Thread: Zowada Website - double bevel info. updated

Thinking about it actually, using Tim's described method, isn't it just the same besides the size of the bevel (his method being much smaller since you only use 10k+ for a few strokes) and the polishing of the first bevel? Say I did polish my bevel up to 12k and it still didn't shave, then taped the spine and started at maybe 8k for the second bevel, wouldn't the end result be similar? Technically for either method the second bevel will be the only one actually cutting the hairs right?

No the results would be different. The purpose of Tim's metod is to use just a very small microscopic bevel at a slightly steeper angle at the end of the honing process to completely eliminate the scratch pattern of the lower grits; not to create one steeper bevel to speed up the honing process. It is like changing the recipe for a food dish. The results might still be good but it will not be the same thing.

On a side note, I test-shaved the razor and it was great! Very comfortable and sharp!

That's great news!

I have to disagree fundamentally with the comment about a double bevel not being as long lasting as a single, the raw physics at work dictate that a steeper bevel produces a more resilient edge.

It's like the difference between a Sushi chef's ultra fine Sashimi knife that would probably shave your face as well as any brand new TI, and his Cleaver, which, while intentionally not sharpened to the same degree, has a much more robust grind to withstand the force of chopping through hundreds of pounds of tuna spine without incurring any damage.

Granted this is a dramatization, but there is no way a steeper bevel should deteriorate faster than it's more acute counterpart, if indeed the steels are of identical quality, and the same abuse imparted to them.

There may be an issue with stropping the micro bevel to the same degree as a traditional edge, and thus leaving the edge in worse condition after each shave, but it shouldn't be an issue of the actual process being inferior.

Stropping is a good point. I didn't evaluate long term stropping nor edge resiliance but I was surprised that razors honed like this draw equally on a strop to traditional methods. I've been studying draw phenomenon for a few years and found this interesting.

I've tried this double bevel stuff on about half a dozen razors lately, and I did notice an improvement in the shave-tests. I'm not sure I'll use this technique very often, but I think it is valid.

Josh

I think if a hanging strop is used, the slight deflection inherent to the stropping motion should be touching the second bevel, but maybe not with the same force as a traditional bevel.

Though, my experience has been positive using a double bevel and plain flat paddle strop, just put a little more pressure than usual (I'm using mostly big wedges and 1/4 hollows so that could be a variable too, as results may very for pressure with full hollows).

Originally Posted by Russel Baldridge

I have to disagree fundamentally with the comment about a double bevel not being as long lasting as a single, the raw physics at work dictate that a steeper bevel produces a more resilient edge.

It's like the difference between a Sushi chef's ultra fine Sashimi knife that would probably shave your face as well as any brand new TI, and his Cleaver, which, while intentionally not sharpened to the same degree, has a much more robust grind to withstand the force of chopping through hundreds of pounds of tuna spine without incurring any damage.

Granted this is a dramatization, but there is no way a steeper bevel should deteriorate faster than it's more acute counterpart, if indeed the steels are of identical quality, and the same abuse imparted to them.

That may not be entirely correct. An acuter bevel might cut with less effort than a steeper one. As a result the material that is being cut could exert more stress on the edge and abrade it sooner. If one would conduct lab test with a given knife and a given material, one could find the ideal cutting bevel that would always be the steepest bevel that could still allow for a fairly strain-less cut, or looked at it from the opposite direction, the acutest bevel that could still offer enough resilience against the cutting forces.

If I'm informed correctly, razor manufacturers have been using bevels of 15 to 17 degrees (someone better double-check this). I think they had enough time (a few ages) to get it right.

I don't know if altering the bevel angle with a degree or so, would be noticeable in the shaving experience. The only one that seems to have done some exhaustive comparison between single and double bevels on the same razors is David (heavydutysg135) and Perhaps Tim Zowada himself.
Actually, the whole hollow grind principle is already a kind of a double bevel thing.
As far as completely removing scratches from lower grit hones, it is my experience that doing enough strokes on my Belgian Blue and there after on the coticule easily takes care of that. I aim for that when I inspect the edge under the microscope between different hones. I understand that Tim Zowada, being a professional knife and razor maker, wants to speed up things a little, aiming for a better production-cost ratio.

Just my random thoughts on this matter,
Bart.

Originally Posted by Bart

As far as completely removing scratches from lower grit hones, it is my experience that doing enough strokes on my Belgian Blue and there after on the coticule easily takes care of that. I aim for that when I inspect the edge under the microscope between different hones. I understand that Tim Zowada, being a professional knife and razor maker, wants to speed up things a little, aiming for a better production-cost ratio.

Just my random thoughts on this matter,
Bart.

I agree with these comments.

Originally Posted by Bart

That may not be entirely correct. An acuter bevel might cut with less effort than a steeper one. As a result the material that is being cut could exert more stress on the edge and abrade it sooner. If one would conduct lab test with a given knife and a given material, one could find the ideal cutting bevel that would always be the steepest bevel that could still allow for a fairly strain-less cut, or looked at it from the opposite direction, the acutest bevel that could still offer enough resilience against the cutting forces.

This comparison deals with cutting in a line parallel to the edge, not perpendicular. I agree when severing a given fiber there is always a "field of stress" that develops as the edge forces it's way through the media. And the the field of stress increases with bevel angle, so the lower the angle the easier it is to cut with that utensil.

But ease of use and edge retention are not the same quality. And the two different cutting motions do not "necessarily" correlate.

This is one of those situations where we are dealing with such a fine edge that a slight increase in angle should not affect the ease of use as much as it ought to increase the edge retention.

Here's a quote about a BIC razor blade taken off a triple bladed cartridge that was inspected under a micrscope:
"The third microbevel is only 0.0009" wide and shows no scratches. It was probably done using an abrasive with grit under 1 micron. In my testing of honing compounds used on leather strops, I have not found any that produces this fine a finish. This leads me to suspect that BIC is using a very fine abrasive paper to finish their edges, or possibly using a sub-micron diamond honing compound. ...Images of a more recent blade, taken from a three blade razor, suggest that the final include(d) angle is actually over 35 degrees."

I think BIC has done their research, and apparently they've found it acceptable to have a dramatic increase in angle if its small enough and polished well. Though I seem to remember seeing a "How it's Made" episode where they attributed the improved edge retention of the micro bevel to laser cutting. but not sure on that one.

EDIT: This is just a frame of reference for the validity of double bevels and edge retention, as that is probably the primary goal of BIC's design, not comfort. It's possible and plausible that 35deg. is too much and would probably suffer in terms of comfort compared to traditional razors, but the point is that the double bevel aids (at least a little) in edge retention.

Originally Posted by Russel Baldridge

I think BIC has done their research, and apparently they've found it acceptable to have a dramatic increase in angle if its small enough and polished well. Though I seem to remember seeing a "How it's Made" episode where they attributed the improved edge retention of the micro bevel to laser cutting. but not sure on that one.

EDIT: This is just a frame of reference for the validity of double bevels and edge retention, as that is probably the primary goal of BIC's design, not comfort. It's possible and plausible that 35deg. is too much and would probably suffer in terms of comfort compared to traditional razors, but the point is that the double bevel aids (at least a little) in edge retention.

I think it would be in BIC's interest to produce blades that cut very comfortably and dull rather quickly. I believe the days that engineers in large multinational firms were actually trying to design something to make it better are long gone. I'm pretty sure the major concern is cost-effectiveness and short term profit. I bet they even conduct tests to make sure that those blades don't stay sharp longer than the marketing division has instructed.

My initial point was that one can draw two graphical curves for each bevel angle when one was to conduct standardized lab tests: one graph that would illustrate decreasing bevel sturdiness with a decreasing (acuter) angle and one graph that would illustrate increasing bevel stress exerted by the material being cut with an increasing (obtuser) angle.
For each given material there is a given point where the best of both worlds meets up.
A slicing motion will lower the bevel stress that the material exerts on the bevel. A guillotining motion will augment that stress. When a bevel hits the material at an angle (that's what happens with a razor 'cause we place in at an angle on our face, in order to cut close enough to our skin), there would be even more stress.
Take all that into account, do the lab tests and you ought to come up with the ideal angle. I don't know what that angle is. I know the angle one holds the razor to his face is another contributing factor.
BIC knows that angle, because they put their blades in a cartridge. That angle could differ from the angle a straight shaver typically uses while shaving. I don't really know that either.

In the end I trust the engineers that designed razors for those lustrous brands like Puma, Dubl'Duck, Thiers-Issard, Dorko and others more then I trust those at BIC.

In the end I don't think the slight angle increase that Tim Zowada suggests would make much difference. I just don't think that you could conclusively say that the edge would last longer, just for the reason that the bevel is a little obtuser. And I'm pretty sure that it would not be sharper than a properly honed edge with a single bevel. Maybe it would not be distinctively less sharp either. All I know, is that my face and the result of the shave tells me a slight decrease in sharpness immediately. Maybe that's what heavydutysg135 meant when he said he liked his razors better with a single bevel.

"I think it would be in BIC's interest to produce blades that cut very comfortably and dull rather quickly. I believe the days that engineers in large multinational firms were actually trying to design something to make it better are long gone. I'm pretty sure the major concern is cost-effectiveness and short term profit. I bet they even conduct tests to make sure that those blades don't stay sharp longer than the marketing division has instructed."

So the double/triple bevels that they spent precious time and money on researching provide a smoother shave? Because then great, we agree on one point. (but not really for the same reason)

And no matter which way you look at it (slicing, guillotining, chopping) on the scale that we are dealing with, the metal composition (and heat treatment/tempering thereof) would play much more of a role than the double bevel in making the blade dull more rapidly. So quicker degradation is not a logical result of the double bevel in this case. It would save them much more to skimp on quality of materials than to spend money grinding double and triple bevels to get the same resultant decreased working time.


"My initial point was that one can draw two graphical curves for each bevel angle when one was to conduct standardized lab tests: one graph that would illustrate decreasing bevel sturdiness with a decreasing (acuter) angle and one graph that would illustrate increasing bevel stress exerted by the material being cut with an increasing (obtuser) angle.
For each given material there is a given point where the best of both worlds meets up. "


But, if things were to work as you claim then both of these graphs would have a similar curvature, like the graph of Ax^2 and Bx^2, both curves are x^2 but are altered by an arbitrary constant, A or B. They would start at 0 and move in a smooth curve up to some asymptotic position or linear slope. More than likely though they'd be different translations of a portion of the sine wave and still separated by some arbitrary constant, which means they wouldn't cross.

And those types of tests are done routinely to determine the best angle to put on a cutting utensil, there just isn't a quantitative point where the graphs cross, the variables have to be weighed in terms of functionality, durability, cost to produce etc.


"In the end I trust the engineers that designed razors for those lustrous brands like Puma, Dubl'Duck, Thiers-Issard, Dorko and others more then I trust those at BIC."


This is a logical inconsistency because they didn't "design the razors", the design was in already place, so it is not a basis for determining whether or not they were correct. And it has no bearing on whether or not BIC's design and the double bevel in general can hold an edge longer. But, if in fact the "traditional design" turns out to be the superior, excellent! I'll re-adopt it.



"In the end I don't think the slight angle increase that Tim Zowada suggests would make much difference. I just don't think that you could conclusively say that the edge would last longer, just for the reason that the bevel is a little obtuser. And I'm pretty sure that it would not be sharper than a properly honed edge with a single bevel."


The argument is not that one or the other is sharper, they would essentially be the same, as the edge can only be as fine as the grit used to polish it. But the double bevel ought to be more resistant to abrasion (chipping really, on the scales we are concerned with) because the cross sectional area would be differentially greater. A=[2x^2(tan(angle~7deg.))].

This argument is like someone saying "my face won't tolerate even the slightest micro chip in the edge." While that statement has a good deal of validity, the truth is that you will never be without some degree of micro chipping, it just depends on the scale you are talking about. The same applies to this. At some point yes, an obtuse angle hinders performance, but at some point it can only help, just like the micro serrations of .5 CrO help to cut through hair, but are too small to be felt by the skin.

BTW I think this is great that we are really getting into the fine details of cutting edges, I wish we could have some more people weigh in with their expertise. It's good to debate, things, life becomes much more interesting with alternate opinions and viewpoints.