honing technique around the point area

[chti_lolo]

I have honed my first razor blade last week (old stained puma 39 6/8 blade) with modified unicot method with 2 layers of tape and have got pretty good results. It shaves quite as well as my new Dovo special 5/8 profesionaly honed (may be I'm not impartial ).
But I have a little problem near the point at the intersection of the straight edge and the rounded side of the blade.
My edge follow the circular curve of the blade whereas on my Dovo the edge is different and more acute at the intersection.
I prefer the Dovo intersection(I have joined a little drawing).
Is there a special technique to do that?

Laurent

 

[Guest]

The 39 should not look like your drawing. Could yours have a turned up point? Here is one in good condition:

A look at the swaying and rolling x strokes might be useful.

 

[Gunner777]

It should be rounded like the other one but sometimes when one is honed a good bit it will have a more pronounced corner rather than one that's well rounded. Most people will go ahead and round that edge to restore it to the original shape.
Also I wouldn't use two pieces of tape--one is all I'd use. Two on a standard hollow blade will make the edge shallow and usually won't last as long before needing more care.

 

[Paul]

It should be rounded like the other one but sometimes when one is honed a good bit it will have a more pronounced corner rather than one that's well rounded. Most people will go ahead and round that edge to restore it to the original shape.
Also I wouldn't use two pieces of tape--one is all I'd use. Two on a standard hollow blade will make the edge shallow and usually won't last as long before needing more care.

Would you mind explaining the math that leads to the conclusion that adding thickness to the spine would cause a shallower angle? As I understand geometry, the opposite would be true. Thanks in advance

 

[Gunner777]

Well raising the spine by adding layers of tape would cause the blade to contact the hone at a more severe angle(at the blade edge) causing it to have a steeper angle of contact on the hone if that makes sense.

 

[Paul]

Well raising the spine by adding layers of tape would cause the blade to contact the hone at a more severe angle(at the blade edge) causing it to have a steeper angle of contact on the hone if that makes sense.

That's exactly true, but how having a steeper angle would cause the edge to not last as long is what's causing problems. Shorter and thicker is stronger than thinner and longer. Right?

 

[chti_lolo]

What I was intending to do is to work again the point area with slurry and no added tape with some small circle like motion, the add tapes and continue unicot on the point area.

Is it right???


Laurent

 

[Gunner777]

Stronger well that may be true but it will dull faster since the sharp point of the edge is thicker and will wear down faster than a longer thinner edge.

 

[Paul]

Sorry, Laurent, I was on my mobile device earlier and couldn't pull up the pictures. I'm not 100% sure I know what you're asking, but I'll tell you that the curve "should" be following the curve of a round tip slightly. In fact, Barbers were taught to change their emphasis in order to hone a slight smile (work a little extra on the heel and toe) in one textbook I read. Personally, I would go with the edge in the first picture. Not the sharper angle...

 

[Paul]

Stronger well that may be true but it will dull faster since the sharp point of the edge is thicker and will wear down faster than a longer thinner edge.

This is specious to my mind. A longer thinner edge will break down because it's weaker. For an extreme example think of an ax shaped versus a sheet razor blade (all other things being equal). Which will dull faster with use?

The differences in the bevel angle are not that significant, but to suggest that an edge that's keen enough to shave with but has a slightly steeper angle will break down faster doesn't add up. If that were true, we'd be just grinding tempered steel down to .5 micron sheets and going to town.

 

[Gunner777]

It does work that way though. We talked about this very thing at a Mid Missouri meet on SRP and honed some razors of both types and looked at them under a microscope. The edge was sharp on both but the consensus was that the more severe thicker angle would dull faster. Just an opinion----

 

[Paul]

It does work that way though. We talked about this very thing at a Mid Missouri meet on SRP and honed some razors of both types and looked at them under a microscope. The edge was sharp on both but the consensus was that the more severe thicker angle would dull faster. Just an opinion----

But you're not stating it as opinion, you're stating it as a fact. If that's the case, we'd see a lot of guys advocating taking the spines to grinders and wearing them down to get those angles shallower in order to obtain that super long lasting edge . Please try that, and let us know how it goes. The more severe angle is less keen by definition, but it's not going to dull faster. This is a scientific impossibility. In fact, after the edge gets too thin, it becomes incapable of holding up and just breaks down (I believe .5-.47 micron is the threshold, ballpark at least). I'm not sure who was at the meeting you referenced, but I'd have a hard time believing Dr. Verhoeven was one of them.

 

[Gunner777]

Ideally the angle should be what the factory sets which is 18 to 20 degrees and that's using the spine they made at the factory. Adding to much tape increases the angle. I go with what the factory sets the angle at. It's just that simple.

Quote from SRP wiki
In theory it does not matter if those sides are flat, convex, concave, or even irregular, as long as the apex is one clean line, as thin as possible.

 

[Paul]

This will be my last post on this subject (I hope). I'm trying to say these things in a way that won't offend, so please understand I'm not attacking you, but rather trying to correct erroneous thinking, and also keep it from being accepted as truth.

The first statement was factually incorrect, you started by saying that thickening the spine will cause a shallower edge, and that's not possible. Then, you corrected that to say it would be steeper, but dull faster. When asked for supporting evidence for that claim the response was essentially "they said so." Despite being presented with an excellent paper on this very subject, again I got "they said so."

You and I share the preference to leave the factory bevel angle the same, but it's for totally different reasons. Your claim is that the "ideal" angle is 18-20 degrees, but this is an unsubstantiated claim that runs contradictory to an effort to get a bit better understanding of bevel angles as they relate to various manufacturers: From SRP- Measure your razor angle. There is a wide range of angles from different manufacturers.

On one hand:

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.

Howeva! The quote from the Bible (SRP Wiki) that you quoted doesn't take into account the following truth.

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, you have to compromise. You have to get a shallow enough angle to cut effectively while having a thick enough edge (and big enough angle) to stand up to the mechanical stresses applied to the edge. This is the point I was trying to get you to realize earlier. Your statement about a thicker edge with a greater angle dulling faster could, in fact, not be any more wrong (all other things being equal) irrespective of who told you and at what meeting.

Another thing to consider when determining the "ideal" angle is the fact that each razor has different steels hardened to varying levels. The ideal will vary from razor to razor.

Your preference to go with what the factory sets the angle at is totally fine; I share that. I do ask that you be more critical in your thinking when it comes to advice from people who make statements that are impossible to support with science, though (specifically relating to a totally scientific topic of which honing and edge geometry absolutely is).

 

[Smythe]

Gentlemen, please let’s not turn this thread into a pissing contest… In some ways you are both correct… but let’s leave that at that... .

Laurent, yes, you must work the point area a bit more to get that area to catch-up on sharpness.
Some folks may simply raise the tang at the end of the stroke to get “round-the-bend”... however in your case you could raise the tang and do a few back and forth strokes on both sides concentrating on the point end... or you may place a finger on the spine near the point to put a little pressure on that area and cut the steel faster.

Occasionally, test the edge by cutting arm hair to check your progress (it should cut them with equal ease as the rest of the edge), and when the point end is sharp enough, then you return to regular strokes with only the weight of the blade (don't forget to raise the tang at the end of the stroke to sharpen “round-the-bend”)…, strop and shave.

Please let us know your results…

 

[Paul]

Cedric,

Please accept my apology. I didn't intend to turn anything into such a foul contest. I can't tell you how much I would appreciate an email from you explaining how he is correct, though. It would be most enlightening.

Cheers

 

[Gunner777]

I'm done. I was just trying to help in the first place so that's that. Anyway as suggested using a finger at the forward edge of the spine you can also make small circular motions to round off that sharp edge. You can even hold it where only that small area touches the hone and round it off just go slow and check often.
Laurent your right that circular motion you mentioned in your post should work fine so yes you are indeed right.

 

[Bart]

Gentlemen, please let’s not turn this thread into a pissing contest… In some ways you are both correct… but let’s leave that at that... .

No let's not. I hate this. In this particular discussion. Paul is 100% correct. Gunner is 0% correct. That has nothing to do with my appreciation for either one of both gentlemen. Neither has it anything to do with opinion. 1+1 being 2 is not an opinion, it's a fact. A more obtuse angle on a razor is stronger and it will not deteriorate easier. If it becomes too obtuse, it will compromise the shaving comfort, but 2 layers of tape are unlikely to achieve that on a modern razor. In fact, 2 layers of tape are not changing the bevel angle more than the resulting angle at the very edge after stropping on a pasted hanging strop. Which is common and accepted practice.

Now, in some surroundings, 100% right + 0% thinks he's right, my go into the YMMV machine (*) and ends up being: "you're both 50% right". Which, as stated, I happen to hate.

I thank you Paul, for the courage to stand by what you knew was correct. And I thank both Gunner777 and Paul, for having a civilized discussion about it. But we're not going to settle for "Let's both be right".


*Your Mileage My Vary, a commonly typed disclaimer among forum posts throughout the Internet, which means I'm nearly stating an opinion that I can't defend with factual information.


About the original question:

What I see in the sketch-up has obviously nothing to do with tape or not. I think that the widened bevel, near the very tip of the blade, is cause by exaggerated rolling of the razor near the end of the honing stroke. In essence, it is the very beginning of this:

We once had a big discussion about this razor, some considered it art, I considered it the mother of all unnecessary hone wear.
Whatever it is, the widened bevel near the tip is cause by steel removal. Once gone, it cannot be put back on. All you can do, it try to refrain next time from rolling the stroke too far. Note that the animated illustration for the rolling X-stroke in the article about honing strokes, shows the idea exaggerated, for the sake of clarity. In reality, a rolling stroke is hard to see. It's often not much more than a gradual shift in pressure, certainly so on a blade with only minimal smile.

Kind regards,
Bart.

 

[Gunner777]

No public comment----

 

[chti_lolo]

Thanks to all for taking time to answer my question

Before asking you, I tried to do an extra circular at the end of the stoke to hone more the point area, then I put my finger near the point and did some half strokes . It improved the point behaviour but it was not as good as the figure 2 point.
So I will try to raise a little the tang and do some extra work on the point (I'll let you know how it works for me).

It's my first honing experience that's why I have used 2 layers of tape. I haven't succeeded in the academic unicot so not to have to start again from the beginning , I have tried the 2 layers tip. The edge I got was so good, that I think it was due to beginners' luck and don't want to hone again my razor till it begins to drag. I have bought some cheap razor, and will follow my trip in the land of coticule to the real unicot and then maybe to the mythic dilucot.

Regards

Laurent