Closeup: Blade Brake Allows Stihl TS440 To Reach Tough Undercuts

Brake protects operators when the guard exposes the top of the cutting wheel but demands a slower cutting speed; here’s how Stihl keeps cutting production up

Stihl Cec10

Stihl says its TS440 Cutquik cut-off machine is the first cut-off saw in the world with a blade brake, but the brake was actually created to support the saw’s adjustable guard.

With the TS440, Stihl engineers addressed the routine challenges presented by cuts like the bottom of walls near the floor, corners, the underside of in-ground pipes, and other situations where traditional cut-off machine guards would prevent the cut.

Safety standards require protecting the operator from the spinning blade in the event the saw kicks back. So guards don’t normally retract to where the operator can cut with the top of the blade.

“The toughest of cutting operations will be performed more easily than ever before,” said Thomas Techow, Stihl Inc. product manager. “You can cut underneath a tube without excavating, for example. It saves time and money.”

Stihl made the TS440 with a guard that adjusts back to expose the top of the blade.

“The standard position of the guard, at the top of the wheel, protects the operator if there’s kickback,” explains Techow. “But the guard on the TS440 can rotate all the way back, allowing it to cut from the bottom up. But by tilting the guard back, you lose that protection. To regain it, we’ve added a brake.”

How does it work?

A blade brake will serve as kickback protection in lieu of the guard, but it must stop the blade in a fraction of a second when necessary. Stihl’s Quickstop brake uses a spring-applied, magnetic-released brake on the spindle.

“We have a generator on the crankshaft, so when you start the machine, electricity keeps the brake lever open,” explains Techow. “But as soon as a kickback is detected, a gyroscope sensor in the machine realizes it, the brake kicks in and stops the wheel within a split second.”

But consistently stopping a 14-in. diamond wheel spinning at conventional speeds is a daunting engineering challenge. So Stihl reduced the working spindle speed of the TS440.

“In order to reduce the kinetic energy of the blade to an amount the brake is capable of ‘catching,’ if you will, The TS440 has a little bit more than half the spindle speed but gives the same power as our comparable model, the TS420, which actually uses the same engine powerhead,” Techow says. “We’ve got lots of torque on that spindle, so you can push like an ox on the saw and it won’t bog down the rpm.”

Stihl slows the blade and magnifies torque with a double-reduction belt drive in the TS440.

“The cutting performance doesn’t vary that much,” Techow says. “The TS440 is maybe a tad bit slower, but the difference is only really noticeable in laboratory conditions.

“When comparing it to the TS420 side by side, the cutting characteristics are much different. The TS440 has more torque, so you can actually push it hard. With the TS420, you have to let the wheel run to get the same power output. It’s speed vs. torque.”

It becomes the operator’s challenge to find the sweet spot of speed and force to get maximum cutting productivity from the TS440.

The other trade-off with slower spindle speed is in abrasive wheel choices. Resins that hold abrasive to wheels are designed to work at the higher speeds of conventional saws. At the TS440’s slower speed, they tend to glaze the cutting edge. Stihl designed abrasive wheels specifically for the slower speed.

“Abrasive wheels need a certain contact speed for the material that’s being cut. As this one turns slower, we have designed a special 14-in. abrasive wheel specifically for this spindle speed,” Techow says. “Diamond wheels don’t care about spindle speed, but if you need to use an abrasive wheel with this machine, make sure it’s the one specifically designed for this spindle speed.”

Maintenance made easy

Anything that simplifies maintenance is welcome in a rental setting, and the TS440 delivers on that score. Once the Quickstop system has experienced a certain amount of wear, the unit will alert the operator to get service.

“At that point, you won’t be able to release the brake anymore,” Techow notes. “It’s a clear indication to the operator that service is needed. You can override it long enough to finish the job, but then we ask operators to please see your dealer for proper maintenance.”

Servicing the brake mechanism is simple, a lot like servicing other Stihl products, such as chainsaws.

“It has a clutch drum with a steel band wrapped around it,” Techow explains. “The brake system is new, and we’ve also added electronic water control for dust suppression, meaning as soon as you release the throttle trigger, the water flow shuts off. If you accelerate again, the water comes back.”

Essentially, the TS440 offers all of the features of the TS420 that users have come to expect. The IntelliCarb Compensating Carburetor automatically adjusts the air/fuel ratio as the air filter becomes restricted to maintain the engine’s correct RPM. Stihl says its well-established X2 Air Filtration System – a centrifugal precleaner added to primary and secondary air filters – and stretches air filter service life up to a year.

The TS440 gets those features, plus the ability to make cuts that other saws’ guards won’t allow for about $250 more than the TS420.