My first FULL convex blade...... impressions so far

[KOLONEL SOPDROL]

I have read a lot about convex blades and never really paid any attention to them until I ended up with one by accident:

(I am not a knife maker at all and this is the first time I tried something like this...)


Last year I decided to make a large camp knife and try my hand at heat treatment for the first time.

I started out with a design that I had done a while ago. I had a piece of 8mm thick 5160 spring steel lying around.

(This was one of the reasons I decided to try heat treatment myself - google says 5160 is not a very difficult steel to heat treat.)


For this knife I did not want to have the profile cut using a water jet - this is a bit expensive for something I might very well screw up, so I had the blade plasma cut. A lot cheaper and faster too. Figured I would deal with the local hardening somehow...

Blade just back from plasma cutting:

I cleaned up the edges using a small belt sander:

Drilled the holes:

Then built a filing jig to do the bevels. I have a BK2 and wanted a similar bevel.

This was a lot of wasted effort and planning. The bloody steel was too thick/hard for the belt sander. It started out fine but after a while as the bevel got wider the small belt sander simply did not cut it ( so to speak).

Gave up at this point and went to bed.


The next morning I cast about me for an alternative way of removing metal and decided to tackle the knife with an angle grinder. This went a lot faster and I kind of got used to the process of eyeing the blade and grinding off a third of an inch contour at a time.

This is where I ran into my first problem - I simply could not get the bevel line straight so I compromised by going for a full convex grind.

Nobody was around to take pics and I was in a rather foul mood at this point, therefore no pics. The foul mood was because I really wanted a bevel like on my bk2....



I finished the blade with a couple of sanding disks - 80 and 120 grit - this really evened out the marks made by the grinding disk and gave a much smoother finish. Took a while since I cooled the blade every few passes.

Afterwards I went back to the small belt sander with a rather slack belt to smooth out the profile.

Made a couple of mistakes with the belt sander like stuffing up the tip of the knife, but learned a couple of tricks in the process.


Heat treatment:

Heated to what I reckoned to be cherry red then quenched in warm canola oil.

After quenching:

Tempered in the oven for two hours. About 260 deg c.

Followed by some more grinding and making the scales from micarta.






So, This is how I ended up with my first FULL CONVEX profile from spine to cutting edge - no edge bevel at all...







Unscientific Testing:

The blade is almost as hard as my Bk2 - tried scratching the two with the other knife's tip and neither really scratched the other. (Unscientific, I know....)

This evening I tested the blade on a wooden dowel - the cutting performance really impressed me. I cut up about a foot of hard dowel to see if it would dull the edge. At the end of my test the knife lost a little bit of its edge but could still shave hairs off my arm.

I then decided to compare the cutting performance with by BK2.

Procedure: holding on to the dowel with my left hand - knife in my right. Push cuts with my left thumb on the spine of the knife to sharpen the end of the dowel into a point.

Bloody hell!

The full convex grind needed FAR less effort than the saber grind of the BK2. It would take off larger pieces of wood with less effort. It could also shave off thinner slivers of wood with far more control.

Remember this is an 8mm blade compared to a 6.3 mm blade.....

The convex blade also bit into the wood at a much lower angle (probably about half) than that of the BK2.

It really felt as if I had switched to a softer wood. Did this test a couple of times back and forth between the two knives to make sure its not my imagination. Asked my wife and sons to try as well. Everyone agreed with my assessment...

For a final test I fetched my BK16:

Same thing - in terms of cutting performance to sharpen a wooden dowel, the 8mm blade with a full convex edge outperformed the BK16 too!


I really did not expect this - the BK16 is a MUCH thinner full flat grind (with an edge bevel, just like the BK2)

I think the difference is made by the edge bevel on the production knives.

Convex and BK2's edge...

Ended my testing by trying to make a feather stick out of a match.

Crappy photo, but heres a spine shot with the new knife and a BK2:

After a couple of months of use, I have really fallen in love with this convex profile. Sharpening is a breeze - I sometimes use the belt sander, sometimes I just use one of the belt sander strips on its own.

I have since convexed my BK2's edge, but it really seems to me that a convexed edge on a production knife does not give you the same performance as a full spine to edge convexed profile.



My next project will be a similar sized knife, but with a blade between 4 and 5 mm. Also with a full convex profile.

 

[LX_Emergency]

I suspect that the really difference you're experiencing is the behind the edge thickness/edge rather than the convex grind.

Factory knives are (in general) rather thick behind the edge. There's all sorts of logical reasons for this from a production standpoint. But from a performance standpoint this doesn't help.

If your blade (even an 8mm thick one) is full zero grind convex...then yes. You'll notice that as long as you're not making very deep cuts. In very deep cuts the Becker would probably beat your blade with ease of cutting.

 

[LX_Emergency]

Also....GREAt JOB on making that knife! I'm really impressed....8 freaking mm thick....man. That must've taken some patience. I think back to my first one...drawfiling and using a crappy sander and such and that was only 3mm took me forever to finish that first one.

 

[KOLONEL SOPDROL]

I suspect that the really difference you're experiencing is the behind the edge thickness/edge rather than the convex grind.

Factory knives are (in general) rather thick behind the edge. There's all sorts of logical reasons for this from a production standpoint. But from a performance standpoint this doesn't help.

If your blade (even an 8mm thick one) is full zero grind convex...then yes. You'll notice that as long as you're not making very deep cuts. In very deep cuts the Becker would probably beat your blade with ease of cutting.

I have noticed this - deep cuts into something like a carrot does not work too well.

In my limited testing it seems that the factory edge also stands up a lot better to abuse - cutting nails in two etc:

I could chop nails in two with my BK2's factory edge without any damage to the blade. But not any more with the convexed edge.

 

[LX_Emergency]

Yeah. Sounds about right. That would once again be edge thickness mostly. If you give your edge a more steep convex grind. It'll stand up to that kind of use better. But will then maybe not cut as well on smaller tasks.

It's really just a matter of balancing and weighing what you need out of the knife.

For me...an 8mm thick blade I would optimise for hard and heavy use. And I'd get a thinner blade to accompany it for smaller tasks.

Or you could have something that does decently but not great at everything.

Jack of all trades, Master of none.

 

[KOLONEL SOPDROL]

Also....GREAt JOB on making that knife! I'm really impressed....8 freaking mm thick....man. That must've taken some patience. I think back to my first one...drawfiling and using a crappy sander and such and that was only 3mm took me forever to finish that first one.

Thanks!

I have tried drawfiling on this one as well and gave up. It simply would not have worked. Without proper equipment the angle grinder was my last resort ; )

Here's a pic of the knife with its kydex sheath as well.

I would love to get some proper equipment for proper knife making, but so far this experiment turned out pretty well.

I started with a certain idea (saber grind), then had to compromise (convex the whole thing) when I got in over my head, but still the end result was a success for me.

 

[LX_Emergency]

I did the same for my first knife though. Wanted full flat...but it's a full convex now

It really looks like a very capable knife. Excellent first attempt.

 

[Natlek]

Thanks!

I have tried drawfiling on this one as well and gave up. It simply would not have worked. Without proper equipment the angle grinder was my last resort ; )

Here's a pic of the knife with its kydex sheath as well.

I would love to get some proper equipment for proper knife making, but so far this experiment turned out pretty well.

I started with a certain idea (saber grind), then had to compromise (convex the whole thing) when I got in over my head, but still the end result was a success for me.

Nice knife and welcome to the convex world :thumbup:

 

[Natlek]

I suspect that the really difference you're experiencing is the behind the edge thickness/edge rather than the convex grind.

Factory knives are (in general) rather thick behind the edge. There's all sorts of logical reasons for this from a production standpoint. But from a performance standpoint this doesn't help.

If your blade (even an 8mm thick one) is full zero grind convex...then yes. You'll notice that as long as you're not making very deep cuts. In very deep cuts the Becker would probably beat your blade with ease of cutting.

I think that there is something else too .When full flat grind blade enter in medium we cut /for example wood / blade wants to keep the angle of entry but with knive in hand is not possible to closely follows that angle and we feel resistance , usually one side of blade has greater friction with wood ......small but is there ...With convex there is no such problem, we can change the angle easier ... . . if I explained well what I mind

And of course ..... convex blade have lower surface of contact with wood and pushes aside the material he cuts ...we must count that too :thumbup:

 

[LX_Emergency]

I'm not certain what you mean there.

Convex pushing material aside makes no sense to me though. The same amount of extra force would be needed extra in pushing it aside as is saved because less surface contact is available....but I have no proof on that...just what little I know about physics. Someone out there might be able to completely proove me wrong.