Swadge early, swadge often
By Trevor Shpeley
Aug. 2, 2017 - As filers we do it every day but we all hate it. It isn’t hard and it doesn’t take a lot of time, but we do our very best to do as little of it as possible. I’m talking about swadging; the process of shaping flat steel into sharp teeth for bandsaws.
By Trevor Shpeley
The act of swadging, or swaging, (both pronounced “swedging”) involves taking saw steel and forcing it between a stationary anvil and a rotating oval shaped rod called a die. The steel is squeezed between them until it is forced to expand into a shape we can grind down to a cutting edge.
A good swadge always starts with a good tooth. The side stock should be even and of sufficient thickness to give you something to build upon. The corners should be present and the pocket on the face of the saw should be gone or nearly so. Ideally you do not want the kerf to be much below your minimum target size since that will directly affect the size of your swadge.
To set up your swadge for the first time, ask an experienced filer for help. You really don’t want to try and figure this out by trial and error. The saw clamps should hold the saw firmly with the handle resting at a comfortable angle when tight. The head should be rotated so that the anvil face is perfectly aligned with the top of the tooth and the anvil should be set in position with the help of an anvil-setting tool. The anvil-stop should be positioned at a point that will not allow the die to contact the anvil but not so far away as to prevent the saw from being pushed against it. The size of the kerf is controlled by the stop at the front end of the cylinder and you should not try and pull up too much material at once as you may experience cracking during the shaping process, which will result in a full grind-down and a repeat of the process from the beginning.
Swadges are designed so that you won’t be able to grind the top of the tooth on your first pass. This allows the grinder to take a little more off the face than the top so that the clamp marks left on the sides of the saw will stagger themselves over successive swadges and won’t run in a straight line right into the tooth where they could cause cracking. The amount of pull-down is controlled by the set-screw at the front of the swadge. More gap means a lower tip on the tooth.
After swadging it’s time to shape the tooth. A shaper has two carbide jaws that reduce the stretched steel to the desired angles and width of the final cutting edge. Setting up the shaper is easy but very important. Squeeze too much and you have a humped tooth with a small kerf that will not hold up. Too little and you end up with weak side-stock and a tooth that will dull quickly. The “goldilocks” setting is one where the tooth is squeezed to the stop with a small amount of resistance and the resulting tooth-shape is flat on top, fat and long on the sides and is the expected pre-grind size. Depending on the type of shaper you are using, you may have to clip the tooth before shaping to achieve consistent results.
From there it’s a simple matter of grinding in the saw. The first pass is critical, even if it is only a clipping pass. The ratio of face-grind to gullet-grind must be correct from the very beginning or you will spend the rest of your time chasing a properly shaped tooth. The face of a newly swadged tooth should have a deep pocket, a top bar that is wide enough to be good and strong yet not so wide as to eat up your whole swadge. There should be small horns extending down from the corners into the sides of the tooth. If the top bar is too narrow, the corners will dull and if it’s really narrow, you will end up with an unintended dull V-top that will cut wood about as well as you would expect hundreds of tiny hammers to cut wood.
Swadging a saw that is already in pretty good shape is faster, easier and results in a stronger saw. If you leave it until the saw is truly worn, the end result will be nowhere near as good as it could be. The job of swadging is easier now than it ever has been before thanks to improved equipment and there is really no reason to try and get six point-ups out of every one. Swadge early, swadge often; it will mean less work for you and better saws for your mill.
Trevor Shpeley is on the executive of the BC Sawfilers Association and works as a filer at Kalesnikoff Lumber in British Columbia.