the back of the throat. Band saws are measured 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 an upper cabinet and a lower cabinet connected by a “column”. The blade travels upwards from the lower (powered) wheel through and inside the column to the upper (idler) wheel before reversing direction and going downwards through the upper blade guide, then the table, then the lower blade guide before returning to the lower wheel.

          Because the column takes up a certain amount of space, an 18” band saw will not normally have a full 18” throat. It will be something less than that, perhaps 17½” (if you are lucky) or even 17”. So, if you need a full 18” of clearance, you will need a 20” band saw. Prices climb with throat depth simply because as throat depth increases, the wheels and the cabinets must increase in size accordingly. In short, the whole machine gets bigger.

          Small band saws with small wheels may not be tall enough to sit on the floor like larger ones. With small band saws, you must either mount them on a bench or purchase or build a stand. Usually the stand is included in the price of the smaller saws. Conversely, when working on a very large, industrial band saw, count on the table top being quite high off the floor to accommodate the lower wheel and its cabinet.


          When you order blades for your band saw, do so in quantity. There are few sure things in life but blade breakage is guaranteed. Always have replacement band saw blades on hand so you don't end up breaking your only blade right in the middle of a project. When you do order blades, you can usually find the best prices online but you will need to allow for delivery time and shipping costs. You can buy blades from the saw manufacturer but it is usually cheaper to purchase them from a vendor who specializes in band saw blades. If you can’t find the exact size your band saw uses, you can ordinarily have your blades custom-welded to any length you need.

          There are times when you want a specialized band saw blade for a specific use like resawing. Here, the challenge is to get a reasonably smooth cut but not to have so many teeth that it causes an undue amount of friction, heat and wandering. In a case like that, it may be best to buy directly from the manufacturer 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 sufficiently 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 accommodate.

          There are two basic types 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 expensive but are much easier on blades in that there is minimal friction and, therefore, reduced heat. There are side guides in any band saw to restrain the blade from moving left or right and a single block or bearing behind the band saw blade to keep 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 obtained from manufacturers such as Carter. The more expensive band saws come already equipped with ball bearing guides.

          Like other stationary power tools, very large band saws usually have three phase motors. You should not consider purchasing one of these unless you have three phase power available at the place where you will be using the saw. Three phase power is usually only available from the power company in commercial or industrial areas and cannot be found in residential areas. The only way to have three phase power in a home 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 useful 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 track 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 up and down to increase or decrease blade tension. You will need to release 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 knob 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 require 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 insufficient tension is used. Always refer to the tension scale on your band saw. Don't guess.

          After the band saw blade is tensioned properly, disconnect power to the motor and turn the upper wheel by hand to verify that the band saw blade is tracking properly. If not, make appropriate 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 purpose. 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.


Bob Gillespie
Woodworker

For similar articles and tool reviews see:

http://www.perfectwoodworking.com/





© 2010 Robert M Gillespie, Jr.

3 comments:

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