Sharpening Question

D

Dune

Joined
Jan 23, 2006
Messages
62
I have a BM Grip 551 (old version in 440C) that I can get shaving sharp on my waterstones. The only problem is that it will only keep this edge for a week at the most; the edge will still be nice, but not shaving sharp. Is this just a function of the steel or is there something that I can do to make the good edge last longer?
 
Opening letters, an occasional package, tape, things like that. Nothing that I'd consider hard use or anything along those lines.
 
I have an older Mini-Grip that is 440C. I run into the same problems cutting the same things. I just bought a DMT Course benchstone at lunch and am about to get to work on it now. I hope it will help! I plan to finish the edge out with a Sharpmaker. I will let you know how it goes.
 
From what I understand, thats just a function of the steel. I don't know much about 440C, but I believe it's a relatively soft stainless, right? Just because it's not quite as razor sharp a week later doesn't neccesarily mean it needs to be re-sharpened, when you create an edge that's shaving sharp you've also created an extremely thin edge which is prone to folding over during use. You could try steeling it after you've discovered it's not quite as keen as you'd like. Feel for the folded over edge with your thumb and steel it accordingly.

I'm not a butcher, so my knives don't require a hair popping edge and frankly a straight razor edge is just too fragile for most kinds of every day use (at least in my experience anyway). I just keep a nice solid work edge that will cut tape, cardboard, rope...you know, the usual.

anyway, those are me thoughts. Hope it helps.
 
440C is not that soft. It's one of those steels that don't hold an ultra fine edge, but will hold that second, less sharp edge for a decent amount of time
 
Dune said:
I have a BM Grip 551 (old version in 440C) that I can get shaving sharp on my waterstones. The only problem is that it will only keep this edge for a week at the most; the edge will still be nice, but not shaving sharp. Is this just a function of the steel or is there something that I can do to make the good edge last longer?
Click to expand...
I use a smith diamond shapener with a course and fine edge..it is collapsable and very compact..it gives a true great edge...I also use a smal leather strap to put the shaving edge on my blades..as far as 440 steel..Im not a big fan..I like carbon steel because it holds the best edge and has been proven for about 2000 years...However as someone else said..when you produce a true shaving edge you also produce a very fine edge that may dull with hard use...Just keep honing when you feel that you need to and deciede what type of edge you want for what purpose...Ashaving edge is not great for hardcore everday use unless you want to really take the time to hone it every couple of days..I dont know what you are cutting but if it is rope or something that will dull an edge...you may think about putting a courser edge on your EDC. Hope this helps.:thumbup:
 
Well two things are the obvious issues here. Non of which have anything to do with the steel. You may safely assume that the steel is NOT the issue here (except if you happen to get one with a faulty heat treat which is really not very likely).
A) you are simply doing more with your knife than you think. Tape is usually no problem, but cardboard and lots of paper will take the shaving edge off a blade relatively quickly, since both (especially cartboard) are pretty abrasive. As Cliff has pointed out many times, blunting is very non-linear. While the really sweet edge is destroyed very quickly, a very serviceable edge remains for a long time, if the steel is decent.
B) You are leaving the edge with a small burr or wire edge. This burr will feel very sharp initially and will be an ideal push cutter (Jeff Clark has pointed out many times that this is what you really want for a straight razor), but it will fold over very easily and will blunt very quickly. On your final hone, try to raise the edge angle at least 5 deg for a few very light passes to take off the burr. Then go back to your original angle for a few more passes. You must take care and it takes a while to develop a feel for it that your strokes at an elevated angle do not change the edge geometry appreciably. At the higher angle it will take longer to build a burr but it is still possible and you don't want that either: You need very few passes with very little pressure. When you go back to your original angle, you just want to finish the edge of polish out the geometry and set the edge. That will also take very few strokes with your normal pressure. If you hone too much, you will simply rebuild the burr and all was for nought.
 
My guess is that you are not getting the burr off the edge when you sharpen if you are getting a dull edge in a week. Either that or someone put the knife on a grinder and overheated it taking the temper out of it.

Here is a link about knife steel that is rather techy and geared towards the maker.

440C is almost identical to ATS34/154CM except it has (1) less molybdenum (spelling?), and (2) more chromium. It is not to be confused with the A and B 440 steels which have much less carbon. A properly hardened and tempered 440C blade will have a Rockwell hardness of Rc60 (compare that to what you have now and see if your knife is that good). It should have excellent edge retention.

http://www.ajh-knives.com/metals.html

You'll have to page down a little to the 440 sections but also look at the ATS34 section.


Benchmade sells a great $30 knife in 440C called a Pika which I recommend to new knife buyers looking for a really good but reasonable knife.

http://www.benchmade.com/products/product_detail.aspx?model=10400
 
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