Can't single pass cut a log bigger than the bar with reduced kickback chain.
Pasting in, didn't type all this now…..
Kickback was well explained (somewhere I can’t find now) if you visualize the spinning chain turning into a stationary caterpillar track. If the tip of the bar touches something, instead of the chain continuing to move, it stops or slows and the caterpillar, the saw bar, moves instead. It either moves up, or backwards, but opposite the direction of the chain motion.
Top and bottom running chain that say binds in the cut tends to push the saw in or out. At the tip it is worse, partly due to the direction (up, instead of back) and partly because the kickback can be more violent. The chain sort of opens up as it arcs around the tight nose, and has more chance of snagging something with one tooth instead of cutting with many teeth. Something smaller, branches for example, can be worse because they tent to snag between the cutter and the depth gauge.
Can’t really describe it well, go to Stihl, Oregon, or Carlton sites for info on chipper/chisel and safety/non safety chains.
Reduced kickback (‘safety’) chain has same rivet pitch, but longer tie straps between the cutters, that extend to the rear of the rivet, overlapping the cutter link. As they go around the tight curve of the tip, they tent to swing outward and act as a skid so the cutters don’t hit wood.
Visualize a pickup truck towing a trailer as wide as the truck. On straight road, life is good. Both truck and trailer pass through a narrow alley or tunnel just the size of the truck. However, on a very tight right hand turn, the left front corner of the trailer can sort of swing out and open up and maybe snag the sides of the alley/tunnel. The analogy breaks down here, but when a cutter does that, kickback can happen.
Now, assume the truck is hauling a 20 foot board, extending out past the rear axle of the truck and over the top of the trailer. On straight road through the tunnel, again no problems. However on that tight right turn, when truck goes right, the end of the board past the rear of the truck swings outward to the left. As it swings outward, it gets beyond the corner of the trailer and protects the trailer from snagging the tunnel wall.
On the AS or other pro boards, many are VERY derogatory to safety chain. It cuts like crap, throw it out, etc. That may be valid for experienced users, but homeowners IMO should ONLY use reduced kickback (‘safety’) chain on a consumer saw. No questions, no options, safety chain only.
There are some good reasons why pros don’t like it. Much of it is sold from box stores, and is poor design or metallurgy to sell cheap in the first place. Second reason, people say it cuts way slower. I have tried to find back to back test data with the same cutter design, safety or not, to see if there really is a measurable difference in cutting speed. I suspect it is not nearly as much as most people think. I did run some identical cutters, safety or not, in small wood maybe 12 inch maximum, and I could not see much difference. Some, but not a lot. Big wood might have been different. And of course, big wood can be cut bar buried with non safety chain.
There is a HUGE difference between chipper/semi-chisel and full square chisel chain, especially in green hardwood or any softwood. Cutting some green ash in the tests referred above, chipper to chisel is maybe 25 to 50% faster cutting.
Chipper chain is a rounded corner, looking like the numeral 2 when viewed from the front. Full chisel chain is very sharp square cornered, like the numeral 7. Go to the web sites and understand how a cutter tooth works, and it will be obvious both the differences and where a tooth needs to be sharp to cut. Most beginners check the top plate and that isn’t the critical place. The side plate is what shears the cross grain, the top plate lifts the chip out. Because of the curved shape of the chipper corner, it is better supported for stresses, but cuts less efficiently.
Now, since Stihl dealers usually sell only chipper (semi chisel) tooth in safety, and the ‘pro’ non safety chain is full chisel, I think the big difference is because of tooth design between them, not the safety bars. Sure, more friction through the wood, but I don’t think that accounts for the performance differences. Dealer here says Stihl does not make a safety chisel chain. Haven’t checked the website, I would think they do. But I have used Oregon safety chisel and I love it.
When full chisel is ground or filed with the proper square wheel or files, it holds an edge pretty well. When ground with a rounded wheel, or round filed, the resulting unsupported hook shaped point tends to dull faster when exposed to dirt and dust in and on the wood. And of course metal or rock takes if immediately.
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