Ginding a Chopper

[Big Chris]

I have just ground and heat treated my first chopper. It's made from a .200 piece of S7 2 inches tall, heat treated and drawn back to 58 the first time. The edge chipped pretty bad during my first tests, I determined it to be too hard so I drew back a little more to around 56 and reground the edge. This time during testing the edge pushed off to the side. Both these failures were from chopping knots. The edge was ground to .020 to .025 prior to sharpening. My question is, is this too thin, is this this steels character, what thickness do you normally grind your bevel to prior to sharpening. I chose S7 specifically for its shock-resisting capbilities.

Thanks for your help.
Chris

 

[AcridSaint]

Hi Chris - S7 has a high impact resistance but generally isn't used in sections as thin as a knife edge. I have mentioned here before that I speculate S7 won't hold up well to impacts in thin sections and this seems to bolster the view. I think you'd be much better off with CPM3V or A2 in this sort of application.

 

[Big Chris]

I was curious about that. 3V is the next choice as well as O1 just for comparison.
Thanks for the reply.

Chris

 

[foxx]

I have one knife and one hawk made from S7, they are both 3/8" thick. The hawk is not sharp, it bounced off of a tree stump, where other hawks/knives/machetes would bite in.
The knife is sharp enough to cut, it got me once. It's still a "thick" edge, don't have a specific measure. It's a hard use blade, limited edition, so, it's unused.
I'm no expert, but for chopping through knots, with that thin of an edge, lots of steels are going to roll. Especially as thin as you have yours.
The GGG Battle Hawk I have is made to beat through cinderblock, trash cars, doors, etc..
It weights 44 oz, and packs a crazy punch. The first time I used the spike was on the same tree stump, it sunk in deep, but slightly rolled/bent the tip.
The hardness of the Battle Hawk is 56-58. I think the "shock resistence" is more for the overall tool, not the edge. You don't want vibrations to snap impact tools.
My favorite chopper is made from forged 5160, spring steel. I can beat on wood, no chips no rolls.
I hope some of this helps.

 

[Bruce Culberson]

Crisber - first off I've never used S7.

I use 5160 for choppers (and sometimes a 6 foot saw blade that is 0.280" thick) and grind the edge to around 0.02" to 0.025" then sharpen. I like to test them on moose antler to make sure the edge is strong.

Sounds to me like either the S7 isn't working for you, or the heat treat isn't right.

Bruce