Edge Geometry

[bigblackjim]

I have the BR and recently chipped the blade. Not a big chip approx. 1mm in depth, but never the less a chip. What I want to know is at what angle is the blade shapened? I used a Lansky and thinned the edge a little it cuts better but does this compromise the chipping factor, I sharpened the edges to 30 degrees each side. It only thinned the tip and thats where it chipped. Thanks.

 

[Eric Isaacson]

Yes, if you thin the edge out it will be more prone to chipping. To be honest I don't know the exact angle at which it is sharpened, I usually just hit it on a strop to sharpen it.

I hope that helps

 

[gitarmac]

I got a small chip in my camp tramp while hacking some small limbs from a tree. I got it smoothed out pretty good but you can still see it. I was worried about the steel integraty and decided to test it by chopping small firewood in the back yard. It ate right through them! No further damage! I used the sandpaper/mouse method and polished the edge with the fine lansky stone by hand and it is very sharp. I only notice it when slicing but I doubt it will affect my slicing and butchering game. The edge sharpens so easy and it works so good as is I am hesitant to do anything drastic like reprofile the blade. SRKWs will fix it for at any rate, id probably let them before I would spend to much time trying to fix it myself. Then again if it was my only rat I might not want to part with it.

 

[Steven Roos]

Edge geometry makes an unbelieveable difference! The edge that Swamp Rat puts on the Battle Rat it tough as nails and shouldn't ever chip (under resonable use of course, no smashing rocks!), but I don't really think it is optimal for cutting.

My Battle Rat now has a very agressive convex edge about 4mm high. It is more prone to chipping (there are numerous nicks in the edge right now), but it still cuts like you wouldn't believe! The Battle Rat has outperformed every knife that I have ever pitted against it!

One of the toughest materials I have every gotten a hold of (aside from cured hardwood stumps) is corrigated plastic, a convience store soda display. It's cardboard's evil cousin! Other knives couldn't cut it well and would bind up in it, while the Battle Rat sliced though every time. At one point, I took two swift strokes and a huge V-shape was missing from the display. Everyone was impressed!

Like I said, geometry makes a difference!

 

[bigblackjim]

I'm not complaining the BR cuts like a chainsaw. It's just that I didn't expect it. I am completely happy, no thrilled with this knife. It was just something I didn't know. Thanks guys for the info.

 

[Cliff Stamp]

bigblackjim :

What I want to know is at what angle is the blade shapened?

There will be some variance from blade to blade, but the Howling Rat and Camp Tramp I used were from 14-18 degrees per side, with the tip falling in the higher part of the range. They are convex so are actually a little greater at the very edge and a little lighter at the shoulder. This puts them near the top of production blades in regards to cutting efficiency, note that this is a nearly identical angle that Spyderco and Buck use on their small folding knives.

I sharpened the edges to 30 degrees each side.

Thirty degrees per side is quite obtuse, even TOPS doesn't have that heavy of an edge bevel. This was probably 15 degrees per side or thirty degrees included. This is pretty close to the existing edge on the Swamprats which is why you didn't notice a large thinning except in the tip.

Yes in general reducing edge angle will cost durablity. However there is a counter acting force which is that the higher cutting ability is inherently less stressful as it will produce less fatigue, gives you greater control and overall produces less stress for a given impact load.

Thus in any knife there will be some angle at which you hit an optimal combination of cutting ability and durability. Since this is dependent on your skill and strength to a large part it can only be found with some experimentation.

If you continue to have a problem with chipping or edge durablity of any kind and if the knife in general cuts well and handles nicely, instead of recutting the entire edge bevel which is a tremendous waste, try applying a very shallow edge bevel which is at most a mm or two wide. Two mm is very excessive and only something I would use on a felling axe.

-Cliff

 

[bigblackjim]

I used a Lansky sharpening kit which includes a 15,20,25 and 30 degree angle clamp. I used the 30 degree to sharpen it this may be 15 degrees each side 30 total I do not know. I do know that after sharpening it it cut like a razor. The blade egde did not thin out only the tip so you are probably right about the edge geometry. Thanks.