Is using a flat file a heresy?

B

BLM4L

Joined
Jan 19, 2006
Messages
194
Well, I have never tried this on anything other than a old beater Machete.
Has anyone used a flat file to reshape a blade on any knife, other than a cheap kitchen or a beater knife, and then finished up with regular stones, or Sypderco sharpener? If so, did it turn out ok, or would the file pretty much ruin a knife?
 
In the past, I have used a file to sharpen large knives like an old Western Bowie. A fine 10 inch mill bastard file worked quite well, actually. I don't think that I'd use one on a good knife other than perhaps for re-profiling a ruined edge, but if you keep your head out of your armpit, I don't see how it could do any harm. Many folks here use bench grinders and belt sanders, and I don't believe that a file could do nearly as much damage, nearly as quickly as one of those. Just MHO, and I AM an amateur, so take any advice I give with a grain of salt.

Ben
 
Good advice. Definitely will keep my eyes on the knife if I try this. If I do I will report back.
 
I use files all the time for knives with thick or uneven edges or for edge rebeveling (sorry Bill ;)).

I clamp the file onto the bench and use it as I would a stone and it works well for me. I then finish the sharpening with stones.
 
i use a file on machetes/axes/lawnmower blades but i cant say i have ever used (or needed to use) a file on a knife.
 
If a knife can be filed and you need to change the angle it is often much more efficient than using even the most coarse hone. The edge, if properly formed also has very high sharpness and edge retention for slicing.

-Cliff
 
Excellent question. Do you mean on fairly harder steels -- I mean harder than high carbon or AUS 8?
 
Even the better files tend to be not overly effective on the 60+ HRC steels, especially the high carbide ones. It is much more effective to use a really coarse stone.

-Cliff
 
Depending on what type of steel and how hard it is you may ruin your file if you try to shape the blade. Hardened steels can only be cut with diamond files and diamond stones.

I know, I tried to file some of my 440C knives that were treated by Paul Bos to 58-59RC just to see what would happen. It destroyed the teeth on the file. The coarse diamond stones I have work much better.
On softer steel (lawnmower blades and less expensive knives) the steel isn't that hard because it was machined on an assembly line. The steel is soft so it dosent wear out their manufacturing equipment. So it all depends on the knife you are working with.
That being said I have reprofiled broken AUS 8 knives with double cut bastard files and fine 5" Nicholson files. It all depends on the steel.
 
One of the ways to guesstimate the hardness of a steel is to try and sharpen it with a file. A new high quality file will work up around to around 58RC. As Cliff points out you can forget it for 60RC or higher.

I have done this often on larger blades like kitchen knives. I like to do it on black-coated tactical blades since it can give you a really nice flat bevel. It does a much cleaner job than a coarse abrasive. If the blade has a rather obtuse grind and you don't want to bother reprofiling it to a lower angle a raw file finish slices well.
 
Well, I guess I will swim against the stream. I don't like to use a file even for the steels that are soft enough. It leaves to deep a scratch pattern for my liking. It is nice and fast for reprofiling, but I think you lose the time you've gained trying to polish out the scratch pattern, but that is probably just me.
 
I have used files for sharpening cheap kitchen knives but not nice knives.

I tested a Bahco file and it cut rapidly into 154CM of a MOD tempest blade that had been previously scrapped. I was surprised how soft it was compared to the file. I think the blade was supposed to be 59-60 RC.
 
Phil Wilson has tested a lot of production knives and found that some of the 60 HRC blades are as soft as 55 HRC.

-Cliff
 
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