Traditional Use of "Flat over Hollow" Grind?

[WhittlinAway]

Over the past few months, in the context of spoon carving and sloyd knives, I've become aware of a style of sharpening scandi-ground knives called a "flat over hollow" grind. It is created by first using a wheel to hollow-grind the bevel and then using flat stones to establish small flats at the shoulder and apex. The idea is that the flats yield the same carving performance as a true flat grind while the hollow allows for quicker resharpening with flat stones because there is less material to remove. It's also supposed to be less prone to convexing the edge while resharpening. Once the hollow has been ground away by many resharpenings, it's back to the wheel to establish a new hollow.

Here's an example I inexpertly put on my Marttiini Lynx Lumberjack, leaving the scratch marks in the hollow since they shouldn't matter for performance:

It's not a great photo, and the flats are new and quite small, but I hope it gives the idea. This knife sees a lot of hard use working outside in the garden and I like the idea of being able to quickly sharpen it with flat stones before putting it back to work. I'm looking forward to seeing how well it works in practice.

It's new to me, but it's such a practical technique for enabling quick and accurate field sharpening that I have to suspect that it's been in use on hard-working scandi-ground knives for a very long time. I'm curious whether history backs up that suspicion and that's why I'm asking here in the traditional forum. Does anyone know whether this is a long established technique for scandi-ground knives like puukkos and sloyds? Are old scandi-ground knives found with this type of grind? Also, is there a more common term for this than "flat over hollow"?

Thanks for reading and I look forward to any insights and discussion that follow.

 

[OLd_gUY]

Thanks for sharing. It's new to me also and I'm looking forward to the performance reports.
OG

 

[Jack Black]

Very interesting post Greg. I believe I've seen illustrations of this type of grind in knife books, as an example of the variety of knife grinds, but don't know if I've seen another name. I'll try and see what I can find my friend

Edit:

 

[Ted01]

The backs of quality Japanese woodworking chisels are ground this way, with a hollow, so that when sharpening, less steel has to be removed by the sharpening stones. The hollow extends over much of the length of the chisel, so it is not part of the primary grind at the edge, but it serves the same purpose - to make it easier to sharpen.

 

[Rich S]

I have been sharpening this way for years on my folders, works great, cut well and sharpen easily.
Rich

 

[WhittlinAway]

Thanks for sharing. It's new to me also and I'm looking forward to the performance reports.
OG

I'll report back on how it goes, OG. It's shaving sharp at the moment. I'm finding myself actually looking forward to the next time I need to sharpen it to see how quickly I can get it back there.

Very interesting post Greg. I believe I've seen illustrations of this type of grind in knife books, as an example of the variety of knife grinds, but don't know if I've seen another name. I'll try and see what I can find my friend

Edit:

Thank you, Jack, that's very interesting and I appreciate your taking the time to track it down.

I think what's shown in your book is subtly different in that it has a flat edge at the apex, but not at the shoulder. It appears to me that it would be sharpened only at the apex, as opposed to laying both sides of the hollow "flat" against a stone, just as you would with a flat scandi grind. In theory, the flat over hollow should be easier to freehand sharpen because the two lines of contact (the edge and the shoulder) form a wide base against which to index the stone.

It is interesting that it is described as having a strengthened area of the blade immediately above the cutting edge as compared to a full hollow grind. I'd not thought of that and it would apply to the flat over hollow approach as well.

The backs of quality Japanese woodworking chisels are ground this way, with a hollow, so that when sharpening, less steel has to be removed by the sharpening stones. The hollow extends over much of the length of the chisel, so it is not part of the primary grind at the edge, but it serves the same purpose - to make it easier to sharpen.

View attachment 1007656

Very interesting. I'd read about that, but had never seen a picture. Thanks for sharing one.

I have been sharpening this way for years on my folders, works great, cut well and sharpen easily.
Rich

Cool. That's good to hear!

 

[Mikael W]

No, I don't generally see hollow grinds in Scandinavian knives, but they do exist.
Mostly seen on made overseas knives.
Personally I use a convexed apex on my Mora's, for better edgeholding.
If flat over hollow works for Your needs, that's ok with me.
The main thing is to keep the edge sharp.

Regards
Mikael

 

[NirreBosse]

Hello. Im very interested in the old knives from our country. Im swedish. I very much like the kind of bevel you describe and have seen it more than a few times. Also on new custom blades. Im sorry to say I belive you overthink the reasons for this. The simple explaination is that they are historically sharpend on big grindingwheels that make them a little hollowground. Sometimes the wheel is wellused and thereby smaller witch makes this even more noticeable. If its not to bad we have let it pass as the flat they were intended to be.

Bosse

 

[kamagong]

I have a friend who did just that. He's a woodworker by trade, and makes puukkos in his spare time.

This puukko was made to be a compact, yet sturdy, "workshop knife".

It started out flat, but is hollow in the new picture. This is because I soon noticed that I had, by pure chance, nailed the heat treat on this one, meaning that the blade could easily hold a hollow grind, which I prefer.

 

[WhittlinAway]

No, I don't generally see hollow grinds in Scandinavian knives, but they do exist.
Mostly seen on made overseas knives.
Personally I use a convexed apex on my Mora's, for better edgeholding.
If flat over hollow works for Your needs, that's ok with me.
The main thing is to keep the edge sharp.

Regards
Mikael

Thanks Mikael. I realize now that I didn’t say it, but I was expecting this grind to perhaps appear from a user’s sharpening rather than from the factory.

The context in which I’ve seen this grind discussed is spoon carving and other sloyd work with green wood. In that case a convex negatively affects the carving ability because the bevel cannot be held flat against the work for stability at the same time the apex is slicing the wood. A flat or slightly hollow grind works better there.

But, you raise an interesting point about edge holding for general use. The Marttiini I showed is used for all sorts of tasks, so I’ll be able to form my own opinion in time. I appreciate your sharing yours.

Hello. Im very interested in the old knives from our country. Im swedish. I very much like the kind of bevel you describe and have seen it more than a few times. Also on new custom blades. Im sorry to say I belive you overthink the reasons for this. The simple explaination is that they are historically sharpend on big grindingwheels that make them a little hollowground. Sometimes the wheel is wellused and thereby smaller witch makes this even more noticeable. If its not to bad we have let it pass as the flat they were intended to be.

Bosse

Thank you very much for your insight and perspective. It was very interesting to read.

I may very well be overthinking it. It wouldn’t be the first time.

I’m new to this sharpening approach, so I was echoing the purported advantages I’ve seen given by others. I like your explanation that they were sharpened that way because that’s how people sharpened back then.

Perhaps the claimed benefits (in the context of green wood carving) are a case of contemporary people realizing that the old traditional way had advantages that weren’t realized until alternative ways became accessible and were tried. Or, perhaps it’s just overthinking. I’ll withhold judgment on that until I’ve built up enough experience to form my own opinion. In the meantime, I’m having fun experimenting

 

[WhittlinAway]

I have a friend who did just that. He's a woodworker by trade, and makes puukkos in his spare time.

It's a beauty. Thanks for sharing it and your friend's comments. It's interesting to see what he said about needing a good heat treat to be able to have the hollow-ground edge to hold up. That's another factor that hasn't really entered into the discussion.

 

[Jack Black]

Thank you, Jack, that's very interesting and I appreciate your taking the time to track it down.

I think what's shown in your book is subtly different in that it has a flat edge at the apex, but not at the shoulder. It appears to me that it would be sharpened only at the apex, as opposed to laying both sides of the hollow "flat" against a stone, just as you would with a flat scandi grind. In theory, the flat over hollow should be easier to freehand sharpen because the two lines of contact (the edge and the shoulder) form a wide base against which to index the stone.

It is interesting that it is described as having a strengthened area of the blade immediately above the cutting edge as compared to a full hollow grind. I'd not thought of that and it would apply to the flat over hollow approach as well.

I was lucky to find that image in the first book I opened Greg (by a Scandinavian author), but I have seen similar images elsewhere. THat's the nearest I've seen to what you describe though

No, I don't generally see hollow grinds in Scandinavian knives, but they do exist.
Mostly seen on made overseas knives.

I don't know about today, but in the 1990's, the Norwegian company, Brusletto, included several hollow-ground knives in their range. A couple of examples are shown in this UK ad from that period (NB the knives described as flat-ground are actually Scandi-ground)

 

[Mikael W]

The context in which I’ve seen this grind discussed is spoon carving and other sloyd work with green wood. In that case a convex negatively affects the carving ability because the bevel cannot be held flat against the work for stability at the same time the apex is slicing the wood. A flat or slightly hollow grind works better there.

But, you raise an interesting point about edge holding for general use. The Marttiini I showed is used for all sorts of tasks, so I’ll be able to form my own opinion in time. I appreciate your sharing yours.

I agree and I use a flat zero grind on the slöjd models for controlled cuts in detailed work.
For allround use, the convex edge works best for me.
When sharpening by hand the flatground Scandiedge tend to be convexed overtime.

Regards
Mikael

 

[Mikael W]

I don't know about today, but in the 1990's, the Norwegian company, Brusletto, included several hollow-ground knives in their range. A couple of examples are shown in this UK ad from that period (NB the knives described as flat-ground are actually Scandi-ground)

Yes and the Scandi-grind can be flat-,hollow- or convex-ground.
Basically a Scandi-grind is just a low Saber-grind.

Regards
Mikael

 

[Jack Black]

Yes and the Scandi-grind can be flat-,hollow- or convex-ground.
Basically a Scandi-grind is just a low Saber-grind.

Regards
Mikael

Yes indeed The term 'Scandi-grind' wasn't in use back then

 

[WhittlinAway]

I agree and I use a flat zero grind on the slöjd models for controlled cuts in detailed work.
For allround use, the convex edge works best for me.
When sharpening by hand the flatground Scandiedge tend to be convexed overtime.

Regards
Mikael

That makes sense. I may very well find the same to be true for me. I didn’t consider edge retention at all earlier, just ease of resharpening.

For what it’s worth, I use and prefer a convex edge on my small whittling blades because I like to carve a lot of concave shapes with them. Exactly the opposite of why I like a flat zero grind on my sloyd blades.

 

[WhittlinAway]

I'm embarrassed I didn't think to do this before starting this thread, but I realized this afternoon that Wille Sundqvist might have something to say on the matter in his book Swedish Carving Techniques.

Sure, enough, his sharpening chapter is extensive. He stresses the need to remove any microbevel or convex edge to give a flat bevel for carving. He also draws a distinction between a grinding step (done on a wheel in his examples) and honing step (done on flat stones in his examples) during sharpening.

Here are a couple of excerpts from the section on grinding:

"... The slight hollow grind you get on the bevel when using a large-diameter stone is no problem. In fact it probably serves as proof that the bevel is not convex. A slight concave bevel can be honed many times without being convex." (Page 40)

"... On your favorite knives, try not to grind up to the very edge, unless they are nicked or very dull. The little bit of old edge left on the blade can be honed away, and you will save steel and make the knife last longer." (Page 40)

Later, while talking about honing with flat stones, he has a photo illustrating the same grind as I described in the first post and a caption that, in part, reads "... perpendicular striations from the grindstone are still visible, but the edge and back of the bevel are polished." (Page 52).

This all lines up with what N NirreBosse said about it being the way that people have historically sharpened. I think it's reasonable to assume that the people I've seen who are fans of this style of sharpening for sloyd knives are simply continuing the time honored tradition. I probably overly latched on to the advantages I heard mentioned because it was a new technique to me. I'm happy to continue in that tradition, though, and look forward to gaining more experience with it.

 

[NirreBosse]

This posts make me so happy. The old men i knew in my youth all used knifes as tools. They wanted a sharp flat grind. They Didnt like ether hollow or convex edges but they didnt need 100% perfektion eather. So this slight concave bevel was a good start. Geting flater as time gone by and when the edge got to much convex they went to the wheel and started all over again. A few of these men could carve art but mabye still thought more about how to press tobaco into a pipe then how the edge of their knife was shaped. The art is in the hands of the artist and the tool dont need to be 100%. Training a lot is the key and good tools help. Im afraid that because of english not is my language the expression overtinking became missplaced. I meant it in the most humble way.

Bosse

 

[NirreBosse]

I thought I would show you a few nice flat over hollow grounds, bouth old and new. But it seams i dont understand how to post pictures from my iPhone into this forum.

Bosse

 

[WhittlinAway]

This posts make me so happy. The old men i knew in my youth all used knifes as tools. They wanted a sharp flat grind. They Didnt like ether hollow or convex edges but they didnt need 100% perfektion eather. So this slight concave bevel was a good start. Geting flater as time gone by and when the edge got to much convex they went to the wheel and started all over again. A few of these men could carve art but mabye still thought more about how to press tobaco into a pipe then how the edge of their knife was shaped. The art is in the hands of the artist and the tool dont need to be 100%. Training a lot is the key and good tools help. Im afraid that because of english not is my language the expression overtinking became missplaced. I meant it in the most humble way.

Bosse

Bosse, thank you for sharing these memories. I enjoyed reading them and I'm glad you're enjoying this thread.

Please rest assured, I did not take the term overthinking in a negative way.

I thought I would show you a few nice flat over hollow grounds, bouth old and new. But it seams i dont understand how to post pictures from my iPhone into this forum.

Bosse

I would love to see your pictures! Uploading directly to the forum requires a paid membership, but you can also include pictures in your posts by using a third-party image hosting service. I use Imgur's free service and have been happy with it. This post from a year ago has instructions that look like they are still relatively applicable. I did notice a couple of differneces: In the current app the camera icon in step 04 is now a plus sign in the top right corner in the current iPhone app. And the "Share Direct Link" button in step 12 is "Copy Link".

If you try it and have problems, please feel free to contact me through a visitor message on my profile and I'll try to help.