can someone please walk me through convex grinds?

SHOKR

SHOKR

Well-Known Member
Hey guys

Here is what i know, convex grinds tend to be tougher at the relative cost of sharpness, like axes and choppers

Was told best way to achieve it is do flat bevel then use slack.
Thats it

What else to know about them? (use and how to do make them)
Also why do convex on smaller knives? Is sharpening on slack considered convex? Well so many questions, if someone can help or point mevin a directoon of tutorial or guide would be great

Thanks
 
Here's my very limited take on it...

A full convex grind is going to be like an axe grind. Going all the way to a zero edge every time, no secondary bevel for sharpening. SUPER stout and very sharp, but once it dulls, you have to regrind to put on a fresh edge.

A flat grind with convex edge (this is how I have started making my knives)... Is you standard flat grind, leaving about 0.020" of thickness at the cutting edge. Then using slack belts, you put the convex edge on only the cutting edge of the knife. To me this is the best of both worlds... you get the strength of a convex edge, without all the extra thickness to 'wedge' into whatever you are cutting.
 
Yes and no. You can do a flat primary grind then use a slack belt for the secondary grind or you can use a slack belt and take the primary grind all the way out to the edge. There's no rule that says that you can't then, in either case, establish a final bevel on a stone or you can maintain the edge with a slack belt. It's all going to depend on the use of the blade and the final angle of the edge. If it works for you, it works.

Doug
 
A convex edge need not be less fine than a 'standard edge... Here is how I'd do it if I wasn't setting up the bevels on the anvil:

I would give the knife a 'scandi grind', ie. I would grind first the actual edge bevel at about 12 degrees all the way down to a burr. This will give you a grind that goes about halfway or less up the blade width, like a sabre grind. I would then grind away the 'hump', the area where the two flats meet, pushing the grind further up the blade but not all the way down to the cutting edge. The last steps would be rounding the resulting bevel transitions until the blade had an even, curving bevel all the way from the edge to the back of the blade. Using various strops (sandpaper backed by a soft material, and finally leather with polishing compound) I would remove the burr and refine the edge. This will result in a frighteningly sharp edge with plenty of meat left behind the edge to support it, which is the primary benefit of a convex grind. If the blade were for heavy chopping, I'd do the same thing but the initial bevel would be 15-20 degrees for added strength... this is what I'd suggest for those throwing blades you are making. I've never liked using the slack belt for anything but handle shaping, but that's just my preference.
 
Thanks a lot George!

I'll need to read this more in detail since you mentioned bunch of stuff thats new to me but i think i got the general idea :)
 
Shokr,
As George stated a Convex grind doesn't need to give up anything in fineness of the cutting of the knife. It also increases strength and cutting ability similar to the way distal tapering a knife blade does with improvements.

You can convex the entire blade from spine to a bullet nose edge or only do the bottom 1/4 or 1/3rd of the blade of a flat grind depending on the end use of the knife. Also I have Convexed only on the Chisel grind side of culinary knives with excellent results.

I would suggest you take one of your full flat ground blades that you aren't' happy with for some comedic reason and convex the bottom 1/3 or so on both sides to test and get a feel for how this grind can improve your cutting chopping & strength of the blade.

The knife maker legends,
Bill Moran, Ed Fowler & Wayne Goddard and others have all tested & written extensively on the subject of the benefits & Techniques of convexing knives and sharpening and I would read up on what they have to say this topic.

Also you are going to need to take the Flat Platen out of your grinder for this!:biggrin:

Laurence

www.rhinoknives.com
 
Lol Laurence youre enjoyong that part arent you

Thanks for the info, and i just might try that, so far i only did convex on sharpening (only today and yesterday really)
But will probably try this with the next 'rejected' blade, which probably wont take long

I have wayne's book, i'll check it out sometime... I hate reading for information tho, get sleepy or distracted
 
Shawn Hatcher said:
Not to sound too pedantic, but I'd be more worried about this than anything having to do with convex grinds.
Click to expand...

This also concerns me.
I taught myself how to make my first few knives by reading,

' How To Make Custom Knives ", By Tim Mc Creight. Books are still the most marvelous for storing and retrieving information ever invented! All you need is daylight or a candle and your are good to go!

Laurence

www.rhinoknives.com
 
Lol ok ok relax guys, i AM reading for info, just prefer if its 'short', books seem endless a bit, i love reading, but when its technical i tend to drift off, and by off i mean OFF!! I learn way better through watching or looking than reading.

But books are our friends!
 
Shokr,
Do not worry my friend! Bill Moran, Ed Fowler & Wayne Goddard are much more hands on craftsman than pointy headed academics types. Their writings have pictures too! :biggrin: LOL.

All joking aside, I am not referring to reading endless pages of just technical data,Thou those have their place when learning about heat treating and composition of steels etc,

Laurence

www.rhinoknives.com
 
Well just as long as there are pictures :eek:

I read a bit in loveless' and goddard's books, learned A LOT, will get back to them again :)

Thanks Laurence!
 
SHOKR said:
I learn way better through watching or looking than reading.
Click to expand...

rhinoknives said:
Bill Moran, Ed Fowler & Wayne Goddard are much more hands on craftsman than pointy headed academics types.
Click to expand...

In my short time as a knifemaker I've come to believe that the only way to get better is by "doing" and being hands on. Reading, watching, listening . . . all very important things, but it's all theoritical until you start doing.

The internet is an amazing thing and the sharing of knowledge by other makers is a tremendous asset. But it all boils down to shop time. I'm a big believer in Malcolm Gladwell's 10,000-Hour Rule. You can't put 10,000 hours into any one thing and NOT become very proficient at it. There are no shortcuts, just time and effort.
 
Shawn Hatcher said:
In my short time as a knifemaker I've come to believe that the only way to get better is by "doing" and being hands on. Reading, watching, listening . . . all very important things, but it's all theoritical until you start doing.

The internet is an amazing thing and the sharing of knowledge by other makers is a tremendous asset. But it all boils down to shop time. I'm a big believer in Malcolm Gladwell's 10,000-Hour Rule. You can't put 10,000 hours into any one thing and NOT become very proficient at it. There are no shortcuts, just time and effort.
Click to expand...

One analogy that I heard from a US Navy Top Gun Jet fighter pilot before Gulf war one, when pressed about our superior technology
over older planes the Iraqi pilots would be flying?

"Nothing replaces air under your butt! " was his reply.
That always stayed with me all of my endeavors and coincides with the 10.000 hour rule.

Laurence

www.rhinoknives.com
 
Shawn Hatcher said:
I'm a big believer in Malcolm Gladwell's 10,000-Hour Rule. You can't put 10,000 hours into any one thing and NOT become very proficient at it. There are no shortcuts, just time and effort.
Click to expand...

ive been meaning to read that book!!

actually i have another thing i believe in and TRY to live by (not doing a great job at it yet tho) read an hour a day in your field and eventually you will shoot to the top (plus practice of course when needed)
 
Ed,
Thanks for correcting me on this finer point of convex grinding. I use a Rotary Platen mostly for convex grinding these days. I started do it by slack belt after reading some literature by Bill and you over 16 plus years ago.

Sometimes I still enjoy just dropping out the platen and convexing the bottom 1/3 of my blades.

Laurence

www.rhinoknives.com
 
thanks Ed, alas light hand is not something i possess, for now :)

i still do lots of mistakes doing simple flat grinding even!
 
You must log in or register to reply here.
Back
Top