What's the difference between full hollow ground, 1/2 hollow ground?

[Bloomey]

This is probably me being thicker than a village idiot, however I need to ask the question all the same:

What's the difference between full hollow ground and 1/2 hollow ground.. or to put it more specifically, what does hollow ground mean?

I already put a thread up here to get peoples input whether to buy a muhle or a dovo best quality. After receiving some good feedback I've decided on getting a dovo, however I have no idea when it comes to people on b and b or other shaving forums talking about 5/8, 6/8 etc and full hollow or 1/2 hollow ground?

The other thing I need to check out is are there any decent honemeisters that are based in the UK and also if anyone knows of decent straight razor vendors in the UK?

All input is much appreciated

 

[BRuhling]

Easiest question first: 5/8, 6/8, etc. refers to the depth of the blade (measured from leading edge of the cutting surface to the back of the spine).

The grind is a measure of how thin the blade is. A full hollow will be much thinner than a wedge; thus, the full hollow will "flex" as you use it, especially if you use too much pressure. For this reason, most people will recommend that you start out with a 1/4 hollow or wedge grind as they are more "user friendly."

There are a number of honemeisters in the U.K. I think Neil Miller is located there: http://www.strop-shop.co.uk. I also think The Invisible Edge is there: http://www.theinvisibleedge.co.uk.

 

[garyg]

Here's some infro from Joel regarding the grind differences ..http://badgerandblade.com/vb/showthread.php?t=28457

 

[Chimensch]

Easiest question first: 5/8, 6/8, etc. refers to the depth of the blade (measured from leading edge of the cutting surface to the back of the spine).

The grind is a measure of how thin the blade is. A full hollow will be much thinner than a wedge; thus, the full hollow will "flex" as you use it, especially if you use too much pressure. For this reason, most people will recommend that you start out with a 1/4 hollow or wedge grind as they are more "user friendly."

There are a number of honemeisters in the U.K. I think Neil Miller is located there: http://www.strop-shop.co.uk. I also think The Invisible Edge is there: http://www.theinvisibleedge.co.uk.

I can wholeheartedly recommend Steve Dempster from the Invisible Edge.

 

[rajagra]

From Dovo literature:

View attachment 137826

Many razors are sold as full hollow ground when they are in fact nowhere near that.

 

[kimfella]

From Dovo literature:

View attachment 137826

Many razors are sold as full hollow ground when they are in fact nowhere near that.

Is it just me or do both the full hollow and half hollow in that picture have bulges halfway down the blade?
I thought a full hollow had a single radius grind, right from the spine to the cutting edge, while a half-hollow ground blade had one radius from the spine to about halfway down the blade and a second radius grind from that point to the edge?

 

[rajagra]

Looks like they have bellies:

http://en.nassrasur.com/razorcentral/grind.html

 

[Brownbear]

I still don't understand what the fractional hollow terminology refers to and as I read the links and the things knowledgable people say about it and look at the different diagrams I get more confused. Ultimately, having honed and shaved with a dozen different razors now I have concluded it really doesn't matter much, my favorite shavers are quite a bit different in terms of grind and they all do a great job. But still the inquiring mind wants to understand.

I first thought that 1/2 hollow referred to the amount of the blade width that was ground very thin with the sides parallel or almost parallel to each other. This makes for a thin edge, easy to hone and flexible at the edge and a bit noisy on the hones and strop and face. So a 6/8 blade that is 1/2 hollow would have 3/8 ground parallel, a 1/4 half hollow would be 3/16 parallel and so forth. But if that were the case, then you couldn't have a full hollow, because grinding the entire blade flat would leave you with a floppy, impossible to use blade. So it must be some other blade dimension that the 1/2 hollow refers to.

Maybe 1/2 hollow refers to a grind that has half as much metal ground away as is possible, allowing for a spine for rigidity. Then we can look at a diagram of a full hollow to get an idea of what the maximum amount of hollowing could be and reduce that by fractions. But this doesn't seem consistent with many of the diagrams. That Dovo diagram seems to leave little room for a 1/4 grind, the 1/2 hollow already doesn't have much of a thin section so it is hard to see how you could take half of that away.

Then there is the presence of a "belly" or ridge between what clearly seem to be concavities ground by either two different wheels or the same wheel applied at two locations along the blade width. Looking at that Dovo diagram, the half hollow and full hollow where clearly ground on the spine side with two different diameter wheels, then the edge side was finished up with another diameter or the application of the same diameter further out.

I have one razor that seems to have been ground with a single wheel about 11" inches in diameter, and another that was done with multiple grinds since the steepest part of the concavity by the spine could only have been ground with a 3" wheel. It would have been finished either with a larger wheel, which would have left evidence of a belly, or by sliding the blade along the smaller wheel to remove metal on the edge side of the radius.

But none of this points to a clear definition of what the fractions in the 3/4, 1/2, 1/4 etc hollow designation refer to. Fractions are ratios and I don't know what the numerator and denominator refer to in terms of actual dimensions of the blade, the diagrams just don't relate to that.

I read the link rajagra referred to, but it is in need of some major technical editing as portions of it are incoherent and the diagrams are so crude as to be physically impossible to create with grinding wheels. And there are things that are simply incorrect such as saying "Hollow grinding reduces the real cutting angle." Not really helpful.

Then that leaves us with the term "concave grind" which some people refer to but which makes no sense as all razors have concave faces, even wedges to some degree. I also assume that the grind profiles differ between old time hand forged and ground blades and modern machine methods. The Thiers Issard you tube seems to show them grinding the faces on a machine with two opposing wheels about 6-8" or so in diameter, then refining it on a smaller wheel.

http://www.youtube.com/watch?v=NcwNqep_Aak&feature=related

So in the end these terms seem to be useful in a general sense but don't bear too much scrutiny. Or perhaps there is a single clear and specific definition and I just can't distinguish which of the conflicting narratives about it is correct. When it comes down to it there are significant differences in how a blade hones and shaves depending upon how wide the thin part is, but assuming the edge has been honed and stropped appropriately for that type grind, I don't yet see a knock down difference in the shave I get from them. The amount of noise yes, the quality of the shave no. The amount of pressure I can use while honing yes, the quality of the shave no. I am new at this so as I get better this may change.

 

[Zot!]

My Dovo Best sold as a full hollow looks like the half hollow in the diagrams. My vintage sold simply as hollow looks like the quarter hollow.

 

[Zot!]

Here is a link to the SRP chart on grinds

Razor Grinds

 

[Jeremysilverado]

full hollow ground blades are skinnier as they progress to the edge. this makes the razor easier to sharpen and easier to damage. some feel the full hollow ground gives a smoother shave.

 

[Joe Edson]

Ehh, get them all!

I love all my full, 3/4, 1/2, 1/4 hollows and wedges and near wedges. They all have a different face feel and just when I'm falling in love with full hollows I whip out the W&B wedge and think, oh man this is nice

 

[Chimensch]

full hollow ground blades are skinnier as they progress to the edge. this makes the razor easier to sharpen and easier to damage. some feel the full hollow ground gives a smoother shave.

I don't think that a hollower grind makes the razor easier to sharpen but it does make it more flexible and, possibly, more comfortable.