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Managing the Tilt

Timberjack's new shift tilt technology on the 608L carrier allows the machine to "stick like glue" to hillsides

By Tony Kryzanowski

The word "breakthrough" is often overused in today's highly commercial world, but when it comes to describing Timberjack's new 608L purpose built carrier and its unique shift tilt feature, the description fits to a tee. Timberjack has upped the ante on the features front with its patented, fourbar shift tilt technology. It is the result of engineers putting science to work to enhance a minimal tail swing and leveling track carrier to allow harvesting in slope conditions in excess of 25 degrees. It also offers contractors an alternative to what's currently available on the market today. The base 608 unit has been available for some time and it is field proven, but to this point it has been designed with a fixed or conventional upper.

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The 608L's leveling system allows the cab to tilt 27 degrees forward, 10 degrees backward and 20 degrees to each side. Leveling the upper back from full back to full forward takes about 10 seconds using separate operator controls.

The challenge is to better manage the centre of gravity on zero tail swing machines, increase productivity and enhance stability while harvesting on hillsides- a tall order. "What happens with a very short tail swing machine is that the centre of gravity of the upper ends up being considerably forward toward the felling head relative to the centre of rotation," explains Timberjack design engineer Terry Robinson. "That's because you have moved the engine, fuel tank, hydraulic tank and all the components in order to get a very small tail swing ." This was confirmed while watching many machines at work, and thus the shift tilt concept was born. "If you cut a tree, pick it up, and swing around backwards, your centre of gravity has moved a long way, something like twice the distance ahead of the centre of rotation," Robinson says. His objective was to find a zero tail swing and leveling design that kept the location of the centre of gravity optimally positioned, both when the load was facing forward or backward, and thus creating more overall stability on steep slopes. "The only way you can do that is by shifting the upper relative to the tracks," he says. "I ended up with the fourbar mechanism to do it ."

The 608L's leveling system allows the cab to tilt 27 degrees forward, 10 degrees backward, and 20 degrees to each side. Leveling the upper from full back to full forward takes about 10 seconds using separate operator speed controls. This feature takes into account different levels of operator experience and allows individual operators to make adjustments according to their own comfort zone. The 608L also offers the added advantage of 360degree continuous rotation, which enhances production, as the operator does not have to worry about swing stops. As the upper housing levels, it physically moves 36 inches ahead into the hillside. The shift tilt system is based on the fourbar linkage principle, using unequal length front and rear links. As the twin tilt cylinders extend, the upper tilts and moves forward, relative to the tracks and to the hillside.

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The objective was to find a zero tail swing and leveling design that kept the location of the centre of gravity optimally positioned, both when the load was facing forward or backward, and thus creating more overall stability on steep slopes.

To achieve side tilt, one cylinder extends while the other retracts, pivoting the upper to the opposite side. "It pretty well sticks you like glue to the side of the hill," says Kevin Meakin, a harvesting supervisor for Meakin Forest Products in Sault Ste. Marie, Ontario. They have been using a Timberjack 608L in their operation since last summer, harvesting marked timber in dense hardwood areas and extremely hilly conditions east of Lake Superior. The carrier is equipped with a Timbco bar saw felling head, capable of harvesting trees up to 33 inches. "We were looking for something that would have enough power to get up the hill to cut the larger trees, still be stable, with enough boom power to be able to hold and lift some of the bigger wood, yet have good tractive effort," Meakin says. Tractive effort on the 608L is rated at 53,550 lbf. It comes equipped with a 230 hp Cummins 6CTA 8.3 engine. Boom reach is 23 feet 4 inches and its lifting capacity is 3,366 lbs when equipped with the Timberjack S547 felling head. Its overall width is 10 feet 4 inches with zero tail swing over the rear and 10 inches over the side when outfitted with 28 inch wide tracks. The 608L has 30inch ground clearance. The terrain Meakin Forest Products works in averages a 30 per cent slope, often in wet and rocky ground conditions.

The slope can go as high as 40 per cent. Tree butt sizes can also vary from eight to 30 inches. "The 608L tilts and levels, and then pushes itself forward as you get to steeper ground," says Meakin, "so the weight of the carrier is actually on the front part of the tracks. If you get going steep enough, it looks like your whole undercarriage is kind of below you and your cab is up front. It has been working well ." Previously, they were using an older 2618 Timberjack carrier, which is an "engine down" versus an "engine up" design. Timberjack still heavily promotes the engine down design because it delivers a lower centre of gravity and greater stability. Meakin says the 608L is more agile and causes less residual damage to surrounding trees than their 2618, an important consideration in the environmentally sensitive transitional forest area north of Sault Ste. Marie. He adds that the 608L also has better ground clearance, resulting in less resistance in wet areas while harvesting on slopes. Their operator is also impressed with the 608L's performance. "It's a little safer for the operator," says Meakin. "It gives him more self-confidence in the stability of the machine with it hugging the slope better, and it doesn't have as much belly drag because of the clearance. There seems to be a little bit less machine effort to harvest the trees."

British Columbia contractor Frank Etchart agrees that the 608L's stability gives operators more self-confidence harvesting timber on steep slopes and that translates into better production. "If the operator feels comfortable, he is going to produce," he says. "I would say that you could achieve a good 10 per cent improvement in production compared with a similar machine because the operator is not rocking and spinning so much trying to get stable." Etchart has been in business harvesting spruce, pine, fir and balsam in the Merritt area for 43 years, and hasn't been shy about trying equipment innovations as they have arrived on the market. The terrain in his area averages about 25 per cent slope, but can go as high as 45 to 50. A lot of their work involves selective harvesting. "I had my reservations when I first saw it because every time you have so many moving parts, that's normally the weak point for wear and tear," he says. It's too early to tell if the moving parts involved in Timberjack's shift tilt technology will develop into a problem, but it has performed relatively problem free after 700 hours, he says. Timberjack has also tackled the "toboggan" effect that can occur when harvesting on a hill in deep snow by modifying its undercarriage design.


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There is a height difference between the front bridge where the links are attached, and the rear bridge where the cylinder is attached. The rear bridge is about two inches higher. "The idea is that when you are going up the hill, if the snow is deep enough the front bridge cuts that snow off and pushes it ahead of it," says Robinson, "but the back bridge clears the snow ." He had the opportunity to observe a 608L harvesting in deep snow on a hill in BC. "When I got there, there was a metre of snow on the ground and it was plus 2 degrees. It was good snowball snow, which is the worst kind for sliding in," says Robinson. "The 608L worked very well. The operator wasn't sliding around at all ." Meakin says testing the 608L's performance over the course of this winter in deep snow is something he is looking forward to, and he expects that it will outperform the 2618. When asked where he discovered the idea for the shift tilt mechanism, Robinson says he found a fourbar linkage system used in a different application. "There was a patent taken out by a couple of employees of the US Department of Agriculture," says Robinson. "They had something along this idea, except that it was quite different. There was no question that it was a fourbar linkage, and they had been issued that patent in the early 1980s. They had not maintained the patent." Robinson picked up on the idea, modified it to solve the challenges they encountered with their own designs and calculations and it worked. Timberjack's shift tilt system is fully patented.



This page last modified on Monday, November 03, 2003