Blade Sharpening Demystified by Red Rock
There is always so much opinion about sharpening anything especially by people who own anything with a blade, but very few people really seem to understand what is going on with "restoring an edge" to a blade. In ice auger blade sharpening, you always hear that "that angle is hard to get right". But if you look at a brand new blade closely, you'll note that you have been looking at the wrong part and drawing all sorts for incorrect conclusions. Here are the facts. Click on a picture to see a larger version of it. Regardless of the style of blade, the principle remains the same for sharpening.
|The bevel that I've highlighted with the little arrows is the slant that has been ground away during the manufacture of this blade. That is NOT the cutting edge of the blade. The angle of the bevel is maybe 15%. It could be some other angle as well. The only reason it exists as it is is because that's the angle they set up at the factory. My guess is that it allows the final step of sharpening to put the edge on blade that does the work.||So, the big obvious bevel is not the bevel that cuts the ice. Oh it does eventually after the lead edge does wear down, but the leading edge on the very bottom side is what cuts. The bevel behind the edge backs it up to give it strength to allow it to plow through the ice without deforming. Imagin how much pressure is behind the final edge of the blade as it rams through the ice.|
|So, while every sales person in every sport shop talks with authority about the bevel and how hard it is to achieve, do you ever hear them talk about the part of blade that actually digs in and cuts?||If you observe the circled part of the blade or anywhere along the edge, you'll note about a 1 to 1.5 millimeter wide region that comprsies the edge of the blade: the cutting part. The angle of this edge looks to me to be about a 40 degree angle which is pretty blunt relative to a 15 degree angle. Nobody notices that.|
|Here's a blow up of the 1 to 1.5 mm edge. All the rest behind it doesn't really pertain to cutting ice other than serving as a backup or reinforcement to allow the edge to be plowed through the ice.||Everybody worries about the top side bevel. This is the important side of the blade. The bottom. The bottom most edge is what cuts through the ice. If the bottom edge is rounded upwards (called "dull"), it is not going to attack the ice. It'll ride around on top. The blade then needs to have it's edge restored.|
|Here's what's going on with the blade when we get a dull one and after has been resharpened. You can pretty much see what the goal is and how the bevel on top is not all that significant when compared to the edge that is formed on the bottom of the blade through grinding. The "edge restored" is what we want. Who cares what the bevel on top does?
The problem is that most people will sharpen the top but not enought to take the blade off to the "non-ski" portion. That's fairly hard to do consistently without a grinder set up correctly and an eye for the dull part. Then, after grinding away on the bevel, there is a bur that hangs down. Everybody flips the blade over and tries to peel off the bur with a grinder. They turn thier brand new edge back into a "ski" and we're back to square one. The blade is dull after all that dinking around.
Chipper Blades - Jiffy models and Strikemaster Mag 2000, etc.
Chipper Blades cut on the exact same principle as shaver blades only upside down. The business end of the blade is the top which is helad in place at an angle to the ice. The bevel that the chipper owners worry about is on the backside of the blade and does not come in contact with the ice. It serves the exact same purpose as it does on the shaver blade above which means it is ground off to expose an edge. The edge is what does all the work in cutting the ice.
Home sharpenings tend to make the same mistake in restoring that bevel on the non-cutting side of the blade. But then, they take the bur off of the cutting edge and dull it right back to square one. The bur has to be stropped only.
discovers that it just spins on the ice. Of course, he "never" pounded that auger into the hole prior to it having it's blade resharpened. Oh, no...not him. Plus, it cut just fine prior to being resharpened. That begs the question as to why he sent that blade in to sharpened? Because it wouldn't cut anymore and was just spinning on the ice. Funny, it got worse after he dropped the auger inthe hole repeatedly. He wonders why that is?
He goes home, re-installs the new blade and lo & behold, it works, sort of. The new blade is at it's longest length. It reaches the ice despite the bending upwards of the blade housing due to icing/not-cutting the old blade provided. It'll work, until it gets a little dull or has ice built up on it. A couple more poundings in the hole, and that new blade will miss the ice as well. It's inevitable.
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