Thread: My razor is too sharp???? I like a duller edge??

Originally Posted by Bart

I believe, the smaller the bevel angle, the easier is will cut, but at a certain point, the long and thin bevel becomes too weak, so a compromise needs to be made.

(It was intended to be rhetorical question but I went and took a nap while the Texans were getting their *ss handed to them by Oakland, and this thread suddenly picked up again before I could get back to it, so I apologise for the delay)

I believe the answer - which you alluded to as well - is that the lower angle reduces the cutting resistance between the keratin and the blade by reducing the amount of stretching of the keratin. This stretching produces resistance via two different forces - a force opposite the direction of blade travel that is related spring force from the keratin acting against the bevel, and is related to the bevel angle by the cosine function, and friction between the blade and keratin that is dependent on the dynamic coefficient of friction between the two. As the blade angle gets too low then the inability of the blade edge to withstand the stresses also becomes a problem. The commercial blade manufacturers and straight razor manufacturers minimise the first (spring) force with a low honing angle, and the commercial guys minimise the second (friction) by coating the blade in teflon. Also, the lower honing angle also causes problems with honing - this shows up in the Verhoeven study, and is only partly caused by the steel - at such a low angle very minor deviations in the honing surface and pressure cause large variations in the edge geometry, and any one of these effects are sufficient reason for the minimum honing angle.

Verhoeven addresses this as well. Here is a paragraph from page 4:

In the absence of burs, the force required to push a knife through a material is dependent on the sharpening angles and the thickness of the knife blade. The force is reduced as the sharpening angles and the knife thickness are decreased. These factors would indicate that one would want to maintain the smallest possible cutting angles and blade thicknesses for ease of cutting. However, there is an opposing factor that must be considered. As the blade thickness and cutting angle decrease, the mechanical stresses (force per area) produced in the region of the blade edge during the cutting action become higher. This can lead to deformation, i.e., localized bending, at the cutting edge. Hence, a compromise is required, and the sharpening angle and blade thicknesses are smaller for cutting tools used for soft materials than for those used for harder materials or for nondelicate cutting applications like chopping.

and later on page 11 (though this was on a honing machine, the same problems arise in a slightly different form when hand honing):

Even on freshly dressed wheels a 2β edge angle of 20 degrees was too small to give reasonable edge quality. At 30 degrees the results were only nominally acceptable, but above around 35 degrees consistently good results were obtained.

Originally Posted by Bart

I also think that an edge with of 0.3 micron is much keener than an edge width of 0.4 micron. It might be a small difference to grasp, because we are not accustomed with dealing dimensions that small, but for severing organic structures, 0.3 is 25% keener than 0.4
I am adding this, because I think that having a keener edge width at the very tip can to some extent make up for having a bigger bevel angle.

I agree with you completely. I believe the shaving characteristics we are experiencing is determined by edge width (bur width in Verhoeven's nomenclature), the spring resistance of the keratin acting obliquely through the bevel, and the friction between the keratin and the bevel surface. So lowering any of these will improve the perceived sharpness of the blade.

But we don't know that this is the sort of improvement in edge width that we're capable of getting. The limitations of Verhoeven's study and the techniques he used have certainly become more apparent to me over the course of this thread, but lacking a fresh study with goals and techniques more specific to our situation we just don't know.

We do know that the one straight razor and the two Gillette blades he studied had the same basic bur width - one of the gillettes (pg 6) had a bur width between 0.35 and 0.45 microns with an unreported average, the other (pg 41) had a bur width between 0.17 and 0.48 with a reported average of 0.32 microns, and the straight razor (pg 7) had a reported average bur width of 0.4 microns.

And we know that honing by hand that he achieved a bur width of 1-1.5 microns at 1000 grit (pg 11), 0.5 micron avg at 6000 grit (pg , and 0.45 avg (reported as 0.4-0.5 range) using 0.5 micron chrome oxide of unknown quality. A fresh close reading of his text reveals that the 1000 grit honing was optimized for edge width, but there is no mention of him trying for minimum edge width on the 6000 grit waterstone or the chrome oxide, so I'm now uncertain as to how much weight should be attached to these numbers. It is interesting that the bur width on the straight razor (honing technique not specified and not discernable from the photos) is at 0.4 microns so clearly finer edges than he achieved with his hand honing are possible, but this is insufficient for us to determine if the relative improvements (not absolute values) in the edge widths that he achieves are representative of our situation or not.

We also know that using a tormek machine with leather wheels loaded with 1 micron diamond spray, honing blades at 40 degrees, that he was able to achieve bur widths of 0.31 microns with a range from 0.18 microns to 0.45 microns, and that replacing this wheel with a leather wheel loaded with 0.5 micron chrome oxide of unknown quality (described on pg 19 "The compound used here is called Micro Fine Honing Compound supplied in the form of a wax impregnated bar having a deep green color") he achieved a bur width that was 0.1 to 0.2 microns larger than from the diamond (pg 41). However, these numbers must be interpreted with a great deal of caution - note that the diamond was sprayed on while the chrome oxide was loaded from the wax bar. It is very likely (almost certain) that this resulted in the chrome oxide being applied much too thickly, and it is quite possible that the chrome oxide stick he mentions may well be the same chrome oxide stick that the woodworking and hardware stores sell that has been demonstrated to be of very inferior quality.

And we know that the differences in bur widths that he was seeing between the finer abrasives are completely swamped by the range of bur widths he was seeing even using the same abrasive - that table 6 on page 41 shows a range from 0.18 to 0.45 microns on four theoretically-identical blades honed on the same leather wheel, using the same 1 micron diamond abrasive, while the gillette blade in the same table ranges from 0.17 to 0.48 microns within the exact same blade.

Originally Posted by Kingfish

If that angle turns out to be true, it explains why many find the Feather so intolerant of shaving technique or lack there of.(I don't like Feathers) A low angle of attack is not possible and you are cutting into you skin. IME the sharper in combination with low bevel angle the better until you reach the limits of steel as mentioned by Bart and others affords the smoothest shave for me.

I will make a prediction that there will be a time in the not so distant future that an newer type of alloy will allow an even lower angle than 17 degrees and a smoother shave will be the result.IMHO. To me that is not rocket science, it is plain old common sense.

The final bevel angle on the feathers doesn't affect the angle of attack at all. The angle of attack with a Feather DE is set by the DE case head and safety bar, and is independent of the honing angle of the blade. The angle of attack with a Feather AC is adjustable by the user within the normal range of straight razors. Also the minimum honing angle is unlikely to reduce much in future due to the honing difficulties as described above, at least for hand-honed reusable razors such as ours. It may come down a bit with better steels that are more resistant to honing issues, but there has been a huge improvement in the quality of steel over the last 200 years, but the honing angle of 17 degrees remains the same, both for straight razors and commercial razors (and if the commercial guys could get a competitive advantage from a substantially lower honing angle they would jump on it in a heartbeat).

(The Texans wound up beating Oakland 29-6 to my complete surprise. Usually they play down to just below the level of their opponents).