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Convex Stones...Legit or Gimmick?

Acmemfg

Ambassador
Thought I may like another coticule to keep my LaVeinette company. Went to my usual source...almost (if not every) stone he had was "made intentionally convex". After sharpening my own razors for many years I am not in the mindset to learn new honing tricks, The old school technique has served me well.
But, my curiosity is piqued indeed. What is the huge advantage (if any) of using a convex stone?
Ironically enough, the one razor I own which arrived with an edge created on convex stones was surely less-than-great. Bevel was reset and finished on the aforementioned LaVeinette. Works fine now😉.
 
So virtually all of the straight razor manufacturers in Germany and France use bench stones that are prepared with a convex surface. They’ve used this for the last 100 years or longer so the use of flat stones is the new kid on the block. The problem is that preparing stones like this is very demanding and most end-users aren’t going to be up for this without an easy way to do it. But the reason the manufacturers use this is to compensate for the slight variations in a razors geometry. So if there’s any slight variations in the razor the small contact area allows for a high degree of isolation so these variances don’t hinder the honing process. I hope this helps.
 
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If you are gonna use a convex stone for finishing a razor, that might necessitate the use of convex pre-finishers as well. If the bevel is wide you are risking the edge not riding on the stone of your curvature is too high. Meaning, you won’t get the benefits of the convex stone. That’s my personal opinion and not based on any testing, but if you apply a bit of geometry to your thought process, you might come to the same conclusion.
the only stones I have seen for use by German manufacturers are round and they spin around. They might not use any prefinishers, so it is ok for them.
If I am wrong, don’t be shy. There might be something I might have missed in my calculations...
 

Acmemfg

Ambassador
"Volume of (production) razors"?? Good point. Perhaps that might be why small makers like Ralf Aust, Ulrik Beyer (Koraat), Brian Brown, and those guys are putting out blades with excellent edges.
@SammieM No, all my stones are quite flat and I can put a most satisfactory edge on my blades using them. I see no need to change the discipline.
 
"Volume of (production) razors"?? Good point. Perhaps that might be why small makers like Ralf Aust, Ulrik Beyer (Koraat), Brian Brown, and those guys are putting out blades with excellent edges.
@SammieM No, all my stones are quite flat and I can put a most satisfactory edge on my blades using them. I see no need to change the discipline.
Funny you mentioned Ralph Aust because I think he keeps his benchstones flat from what I observed in a video on YT. He may not be part of the trade guild that requires the use of convex stones...
 
"Volume of (production) razors"?? Good point. Perhaps that might be why small makers like Ralf Aust, Ulrik Beyer (Koraat), Brian Brown, and those guys are putting out blades with excellent edges.
@SammieM No, all my stones are quite flat and I can put a most satisfactory edge on my blades using them. I see no need to change the discipline.
I don’t either, hence me not ordering the convex stones. I am perfectly happy with my flat stones and get excellent edges from them.
 
the only stones I have seen for use by German manufacturers are round and they spin around. They might not use any prefinishers, so it is ok for them.
If I am wrong, don’t be shy. There might be something I might have missed in my calculations...
What you’re seeing here is 1000-2000 grit grinding wheels that they use for setting the bevel. Then they move to two different convex bench stones followed by stropping on red paste on leather.
 
There is a huge thread on convex hones with much controversy. Much of any thread on any razor forum can be read on Jarod's website with one sided ridicule if that's your thing to read.



You rarely hear anyone raving about it now.
 
I'll start out by saying that there's nothing at all wrong with flat hones.

I unintentionally created a super long thread on convexity after being one of the first to buy when Jarrod starting convexing.

A lot of guys interpreted enthusiasm about convexity as being a criticism of flat hones. It's not.

The explanation from @lightfoot is correct. But imperfect razors can also be honed on flat stones. Techniques like the X stroke and others can handle that.

But the issue of imperfect razors is not why I bought it. I just think convex makes sense for ark, and only for ark. For everything else I buy flat stones.

It's because arks are so hard and so difficult to lap and finish. The convex hill on something as hard as an ark means it won't dish in my lifetime. So I don't expect I'll ever have to lap it. I only use it for light finishing on oil, so it should last.

Jarrod honed on his convex black ark on a commercial basis, lots of razors every day and after two years he finally wore down the hill and had to lap it convex again.

So that's a lifetime for a civilian like me.

I prefer flatness on everything else. Because on other stones, convexity will get worn down and it will dish and need lapping. And I don't want to get into maintaining convexity. You have to get a huge marble plate and SIC powder and create a convexity making machine, and well, forget it.

BTW I think the reason Solingen uses them is because they're commercial. If you have to hone a thousand razors a day you don't want to stop and lap every thirty minutes. They use convex arks to increase profits. That doesn't apply to us.
 
I get the part about saving time. But it's supposed to save time honing. These factory edges are imo garbage. I would prefer they grind them and let the end user deal with it. But imo anyone can get used to honing with a convex or flat stone. And I can't see how they would be objectively different.
 
I get the part about saving time. But it's supposed to save time honing. These factory edges are imo garbage. I would prefer they grind them and let the end user deal with it. But imo anyone can get used to honing with a convex or flat stone. And I can't see how they would be objectively different.
Jared had a lengthy post on the benefits of a convex stone on one of the U.K. forums. He quoted a blade smith from Solingen and apparently the keenness of the razors is much better because you get a thinner grind. He also mentioned that the razors are comfortable, but not “sharp”.
 
Jared had a lengthy post on the benefits of a convex stone on one of the U.K. forums. He quoted a blade smith from Solingen and apparently the keenness of the razors is much better because you get a thinner grind. He also mentioned that the razors are comfortable, but not “sharp”.
There are potentially, MARGINALY sharper to the same extent that they are a less durable edge also.
I posed the main reason for it was for economics, more razors out the door.
Any one who believes that it had nothing to do with that is irrational.
Yes, can be a sharper (undercut) bevel. I'd rather have a 16 degree flat honed edge than a 16 degree undercut for more strength behind the bevel.
I've seen what happens to edges with regular use. If they were any more "sensitive" to damage I would never stop honing.
It has been pumped by him that it is sharper and that every major Solingen MFG uses it for a reason, as it was just better.
Never to admit that more razors out the door is just good business sense and the primary reason.
I have seen the consistent bevel on brand new WARPED razors. There is no denial that a slightly warped razor will get through the door. What happens to the poor schmuck who gets it?
 
There are potentially, MARGINALY sharper to the same extent that they are a less durable edge also.
I posed the main reason for it was for economics, more razors out the door.
Any one who believes that it had nothing to do with that is irrational.
Yes, can be a sharper (undercut) bevel. I'd rather have a 16 degree flat honed edge than a 16 degree undercut for more strength behind the bevel.
I've seen what happens to edges with regular use. If they were any more "sensitive" to damage I would never stop honing.
It has been pumped by him that it is sharper and that every major Solingen MFG uses it for a reason, as it was just better.
Never to admit that more razors out the door is just good business sense and the primary reason.
I have seen the consistent bevel on brand new WARPED razors. There is no denial that a slightly warped razor will get through the door. What happens to the poor schmuck who gets it?
I agree with you. Perhaps you misread my post. I would not use a convex stone myself as I don’t see how it will work unless I get a convex prefinisher as well. I am perfectly happy with my flat JNATs. As to the poor schmuch, he can do the “wobble test” and then kill his razor on the bevel setters or send his razor to be sharpened to one of the guys here...
You are absolutely correct. The bevel becomes thinner and the edge doesn’t last on thin bevels. I have honed few. You would be hard pressed to get a decent shaving edge...
 
I can’t support the idea of catastrophic bevel failure due to a 25’ radial curve...
Not going to happen.
I’ve prepared a number of hones this way. A 5K synthetic, a small Coticule bout, & a Thuringian. Honestly they’re a lot of fun to hone on. But without a dedicated lapping plate they’re very difficult to prepare consistently. That’s probably the only reason I haven’t switch completely over to convex hones. Preparing an entire progression of stones in this manner is definitely demanding no doubt about it.
 
I can’t support the idea of catastrophic bevel failure due to a 25’ radial curve...
Not going to happen.
I’ve prepared a number of hones this way. A 5K synthetic, a small Coticule bout, & a Thuringian. Honestly they’re a lot of fun to hone on. But without a dedicated lapping plate they’re very difficult to prepare consistently. That’s probably the only reason I haven’t switch completely over to convex hones. Preparing an entire progression of stones in this manner is definitely demanding no doubt about it.
The failure won’t be catastrophic. You will just have to hone more often as a wider apex will be more durable in the long run.
 
The failure won’t be catastrophic. You will just have to hone more often as a wider apex will be more durable in the long run.
Oh for sure. More steel=stronger bevel. I do like the honing sensation on them especially at the final stage. But it’s up to the end-user to decide if such a creature fits into their honing gear.
 
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