Blade Chips and angle grinder

A

alephlex

Joined
May 4, 2005
Messages
151
Some advice needed.

I had some chips on a knife (440c) and I wrote before asking whether I can use a file to reprofile the edge to salvage the blade.

I've now got pictures of the knife and damage and I'm posting them here as I might be able to get better advice if you can see the blade.

What would you advise? Shall I use an angle grinder or rough cut files to tackle this problem? I don't have a belt or bench grinder I'm afraid.

Thanks

244754d51e4958298be345cb8009e477.jpg
 
ugh
I'd use the grinder, cutting perpendicular to the edge. If the hollow grind doesn't leave the stock thisn enough at that height, I'd then take the grinder and cut a new, higher hollow in the blade. Wouldn't necessarily grind the entire edge, might be able to just make a very pronounced recurve and leave the edge ahead of the chips (toward the point) intact.

But I'd buy a new knife before doing any of that anyway.
 
Its hard for me to see the pic but from the looks of it those are big ones. I'd turn them into serrations sharpening up inside them like you see on wider serration patterns rather than take away good steel in advance of using it but I'm on the conservative side when it comes to that.

I'd do it by hand also, or at the least by a variable speed belt driven grinder. A long belt will be lots cooler running than a small wheel will be. Dip the blade often in ice water to keep it cool if you use a machine of anykind.

STR
 
Considering that the primary grind failed as it was too thin, I would use a file and convert the primary to a sabre flat grind of the same height which will make it more robust. You can also flat grind on a wheel if you turn the blade sideways.

-Cliff
 
I couldn't see much from the pic, but what I did see makes me ask..."How'd you do that in the first place!??"

Jim L.
 
Amen. I think its just so thin it chipped. Grinding it will just make it thinner unless you just want to reprofile the entire edge and make the entire cutting portion of the knife less in width and bring it up to thicker parts of the primary grind.

STR
 
My primary blades are a BK10 or Ka-bar so I am definitely covered in terms of having a more robust blade normally. This chipped blade was rarely used -- it was actually a gift to me when I first started collecting knives. I have outgrown pronounced hollow grinds for fear of precisely this kind of damage. Unfortunately, I decided to use it that once for sentimental reasons -- and well, you can all see what happened.

I am thinking of changing the blade from a hollow to a flat saber grind as Cliff suggested and also of taking up STR's idea of narrowing the knife so that the cutting portion could be brought up to the thicker parts of the primary grind to prevent this happening again. I worry about making the recurve any more pronouced than it is now hardheart and serrations have never really worked out for me. So thanks for all your suggestions.

As to how the knife got the damage Jim.... Well, I was out camping in a state park in late autumn. That was ok in itself. Unfortunately all the designated camp sites in the area that were open were situated in a _valley_. The state forest service had closed off all the other camp sites including my regular one situated midway up the mountain. According to the met service, a cold front was expected the night after I was supposed to leave but I had a gut instinct that the weather was shifting faster than predicted. I was already starting to feel the temperature dipping. So I made a contingency plan and gathered together a good stock of firewood. However, because of the temperature dynamics of the valley, much of the wood at ground level was water-logged. So I looked at the banks of the river and managed to salvage old branches from floods which had been trapped in higher tree branches and had dried out.

I used the knife to lightly chop a v-notch in some of the thicker branches so that I could break the rest using another log as a fulcrum and my boots. The branches were about 2 inches thick. I had done this previously with the same knife with no problems in the tropics. Unfortunately, after a few cuts, I felt that the knife wasn't handling properly. I examined it and found the chips. This surprised me as the wood sections were fairly knot-free. I had a frost mora as back up blade and used that instead to finish the job -- which I must say it did admirably.

The two most likely factors causing the failure were perhaps
a) the thinness of the hollow grind and
b) lateral stress on the blade from insufficiently attentive chopping (I was tired)
Unlikely candidates include
c) temperature? (I don't know if it could have dipped below zero by the time this happened). This knife hadn't been used below 12 or 13 centigrade before.
d) poor heat treatment of the blade?

So that's how it happened.

This knife probably wasn't the best suited to the task at hand but it was the knife I had available and I judged it capable of taking light directed chopping. Obviously I was wrong. Although I'm surprised as it had held up before to similar use. Can any of you point us other reasons for the failure?
 
Many of you mentioned the importance of keeping the blade cool while using machine tools. This is probably a dumb question but would it help if I stuck the knife in the freezer for a half hour or something before starting the grinding? I've ground down serrations on the back of the spine before without difficulty but I worry about this particular operation because it's on the edge and it appears to me that the thinness of the stock would make heat build-up a much larger problem.

Is this an idea to consider or am I demonstrating that I am just a complete philistine here with this question?
 
Just dunk it in cold water between passes. The steel will absorb heat from grinding. It doesn't have enough mass to stay cold for very long.
Bill
 
alephlex said:
Can any of you point us other reasons for the failure?
Click to expand...

The wood could have simply been very hard and like you noted, hollow grind don't react well to sloppy chopping because lateral loads across the edge tend to focus the forces on the edge itself.

alephlex said:
... would it help if I stuck the knife in the freezer for a half hour or something before starting the grinding?
Click to expand...

Yes, at the start, but the metal will heat up rapidly due to the surrounding air and thus you will still want to cool it while grinding. With the bench grinders, you have to be fairly careful because they tend to overheat blades way easier than a belt sander. Just grind a butter knife or similar first and see what it takes to overheat that. All steels will behave essentially the same in that regard.

-Cliff
 
But, other than that, how was the camping?

Jim L.

alephlex said:
<snip>
As to how the knife got the damage Jim.... Well, I was out camping in a state park in late autumn. That was ok in itself. Unfortunately all the designated camp sites in the area that were open were situated in a _valley_. The state forest service had closed off all the other camp sites including my regular one situated midway up the mountain. According to the met service, a cold front was expected the night after I was supposed to leave but I had a gut instinct that the weather was shifting faster than predicted. I was already starting to feel the temperature dipping. So I made a contingency plan and gathered together a good stock of firewood. However, because of the temperature dynamics of the valley, much of the wood at ground level was water-logged. So I looked at the banks of the river and managed to salvage old branches from floods which had been trapped in higher tree branches and had dried out.
<snip>
Click to expand...
 
Just a quick note to thank everyone who offered advice on this thread.

I have reprofiled the edge of the knife. I use an angle grinder for the basic shaping and then moved on to files for more controlled work. I didn't bother to give a fine polish on the knife because it looks like I'll be using it now.

Here are pictures of the blade before and after reprofiling.
Original chipped blade
244754d51e4958298be345cb8009e477.jpg


Reprofiled blade
2270be553d5c7e991bcec9d8cbba6353.jpg


If the pictures are too small, larger versions of the same photos are available here:
http://www.fotothing.com/alephex

I want to state that I wouln't have thought of embarking on this project on my own without the advice of members of BF. In fact, I had actually approached 2 knife makers in Australia via email for a reprofiling job.I only took things into my own hands because they didn't bother replying. However, the good thing is that I've saved a huge lot of $$$ and learnt something new along the way. Also because the knife is now a sort of hybrid between a hollow and a flat grind (do we call this a very thick hollow grind?), it is actually much stronger than it was with a very extreme hollow grind and I can now use it with much more confidence. I won't treat it in the same way as a BK10 but it has become much more useful now.

Thanks guys.
 
Nice to see new life given to a fairly heavily used blade. These are usually just thrown out but there is still a lot of cutting left in them.

-Cliff
 
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