Sharpening Mild Steel Blades

N

numbersman

Joined
Nov 28, 2010
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Hi guys, I am having trouble sharpening blades with a mild steel. I am using a SharpMaker, and trying to sharpen a couple of Gil Hibben throwers. I started off on the medium stones, and got them feeling better. Then I stropped briefly on a piece of leather and went over to the fine stones. Unfortunately, once I got to the fine stones, they went backwards. They are now worse than when I finished on the medium stones. Any ideas what is going on?
 
My .o2 on sharpening. No matter what you are sharpening, no matter the steel, or the sharpening device, you must work to a burr before moving to fine stones and then a strop.

My free hand skills are lacking, I use a KME sharpening system with diamond stones at what ever angle I set it at. I work the coarse stone until I have a nasty burr the entire length of the blade, then move to the fine, then extra fine THEN strop.

My problem with the sharpmaker is that if you don't hold the knife in the correct position every time, you can mess up your edge. There is plenty of room for user error with that system.

Got to raise a burr first.

Hope this helps and good luck-

Drew
 
So-called 'mild steel' is generally defined as a steel having VERY low carbon content; usually no more than 0.3% carbon, and often much, much less. This excludes the vast majority of true 'cutlery' steels, possibly excepting 'knives' like butterknives and table flatware that aren't engineered to hold a sharp edge.

The Hibben throwing knives may very well be down in that low-carbon territory. I've no doubt they were made for toughness (resistance to breakage from shock or hard impact), and not for hardness (ability to hold a fine/sharp edge). Carbon in higher quanitity is what makes steel hardenable, and more so as the carbon content increases. Most knives made/designed to take a sharp edge will have at least 0.4% carbon or more. A throwing knife with much hardness at all would be more brittle and prone to breakage, for obvious reasons.


David
 
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Drew, I would also add in there patience. Some folks swipe a blade a couple times expecting a scalpal like edge, and it's not so simple.
David, good info as usual. Thanks
 
David that is great info, would steels like the ones in the low carbon still be able to sharpen to a burr???

RevDevil- you are absolutely correct! I am using a guided system, WITH diamond stones and when I reporfile a crappy initial grind I am sometimes floored at how long it takes to raise a burr! I recently redid a 5" blade in 5160 and it took FOREVER!!!! I could not even being to imagine how long it would take on something like a sharpmaker...
 
DREW78 said:
David that is great info, would steels like the ones in the low carbon still be able to sharpen to a burr???

RevDevil- you are absolutely correct! I am using a guided system, WITH diamond stones and when I reporfile a crappy initial grind I am sometimes floored at how long it takes to raise a burr! I recently redid a 5" blade in 5160 and it took FOREVER!!!! I could not even being to imagine how long it would take on something like a sharpmaker...
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I'm sure a burr could be created on it. But, if the carbon content is as low as I'm assuming, the steel is likely so malleable that scrubbing the burr off would likely blunt the edge again.

If you're inclined to do so, you might try a less-aggressive abrasive (sandpaper, or perhaps a simple natural stone like an Arkansas). I've noticed before, with very low-hardness/low abrasion-resistant steels, diamond hones can easily create and scrub off a burr before it's even noticed. A really soft steel is almost like butter to a diamond hone, and sometimes it literally feels 'buttery', when sharpening on a dry diamond hone.


David
 
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David's on exactly the right track. When SMKW began carrying Hibben throwers, I bought a bunch to experiment with. Sharpened them, made wrapped-leather grips for them, etc. I have no idea how durable the edges are simply because I never cut anything but some newsprint with them. I did find, however, that this is very hard to sharpen steel on anything aggressive. I used a fine file to cut the new bevels; like filing putty-clogged the file. Clogged my diamond hone. Loaded up my sandpaper. The Hibbens LOVED my Arkansas stones. Gave a razor-sharp, polished edge(again, no promise of it lasting). A soft or medium stone combined with a fine is the ticket. Sometimes, in our hobby-est ways, we pursue the latest and sexiest so hotly that we overlook the fact that old steels and old stones play very well together.
 
StevieWunders said:
David's on exactly the right track. When SMKW began carrying Hibben throwers, I bought a bunch to experiment with. Sharpened them, made wrapped-leather grips for them, etc. I have no idea how durable the edges are simply because I never cut anything but some newsprint with them. I did find, however, that this is very hard to sharpen steel on anything aggressive. I used a fine file to cut the new bevels; like filing putty-clogged the file. Clogged my diamond hone. Loaded up my sandpaper. The Hibbens LOVED my Arkansas stones. Gave a razor-sharp, polished edge(again, no promise of it lasting). A soft or medium stone combined with a fine is the ticket. Sometimes, in our hobby-est ways, we pursue the latest and sexiest so hotly that we overlook the fact that old steels and old stones play very well together.
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Thanks for that feedback, Stevie. It's always nice to hear some real-world confirmation of what I'd suspected. :thumbup:


David
 
Some good stuff here. My personal recipe for soft steels is to whip up a mud of black compound and mineral oil - apply liberally to a sheet of paper over a hard surface and strop away. Is amazing how much metal can be removed, and the mud can hold a lot of it before it becomes so choked up as to stop working. Is also a "gentle" way of taking material off.
You can do this again with a finer white compound and get a finer edge to finish.
 
HH-

What is the aprox ratio of mineral oil to compound? We talking a thick like paste? Interesting idea, never thought of this concept before. now, I don't have any mild steel blades, but its always cool to learn something new!

Drew
 
DREW78 said:
HH-

What is the aprox ratio of mineral oil to compound? We talking a thick like paste? Interesting idea, never thought of this concept before. now, I don't have any mild steel blades, but its always cool to learn something new!

Drew
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Not sure the ratio, but you want it to feel a little tacky - the binder on most commercial crayon-type compounds is a form of tallow, the oil will break it down a bit. You don't want a thin gritty oil, you want a smeary type of mud. Its not realistic to create a large amount of this, but you can smear a fair amount on a sheet of paper, add a few drops of oil, stir it around, rub some more compound on it, repeat as needed. Makes a good medium for working softer metals. If you do this on hardwood, you can work the harder stuff, but is a lot easier on paper over a combination stone or similar.

Martin
 
I was using the term "mild" in a fairly non-technical way. The steel is supposed to be softish, so it doesn't break under the shock of being thrown into a lump of wood, or tree. I have no idea of its carbon content. I'll try on the fine stones all the way, and give it plenty of time. Thanks all, for your input.
 
numbersman said:
I was using the term "mild" in a fairly non-technical way. The steel is supposed to be softish, so it doesn't break under the shock of being thrown into a lump of wood, or tree. I have no idea of its carbon content. I'll try on the fine stones all the way, and give it plenty of time. Thanks all, for your input.
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Don't know what vintage(?) your particular knives are, but I was looking around the web at various dealers' listings for some of the Hibben throwers. Didn't find any specifics on the Hibben Knives site, but some dealers' descriptions describe them as being in 420HC or similar. If so, maybe they're not quite so bad; just a little bit beyond the upper carbon limit for 'mild steel' (420HC's carbon varies somewhere between 0.45 - 0.60% or so). I'd still assume relatively low hardness though.


David
 
I throw hibbens knives myself, for "throwers" an edge is dangerous and not really needed. I simply use a fine file and maintain a point that will stick in your target. Much easier than sharpening all the time.
 
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