Features Equipment Sawmilling
Proper pairing: Matching saw with the machine

Sawmills have changed in design over the last 50 years. And now, it seems they are literally changing every few years.

In my early days of sawmilling, the trimmer was a two-saw simple piece of equipment. One stationary saw and one floating saw that would move and cut in two-foot intervals. In those early machines, almost any saw would work. I know this because the saws used in these trimmers were wire-tooth steel saws that were hand-ground with a post grinder and finished to a point with a mill bastard file.

The filers were skilled, but hand-grinding isn’t exactly an accurate science.

Trimmers have changed over the years; from the simple two saw bottom arbors where the saws pop-up, to the same except with multiple saws every two feet. This proved to be a game-changer allowing so much more footage of lumber to get over the trimmers and out of the mill. Higher production came with a few issues though. For one, operators had to deal with the cut-off pieces getting cross ways and stopping the flow of lumber.

The somewhat simple answer was to design a top arbor trimmer. This allowed the trim pieces to simply fall between the chains that pulled the boards through. On paper and in the mill, it did prove to solve most of the problem that the bottom arbors had. The negative hook held the board down and pushed back on the lugs holding the board in place. Many of these machines were installed in sawmills across the country.

However, they only performed well using a negative degree hook (sometimes as much as a negative 10-degree) with the saw cutting counterclockwise while the lumber flowed from left to right under the arbor. This design was acceptable in green lumber but could not be used on dry lumber as the negative hook would tear the fiber. This caused the mill to have to use two different brands or makes of trimming machines with different saw specs. And different trim saw specs caused issues when the saws were mixed up and the wrong saw went to the wrong trimmer.

This gets us to the grandest and latest modern trimmer of today. Same configuration, drop saw trimmer but trim saw configuration changes to what is now called a power cut. This consists of the saw itself turning clockwise when lumber is traveling under the arbor from left to right. As the saw cuts, it forces the lumber up and back against the lugs. Therefore, the trim saw must have a positive 10-degree hook or very close to 10 degrees. In some instances, they are getting by with a positive five-degree or even zero hook, but to work properly and with decreased horsepower, it needs to be a full positive 10-degree hook angle. Even though these machines work great for both green and dry lumber at the sawmill, the planer may choose to order saws with more teeth just to get a smoother end cut.

It’s always been the norm to have more teeth in a trim saw; creating a good, clean end cut and to help keep horsepower low. Trim saws in the past were ground with alternate top bevel (every other tooth had an alternate LH or RH point). With trimmers today being fed so fast, a trim saw could literally require more teeth that would fit in the circumference using the alternate bevel tooth design. Remedy: by using a trim saw with a V top (point on both sides of top), the number of teeth in the saw can be cut down to half of what was needed. Therefore, if you’re using a 160-teeth alternate bevel tooth, this could be cut down to having 80 teeth instead of the full 160 teeth.

You may say pairing trim saws with the proper trimmer is like pairing wine with the right food. Mis-matched, you may be able to get through the meal, but it wouldn’t be the best experience.

 Paul Smith is a saw filing consultant and founder of Smith Sawmill Service, now part of BID Group. You can reach him at paul.smith@bidgroup.ca.