USNR has acquired a number of companies and associated product lines over the years. This article chronicles the history of one of those companies, Letson & Burpee, and the development of the high-strain bandmill.

High-strain band sawing is now considered an industry standard, but that wasn’t always the case. How the method came about is an interesting story in itself, with a significant breakthrough literally discovered by accident.

High-strain band sawing was originally developed by a company called Letson & Burpee in the late 1960s and early 1970s. For 50 or so years before this, bandmill technology had remained static.

L & B had been manufacturing bandmills under license with the Monarch brand name. These were what might today be called low-strain machines (strain meaning the load applied to a band saw blade to tension it).

It’s important to note that the type of strain mechanism used is critical to the performance of any bandmill. It had been well established that you need to apply sufficient tension to keep a blade straight as it cuts wood, to prevent it from snaking in the cut. Like all the other machines on the market in the early days, a weight hanging on the end of a lever arm was the standard method of tensioning the band saw blade on Monarch equipment.

In 1965, L & B management decided to build its own bandmill to improve on the Monarch design. At the time, only single bandmills were in use and the first machine built at L & B was a seven-foot (wheel diameter) headrig machine for a customer in Quebec. This machine carried the name Letson & Burpee for the first time.

An Accidental Breakthrough

The concept behind the design of this machine was to retain the strain knives as part of the mechanical strain system, still using a weight arm to apply the strain. As part of the new design, the Monarch-style gibbed slideways for the top wheel lift were replaced by cylindrical plunger tubes to reduce friction.

The new seven-foot bandmill was packed and shipped to the customer in Quebec. Shortly after the machine was installed and put into service by mill personnel, a follow-up phone call from the mill revealed that the customer was not only pleased with his new bandmill, he was raving about its outstanding snake-free cutting accuracy on frozen logs.

Then, after running for a time, the bottom arbor suddenly broke. L & B sent a new arbor, which also soon broke. This puzzled works manager Dick Crawshay, who flew east with another replacement arbor to find out what was going on. What Crawshay found was a shock.

Despite warning notices, the customer had inadvertently been running the new machine with the shipping blocks still in place. It was normal practice at that time (as it is today), to fit shipping blocks and wedges into the upper wheel lift assembly and other moving parts to prevent movement and potential damage while in transit.

It seems the mill personnel had been raising the top wheel until the motor stalled out, ignoring instructions. After removing the shipping blocks and fitting the new axle, Crawshay supervised start-up of the machine with the correct (low) strain setting. Immediately the sawyer exclaimed: “What have you done with my lovely machine? It worked so much better before.”

Back at L & B, Chief Engineer Ed Allen figured out the strain at which the mill had accidentally been running, which was way more than recommended. In effect, this incident later turned out to be the first true high-strain bandmill installation. Allen realized that if they could design a bandmill to handle the strain accidentally experienced in Quebec, they could achieve much greater accuracy and recovery.

The company decided to design a new machine with an improved strain mechanism, both to find the optimum shape for the pivot knives and hopefully get much faster response and damping times. The broken arbors also caused a complete machine re-design which resulted in dead arbors (fixed axles) then becoming a standard feature of L & B bandmills.

The new machine was designed to withstand a maximum strain of 25,000 lbs in the case of a five-foot model, which typically only ran with 3,000 lbs of strain and using a 15-gauge (0.070-inch) saw.

Another notable innovation introduced by L & B in 1967 was the use of twin bandmills with a Sharp Chain log feed. The first of these was installed at Jacobson Brothers in Williams Lake, BC and attracted a lot of industry interest.

Taking high strain band sawing further

Once work had started on high strain band sawing, the innovators behind it took it further, developing the improved final design that later became famous as the Letson & Burpee Air Strain system. This was the first full air system, without weights or knives. It used Bellofram airbags, one under each upper wheel bearing.

The system uses a custom-built air cylinder strain mechanism that protects thin kerf blades by its quick response and short damping time, momentarily dropping the strain loading if the blade hits a knot, for example.

Saw filers at the first test mill liked the new system and wanted to keep it, as sawing accuracy was improved and the saws needed less work. A patent was granted for the air strain system, based on this design.

The L & B machines became known as the Rolls Royce of bandmills and it was some years before other machine makers devised their own high strain system using hydraulics and other methods. As a result, L & B air strain bandmills were shipped all over the world and sold as single headrigs, twins, quads and horizontal resaws. A variety of different feed systems were also built to complement them.

In later years, Kockums Industries purchased L & B and later still, merged with long time rival Canadian Car to become Kockums CanCar. USNR purchased Kockums CanCar in 1996 thus acquiring the L & B designs. USNR still builds L & B style air strain bandmills today.

One of the original design engineers, Ralph Wijesinghe, is occasionally called in as a consultant on the machines. “In my opinion, over thirty years later, it is still the best bandmill available,” says Wijesinghe.