Fiskars 15-Inch Replacement Saw Blade for Pruning, High-Speed Steel WoodZig Blade for Lightweight Extendable Tree Pruner, Fits Fiskars pruner models 6391, 9388, 9390, 7889, 7831, and 8391
$ 4.54
- I have considerable engineering experience in cutting tool design, and in conjunction with a new ATSS pole saw, have just completed a rather extensive comparison of competing blades.BACKGROUNDBasically, I was a bit flabbergasted to discover a critical design flaw in common with virtually all pole saw blade designs.We needed several thousand dollars worth of tree de-limbing on extremely large pines. Climbing gear. A dozen trees up to 4 feet in diameter. Branches up to 10 inches in diameter and 25 feet in length. A lot of heavy cutting, up to 35 feet off the ground. Unable to get anybody out to our remote location, I decided to get a 6-section all-aluminum American-made pole saw from ATSS, and do the job myself.The ATSS pole saw kit is an awesome unit. I bought an extra Marvin 330 blade, and went right to work when the kit arrived.The Marvin 330 has 13 inches of teeth, and I’m a pretty strong guy. But the relatively pronounced curvature of the stock blades would stop a cutting stroke with 4 inches of blade still sticking out the far end of the branch. The curvature stopped the cutting stroke dead in its tracks.That’s a loss of virtually the outer 1/3 of a cutting stroke; and a heck of a waste of energy as well, because believe me, that sudden arrest of cutting progress is much harder on you than a curvature would be that allowed you to use the whole length of the blade evenly.SEARCHES FOR BETTER DESIGNI attributed the arrested stroke to excessive curvature, and began to conceive of curvature ideals. A lot of research later, and I found however that virtually all pole saw blades share the pronounced curvature of the original Marvin.At no cost, American Tree Service Supply sent us some other blades to experiment with. Our job was huge, and when I needed to take a breather, I was still looking for other blades because the short cutting stroke was so consistent, and it was so obvious how much room for improvement there was. It took a considerable amount of searching before I found a 17.5-inch Fanno blade, with carpenter saw style teeth and the flatter curvature I was looking for.The Fanno was excellent. Do the math: Being as the flatter curvature allowed a full cutting stroke, then if the efficiency of the teeth and cutting action (*while* the blade is cutting) are equal, we should be doing 50% more work than the Marvin 330 (which has a pretty wicked looking tooth style itself). With the 4.5 additional teeth, if the cutting efficiency of the teeth were equal, the Fanno blade could potentially have produced 200% the cutting per stroke. Being as generating the power of the stroke is what taxes your energy, a person could potentially get twice the work done with half the effort.In use, the Fanno blade’s flatter curvature proved a great improvement. It was very smooth to use. Much less energy expended. But owing to a less efficient tooth style, I figured I was only getting 150% of the work done with the pronounced curvature blades (of a prospective 200%).FISKARS TOOTH DESIGN — WHY THIS IS SUCH A GREAT BLADEWhen I found the Fiskars with the same flatter curvature of the better Fanno and the improved teeth, I had to order a pair right away.What is not evident from Fiskars images, is the sophisticated tooth design. Each of the alternating teeth are kicked out about 0.015 to each side, making the cutting path through the wood about 0.030 wider than the blade body itself. But the cutting with of each tooth is that of the blade body. Just like a chainsaw then, the blade body offers no impediment, and the tooth design is just unbelievably efficient compared to the usual ragged pole saw teeth. The kerf and tooth design or the Fiskars put it in a class of its own.What is happening with the generic tooth designs (including the carpentry-like Fanno blade I tried), is a sharp point is just tearing or abrading the wood away. A true *cutting* tooth, on the contrary, is actually slicing material and drawing it up into the gullets between the teeth. There’s a huge difference. The solid, chiseling center of a drill bit is similar in its disparities between the outer cutting flutes of the drill bit. As there has to be a center, drill bit designs suffer the very disparate efficiencies between the center (however improved by modifications) and the outer cutting flutes. But it’s the same kind of design disparity which make this Fiskars blade so superior to the generic tooth designs.In any case, the teeth on the Fiskars are nasty. They are very sharp. They slice wood… pulling the chip up into the gullet and pulling the tooth down into the cut — with the back relief angle partially regulating a rate of cut which is awesome for any hand tool. Think of the Fiskars as a narrow chain saw, which reaches any depth of cut with far less numbers of teeth crossing the cutting area, because the narrow cut allows the saw to go much deeper into the wood with far less effort.SHARPENINGI think the Fiskars will be far easier to sharpen as well then, because (just as you sharpen a chain saw) all you have to do is mount the blade in your vice and use a round file, seated in the existing curvature.HOW TO MODIFY A PHOENIX POLE SAW HEAD TO MOUNT FISKARS BLADES TO ITIt was very easy to modify my Phoenix pole saw head to mount the Fiskars to it. There are two horizontally-aligned holes in the Fiskars. I bolted the back hole in the existing Phoenix rear (universal) hole. Then I used a straight edge to align the first 3 inches of Fiskars teeth to be parallel to the bottom face of the Phoenix head. With the head supported on a spare piece of 2×6, I bored a 13/64 hole through the Phoenix head using the forward Fiskars mounting hole as a drilling jig. This didn’t even take five minutes; and the alignment was perfect for the blade.TRIALS WITH THE FISKARSLong story made short — from the moment I started to cut, it was obvious the Fiskars is in a class of its own. I had a huge pine de-limbed up to 35 feet off the ground in less than half the time I could have done the job with any of the other blades.DIFFERENCES IN HANDLINGBECAUSE it cuts so efficiently, the Fiskars does however require a more forceful stroke.SUGGESTED IMPROVEMENTIn fact, because the Fiskars is so much more efficient, I think the curvature could be mellowed out a bit more; and I think it would also benefit from another 2 or 3 inches in length, because pulling so much harder, you tend to pull it out of the tree.SUMMARYI also did some smaller 30-40-ft trees which were heavily branched to the ground. I was pretty damn impressed to find how many of the branches I could take off with a single stroke. Hard dead branches way up on big trees came off easier. Huge green branches which hung up and pinched, could be ripped from the tree, right through the pinch, by sometimes a single forceful stroke, or at most a third or a quarter the strokes required by the other blade designs we tried.If I were Fiskars, I’d mellow out the curvature a wee bit more, and extend the length 2 or 3 inches still. I prefer the hookless end, because you often need to save a pinch by pulling the saw out the bottom of a cut. Despite a little room for design tweaking, the Fiskars 9333 is a killer.
