Saw Filing 101: Evaluate and experiment with frost-notches
By Trevor Shpeley
As you read this column, winter has settled in and you have long since employed your cold-weather strategies and convinced mill management (as you do every year) that they need to run a little slower if they want to run at all. Now that everything is running smoothly, it is a good time to evaluate your frost-notches and to experiment a little.
Frost-notches have been used to keep winter saws from snaking in the cut for as long as mills have been trying to make saws work in cold weather. Strangely enough, the core problem with cutting frozen wood is the build-up of heat. Typically, a sawyer will slow down the feed on a frozen log to keep from stalling the rig. In doing so, the saw takes a much smaller tooth bite, which creates a flour-like dust instead of the usual granular chips. The fine dust does not carry heat away from the saw-tip in the way that larger chips do. It also tends to spill out the sides of the gullets and freeze back onto the log, creating friction and degrading saw performance.
To combat this, filers discovered a long time ago that if you gouged a groove in your grinding wheel, the saws would perform better. Since then, there have been minor improvements and modifications, but effectively nothing much has changed.
A frost-notch functions by changing the flow of sawdust through the gullet of the tooth. It reverses the direction of the sawdust as it hits the notch, causing the gullet to fill and empty in a different way. You can see this in action for yourself if you watch a headsaw as a log is cut. A summer saw will typically eject the sawdust from the bottom of the cut at an angle while a notched saw will tend to shoot it straight down.
The original method of scratching out a groove with a nail is still used and you will find many who swear by it. Since a slot cut this way can be sloppy, some filers use a cutting disc by itself to individually shape the point in the gullet. Far more common is the practice of taking a grinding wheel and putting it together with a cutting disc, usually with a paper blotter in between to create the space that, in turn, creates the notch. Special large blotters are available specifically for this purpose.
This works very well, but there are problems you might encounter such as the cutting wheel breaking when it is bent the wrong way by the wheel dresser. The other common problem is that, because there is some flexibility between the two wheels, the front notch can become long and skinny, which then gets in the way of the swage-die, causing an inconsistent tooth size.
In my opinion, a better way of running a two-wheel system is to remove the blotter entirely and glue the wheels together and cut between them with a lathe-chisel. The advantage to this is a well-defined frost-notch and wheels that will not break apart easily. To glue the wheels together, run a small track of clear silicone in a spiral from the centre hole to the outside edge, spacing each bead about every 1/2 inch. Use a press made from ready-rod and a couple of steel plates to apply pressure while they dry. Be sure to check that the edges are lined up and that the centre hole does not overlap anywhere – this is very important. No matter which way you put the wheels together, make sure the overall width matches the summer wheel as closely as possible to preserve your tooth profile.
Another common problem with sawing logs in the winter is sawdust freezing to the sides of the boards. This happens more often with whitewood species and will cause deviation. An effective solution is to “chisel” the saw gullets. The filer will take a sturdy metal chisel and place it right at the bottom of the frost-notch where it meets the throat of the tooth. The idea is to strike hard enough to cause a flair that is smaller than the saw kerf, but large enough to scrape the frozen sawdust from the boards. This is not a fun job and is best suited for apprentices as a character building exercise.
Love them or hate them, you are probably going to be notching your saws for the rest of your career – you might as well try a few things and pick a method that works for you.
Trevor Shpeley is a former executive of the BC Saw Filers Association and works as a filer at Kalesnikoff Lumber in British Columbia.