Edge angle steepens towards tip?

[Abe]

Just got a new BM705 and noticed that the edge angle varies along its length, from 21 degrees at the base to 24 for the last 3/4 of an inch to the tip. I noticed similar though not quite so pronounced on the BM 690 I bought too. (measured on EdgePro)
Is this a common trend amongst other makers as well?
If so, is it to promote stronger tip strength or purely for aesthetics in that it keeps the width of the grind even along the full length of the blade whereas keeping the same angle would obviously produce a wider bevel as the metal thickens towards the tip?
And, just wondered if anyone keeps this set up or removes the variation and accepts the look of the wider bevel?
Thanks

 

[mete]

Last year I got a Helle knife and used it to take apart a deer.There was something not right about it so later I took a close look. The straight portion of the blade had an angle(scandinavian grind) of 30 degrees which is about the max for use. As the edge curved up to the point the angle increased to at least 40 degrees ! No wonder I had problems. I changed that immediately. I don't understand why but they ground it that way but if you don't like the grind just regrind it to your preference .

 

[Cliff Stamp]

If so, is it to promote stronger tip strength or purely for aesthetics in that it keeps the width of the grind even along the full length of the blade whereas keeping the same angle would obviously produce a wider bevel as the metal thickens towards the tip?

The bevel would not significantly effect the tip strength as it is only a small part of the total cross section, however as you noted with knives with a lot of distal taper, keeping a constant edge angle would result in an immediately large discrepancy in the edge width which you can see by eye unlike the angle. If you don't mind this, then just grind it equally. I usually grind the tips more acute as they typically get finer work, except on larger chopping knives.

-Cliff

 

[Blop]

Try freehand and have a look, how difficult it is, to keep the angle at the belly and the edges end.

So you might think, it surely wasn´t a certain plan or idea, it´s just what happens in a factory. How much time shall a guy at the grinder spend for one knife? That´s how i see it.

To get a real tip, where all grinding lines meet in a point and the bevels are equal all the way the edge, is a thing a would only expect from custom knifemakers.

 

[HoB]

No, I don't think it is a question of time but of aesthetics. If you set an angle for the straight part and keep that angle towards the tip, then the effective angle increases as the edge curves away from the belt/wheel/stone/rod. To maintain the angle, you always have to grind perpendicular to the edge. I don't think that that is any more difficult to do (I always do it when I sharpen free hand), but it changes the direction of the scatch pattern on blade, and if the blade is not strongly tapered towards the tip, it also changes the bevel width. I find the half inch closest to the tip the most useful part of the blade and I want it as sharp as possible, so I keep a constant bevel angle along the entire edge and don't give a damn about the looks.

 

[Abe]

Hi Blop,
I take your point (no pun intended) on factory knives but on this occasion I have to agree with HoB in his assertion that it is down to aesthetics. Despite the angle being different at the tip from the base, the bevels on either side match perfectly and both sides converge on the spine / swedge at exactly the right spot producing probably the nicest looking tip I've seen in a while. (It would be amazing if this had all been achieved by chance through sloppiness).
Still, I agree that the point would be much more practical if the edge grind wasn't so high, so it's back to the EdgePro for a little thinning I think.
Thanks for the input guys.

 

[UnknownVT]

If so, is it to promote stronger tip strength or purely for aesthetics in that it keeps the width of the grind even along the full length of the blade whereas keeping the same angle would obviously produce a wider bevel as the metal thickens towards the tip?

however as you noted with knives with a lot of distal taper, keeping a constant edge angle would result in an immediately large discrepancy in the edge width which you can see by eye unlike the angle.

Perhaps I've misunderstood something -
I was always under the impression that the lack (or not enough) of a distal taper - makes the tip thicker - hence sharpens to a more obtuse edge.

I have a Benchmade Axis 710 - that came with a pretty obtuse edge toward the tip - a fairly common complaint. (I recall Joe Talmadge had similar problems from a BM 710)

BM 710 thread at rec.knives

and
Joe Talmadge's post at rec.knives

Pics of the tip of my BM 710 Axis after radical resharpening to semi-convex edge finished with crock-sticks

--
Vincent

http://UnknownVincent.cjb.net/
http://UnknownVT.cjb.net/

 

[Cliff Stamp]

... that the lack (or not enough) of a distal taper - makes the tip thicker - hence sharpens to a more obtuse edge.

Thickness and angle are independent, the edge can be very thin and very obtuse, or very thick and very acute.

For a given angle, the thinner the edge is behind the bevel, the more narrow the bevel.

Thus on blades with a distal taper, as the edge gets thinner towards the tip, with the same angle the bevel gets wider [correction - narrower].

The included angle of an edge is roughly 60 * thickness / width (57.3 is a closer estimate).

-Cliff

 

[UnknownVT]

Thickness and angle are independent, the edge can be very thin and very obtuse, or very thick and very acute.

Yes, you're absolutely correct - I should have been clearer about maintaining the same bevel width.

For a given angle, the thinner the edge is behind the bevel, the more narrow the bevel.

Thus on blades with a distal taper, as the edge gets thinner towards the tip, with the same angle the bevel gets wider.

Again I'm probably misreading something here -
don't those 2 paragraphs contradict each other? -
If there is a good distal taper - and the blade does get thinner toward the tip (ie: the edge will be thinner behind the bevel) wouldn't the bevel (with the same angle) be narrower?

Thanks,

--
Vincent

http://UnknownVincent.cjb.net/
http://UnknownVT.cjb.net/

 

[Cliff Stamp]

Yes, got it right in the first sentance, then contradicted myself with the next. Fixed it.

-Cliff

 

[Joe Talmadge]

Most of my factory knives, once I'm through sharpening them to a consistent angle throughout, seem to end up with higher edge bevels near the tip (i.e., they all look like VT's 710, some more so, some less so). This seems to be very common on factory folders.