Convex stones. New trend for the end users?

[Acmemfg]

I recently noticed one particular well known vendor is now marketing convex hones. I understand Dovo (maybe others) are using stones configured like this to set the factory edge. Ok.....
Other than probably having an advantage when working on a smiling blade, is this a bona fide improvement or more of a gimmick?

 

[bluesman 7]

Actually there is no advantage with a smiling blade. The advantage is when honing a straight edge as the edge presents to the convex stone the same way that a smiling edge presents to a flat stone. JMHO

 

[lightfoot]

I like them for blades with certain issues. Had a wedge with poor contact from the mid point all the way back to the heal on both sides while making an initial evaluation on a flat 1k. I convexed the edge of a few synths to correct it while saving the maximum amount of steel. I know others don’t really support this but I think a convexed hone can have its place. That being said they’re not a solution for every geometry issue but using the edge of my 1, 5, & 8k did a very good job on my problematic wedge. Took care of it fast too.

 

[buca3152]

I don't see any advantage. And I guess you would need a convex lapping stone?

 

[lightfoot]

I don't see any advantage. And I guess you would need a convex lapping stone?

Well, lapping them into German specs is way beyond what I’m willing to do but putting a gentle curve along the length of the edge of a few Hones has really came in handy a few times for me at least...

 

[PaulMallorca]

Many PSD are found convexed. I tend to lap one side flat as I've never got better edges from the convex side. Magnified I only hone the back of the bevel.

For this to work, all the ones in the progression would require to be convexed. On coticules, as a one stone solution why not.

 

[buca3152]

Well, lapping them into German specs is way beyond what I’m willing to do but putting a gentle curve along the length of the edge of a few Hones has really came in handy a few times for me at least...

I hear you. But how long would the convexing last? It will start to degrade rather quickly. Especially since that crowned area would get all the use. For me I prefer flat stones. I don't think there is anything there about it. But that's just me.

 

[Sdm84]

I think we are talking about convexing coticules and Arkansas. The Arkansas will hold the shape basically forever and the coticule you just have to be careful with the slurry stone.

I work on convexed stones and find them useful. Just be careful once you use a convex stone you can’t go back to a flat stone in your progression. So if you set bevel on a convex home you are locked in.

Lately I have been setting bevel on a flat hone then moving to my convex coticule for midrange and finish.


Sent from my iPhone using Tapatalk

 

[lightfoot]

I hear you. But how long would the convexing last? It will start to degrade rather quickly. Especially since that crowned area would get all the use. For me I prefer flat stones. I don't think there is anything there about it. But that's just me.

Well I need to draw a distinction in regards to what I do with the edges of my stones vs a fully convex hone with a true spherical gradient. I only use mine if a have a serious sharpie test fail on a flat hone. Then if my curved hone edge doesn’t give me a good hit within a few strokes I know I’ve got bigger issues in front of me and then I’m probably looking at cutting back a lot of steel. Hope this helps.

 

[buca3152]

If I was going to try this I would get a length of 2 inch pvc cut into 12 inch pieces and use psa lapping film to stick to the pipe. Now I don't think it matters but at least you would be able to produce the same angle without the need to lap anything .When the film wears out renove and stick another piece on. The change in the crowned hone as I said won't last long. And if there's a lot of steel to be removed probably before you get 1 or 2 razors done before the stone is now flat or whatever. Lol.

 

[lightfoot]

If I was going to try this I would get a length of 2 inch pvc cut into 12 inch pieces and use psa lapping film to stick to the pipe. Now I don't think it matters but at least you would be able to produce the same angle without the need to lap anything .When the film wears out renove and stick another piece on. The change in the crowned hone as I said won't last long. And if there's a lot of steel to be removed probably before you get 1 or 2 razors done before the stone is now flat or whatever. Lol.

You could do this for sure. Just keep in mind that what the O.P. is referring to is a stone that is curved along both the length and width of the stone. You can go to TSS’s YouTube channel to see exactly how he achieves the spherical gradient if anyone is interested.

 

[kcb5150]

There's more than one way to skin a cat. I would say if you have an expendable stone where you don't mind losing material if you dislike it and wish to reflatten it then give it a go and see if it is for you.

 

[kelbro]

Life's too short for all of that. Toss the razor! There are more than enough with straight edges!

 

[bluesman 7]

Many PSD are found convexed.

What are PSD?

 

[bluesman 7]

Here is an older thread, oddly containing updated info on the Dovo hones.
Convexed Dovo Hone

 

[bluesman 7]

Well, lapping them into German specs is way beyond what I’m willing to do .

Does anyone here know the actual German specs? Just a curiosity as I like thinking about this stuff. I'm most curious about the radius on the long dimension and whether it matches the short dimension, making the hone truly spherical.

 

[lightfoot]

Does anyone here know the actual German specs? Just a curiosity as I like thinking about this stuff. I'm most curious about the radius on the long dimension and whether it matches the short dimension, making the hone truly spherical.

I think Jarrod suggested that it was a 2% gradient which almost demands a rather large stone. I’ll try to post a link to the video in which he and I got into some detail about this particular issue down in the comment section. But I would just comb through any of his videos on his YT channel to try and put it all together. But roughly if you were dealing with a 10X8X1” hone you would wind up with a difference of around 1mm from the center high point to the edge along the length of the sloping down in a curve. Same with the width but the drop along the width would be less perceptible. I don’t think most here on the forum will go so far as to prepare a stone along this criteria but some may still find it interesting nonetheless.

 

[buca3152]

So a 1mm rise in the center of the stone is going to do what? Make it easier to.hone certain razors? Has anyone done any testing like a magic marker test to at least suggest there is more of a wonky bevel being covered?

 

[lightfoot]

So a 1mm rise in the center of the stone is going to do what? Make it easier to.hone certain razors? Has anyone done any testing like a magic marker test to at least suggest there is more of a wonky bevel being covered?

They do this in Germany because the razors are run through the grinding wheels by hand which can introduce unwanted variance and the razor is no longer “truly straight”. The purpose of the spherical gradient is to help compensate for this. This is the explanation I’m familiar with at least. A likely fix for this would be to set up the razor to where it can’t move during hollow grinding for super tight tolerances but they do their initial grinding by hand.

 

[Alum of Potash]

For me, the convexed hone approach with a wide stone seems analogous to a rolling stroke on narrow stones with warped-spine razors in that it involves more of a point-by-point relationship between spine and edge than a linear one with a flattened stone and a presumed flat-spine razor. Another thing I wonder about is the emphasis on Dovo/Solingen production in that Solingen razors are often considered to be of tighter tolerances than Thiers production. If so, it would seem that Thiers-production razors would stand more to benefit from such an approach. I also have heard that the convexed hone under consideration renders a concave-shaped bevel, but I can't really really fathom this. Is the goal to create a kind of "bellied" full-hollow grind? And is any such concaving of the bevel being introduced by the secondary convexity (or spherical gradient) involving the length of the stone? Otherwise, I would be more inclined to experiment with a stone shaped more like a cylinder. Finally, if a bellied full-hollow grind with a concave bevel is the ultimate goal in this approach, what is the benefit of doing this relative to, say, a rounding or convexity of the bevel (presumably with concaved, dished stones or slackened strops) as applied to old-time, full-wedge razors?