Primary Bevel Suggestions

R

Ricky-O

Joined
Oct 30, 2021
Messages
61
I am a fairly new knife maker and have been making kitchen knives out of AEB-L. On some of my knives I’ve made a flat primary bevel from the spine to the cutting edge. So if my knife is about 1.75” wide and about .1” thick, the primary bevel was about 1.6 degrees. I have noticed that food does stick to these knives at times.

On other knives I’ve made a primary bevel that is about half as long, and so on a 1.75” blade that is .1” thick, the primary bevel is about 3.5 degrees or so.

I’ve also experimented with making the primary bevel even thicker and using a S grind. So if my blade is about 1.75” wide and .1” thick, I tried a primary bevel of about 4.5 degrees, and then used a 36” radius platen to make a shallow S grind. (I haven’t tried this one in the kitchen yet). On all of these I try to get the edge to somewhere between .006” and .009”.

Since I am very new at all of this, I thought I’d ask for advice as to what primary bevel angle people generally use for kitchen knives that are about .1” thick. I’m wondering whether the most important thing is to pick a geometry, such as full flat grind or primary bevel half the width of the knife, or if it is more important to pick a certain primary bevel angle and let that determine how far up the bevel goes towards the spine. Also, if I want to do an S grind, should I make the primary bevel steeper than I would if it wasn’t an S grind, or should the primary bevel remain the same?
 
I use a shallow convex. To the casual observer, it comes across as a full flat grind, but under closer inspection there is a slight convex about 1/3 the width of the blade above the edge ((2/3) down from the spine).
 
I haven't yet done a convex grind, so I want to make sure I understand you. If the steel were .1" thick at the spine, it would stay about .1" thick for 2/3 the width of the blade, and then the last 1/3 would be the convex grind?
Thanks!
 
My view is that food sticking is more about cutting technique than geometry. Proper slicing will limit it sticking, but some foods are just sticky. Make it thin and sharp so you can focus on cutting
Doing a thick enough S grind to stop it will cause wedging issues
 
when doing an s grind, does one typically flat grind the whole thing first?
 
Ricky-O said:
I haven't yet done a convex grind, so I want to make sure I understand you. If the steel were .1" thick at the spine, it would stay about .1" thick for 2/3 the width of the blade, and then the last 1/3 would be the convex grind?
Thanks!
Click to expand...
To execute the grind he's describing, I would flat grind until the edge is 0.03" (spine still 0.100"). Then convex the lower 1/3 to zero.
 
I've used F3 (amazon) and S2-32 (Mcmaster Carr) Felt on a platen to give a nice convex edge. Most of my blades are around 2-2.5" tall for a 210-255mm chefs knife/gyuto/kiritsuke and from .090-.10" stock.

What I have found is that a full flat grind will stick. I have done a S grind using a 36" radius platen for the upper 2/3 of the blade and a convex going down into the edge. It will sometimes wedge a bit on taller/harder ingredients and food release is just OK. I have done full convex and getting it nice and thin behind the edge and it does pretty well. Some wet foods my stick on the blade, but they come off with a flick; they aren't suction cupped to the blade. I have also done the 36" radius platen grind for about 4/5 of the blade height and then the convex to the edge. The shoulder where the S is the thickest is around 1cm or so up the blade face and around .040-.045" thick. The concave portion gets a bit thinner than that and it goes up to the spine. Food penetration is excellent, and release is very good typically. Again, wet stuff like zucchini will stay on the blade, but if I am cutting quickly, it often flies off the blade on it's own or gets pushed up on the next cut. It's not suction cup stuck to the blade.

Cutting Technique has a lot to play with food release, wedging and food penetration, too.

Full convex .10" Nitro V to the edge:
opal funy.jpg

S grind 52100:
s hollow.jpg
Choil from the same 52100; I start the S grind a bit forward of the heel:
s hollow 2.jpg

Magnacut S Grind similar to the 52100 (wide hollow, shallow convex bevel). This is .040 at the thickest where the convex and concave meet up:
mcc handle.jpg

1/8" spine full convex 80CRV2:
8c2.jpg

And a damascus blade where I did the 2/3 hollow and 1/3 convex:
HHH S.jpgchoil HHH.jpg

I ended up thinning the damascus one down and widening the S hollow since it didn't perform as well. Wedged more, food release was just OK.
 
Taz, thanks for those clear photos. It sorta looks like you use the 36" radius platen to do a full flat grind until the edge is down to perhaps .030" or .040", then finish with a convex grind to zero? My understanding of the convex grind is a 3/16" to 1/4" felt on platen which allows a radius for the bevel? Am I anything close? I'm liking that idea of the "S" grind.
 
This is an 80CRV2 S Grind I did, with cutting technique like this, it performs really well. If the slices can be pushed away from the knife, performance is much better. So in hard ingredients, starting one end and working your way down will work much better than trying to cut it in half first.

If the slices can move apart, straight chop does pretty well:

A K tip S grind vs a wet potato:

For me, there is a difference when food is suction cup stuck to the blade versus it stays on the blade, but comes off easily, like with a wrist flick or by the next slice cut. Wet foods and soft foods do this more and can conform into the hollow S curve, so sometimes the full convex does better, or the lower convex and then the full thickness. A lot of Japanese knives with a Kurouchi finish have a grind about half way up the blade as a steep convex, then it goes flat or slightly concave from the bevel to the spine. I have tried several of these and the food release is decent, but the wedging in thicker/harder foods is really bad. I do a lot with Rutabage, Turnips and other root veg that are hard and tall, so I tend to favor a thinner lasery S grind blade. So a lot depends on what people are cutting!

I use sweet potato, regular potato, onions, carrots and apples typically to see how the knife cuts. Mushrooms and peppers give a good idea of food penetration

More convex and then the shoulder at the top of the blade can help push food away, but some softer foods will still stay on the blade. It may wedge or crack on taller/harder foods, too.

Full convex with 1/8" spine. It took a lot of testing to get the grind where it performed well with a thicker/heavier blade!
https://youtube.com/shorts/3CKOzsiJJQk?si=sAqkV0awUU-qQxVV
https://youtube.com/shorts/BN_e1A37_Pw?si=yq_L_EME3n6yuWBe
https://youtube.com/shorts/n5_8UW-VMHk?si=qbafDan6XtoS46yi
https://youtube.com/shorts/wh_V4zKKiZI?si=c-WtW6UjxnNXF1nG
https://youtube.com/shorts/pY2mTQit7nM?si=nZUgTO3e3KJWzIkc

For my laser thin S grinds, I tried to mimic a Shosui Takeda knife where the hollow section is around 4/5 of the blade height and the convex edge bevel is around 1/5 of the blade height. I tried grinding the hollow first and then the blade, but now I get my main blade grind mostly done and then add in the hollow; less material to remove with the Radius platen, less heat generated and I don't have to go back and forth as much.

I tried doing different thickness at the shoulder where the Convex and Concave meet; I tried .06, .05 and .04. The .04 definetly was better performing and less wedging, so I try to go between .030 and .045 at that shoulder around 10mm-12mm up the blade height and then do the rest as the hollow. The blades where I did around 16-17mm convex and then the remainder hollow didn't perform as well; more wedgey.

Blade finish can play a role, too. A coarser finish may do better or worse than a more polished one. I try to go up to a fairly high belt satin finish; food seems more likely to slip off compared to a lower grit finish that has more texture/grip to it. The soft felt platens make it easier to go to a finer belt finish without the splice bump messing things up, or the VSM Compact Grain belts, which are thicker and have less belt splice bump, or Trizact Gators or Ceramic Norax.
 
Thanks Taz, the 2nd photo shows the grind very nicely - and that style in a petty chef size is my wife's favorite knife.

Ken H>
 
Ricky-O said:
I haven't yet done a convex grind, so I want to make sure I understand you. If the steel were .1" thick at the spine, it would stay about .1" thick for 2/3 the width of the blade, and then the last 1/3 would be the convex grind?
Thanks!
Click to expand...
No, it's a full flat grind that convexes slightly above the edge. So in reality, it isn't a full flat. It is more of a convex. Sort of like the S grind but without the hollow grind above the convex. If I had a large radius platen or wheel, I would more than likely use it, much like Taz's info above.
 
A convex can be just above the edge area and transition info a flat grind, or be fully convex from spine to edge and vary in the convexing. It's about the belt having some give/slack to it to produce a rounded grind than a straight flat grind.

A Rotary Platen using a rubber belt between metal rollers under the actual grinding belt. This supports the grinding belt and can be adjusted for the amount of give the rubber and sanding belt have to adjust the amount of convexing. The distance between the rollers also effect the amount of convexing; most Rotary Platens have 4 rollers, usually at different distances apart from each other to give more adjustment. The Rotary Platens usually around $350-$2000. This has the best and most repeatable adjustment, but it's expensive!

F3 felt is fairly soft and gives easily to give more of a convex with less pressure. The S2-32 felt is much harder/firmer and gives less of a convex to the grinding surface. Thick leather can be used as well since it has some give and can help create a convex edge; it may be a touch harder than the S2-32, but it depends on the piece of leather!

Others use a section of a non woven abrasive belt under a piece of leather for some give, but more firmness from the leather. Leather edges hold up better than the felt. Mant start Convex grinds as flat grinds to get the bulk of the grinding done on a normal platen and get the plunges cleaned up and then transition to a convex grind from there with a rotary or other soft platen.

You could also to the opposite of a Radius Platen and shape a platen so it has a concave surface to it to grind a convex edge, but it will generate a LOT of heat/friction!

Some companies slack belt grind on an area just above/below a contact wheel where the belt has some give to it for a convex grind, too. I saw someone who added a 2nd contact wheel to a 2nd tool arm to leave a 3-4" gap between the 2 wheels to mimic a rotary platen, but without the supporting rubber belt. By adjusting the 2 tool arms in and out and varying the distance apart, they could control the tension on the belt and convex it applied a bit more than felt/leather could!

Lots of different ways to do it at various price points!
 
I made leather platen faces for convex shaping. They hang from the top of the platen and are held in place by the belt, different thicknesses. They hang over the radial platen as well which is nice for those hollow grinds
 
I use 1/4" F3 and S2-32 (McMaster Carr has the S2-32 and other firmnesses). Leather, I try to get 8-9oz at least if not thicker, but leather varies a lot more than the felt does in terms of firmness. I have some F3 that is worn down a good bit and still works pretty well, but I would go with 1/4". 1/8" may have the give restricted by the thinner material and will need replacing more often.
 
I used double sided carpet tape to attach the soft platens to a mild steel backer, which goes onto my magnetic platen face set up. I also put leather on the Radius platen after the rough grinding to get a cleaner belt finish if I am not hand sanding the hollow.
 
You must log in or register to reply here.
Back
Top