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The Newbies Arena Are you new to knife making? Here is all the help you will need. |
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#1
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Blade Geometry Question
I have to admit, I am confused on how to calculate primary and secondary bevel angles. Using angle blocks or angle gauge, I have in the past determined the primary grind angle at say, 4 degrees. Other sources describe the angle as much larger. For example, one article describes the idea of "doubling" angles: "The complete cutting angle of the knife (which is rarely referred to and is composed of the sum of both edge angles) is called the included angle. Since most knife blades are ground symmetrically, in most cases, the included angle for a knife is simply twice the edge angle." http://kitchenknifeguru.com/knives/knife-edges-101/
I think I understand the doubling aspect of the knife edge angle; but are we talking about the primary or secondary bevel? In my 4 degree illustration above, is the primary complete cutting angle 8 degrees? If I grind the secondary bevel at 15 degrees would the complete cutting angle be 30 degrees? Still confused. |
#2
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I've been making knives for 20 years and with the exception of about the first 15 minutes as a newbie trying to understand exactly the same thing you are puzzling over I have never needed to calculate an angle. I'm pretty sure the vast majority of makers who have been making knives for a while long ago gave up any such thoughts because it simply is not necessary.
You take your profiled blade and scribe a line down the center (or two lines slightly apart if you like that way better). Then you grind the blade by hand from the edge to the spine, working each side alternately, until you have the primary grind completed. That's all there is to it, who cares what that angle might be? It will be different for every thickness of blade stock and every different width of your blades. For the secondary - which only gets done after the HT and all finishing work is completed - I like to set my platen to the angle I want, say 10 degrees. Then I can hold the blade perpendicular to the floor and just stroke the belt working side to side until the edge is sharp. Then I go to my Edge Pro (a large Lansky) which I set to the same angle and finish the edge. That gives me a 20 degree included angle which is good for most general purpose work. There are many other ways to do the same thing and other guys will likely throw some out here for you but they are all more or less the same. Finally, you might use 8 degrees included angle on a sushi knife or some such but for most knives that would be too thin. The secondary angle is chosen based on the work you expect to do with the knife but probably the majority end up around 20 degrees ... |
#3
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Ray said exactly what I was thinking. Don't over think it. Just make knives till you figure out what works.
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#4
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I would look for a better, or at least clearer, source of information than that page you cited. For example:
Quote:
Some of the confusion stems from the fact the Japanese terminology (which is often used in the context of kitchen knives) reverses the two terms. What they refer to as the "primary bevel" would be better translated as "primary edge bevel" and is what we think of as our secondary bevel. Their secondary bevel is our primary. The "compound bevel" examples on that site we would refer to as a secondary bevel plus a micro-bevel. The figures on the size are misleading because they are only showing the geometry for the very edge (maybe the last 1/8 inch) rather than the cross section of the full blade. -b __________________ -bill rankin |
#5
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Hey, I appreciate your suggestions! Especially with years of experience behind it.
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#6
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As said above material and use makes a difference
I am going to make some filet knives out of 3/32 CPM S30V and will put a compound bevel on the edge. I will make the edge a little steeper than the rest of the 10 degree edge as it will have to cut through bones and a 15-20 degree or so edge is what I'll use. For a skinning knife I wouldn't go so steep. Now I read, but have never used it, but CPM 3V can take a much thinner edge without chipping as it is very tough, but at only 7.5% chrome it isn't stainless and many fishermen don't want a non stainless filet knife even though 7.5% would definitely be noticeably more resistant to rusting and won't rust if cared for.
I have angle blocks and precision protractor (worked in metal trades), but I never use them except to set my grinding table to the platen. I finish sharpen by hand anyway and use no guides at all. Mostly I use an almost 20 year old EZE Lap medium diamond on a wood block for most things and that's where I stop as it has worn down to a medium fine and that's good enough for most applications, certainly don't need hair popping sharp for a filet knife as it cuts through the skin when trying to take the skin off. Same for a kitchen knife, just needs a working edge not a leather cutting edge or for wood carving. Last edited by jimmontg; 12-14-2016 at 04:09 PM. |
Tags |
angle, bee, belt, bevel, blade, blades, degrees, edge, fishing knife, grind, hand, how to, japanese, knife, knives, make, makers, making, newbie, sharp, thickness, throw |
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