Mdi/Yutani Kobelco Mitsubishi MD 320-LC Rotosaw

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Swinging around

In the beginning there were Norwegian fiddles, then chain saws and now feller bunchers. This Jewell (it says that right on the boom) joined our collection of things in 1999, though the machine is a 1989 Yutani MD320B-LC with a Jewell boom and a 'Tepee House'. Since the days of Paul Bunyon, loggers have dreamed of a machine that would drive out through the woods like a corn picker gathering trees like a corn picker gathers stalks. A feller buncher is a dream come true. There have been a whole host of approaches to mechanical timber harvesting. This is but one solution. For an alternative, or a companion processor depending on how you use it, view our page on the Thunderbird 840 and dangle head Keto processor.

Update 2012

This article was written around 2000. Since that time 'Hot saws' have become popular. The Hot Saw head looks similar to this head, but the saw is on a swinging arm, instead of a slide, and the saw turns all the time at a fairly high speed. Because of the design they are not restricted to just wood that will fit between the slides and can cut oversize by cutting in from alternate sides. In the last decade the Hot saw has become the preferred saw head for felling timber in high production operations in Oregon.

When it comes to falling the tree, there are at least three technologies in use that I know of. The crudest, but cheap and quick, is a shear which is really just a big pair of scissors. You simply drive up to the tree and bite it off. The shear usually has one flat anvil and a sharpened blade and functions exactly like the similarly designed pruners that you might use on your rose bushes. The drawback of the shear is that it does a lot of damage to the log (which looks like it was bitten off). This is not that important if the wood is going for pulp wood, but obviously is not acceptable if the tree is destined for lumber.

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Over the bunch
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Drop it!

The other two solutions are cutters. Both have an assembly which includes arms to wrap around the tree to steady it while a cutter at the bottom cuts it off. One design uses a chain saw bar (with a very large chain) and the design shown here uses a circle saw. The saw blade is about an inch thick and actually has carbide cups on it for cutters instead of 'teeth'. The saw only turns during the actual cutting process. The downside of this exercise is that you must have a machine large enough to man handle the tree. As a consequence the machines are not as small and nimble as you might hope. To be sure mechanical harvesters are mounted on all sorts of things from fairly small 3 wheel rubber tired machines to what you see here--a moderately large excavator.

The Yutani name in excavators is not one that you are going to see much of, but the machine is a pretty familiar one. The Gimmick here is that there are a lot more Japanese brands of excavators than there are manufacturers. If I have this straight, Cat made a big deal with Mitsubishi about this time to market excavators made by Mitshibushi under the Cat name. As a part of the scramble to differentiate the Mitsubishi made Cat excavators from the others, the Yutani name was knocked off in favor of Kobelco. Now Kobelcos are 'different' in that they use Cummins engines instead of Mitisubishi engines. This machine features a Mitsubishi 6D22T engine is is reputedly only a heater different from a certain popular completive product.

The appearance is a lot different because of the Jewell Tepee house. Although the present trend is to put feller bunchers on standard house machines, 1989 is fairly early in the cycle of mechanical feller bunchers of this size, and at that time the custom house was the 'in' thing. The house is elevated in the middle so any thing that falls on it is suppose to slide off and everything about the house is made of heavy steel plate. NO sheet metal -- 3/8ths T-1 Steel. The access doors are similarly made, and instead of having the muffler on top the house as is common on excavators, it is wrapped with insulation and is inside the house also (along with a massive fire suppression system).

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RotoSaw head

The cab is the standard excavator cab with a heavy steel cage built over it. The hydraulic system is the state of the art high pressure system (5,000 PSI) with variable displacement pumps. The controls are electric. The drive is managed with two rocker pedals, while the swing and arm are on the left joy stick with the 'bucket and boom' functions on the right joystick in traditional fashion. The additional functions associated with the cutter head are handled with rocker switches on the joy sticks. The inside buttons handle the left and right arms while the outside rocker buttons have the saw on the right and the pivot on the left. The pivot function allows you to rotate the head assembly left and right to compensate for being on a sidehill.

Jewell also provided the boom assembly which varies from an excavator boom in a number of ways. Notably it is configured for working above ground and not in a hole, so the boom is straight, and the arm (elbow) and bucket (wrist) cylinders are mounted for lifting instead of digging. Recall that hydraulic cylinders will always expand with more power than they will contract with so the heavy working direction of a hydraulic cylinder should be the expansion direction. The reason for this is of course that the effort that a hydraulic cylinder will make is a function of the number of square inches of surface area on the piston multiplied by the pressure. When the cylinder is contracting, an area the size of the cylinder rod is not being displaced so the cylinder is less strong by the area of the end of the rod during the retraction cycle.

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The Cutter Head
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Dump cylinder
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Removing the Nut
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Broken repair
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Broken 3-3/4" pin

RotoSaw Head

The Rotosaw head itself is not made by either the makers of the excavator or the boom. It comes from Canada and can be mounted on a variety of machines as long as they are big enough and have the requisite hydraulics. This particular saw head is a 26" one which is one of the larger models. The middle three arms are controlled with hydraulics. There is a double arm on the right and a single 'broken arm' on the left. The operational idea is to hug the tree firmly with the arms and then saw it off. The idea of the broken arm is that you can after cutting one tree, open the right arm and grasp a second tree, while holding the first with your left 'broken arm'. Then after grasping the second tree, you can open the left arm and the spring loaded 'elbow' will let you slip the left arm out from between the two trees so you can then reclose it and hold both trees with both arms. In this fashion if the trees are quite small (meaning that the machine can handle several at once), you can accumulate an armload of trees before swinging and dumping them in a pile.

The saw itself is a two piece affair. Only the outside ring of a couple inches rotates, and only on demand. The same action advances the blade and turns the blade so it is self feeding.

If you notice a couple colors of heads, that is no illusion and we didn't paint them. The Rotosaw head is expendable. We broke the yellow one beyond repair in a few years and rounded up another. As I write this in 2006 it is in the shop for serious repairs.

The good news is that the saw is ok. That is a real spendy part. However, there are issues with these saw heads. They simply come apart. As it sits here it has two major issues. The first is that the pin that hold the dump cylinder broke. It is a 3 3/4" pin and it was snapped right in the middle. This shouldn't happen, but as you study the engineering you can see why. As you look at the back side you can see the two side plates with the pin bosses welded inside. The side plates are only 3/4" material and not braced or webbed so they can flex. This means that the pin bosses really can't do their job so you really have an 18" pin largely unsupported with a big hydraulic cylinder in the middle. Well Guess what, the pin broke. Shown here we removed the nut and put spacers behind it and used the nut for a puller to extract the broken piece. Then we drove a new pin in the hole with a 20 lb sledge hammer. The pin we put in was made for a different machine (but the right size---only a little long so it hangs out on the ends. Pins like this should go in easily, but remember the old pin broke because the pin bosses flexed too much---so everything is sprung some. We did get the pin in, and will add gussets to the pin bosses trying to reduce the flex that they have. After if they can flex more than the pin can they aren't holding anything. It reminds me of our highway department who built a bridge with support beams that would flex 4" under normal use and a deck that could only flex 2" before cracking. And then they wondered why the deck cracked!

The second problem is that the poor things back is broken. The saw housing on the bottom is made of 3/4" and heavier materials, but the back that stands up which has the swinging arms and the mount to the machine on it is only made of 3/8". Well it is all cracked where the two are joined together. You can see in one of the photos previous efforts as welding it. It was done by a 'crack welder'. He did a good enough job welding up the cracks, but added no reinforcement. This was bound to fail and it did. The thing wasn't strong enough to start with, and when you weld up a crack you don't make it better than new. We will, and the previous repairman should have,add various plates and iron to the thing to make it stronger and more rigid where it is cracking.

Evolution of controls

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In for Repairs
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Going for a Ride

You don't fully realize how far controls of one of these machines have come until you really just think of what has happened in the operators compartment of an excavator in the last 50 years. We used to call these things 'steam shovels' While I have never seen one that actually had a steam engine in the back, you get the idea. It didn't have 'in seat starting', and the controls were long levers working frictions and usually required a foot for the brake, and 3 arms to work the rest---a swing lever, and a left and right cable. Then we got hydraulic ones. The early hydraulic machines which include both the American 35 and Hopto 900 found on this site have long levers going to spool valves. Not bad, but you have 3 foot long levers to pull all day.

Next along came various schemes for power assist. Koehring went for an air assist on the controls. The big levers were replaced by joysticks that tripped little air servos. This took the effort out of the operation, but made for a plumbing nightmare of little air lines and air valves, and on a frosty morning the probability of all the valves working (and none with frost in them) was about zero. Another alternative was hydraulic pilots. This sort of a system has a small hydraulic system which moves just enough oil to activate small hydraulic cylinders to activate the main spools. It is more reliable than the air activators but is still a plumbing nightmare because you have herds of little tubes running to the joysticks. With the electric over hydraulic they finally got it right. The joysticks are little different from the ones used for computer games, and all you need is a wiring harness between the joystick and the spool valve. With closed center hydraulics and a variable displacement pump you can even modulate the thing fairly well.

Broken Track Repair

Broken track repair
Broken track repair
Broken track repair
Broken track repair

You may wonder if these things ever break or if they do how you fix them. The basic key has always been to get up in the morning with determination. Driving around in the woods tracks take an awful beating. You are constantly driving on uneven ground or over the corners of stumps or logs which with the wide pads puts a twist this way and that way on the rails. Any machine with tracks is ideally run on level even ground. Of course, if who would need tracks then (except for places where the ground was soft). Indeed the track was invented for use in the Sacramento Valley of California and soft ground was the problem.

This machine, however, is a feller-buncher. It's job is to drive up to a tree, put its arms around the trees and saw it off and lay it down. Not all trees have a level road up to them, so track breakage is a possibility. Interestingly the track here finally gave it up right in the middle of a rocked haul road which made it convenient. Regardless of the location the methodolgy for track replacement is about the same.

Since we were in a good location, we laid out the replacement track end to end with the broken track and simply drove the machine off the broken track and onto the replacement track. If that is not possible due to location, one can alternatively jack up the machine---it will jack itself up, and then winch the old track out of the way and winch a replacement track under the machine.

Once, the machine was sitting on the replacement track, you have to take a long cable or chain and hook on the the long end of the track and pull it right up over the top of the swing frame. At some point you will have released the track tightner so you will have some slack. Positioning the track to be linked up works best if you do it on the sprocket end. Normally a block of wood works just ducky for holding up the last couple of links of the track on the bottom while the upper part will drop into position over the sprocket teeth providing approximate alignment. Then you simply drive the master pin in and bolt on a couple of pads and readjust the track and you are good to go. Here where the conditions were favorable it took less than 2 hours to change the track with the aid of a service truck crane to winch the track over the top. If the work must be done on uneven ground or in deep mud it can be much more difficult.

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