Uneven Primary Bevels?

[FlyingMuskrat]

Is if fairly common to have the primary bevels on a knife uneven, so that when they are jig sharpened the edge bevels will be uneven? I have been reprofileing most of my collection to 30 degrees on my Sharpmaker by leaning a course bench stone against the rods, and I seem to be getting uneven edge bevels. I checked the angle of the rods with a protractor and they both seem to be about 17 degrees from 90. So why am I getting uneven bevels?

 

[Cliff Stamp]

Is if fairly common to have the primary bevels on a knife uneven, so that when they are jig sharpened the edge bevels will be uneven?

Yes.

-Cliff

 

[FlyingMuskrat]

Thanks, I now feel better about my sharpening skills.

 

[db]

Originally Posted by FlyingMuskrat
Is if fairly common to have the primary bevels on a knife uneven, so that when they are jig sharpened the edge bevels will be uneven?
Yes.

-Cliff

WOW! Without knowing more this is just spreading misinformation and rumor. It could very well be a uneven blade grind, uneven sharpening strokes on one side or the other, a natural tilt inyour Sharpmaker strokes, or all of them and other reasons as well. Are you sharpening on one side only until you get a burr? Are you seeing the wider bevel on the same side of every knife? Are you seeing this uneven grind on every knife? Don't just assume every one of your factory ground blades are uneven. Even if they are uneven it may not be enough to be the cause of what you are seeing.

 

[Cliff Stamp]

Thanks, I now feel better about my sharpening skills.

You will notice this a lot if you really lower edge bevels because the width of a bevel is inversely proportional to the angle and the wider the bevels the larger the differences. Take the angles down to 5-10 and the uneven bevels really tend to stand out, even on customs. The worse I have seen was on Martindale machetes where the edge bevel was almost chisel ground when I reground it as the primary was so uneven. The early Strider's were really bad as well, you could actually see the primary sabre grind was high on one side by eye. If you really want to see it in a dramatic way then sharpen a hollow grind knife to a low edge bevel so the primary is hit as well and it is common to see one side have the hollow almost removed and the other side not. I would be curious to see if the makers are favoring one side over the other. As a consequence of this a lot of people will sharpen the knives initially with an uneven edge bevel angle so that the bevel has the same width. This is one of the most common problems people have with sharpening because one side will burr immediately and the other side will basically ignore the hones. The bevels are often really uneven like 15/25 or worse.

-Cliff

 

[gunmike1]

From my experience thinning out my Jess Horn (and just plain looking at it before I sharpened it) yes, primary grinds can be very uneven. In the case of that particular knife when I sharpened it flat to the stone one side went from hollow to flat grind rather quickly, while the other side kept it's hollow much longer. As Cliff said, I have noticed it much more on knives that I brought under 10 degrees per side, while the ones in the 12 to 15 degree per side range don't show off the uneven grinds as much. I think if you look closely at most blades you will see this. Unless the blades are jig ground, the human factor almost assures the grinds won't be perfectly even. As I thin out more of my knives I will report on how uneven some of the primaries are. PS, sorry for spreading misinformation, db (J/K, I know you and Cliff have your history).

 

[db]

while the ones in the 12 to 15 degree per side range don't show off the uneven grinds as much. I think if you look closely at most blades you will see this. Unless the blades are jig ground, the human factor almost assures the grinds won't be perfectly even.
...
PS, sorry for spreading misinformation, db
(J/K

Nothing is truely perfect. I was saying the same as you are in my post. The uneven edge grinds can be caused by other factors than an uneven blade, and at the Sharpmaker angles the uneven blade grind may not even be very noticeable.
Hopefully you don't think I am also misinforming.

 

[Cliff Stamp]

Unless the blades are jig ground, the human factor almost assures the grinds won't be perfectly even.

Even if they were jigged there are still possible issues, the difference in hollow grinding you saw on the Horn for example was simply due to one side being ground in more than the other, that is really common. That issue and the uneven edge bevels on most knives are two of the most common problems for people when they start sharpening.

-Cliff

 

[annr]

I must use hollow ground knives for my daily living as a professional reedmaker, oboist, musician. I own dozens of these knives and many come uneven from the factory. I've been freehand sharpening for years and in the last year went to using the Tormek from the get-go for "fixing" the knives. My questions: what's the best cure for these defects? and how much do you think the uneven edge grinds matter on a double hollow ground? Sorry if these are sillly questions, but cut me some stack I'm just a musician

ann

 

[FlyingMuskrat]

Are you sharpening on one side only until you get a burr? Are you seeing the wider bevel on the same side of every knife? Are you seeing this uneven grind on every knife?

db I am not really sharpening on one side until I get a burr, I usually switch sides after awhile if I am not getting a burr then return to it after awhile on the other side. I knife that spurred me to start this thread was my BM Griptilian, which I ground down to 30 degrees included. On one side the knife took about 2-3 minutes to get a burr, while on the other side it took 30 minutes or more. Of course the side that took longer ended up with a much larger edge bevel. Also on the side that didn't take as long the thumb stud didn't interfere with the sharpening, while on the other side it did. I don't seem to be seeing the wider bevel on the same side of the knife every time, before yesterday most of my knives ended up with the larger bevel on the right side of the blade if you are looking down at the spine. But yesterday the 2 knives I reprofiled (A.G. Russel Ultimate Pen Knife and BM Griptilian) ended up with the larger bevel on the right side of the blade if you are looking down at the spine. On almost every blade I reprofile I end up with uneven edge bevels.

 

[db]

db I am not really sharpening on one side until I get a burr, I usually switch sides after awhile if I am not getting a burr then return to it after awhile on

If you grind on one side more than the other you will likely have a wider bevel on that side. All other things being equal.

knife that spurred me to start this thread was my BM Griptilian, which I ground down to 30 degrees included. On one side the knife took about 2-3 minutes to get a burr, while on the other side it took 30 minutes or more. Of course the side that took longer ended up with a much larger edge bevel. Also on the side that didn't take as long the thumb stud didn't interfere with the sharpening, while on the other side it did.

Do the studs stick out the same on both sides? If so I'd have to guess it's not a blade grind issue but something else.

I don't seem to be seeing the wider bevel on the same side of the knife every time, before yesterday most of my knives ended up with the larger bevel on the left side of the blade if you are looking down at the spine. But yesterday the 2 knives I reprofiled (A.G. Russel Ultimate Pen Knife and BM Griptilian) ended up with the larger bevel on the left side of the blade if you are looking down at the spine.

Did you mean right side?

On almost every blade I reprofile I end up with uneven edge bevels.

Could be your unlucky and all your knives have pretty bad grinds, but it would be my guess it's some thing your doing wile sharpening them. My first thought would be try and keep to fairly equal sharpening strokes on each side if the uneven edge grinds bother you.

 

[cbwx34]

One thing I found with the Sharpmaker, is I have a tendency to apply more pressure to one side of the knife vs. the other. May be something to consider.

cbw

 

[FlyingMuskrat]

Sorry, I did mean the right side. I'll edit the above post. I am also left handed so I may apply more pressure on the right honing rod than the left. This would explain the previous results but not the Griptilian and Pen Knife.

 

[Cliff Stamp]

My questions: what's the best cure for these defects?

Abandon asthetic concerns.

I am not really sharpening on one side until I get a burr

It would not matter if you did. This was discussed in detail years ago when Joe first started to popularize this method. One of the complaints was that it would produce chisel ground edges, which it doesn't. A little basic math shows that proposition is completely unfounded. A sharp edge is about one micron wide, a very dull one is about 10, thus the most you will move the bevel is 10 microns. Forming the burr again on the other side will induce a 2-4 micron travel, so in total you will induce a 6-8 micron shift in the bevel. A typical knife edge is about 500 microns wide, since you are working with similar triangles, you will see a 1-2 percent change in height.

There will actually be a much larger difference in bevel wear due to the fact that most people use knives unevenly because one side of the edge usually isn't in contact with the media significantly, carving woods, stripping wire, etc. . This is fairly significant with heavy bushcraft knives which can tend to be really unevenly used and thus all the wear can dominate on one side only so each time the edge dulls it keeps shifting the bevel. In order to keep it even you would actually want to grind unevenly. However even here the changes are still so small (we are still talking microns) that it takes a long time to see even a small difference. You will basically never see a significant effect on the cutting performance.

Note a bevel which has an even angle but an uneven height will be much more stable force wise than the same height but a different angle. So when you regound the knife and the bevels looked different the knife in fact would become more even to cut with. As is often the case this is just an example of aesthetic concerns causing issues with performance.

I knife that spurred me to start this thread was my BM Griptilian, which I ground down to 30 degrees included. On one side the knife took about 2-3 minutes to get a burr, while on the other side it took 30 minutes or more.

Most production knives I have seen (through several hundred) are very uneven in angle of the edge. They are made that way intentionally to make the angles the same height. When you regrind them to the same angle one will be much wider than the other due to the uneven primary grind.

-Cliff

 

[HoB]

do you think the uneven edge grinds matter on a double hollow ground?

ann

It is really not an issue. If you grind the edge well, it will be very even at the edge. So it is really up to you. The possible exception are chisel ground tools, because you sharpen them directly on the bevel. But even there you start by hand flattening them before the first use.

Often knifes are intentionally left thicker at the tip, and are ground at a different angle to maintain an even edgebevel width. If you grind them with the same bevel throughout the blade, the edge bevel will get wider towards the tip.

 

[Cliff Stamp]

The possible exception are chisel ground tools, because you sharpen them directly on the bevel. But even there you start by hand flattening them before the first use.

I wish this was more common, all the ones I see have never had this done so it is always the first thing I have to do. But it still beats the ones with big pieces out of the edge.

-Cliff

 

[db]

Also on the side that didn't take as long the thumb stud didn't interfere with the sharpening, while on the other side it did.

This part of your post really makes me think it is not an uneven primary blade grind issue. Is it possible you had your Sharpmaker sitting on an uneven surface?

 

[FlyingMuskrat]

I just checked the surface with a level, and it isn't level. The bubble is still within the lines but it is over towards one side. The surface is higher on the left side, this would raise the angle of the left ceramic stick, and thus explain the result I got on the Grip and Ultimate Pen. I propped up the sharpmaker to make it level and now the thumb stud is interfering fairly equally.

 

[FlyingMuskrat]

Here is another question: Will the uneven bevels that I have put on my knives affect proformance? Should I just make sure I sharpen them on a level surface next time or fix them now?

 

[sodak]

I must use hollow ground knives for my daily living as a professional reedmaker, oboist, musician. I own dozens of these knives and many come uneven from the factory. I've been freehand sharpening for years and in the last year went to using the Tormek from the get-go for "fixing" the knives. My questions: what's the best cure for these defects? and how much do you think the uneven edge grinds matter on a double hollow ground? Sorry if these are sillly questions, but cut me some stack I'm just a musician

ann

I agree completely with Cliff and HoB. I wouldn't worry about this. A lot of the aesthetics depend upon how wide these bevels are, but they really don't affect cutting efficiency. Most of my knives have some variation, and sometimes it's pretty obvious, sometimes, you really have to know what you are looking for in order to see it. All of them cut just fine, and I can't tell the difference. Maybe a master carpenter could, but I can't.