Recurve edge question

C

CMN

Member
so i was looking at some of my knife books with big shiny pictures, and I came across the Persian / middle eastern section. I found a very cool Persian single edged, kinda half dagger thing and thought wouldn't that be cool if it were double edged. Yea. well. So anyway everything went fairly well up until I got the the point of putting the rough grind edge on before HT. The normal upward curving side went good, no problems there. The reverse curve side however, did not go so well. I put the blank in the jig, up ended the belt arm and commenced to grinding. What i got was a reverse curve edge with a straight grind line across the steel and dull as hell in the middle. Why ? and how do i over come this issue ?

I see other knives with a re curve edge but those seem to be a fairly low curve. The one I tried was pretty steep. If you are familiar with older style middle eastern blades then you understand. So anyway is it possible to put an edge on a steep re curve ? and what technique or process would you recommend ?

thank you,
CMN
 
Yes it is possible but I'm not certain you can do it with your current grinding jig. If you're flat grinding with a jig when you do a recurve or something like a karambit you are grinding with too much surface area in the platen to actually grind that negative arc. Instead what you get is similar to grinding a straight edged blade with your current setup and then later grinding in the recurve profile; thin at the ends but too thick in the middle... either get a radiused platen, grind on the edge of your current platen, hollow grind it free hand, or grind it perpendicular on a small wheel. Either way you'd have to turn the blade some with the hand holding it. And that's all I got. Good luck!
 
( little bit of time spent in research ) Ok now that I know what a radiused platen is, where it would go and a rough idea of what its used for, my next question is 1) how much of a curve would I need ? and 2) would i use the platen by going across the width of the belt or with the length of the belt to put an edge on a re-curve ?
oh, and how do you pros measure or describe a re-curve edge ? inches ? degrees ? radians ? ( lol, please not radians....)

and, thank you very much Mr. Rosa for the quick reply and great info !
 
You can make a radiused platen 2 ways; with either the radius running the lenth of the platen or the width. If the radius runs the length you basically have a section of a contact wheel. If it runs the width it's like the wheel is now horizontal and 12" wide. For your project I'd do the second one. Here's a tutorial another knife maker did using this method. http://www.bladeforums.com/forums/showthread.php/641965-A-quick-tutorial

If you don't do it that way you'll have grind on the edges of your platen or contact wheel or grind the blade perpendicular to a small contact wheel. As far as measuring the arc of the recurve.... i guess you could do it a number of ways but I'd keep it simple. I'll leave that to someone more knowledgeable than I. You don't need much of a radius on the platen to make a difference and you can make a radiused platen from some hardened steel, a platen liner, or some other material and make it another attachment for your grinder or just temporary glue it to your existing platen and use a heat gun to get it off later and then just resurface the platen . Now all that said I tend to grind on the edges of the platen or contact wheel free hand with the belt a little offset and with the edge parallel to the belt as I make sweeping passes... eventually when I upgrade my grinder I'll make a platen like Mr. Patton.
 
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