is your mora too sharp?
- Thread starter robin wood
- Start date
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Generalisation, is, generally speaking, an unhelpful thing to do, and specifically if one is interested in specifics...
I cant help thinking that there is something of these very well known words (below) in the above statement of mine
Now what is the message there? The message is that there are known "knowns." There are things we know that we know. There are known unknowns. That is to say there are things that we now know we don't know. But there are also unknown unknowns. There are things we don't know we don't know. So when we do the best we can and we pull all this information together, and we then say well that's basically what we see as the situation, that is really only the known knowns and the known unknowns. And each year, we discover a few more of those unknown unknowns.
Come to think of it, it might be a nice idea for a Mod to add these well known words to the title of this thread <chuckles>
Cheers,
Paul.
Hmmm...well, if these thin single bevels are so fragile, I'm at a loss to explain why the edges on these chisels don't crumple when I pound on the ends with a mallet.
That is very interesting isn't it. I don't have anything against single bevels as I said I use them most of the time because mostly I carve wood. In fact it was because that is my standard sharpening system that I started using it when I bought a bunch of new expensive hand forged blades (with similar geometry to clippers) and was most disappointed to find the edges folding.and not working as well as my £10 frosts sloyd. The reason I found was that they tend to be 20 degree primary grinds and so far I have not found a blade that will hold a 20 degree edge with the work that I do. So I reground some of those blades to 25 single bevel and put a small secondary on others which are now "general purpose" rather than carving knives, both systems work for me with the pros and cons of each mentioned before.
Out of interest what bevel do you have on your carving chisels? I actually find a curved cutting edge much stronger (less likely to fold) and will work with a finer edge angle than a straight edge. My day job is woodturning for which I use my own forged hooks. I also use Bo Helgesson's hook knives which hold 20 degrees and the edge never folds. Perhaps it is due to the tension a little like an umbrella or the dish put in wagon wheels that makes a curved tool stronger. Hurdle makers make their hurdles slightly curved because the tension makes them stronger and less likely to buckle I suspect the same is true with blades.
Quite agree here, there are of course lots of factors which affect how long that edge holds. I like to learn the effects of each by holding as many of the variables as I can constant and then changing just one aspect and seeing what effect it has with the work I do. So if I just work with the clipper blade the steel and tempering stays the same and I can play with the grind angle until I get the narrowest profile that will hold an edge for an acceptable time. It would be equally interesting to see identical blades made of the same steel with the identical grind and hone but different temper, then different steels, then the same steel and different blade thickness or profile.
This sort of semi scientific analysis has been done for plane blades and it would be interesting to see it done for knives.
Robin, I don't know the particular angle on those tools. They are factory-ground Flextool gouges. I have straight edge chisels that work just as well too.
There's no doubt that more obtuse angles and secondary bevels will take more punishment. My argument is that single bevels hold up pretty well if you can deal effectively with the burr. Check out Old Jimbo's site. He's beat the crap out of more Moras than anyone I know.
Often one of the problems with new knives, factory or custom, is that laser cutting and/or heat treat can leave the edge somewhat brittle. Once you've sharpened it back a ways, the edge holding improves substantially. Again, check out Old Jimbo's site.
In my mind the real question is, when you go out into the wilderness, what is it you use your knife for? If you need the more robust edge because you baton your knife through a lot of knotty, seasoned wood, then maybe a secondary bevel might be the way to go. For the stuff I do, I rarely have a problem with single bevel knives. I do carry more than one knife though. Knives with LARGE secondary bevels I often find a pain to use for a lot of chores. Not all, but a lot.
For green wood, I've found that a tiny seconday bevel like you suggest really doesn't interfere with carving very much. I have a flat ground Grohmann with a tiny secondary bevel that carves green wood fairly well and is not all that bad for roughing out dry wood. Certainly well enough for most bushcraft.
There's no doubt that more obtuse angles and secondary bevels will take more punishment. My argument is that single bevels hold up pretty well if you can deal effectively with the burr. Check out Old Jimbo's site. He's beat the crap out of more Moras than anyone I know.
Often one of the problems with new knives, factory or custom, is that laser cutting and/or heat treat can leave the edge somewhat brittle. Once you've sharpened it back a ways, the edge holding improves substantially. Again, check out Old Jimbo's site.
In my mind the real question is, when you go out into the wilderness, what is it you use your knife for? If you need the more robust edge because you baton your knife through a lot of knotty, seasoned wood, then maybe a secondary bevel might be the way to go. For the stuff I do, I rarely have a problem with single bevel knives. I do carry more than one knife though.
Knives with LARGE secondary bevels I often find a pain to use for a lot of chores. Not all, but a lot.For green wood, I've found that a tiny seconday bevel like you suggest really doesn't interfere with carving very much. I have a flat ground Grohmann with a tiny secondary bevel that carves green wood fairly well and is not all that bad for roughing out dry wood. Certainly well enough for most bushcraft.
A secondary bevel can actually do a nice job of "rolling" curls from wood. If you've ever read "Whittling Twigs and Branches" by Chris Lubkemann he makes that very point about carvers who can't get the curl in their rooster tail because of the long thin flat bladed carving knives they use. For curling rooster tails, he prefers a slight convex bevel on his knife. In other words, a secondary bevel that's been convexed but not flattened.
Thanks for this Hoodoo, I've been watching this thread closely trying to figure out why I can now do pretty good feather sticks and it would appear it is because I am now adding a small secondary bevel to my Ben Orford blade.
I descovered by trial and error that not adding the bevel gave my feather sticks straight feathers rather than curls but as soon as I changed I got curls.
The only reason I experimented with the bevel was because I couldn't figure out why my Frost Mora was so much sharper when sharpened in exactly the same way. I was also getting the dulling as previously mentioned after very little use but it now keeps the edge much longer.
Excellent thread by the way , thanks Robin Wood.
For that kind of systematic testing one would also need a material of perfectly consistent qualities to be cut by the various batches of knives. I wonder what the chances are of finding a wood that would have that kind of consistency in its structure?
A system of testing has to rigorously follow understood and accepted scientific protocols or not at all, with respect, tests that are semi-scientific are a by nature a non sequitur.
Im guessing that even if we confined such testing to that of buying numbers of knives from different batches of the same model of Mora knife, then sharpened and honed each knife with a sharpening system that could produce an identical grind angle on each of those knives, and used a synthetic material for the cutting tests, there would still be a difference in performance between those knives. Slight inconsistencies in the method of manufacture from batch to batch would most likely, I believe, make the results unreliable or at least make any results inconclusive or doubtful.
I think that in terms of the performance of the Mora knife, what Ive taken away from this useful and interesting discussion, is that a micro bevel that has been carefully de-burred can make the edge more robust than the same knife with zero ground edge when cutting the same material. It has also been claimed by persons far more experienced than me, that a correctly de-burred zero ground knife of the same type can be just as durable as one with a micro bevel that has been poorly de-burred. And I think that, for all useful purposes in real world situations, this is about as much that can be usefully and reliably said. Of course, further discussion of other types of bladed tool is another matter.
Kind regards,
Paul.
Been ferreting around for a post that Old Jimbo made, way back, about honing a convexed Mora, cant find it yet, but in the process, stumbled upon this thread over at Outdoors Magazine, Jimbos posts are a remarkable read, as ever, as is his site:
http://forums.outdoors-magazine.com/viewtopic.php?f=4&t=571&start=0&st=0&sk=t&sd=a&sid=52a4f03c0f00e65c8d4d6fa89a729c24
Whenever I read the master's words, it never fails to renew my interest in the Mora knife. I find that his experience and understanding is a truly humbling thing, for me personally.
Best regards,
Paul.
http://forums.outdoors-magazine.com/viewtopic.php?f=4&t=571&start=0&st=0&sk=t&sd=a&sid=52a4f03c0f00e65c8d4d6fa89a729c24
Whenever I read the master's words, it never fails to renew my interest in the Mora knife. I find that his experience and understanding is a truly humbling thing, for me personally.
Best regards,
Paul.
Howdy!
Upon rediscovering this thread I decided to try giving one of my moras a secondary micro-bevel, as there's little I hate more than having to stop what I'm doing to sharpen the whole primary bevel. Have to say, very impressed I find edge retention to be much better, and while it doesn't instantly "feel" as sharp it still carves great and sharpening is much easier, with a few passes on either side with a small sharpening stone bringing the edge back.
I PM'd Robin and he suggested I post here to bump the thread back up for new folks who haven't seen it yet, so here it is!
Cheers folks, very interesting discussion
Pete
Upon rediscovering this thread I decided to try giving one of my moras a secondary micro-bevel, as there's little I hate more than having to stop what I'm doing to sharpen the whole primary bevel. Have to say, very impressed
I find edge retention to be much better, and while it doesn't instantly "feel" as sharp it still carves great and sharpening is much easier, with a few passes on either side with a small sharpening stone bringing the edge back.I PM'd Robin and he suggested I post here to bump the thread back up for new folks who haven't seen it yet, so here it is!
Cheers folks, very interesting discussion
Pete
after watching RMs sharpening vids on Utube
im sure he uses a secondary bevel anyway in a similer way Mors was pointed out to do in an earlier post here
he after sharpening polishing on stones and then stropping on a belt
says if possible likes to do a final swipe or 10 on a car door window edge very lightly but obviosly from the vid at a differnt angel than the main bevel this i assume does wwhat moors did with a tile ?? and forms a micro secondary bevel
http://uk.youtube.com/watch?v=0a2Jm3pkXqk
at time stamp 2 min 10 seconds
ATB
Duncan
im sure he uses a secondary bevel anyway in a similer way Mors was pointed out to do in an earlier post here
he after sharpening polishing on stones and then stropping on a belt
says if possible likes to do a final swipe or 10 on a car door window edge very lightly but obviosly from the vid at a differnt angel than the main bevel this i assume does wwhat moors did with a tile ?? and forms a micro secondary bevel
http://uk.youtube.com/watch?v=0a2Jm3pkXqk
at time stamp 2 min 10 seconds
ATB
Duncan
I think you're right, when I first watched that I couldn't understand why he would bother with the car window, but making a secondary micro bevel seems like a good reason to me.
I once discovered that my Wenger SAK made far better (read: tighter curled) feather sticks than the mora I was using at the time, and it seemed obvious then that it was because the SAK had a more obtuse edge thus pushing the slivers further away from the stick sooner. Unlike feather sticks however, learning 'simply' to sharpen the knives I have has turned out to be much less obvious.
Personally I don't buy that one. I think he has been shown that trick by someone and not really understood what it is for.
To create a tiny secondary micro bevel you must remove metal. I don't believe that the top of a landrover window is going to remove metal, it is far harder than the steel and extremely smooth, I just did it on a freshly honed edge and looked under the microscope and saw no effect (maybe VW windows are not as abrasive as landrover) I would be very happy to be proved wrong on that one if anyone can show me any evidence, photos or personal experience that shows that toughened glass can remove metal.
Now one of the most common ways of a knife becoming "blunt" particularly fine edges like kitchen knives and Moras with their secondaries removed is what is called edge roll. What happens is if you visualise the edge of a piece of paper pulled tight then push on the edge, it will buckle one way or the other. That is what happens to the fine edge of the knife, it is not "blunt" and if you can push the edge back into line then it will cut well again. Enter the sharpening steel, or landrover window. To use a steel or window on a freshly honed knife seems pointless to me, to use one on a fine edged knife that has done some work and become edge rolled is an excellent idea and save wasting steel.
Now if Ray was wanting to use a knife with a secondary bevel why spend all that time polishing the primary, it plays no part in cutting if you are working with a secondary.
Incidentally chefs use 2 different kinds of steels, most are nonabrasive and simply for realigning the edge, some are abrasive and designed to remove a small amount of metal.
I think he knows what it's for and he doesn't mention a micro secondary bevel, he explains that it is to give the very edge 'bite'. This is necessary because he has just stropped the edge vigorously for 'strength', he says, which is given by a slight convexing of the very edge. He also mentions that stropping isn't necessary to make the blade sharper, just that it gives strength. The passses on the window edge (which are far from ultra smooth from what I've seen, you only need to compare it visually to the polished glass surface on the side to see this, but it's possible they vary) give back the 'bite' that is lost to stropping.
I don't agree that, even with a slightly less than micro secondary edge, a polished main bevel doesn't have any effect on cutting. It may not affect the very edge, but it does affect cutting efficiency. Also, despite the fact that it doesn't directly affect the very edge, the process by which his knife in the video became smooth in the first place (6000 grit waterstone in this case) is precisely what made it possible for the stropping to have had any effect at all.
The point is, it is not a secondary bevel, it's a micro convexing of the edge (the stropping that is, not the car window).
This at least is the theory of what he is doing. To prove it actually works I think it's necessary to use his knife after he's sharpened it, because it seems to work for him and it's inevitable that when the process is attempted by other people that the result is not exactly the same.
I think it's also useful to remember that RM has money, so when he wants to know something he doesn't just have to ask a mate, it seems to me he asks a scientist more often than not, or at least the current leader of a certain field. I think it unlikely he'd do something such as this without finding out why first.
HTH
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