Blade Grinds, Edges and Geometry

[Stuart Mitchell]

Hopefully this could develop to be a thread that members can access for guidance?

There are a load of these diagrams online, I quite like this one though as it clearly shows the options that I suspect most here make or use. It is by no means definitive, you can do whatever you want, you could put a secondary on a convex, I have regularly brought a full flat to edge by means of a convex. Even my Scandi's are hollow, bearing in mind that historically these would have been done on a stone, not a grinder with a flat platen.

I think the Full Hollow, the Full Flat and the Sabre though are spot on, the most important comment I'd make about the attached refers to the Sabre, they can be hollow too and regularly are.

 

[Border]

Which grind have you used for the Muntjax and YDS knives Stuart?

 

[Stuart Mitchell]

Which grind have you used for the Muntjax and YDS knives Stuart?

The Full Flat, I suspect that gets used on 80% of what I make.

 

[FISH BOY]

Very interesting, but please can you give a bit more detail to the term hollow.

 

[Tim.243]

Very interesting, but please can you give a bit more detail to the term hollow.

Think in terms of these words Russ.
Concave. the profile of a cave so hollow (grind) radius or inside of a circle.
Convex, the reverse of concave the outside of a circle.

 

[Stuart Mitchell]

Very interesting, but please can you give a bit more detail to the term hollow.

I'll try.

Imagine I have a grinding wheel rotating and I grind a blade on the surface of that wheel, the profile of the grind will be the same as the circumference of that wheel, so it will be concave, as Tim rightly says.

Have a look at the attached photo.

 

[Stuart Mitchell]

I just tried to edit the first (don't know why I can't?) to say that this at the Stuart Mitchell Knives thread of grinds and edges etc, other makers jump in, add your knowledge.

 

[Stuart Mitchell]

Imagine I have a grinding wheel rotating and I grind a blade on the surface of that wheel, the profile of the grind will be the same as the circumference of that wheel, so it will be concave, as Tim rightly says.

Just to complicate further I should also point out that this is not always the case, you can grind 'flat' on the surface/circumference of a wheel, I'll get some photos today to explain better, you know what they say about pictures and a thousand words.

 

[Overlay]

Morning Stuart
for a 4” or less blade for use on Roe/Muntjac/CWD what grind would you recommend for re sharpening, holding an edge and fit for purpose

most of mine are flat grind with a couple that have a micro bevel flat grind

scandi, hollow grind I do find a problem to get sharp, I’ve used lansky guided sharpeners for years but just recently changed to the worksharp
system with variable grits and found that a lot better / easier to maintain the edge

cheers

phil

 

[deerstalker.308]

Question for the idiot in the room, but the image in post 1, full flat grind, appears to have a micro bevel to it if you zoom in, Is that correct, or would a classic full flat simply taper to an edge in one straight line?

 

[Tim.243]

Just to complicate further I should also point out that this is not always the case, you can grind 'flat' on the surface/circumference of a wheel, I'll get some photos today to explain better, you know what they say about pictures and a thousand words.

Just to add more confusion Stuart lol

Convex profile to form a concave profile

Concave rake clearance (as it was nylon 66 )

Front Rake clearance as well lol

Free hand ground

 

[Stuart Mitchell]

Morning Stuart
for a 4” or less blade for use on Roe/Muntjac/CWD what grind would you recommend for re sharpening, holding an edge and fit for purpose

most of mine are flat grind with a couple that have a micro bevel flat grind

scandi, hollow grind I do find a problem to get sharp, I’ve used lansky guided sharpeners for years but just recently changed to the worksharp
system with variable grits and found that a lot better / easier to maintain the edge

cheers

phil

I'd go full flat with micro secondary, I do like a hollow but the full flat gets a bit more material just behind the edge, it is a little stronger... that said for soft stuff, flesh work, you'll not beat a hollow, just take a tad more care around the harder stuff.

I wonder if your different and varied experiences of re sharpening are due to the knives/brands rather than the grinds/geometry?

 

[Stuart Mitchell]

Question for the idiot in the room, but the image in post 1, full flat grind, appears to have a micro bevel to it if you zoom in, Is that correct, or would a classic full flat simply taper to an edge in one straight line?

Yes, it has a micro bevel, a full flat with no micro, as in straight line as you say, would worry me.

 

[deerstalker.308]

Just to add more confusion Stuart lol

Convex profile to form a concave profile

Concave rake clearance (as it was nylon 66 )

Front Rake clearance as well lol

Free hand ground

View attachment 263053

View attachment 263054

If that’s your knife sharpening Tim no wonder you have wrists like a 17 year old lad locked in his bedroom…!

 

[deerstalker.308]

Yes, it has a micro bevel, a full flat with no micro, as in straight line as you say, would worry me.

Thanks

 

[Tim.243]

If that’s your knife sharpening Tim no wonder you have wrists like a 17 year old lad locked in his bedroom…!

A concave reply Andy....Hollow

Any way back to Stuarts thread as you don't need to add any more micro replies......

Back to SM

 

[Overlay]

I'd go full flat with micro secondary, I do like a hollow but the full flat gets a bit more material just behind the edge, it is a little stronger... that said for soft stuff, flesh work, you'll not beat a hollow, just take a tad more care around the harder stuff.

I wonder if your different and varied experiences of re sharpening are due to the knives/brands rather than the grinds/geometry?

Hi Stuart
blade wise I have one of yours, Danum, Smyth, Emberleaf, Alan Wood, Zabrowski all are cracking blades and sharp

your blade, Danum, Alan wood i can get a really good edge on these that lasts and is really sharp the others are ok sharp
i also have a McMillan caping 21/2“ blade that is like a scalpel and been using it for years and it just needs a brush up now and then

I've Got a Wellie full of other makes, that have either fallen by the wayside or I got it wrong again on the sharp up, so there is always something to do

cheers

phil

 

[Stuart Mitchell]

Hi Stuart
blade wise I have one of yours, Danum, Smyth, Emberleaf, Alan Wood, Zabrowski all are cracking blades and sharp

your blade, Danum, Alan wood i can get a really good edge on these that lasts and is really sharp the others are ok sharp
i also have a McMillan caping 21/2“ blade that is like a scalpel and been using it for years and it just needs a brush up now and then

I've Got a Wellie full of other makes, that have either fallen by the wayside or I got it wrong again on the sharp up, so there is always something to do

cheers

phil

Why don't you stick them all in a bag and come and have a day in Sheffield, they'll be sharp when you leave

 

[sh1kar]

Apart from the profile of the grind. Say a little about the angle of edge. 15-30 degs say. And why. Related to profile or the steel used?

 

[Stuart Mitchell]

Apart from the profile of the grind. Say a little about the angle of edge. 15-30 degs say. And why. Related to profile or the steel used?

Good idea, I'll have a look later, I have a mate in the workshop today, we are working on a rather funky commando knife project