I am just presenting the math, Glen. I asked people to hold up while I researched all this and assimilated all of the information, but no, you had to have answers... I am not as certain of this information as I'd like to be. The theory checks out and the math checks out to my satisfaction. I am in the process of having people that are smarter than me double check the math. As for "real world" results, I'm still looking into it. I absolutely think it weakens the edge. That's why all these convex honed razors have to hit the stones (if however briefly) every 6-10 shaves. And, anticipating your next question, yes, this shortens the lifespan of the razor. Is that trade-off worth it? I don't know.
The advantages... It makes the very edge of the razor more flexible. Theoretically, since that edge is more flexible, and you are only sharpening the last 20% of the bevel, you should be able to get a keener edge, within the limits of the steel's ability to handle it. You can also hone warped razors easier with a convex hone, but that was never the primary intention of the technique. Call it a nice side benefit. It also speeds up the honing process on subsequent honing sessions, another nice side benefit. I am not responsible for what other people might claim. That's between you and them. All I care about is the truth of the matter. At this point, I believe it is a valid honing technique. I don't believe it is an easy one, or that most honers would find any benefit to it. Edit: As you pointed out, it does leave scratch marks on the hollow, down by the bevel, usually at the toe and heel. People who own "safe queens" don't want to scratch them up. So call that another disadvantage.
What have you Personally found to be true, what types of steel and grinds have you found to be better than flat hones What have you found to be better about using this technique so far ??! Have you used it on a few different types and grinds to get a good idea of the attributes if any I am not really interested in what others have told you, what have you found so far since you have claimed it to be valid tell me the advantages you have realized If any are you sure it is the technique or that you are paying more attention ps: Yes I have tried it and the reverse as these ideas came forward long before Jarrod did his pitch As always I say the same thing about new techniques/hones or old techniques we rediscover “If is easier, faster, better I would be all over it”
I have a machinist making a 1.2m radius cylindrical 8" x 11" plate and a 5m and 8m radius cylindrical concave 8 1/2" x 11" plate right now. He's already done with the 2m x 7m 8 1/2 x 11" elliptical plate. I've discussed backing the cylindrical plates with .10" steel to be able to use SiC grit for lapping. Soon enough I will know for myself. This reminds me of this sign, the same applies:
You might as well come back and read it here. This thread is sparse on details, but all the concepts are laid out plainly, at long last...and earlier than I had planned on. I still plan on doing that in depth write-up, this is not it. This just basically hits the highlighted portions.
For anyone who likes to go through the numbers, please find one example calculation. The main conclusions just from the numbers, without reading anything into what this means in terms of razor performance, or how/if it may be relevant to anyone is; A 6/8" razor, honed over a 2 meter wheel can change the bevel angle by 0.6 deg (excluding any effect caused by the bevel flexing over a curved surface). This is not significant enough to make any difference. However, this can be exploited in different ways (can be covered in part 2) However, the bevel flexibility can be changed by a factor of two, provided the razor is allowed to flex, and the bevel length increase by 20%. This is actually hard to avoid, because of the flexibility of the razor and your ability to manage your pressure. This might not be all that relevant if the razor is a extra hollow grind blade. However, most of my TI razors feels a little stiff on the face. Fine tuning the flexibility of that razor will add something to the feel of that razor. It it is like changing the driving performance of a car, by changing the suspension, or the profiles of the rims. Is it better? To me, yes. To someone else, maybe. Why not just try it? The razor will not get any sharper, but it will be more flexible. The bevel length is raised to the power of three, and the width of the razors bevel is raised to the power of three in the bevel flexibility calculations. By changing both of these values i think even without knowing anything about the math, it is not difficult to assume there will be a felt difference. How the razors leave the major razor manufacturers is totally irrelevant, and should be left out of the discussing, because it is just a distraction. The small nuances of the other benefits can also be outlined if anyone is interested.
I liked math. Took all 4 years in High School. High Bs, low A's every year. I did well because math has rules; follow the rules, you'll do fine. But even that is too much for me! Now I just shave.
If the edge is not sharper, i.e. the edge width is not changed. Why is the concave bevel less durable. If you lock the suspensions on your car, will the wheel bearings get more ware, or less? Adding flexibility distribute force. This means less force will be going to the most fragile part of the edge. According to MIT research, the main reason an edge dulls is micro chipping. As the edge is going through the hair, the bevel, and the hollow ground blade is flexing. Less flex, mean more force to the local load concentration. when you are stropping your razor the same principle applies. If the blade is twice as flexible, the bevel will get 50% less force at the tip, and will follow the contour of the strop better. It is not that simple, because you have also changed the bevel angle slightly. However, the practical experience i have tells me that the razor is not affected in an adverse way.
Here is one practical example. Please note that this is not an example of a perfect edge. However, it shows how you can hone a razor using a really coarse 800 grit stone, and jump to a flat finishing stone in one step. Putting in a intermediate stone makes it easier, but this was just as a demonstration. If the bevel is honed from the back end of the bevel, and coarse striation are not allowed to go all the way to the apex, you can skip some of the intermediate steps. It also only takes a few minutes. Why this is not important to someone who value their time, or hone for others is beyond me. This only took a couple of minutes. It shaved ok, but can benefit from spending some more time on the finishing stone. The magnification is 600-700x Coarse 800 grit bevel striations We are only looking at the actual tiny bevel here. The bevel shoulder is not in the image. Finished edge with focus on the apex. A slow Blue Black Arkansas was used.
"You would also be limiting them to using a Convexed hone At least with a Microbevel they just need 2 cents worth of tape." This last step is from a flat stone in my example. You will actually make it easier for someone maintaining the edge. The slight concavity will just gradually go away. Someone maintaining it only needs a finishing stone for quite some time. A convex stone is not a quick fix solution. I do think someone needs to master a flat stone to get the most out of it. I Don't understand the logic here.
Anyone who has ground and honed a chisel should get the concept. Look at diagram (A). "Less Rubbing Here." A concave bevel allows for a much quicker and shorter amount of time on hones, even flat hones. Or perhaps, especially on flat hones. Since you are only honing the last 20% or less of the bevel, it saves time and decreases hone wear on the finishing hone. So we ended up doing the math, and using stones with convex contours, on an arbitrary 6/8 razor the person doing the math happened to have, the bevel would be ground 3.5 microns into the bevel (on one side), and the bevel would be extended by .1mm. Both the person doing the math and I realized that due to blade flex, this could only be considered an absolute minimum bevel concavity depth and width. Bevel depth therefore is dependent on how much pressure the person doing the honing uses, and how flexible the razor is. Most straight razors tend to be fairly flexible. A Theirs-Issard razor is on the upper end of the stiffness and hardness scale. That's using the whole range of stones. The final convex stone would be affecting .2mm of the bevel or less, and could serve as an alternate to a flat finishing hone. And then I get on here and see that @JPO has already posted all the math calculations, including the stuff we knew about but didn't have a formula to be able to calculate it. In short, yes, the math holds up under scrutiny.
Exact same answer as was used about Microbeveling exact word for word almost basically you are not giving any advantage, except the same unprovable claim that it “might” have a better feel micro bevels do give an advantage when testing at least when dealing with Wonky steel You can test the ability of a higher angle that might hold the edge.,
Now you are introducing specific tools and grinds made for a specific task The exact opposite can be found about sharpening Chisels to a 20° angle and introducing a 25° Convexing microbevel FOR strength This is all old knowledge and it is common knowledge the a Convexed bevel is the stronger and longer lasting of the two Most every idea we have found for SRs comes from tool sharpening
Glen, whether you like it or not, 100 years ago, almost all European blades were convex ground, including almost disposable blades like French frameback razors. The question now has to be, why wasn't it done in America and the U.K.? Obviously the Europeans found it a superior method for a reason. What was that reason? As you said it yourself, if "it's an easier, faster, better way I'd be doing it." At least one of those, "faster," "easier" or "better," is the answer the Europeans found. If Germans of all people, said that razor makers used it, but only the most skilled of them preferred this method, and there is proof on every NOS Leresche frameback blade, you have to ask yourself "why?" Otherwise, you'll be saying that French and German razor makers didn't know the best way to make razors. The Germans, maybe. The French, Maybe. But both together!? You've honed a thousand razors, Glen. Were the old German and French razors you honed bad razors? Was the average razor of 1900 a bad razor? Had it reached the pinnacle of the craft? If not, then where would it fall on the quality scale? Did the people making them, know what they were doing? If the answer to that is yes, then again you must ask yourself "why?" Edit: Yes, I asked myself those same questions about convex hones. This is where I've ended up. Because there had to be at least one good reason. The old long dead German said they "found it a more advantageous way of honing." So. What. Is. That. Reason?
... If Jesus himself came down and said "I hone my razors on convex hones," you probably wouldn't believe him. It is what it is. I will continue my own research in an attempt to find the truth. I wish I could be as unswerving in my faith of my rightness as you. But I still question.
OK, I’ll bite, knowing I may live to regret posting on this topic. The math is beyond me and my experience is slightly better than none but I read this stuff out of curiosity and hoping to learn a thing or two. However, how is it that we know that 100 years ago (1920s) almost all European blades were honed with convex hones? And, what about before then? For those who do have experience honing many razors, wouldn’t this have been noticed and commented on before?
