Need hollow grind info

Chris Railey

KNIFE MAKER
I have never tried a hollow grind but I intend to this weekend. Can someone give me a real quick how to? Do I hold the blade exactly perpendicular to the wheel or do you use angles like a flat grind. Do you grind your edge down first like a flat grind? Pitfalls? Thanks in advance.
 

opaul

Well-Known Member
Hey Chris this is how I have done it.
I use the center line axis to grind the initial 45 degree angle. Then find the sweet spot just under the CL axis to do the final grind. But that’s me. I’m sure there is a betterway. If you use a work rest the set up is a little different.
 

EdCaffreyMS

"The Montana Bladesmith"
Can someone give me a real quick how to?
Uh....unless you're making a straight razor.....just don't.

Do you grind your edge down first like a flat grind
You grind edge down? Wow! I've only seen one other person ever do that successfully. Every grind I do is edge up. For a hollow grind, that is doubly important to me....because that grind SHOULD intersect in/at the cutting edge. When a true hollow grind is done, it should already be sharp, and at the very most, a very light pass or two on a super fine grit belt or stone.

The first couple of passes are the most important ones, because they "set" where the hollow will be centered/begin. From that point as you grind deeper, the edges of the hollow should go towards the spine and the edge equally. The diameter of the wheel you use for hollow grinding dictates how small or large the hollow can/will be, for the thickness of the blade/stock. Very often the first couple of attempts results in grinding through the middle/center line of the blade.... that is IF you are going for a true hollow grind. Doing what I called the "bastardized" version is super easy, because you don't care about how thick the edge is, you just try to match the hollows distance from the spine on each side, and call it good. Then you grind the crap outta a huge blade flat until you get a huge chisel edge, and call it good. Is it showing that I don't like that grind? :)

Just my opinion, but hollow grinds are for very specific knives/uses. Straight razor and/or SOME culinary blades. To explain, a true hollow grind, is two arcs, one on each side of a blade, that start at the spine, and intersect AT the edge. This makes for an extremely sharp, but also a very delicate blade/edge.
What most call a "hollow grind" these days is just a bastardized version that was made popular way back when Buck knives did it on their 110 folder for all the wrong reasons. It was done to increase strength at the edge of an overly hard blade, but at the same time it built/builds in a huge amount of cutting resistance, due to the huge, obtuse edge bevels required to create an edge. What's funny, is that if you search for "knife blade grinds" or "hollow grind", you will not find what most do/call a "hollow grind". What I see the vast majority of the time is something like this, and closely resemble what you see to this day on Buck's 110 folders:

hollowgrind.jpg
Sorry for my crude rendition. I looked for my images, but couldn't find them, so I scribbled this one on my white board and took a pic. :)
 
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Chris Railey

KNIFE MAKER
You grind edge down? Wow! I've only seen one other person ever do that successfully.
Sorry I should have been more clear. I meant do you scribe a center line on the edge and grind that down to a dime’s thickness first. Like a flat grind. Or do you grind perpendicular to the wheel until you have an edge.
I am making a kitchen razor. Really its gonne be for thin slicing tomatoes and soft stuff. I guess I could just take some .063 and do a high flat grind.
I grind edge up like “normal” people.
 

EdCaffreyMS

"The Montana Bladesmith"
Was I the only one who thought you were grinding edge down? Hmmm.....OK, I can blame it on the meds! :p
For what you're making, a true hollow grind would be ideal. Yep.... centerline, then grind down until you're ready for heat treat. The big point being that after heat treat, grind that hollow/edges down to where the arcs insect at the edge, and have very tiny or no sharpening bevels.
 

EdCaffreyMS

"The Montana Bladesmith"
YUP! YUP!! Super slow and easy to prevent burning. When I do a straight razor, the finish grinding takes longer than the entire rest of the razor put together. It's also where I use a lot of belts. Not uncommon for me to go through 3-4 each from 120 to 600 finish grinding a true hollow grind.

Of course those belts are still good for other things, but you have to pay close attention, and not let the belts get too dull before changing out.

I suppose I could be a knucklehead and tell you..... you'll know it's time to change belts when you burn the blade. :p:cool:
 

opaul

Well-Known Member
Another thing about using a wheel. You can do your initial grinding to a point and then switch over to flat grinding. I believe Travis Worsh (SP?) has a video about doing this. In fact he has a video that describes how to do hollow grinds - you might want to check it out. It's under his grinder videos.
 

KenH

Well-Known Member
Ed, another good write up. I especially like your comment on Buck knives, that was always my big gripe on Buck, even though that is the folder I carried for many years.
Buck knives did it on their 110 folder for all the wrong reasons. It was done to increase strength at the edge of an overly hard blade,
 

EdCaffreyMS

"The Montana Bladesmith"
Although the Buck 110 pretty much revolutionized the knife world, it was in the infancy period of "modern" production and custom knives. It was what I consider engineered "backwards". The designers/engineers decided the knife would have a blade of 440C and be a Rc64. Problem was, the first "run" was pretty much a disaster. Many of the blades either outright broke, or the edge chipped out badly, and they had a product disaster looming if they didn't find an answer.

For whatever reason, rather then rethink the steel type or the hardness level (I suspect it all had to to with economics), they looked for a way to make the blade hold up, and they came up with what I referred to as the "Bastardized" hollow grind.
At the same time, people were just dipping their toes into custom knives, and those that were, saw what Buck was doing for grinds, and decided if it Buck was doing it, it had to be "right".

For many, that mindset still exists today. I'm not trying to belittle anyone who does those type of grinds, but what I have found is..... if you ask people who do that type of "hollow" grind why they do/use it..... 8 out of 10 will give you a reason that has nothing to do with usability. The most common answer I've gotten is ..... "Because XXXXX said it's the best grind." Or "I've always done it that way". Many think that I dislike hollow grinds.... that's not true. What I dislike is the "bastardized" version.
 

tmr

Active Member
a few years ago i went to the las vegas show n janurary........there were a few south african makers there with these gorgeous hollow ground chef style knives with wide blades full hollow.......when i asked about it they told me they used large diameter contact wheels......now burr king and others are producing 20 in contact wheel grinders......i now have a 20 in my shop with variable speed and it is producing great hollow grinds tall enough that you almost think it is a flat grind......bonus is you can finish blade grind without hand sanding
 

EdCaffreyMS

"The Montana Bladesmith"
That's always been "the quest" for Knifemakers who understand hollow grinds and their proper application(s)..... finding BIG contact wheels to properly make hollow grinds on larger blades.
As with anything in knifemaking, there is a "give-n-take" there too..... for most, the bigger the contact wheel gets, the more difficult it is to establish that beginning hollow to follow :) which meas the learning curve is longer (for some/most folks....others who have a lot of hollow grinding experience, pick up on it rather quickly). There's also the fact that many grinders have a physical size limit of contact wheel you can use....at least without making extensive mods.
So again.... things have to be "setup" to make knives in a given manner.....and then either reverted when you wanna make flat ground blades.....or you just leave what you've created, and make knives with big hollow grinds. That's just another example of that "give-n-take" thing that I always talk about. And why you see specific knifemakers "gravitate" towards a particular style and/or grind in their knives. :)
 

tmr

Active Member
Chris.......there is a video on youtube of Tom Mcginnis grindning a knife on the burr king BBA20 grinder at the Blade Show........check it out
 

MikeL

KNIFE MAKER
I use a 16” wheel a lot for my hollow grinds but, as Ed says, that is the max size for my grinder. I just wanted to add that I spend most of my time on instagram and ran across Bill Behnke who makes radius platens. For my larger hollow grinds I now use one of his 36” platens. It works well for those that might be inclined for larger hollow grinds (or maybe I should say shallower hollow grinds).
 

Chris Railey

KNIFE MAKER
Thanks for the replies, I am just doing a one off small petty knife just to do a hollow grind and to see how I like it. I think I have a good starting point now, thanks again to all.
 

Nick Riggi

Well-Known Member
Thanks for the replies, I am just doing a one off small petty knife just to do a hollow grind and to see how I like it. I think I have a good starting point now, thanks again to all.
Theses pics are all deep hollow grinds- done on an 8 inch wheel. I have since gotten a 10 inch- I find hollows easier than using the platen. Can also manipulate the way you hold the blade to the wheel when you get comfortable so that you can extend the grind height.

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Austin Thrasher

Well-Known Member
My neighbor Tony Bose also uses a 20” wheel on his Burr King. He tells me he contacted them wanting one and his was one of the first they made. He loves it.
 
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