Won't take an edge!

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I'm new to knife making and just made one using steel from a circular sawblade from a log processor which I assume to be real good stuff. It grinds and drills like really good steel , but when I tried to sharpen it I could not get the blade to get a sharp edge. Any ideas as to what the problem is and how to correct it would be much appreciated.
 
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I hate to break this to you Ledco but you can't tell much about steel from grinding and drilling. As a matter of fact, if you can drill it easily, it's too soft.

But....

You can take dead soft low carbon steel and put a hair popping edge on it. It just won't last. My guess is your blade geometry. Most newer makers tend to have too much meat on the edge.

Try to take it back to at least a 22 degree angle and resharpen. Getting a good edge is a learned art. It doesn't just happen for anyone.

Also, make sure you get rid of the wire edge. It will feel like the sword of Michael but the wire will just flop back and forth until it breaks off and you have a dull blade underneath.

Also, decide what you want the edge to do. I made a blade for a friend a few months ago. He wanted it for a patch knife. He told me he took it down to a stropped edge and it shaved hair like a razor but he had to saw through the patches. I suggested he resharpen with a little coarser stone and forget the strop. Like magic it cut patches. The micro saw teeth on the coarser edge just cut cloth better.
 
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Ledco said:
I'm new to knife making and just made one using steel from a circular sawblade from a log processor which I assume to be real good stuff. It grinds and drills like really good steel , but when I tried to sharpen it I could not get the blade to get a sharp edge. Any ideas as to what the problem is and how to correct it would be much appreciated.

First
tell me the way you heat treated it?
and did the Blade have Carbide teeth?
 
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Dan Gray said:
First
tell me the way you heat treated it?
and did the Blade have Carbide teeth?

Yep, give us some details an we (they :footinmou ) might be able to help you out :)
 

Stacy E. Apelt - Bladesmith

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Ledco doesn't mention hardening the blade.If it is just a ground out knife ,it will never take an edge.Give us some info.
 
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Dan Gray said:
First
tell me the way you heat treated it?
and did the Blade have Carbide teeth?

the reason I asked these questions this way was to get two of three answers. :rolleyes: :)

Asking for the heat treat would cause him to answer his own question.
hopefully :)

if it had Carbide teeth then there was no sense in the manufacture
in putting good steel (as in Carbon steel) into the whole blade,,$$$ savings.
older blades maybe, now? not so likely.

and I would also like to know how the profile was cut from the blade.
this would be an another trick question :)
 
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The saw blade was non-carbide tipped and I just ground the knife out of it.
I didn't heat treat it because the material is quite hard to work and it is not easy to drill. In fact at one point I tried to mill some material off and The end mill dulled almost immediately. I am using a 20 degree sharpening angle. It sharpens till it almost has a good edge and when I go just a bit more the edge disappears and it feels dull.
 
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Oh yes, I cut the profile with a bi-metal band saw blade and by the way it cut I could tell it was a high carbon steel.
 
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I use to make a lot of knives out of old saw blades, it's uaualy very good steel but it needs to be heat treated. The old blades had a spring temper, hard enough to hold its shape but not hard enough for a knife blade, I would guess around 40-45 rc. Also a soft steel is difficult to get a keen edge on. Saw steel is very easy to heat treat and it's part of the fun in knife making :)

Don Hanson lll

Edit- Todd, I may be a little low on the hardness, I think you are probabaly closer but I'll say 45 - 50 rc seems about right :)
 
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Ledco

I believe that most saw blades that don't have carbide tips were run in the low 50s Rc. If they were run higher, they tended to chip or crack. The low 50s is a little soft for a knife, though it would be tough to drill with a HSS drill bit, I guess. If the blade got very hot when you cut/ground it out, it could be even softer. With that said, I once heard of a man sharpening a sardine can lid to a shaving edge to prove that inferior metal would still get scary sharp. I learned to sharpen knives on those old Pakistan lockbacks when I was around 12. I could get a scary sharp edge on them, which goes to show that even inferior steel will get sharp. It just won't stay that way.

Todd

Edited to add: I'll defer to Don on the hardness of the old blades. His reply came up while I was typing mine.
 
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yeahup
it needs to be Heat treated. but if I were you, I'd mess with a test piece first. :)
 
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Thanks for the info. Now I guess it's time to build a forge. What Rc should I aim for ?
 
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There's lots of good forge building info in the this forum if you do a search. Another great resource, and the place to get the materials is Darren Ellis ( http://refractory.elliscustomknifeworks.com/ )

As for the sawblade knife. Since you don't know the exact composition we can't really give you a specific recommendation for RC, or what temperature to temper at. The general rule is to heat to non magnetic, quench in a light oil heated to around 110 deg F. Then temper for 2 hours at 350 deg F, this is usually too low and will leave the blade brittle but anything other than a real HT oven is usually off by a bit(or a lot). Better to start out low and work up to what you want than ruin the heat treat.
When it comes out of that temper cycle, do the brass rod test. You can find more info on that by doing a search in this forum. If the blade is too brittle, raise the temp 10- 15 degrees and temper another 2 hours,then test again. If the blade is too soft its probably going to stay that way, but you can try another quench if you want, and restart the tempering process.

Oh yeah, you need to blunt the edge before you try heat treating it. Take it clear back till its around .040" thick. If you leave it sharpened it will be too thin and may warp or crack.
 
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I agree with everyone else about heat treating. I don't necessarily agree that the hardness is why it is not taking an edge and that was the original question.

I'm reading between the lines on some of this an assuming you have your geometry right at 20 degrees....we will go on go on.
It sharpens till it almost has a good edge and when I go just a bit more the edge disappears and it feels dull.

How are you sharpening it? are you using the grinder and if so are you grinding with the edge following the direction of rotation?

If so you may be drawing the wire edge out. This is quite common and gets worse of faster grinders and worse yet on softer steel.

Try to sharpen it on a stone and see if you get a wire edge. Then use a brass rod to move the edge to one side or the other. If it moves to the side and stays, it's too soft and you solved both issues. If it springs back, strop it against your hand until it breaks off and resharpen. It should hold that time and the steel is IMHO hard enough.

Good luck!
 

Stacy E. Apelt - Bladesmith

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Rockwell hardness is not exactly something you aim at.It is a rating of how hardened a steel CAN get.The final RC is a product of the quench and temper.Learn to do a good quench that is repeatable and learn how to temper to a tough enough blade with good edge retention and the Rc will be whatever it is- but the blade will be the BEST it can be.Too much emphasis is made on the RC of a knife.Unless you are doing some very complex carving of hard wood or something,you don't need a knife with a high RC.
What you need is a GOOD reliable knife.The blades of ledgend probably never had a blade above Rc50.
 
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What you need is a GOOD reliable knife.The blades of ledgend probably never had a blade above Rc50.

Amen!
 
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I'm using a Lansky sharpening system set at 20 degrees. It seems as though the blade won't get to the wire edge stage . It gets just about to that and then a few strokes more and I can actually see the edge again. It's as if it goes right past the wiire.
 
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