QUESTION: Convexing RAT's and RC's. Anyone?

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Mikel_24

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Not long ago I discovered the joy of convex sharpenning with an F1. I should say the no need of any special equipment (mousepad-sand paper-strop lover here) or complex mechanical skills is what I really like. I won't say it is idiot proof, but it comes very close.

Let's face it, even while being designed for completly different tasks, the F1 blade profile outcuts (for me) the RAT-7 I own. The RAT-7 doesn't chop as well as I expected either having the factory edge on it (well, I did some wood work with it, but after getting rid of the burr it developed, it shaves in some spots yet).

I read somewhere that lot of guys here thinned the edge of their RAT's. I just own a crappy two sided stone made by Aitor (too small for any serious sharpenning job), a Carborundum brand oval shaped stone, a Fishkars two rod sharpener (one of the black plastic ones with the rods making a V shape) and a Sharpmaker.

Reprofiling such a big chunk of D2 with the Sharpmaker could take forever, same goes with the two sided stone and I don't want to take my knife close to the Carborundum oval shaped stone. So... I was thiking about getting a handfull of coarse grit sandpaper (220 or lower) and convexing the damn thing (then polishing the blade up to 2000 at most).

I did this recently with a beat up Solingen knife (4" blade, stag handle, brass guard, aluminum cap) I got on ebay for little money. Some idiot took a grinder to it and it was all scratched up, edge dented, blade slightly bent (blade and handle not in line I mean) and I bet they even reprofiled it from a clip point to a spear point. It was a mess! I used this beater as a trainning before getting any sandpaper close to my beloved F1 (I didn't want to screw up) and I am very happy with what I get! Then I touched up the F1 with some more sandpaper and it is shaving sharp again.

Any input? Anyone here thinks I am about to ruin a great knife? Should I forget about reprofiling anything with my tools and get some diamond stones? I think that lifting the spine the advised 13º or so I will avoid scratching up the whole blade, maybe some tape on it to protect it while sanding?

Mikel

PD: I saw someone who convexed a brand new RC-4 here but they are made of 1095 and he used a belt grinder. I don't have the tools to do so.
 
Hey Mike

I've also got a rat7d2 and I've been tempted to convex it. Right now I'm doing a practice run on my kabar (1095steel) to see how things go on a long blade.

Expect that it will take a lonnnngg time. I reprofiled my Scrap Yard "Yard Keeper" (4" blade aprox) using a 150 grit diamond plate and I spent HOURS working away on it.

If you do decide to do it, I'd suggest grinding down the shoulder of the bevel on one of your stones, or mount the sand paper on a solid backing, because youre going to want to bear down on it with some pressure to get started and take down the bulk of the excess steel. If you use enough pressure to make reasonable progress on the mousepad it will probably be wrapping around the edge.

Apply some tape along the blade, about 5mm back from the edge (varies depending on what angle you want) then you can feel if youre dropping the spine too low.

I'd recommend practicing the whole thing on a cheap knife with softer steel. The Rat7d2 not only has a pretty obtuse asymmetrical grind, but is also very wear resistant so there will be lots of slow going work to be done and you'll want to be sure of what youre doing. I find there's nothing worse than second guessing yourself half way through a mod.

just my 2c
 
Hey fellas, I was taught by my father to convex when I was ten or so. That gives me almost 30 yrs convexing every blade I buy. I have a new RC-4 that has been convexed, and it is sharper than sh!t. I don't use the mouse pad, I put the sand paper over my strop. The beauty of a convexed edge is that it has nearly 4 times the metal carbides behind the edge, compared to a bevel edge. It also has less drag through the medium being cut. You don't need to thin the edge much to get the convex. Generally speaking. when you convex, if you hold the spine of the blade at about 10 degrees off the strop, you are creating a slicer. I would think for a RC knife you want a utility edge, that is created with the spine at about 15 degrees off the strop. Start with 220 grit and really be consistant with the angle. you will see the scratches from the paper working there way up the edge, until you see the old bevel fall off. That is when the convex is on the blade. Be careful with the pivot also. The edge must move in a straight line accross the strop, so the knife has to be pivoted as you strop. Once the new edge is established, move to 500 grit paper. You will feel the scratches smooth out. Once smooth, go to 800/900 grit, then 1000, then 1200. Once smooth at 1200 you are ready for compound and leather. I use the Black and green from Bark River. The Black is about 1500-1600 grit, IMO, and the green is 2000 or higher. Once done with the green the edge should be a mirror. I think that about covers it. Reid from sharpshooter sheaths has a good tutorial on convexing that many people have said helped them. Here is the link. http://www.barkriverknives.com/convex.htm Convex a crap blade first, so you get the hang of it. it's not hard. Most of my friends screw it up by raising the spine as they move accross the strop. Be consistant with the angle and all will be good. Hope that helps! I'm new to this forum, but you will see me often on KF. :thumbup:
 
I convex everything these days. I use sandpaper on top of leather glued to wood.
 
I've found the best way to reprofile an edge or to get an extremely dull knife sharp again is to use diamond stones. I know they're pricey, but get a couple (coarse and fine) large bench stones.

There's two ways to convex, either use a soft medium (strop or emory paper/mousepad) or to use a stone and move the stone. Most people will conves an edge by accident when using handheld stones anyway.

When using stones there's two ways to do it. Since stones are grit based, you can use them in any direction, unlike a file. To initially convex a large blade, I put the bench stone on the table, and draw the knife BACKWARDS across it. I keep my wrists fixed and pull the blade toward me. This naturally makes a convex edge. Once the edge is convexed this way, there will be a wire edge to remove. I'll usually just pick up the stone, hold it in hand, and run it over the blade (keeping the blade steady) in the conventional way, until the wire edge is gone. Then I'll runt he fine stone over it until I have a uniform edge finish (you can also color it with a Sharpie to make sure you're "honing" the whole edge). Finally on to stropping with a strop or emrory paper/mousepad.

The good point and bad point to diamond stones is that they will remove material quickly, so be careful.
 
I convexed and stripped my rc-4 up to the rc-4/rowen engraving. It looks pretty damn good.
 
The images really do not do it justice. Stripped and convexed. Well still working on it a bit.





I started with 80 grit to remove the coating - the stuff was on pretty damn good.

Then I went from 180, 320, 600, 800, 1000, 1500, 2000 and a quick polish.



 
sketchbag said:
...I'd suggest grinding down the shoulder of the bevel on one of your stones, or mount the sand paper on a solid backing, because youre going to want to bear down on it with some pressure to get started and take down the bulk of the excess steel. If you use enough pressure to make reasonable progress on the mousepad it will probably be wrapping around the edge.
Click to expand...
I will try to grind down the shoulders with my crappy Carborundum brand stone... I hope I can scratch it at least! Instead of a mousepad I use a large piece of 1cm thick high density foam I have for making shinguards (the go between the boots and my sheens, they are too stiff there). It is definitely harder than a mousepad so I won't round be rounding the edge. I will probably give it a few licks with a harder backing though...

sketchbag said:
Apply some tape along the blade, about 5mm back from the edge (varies depending on what angle you want) then you can feel if youre dropping the spine too low.
Click to expand...
:thumbup: Good point... I don't want to thin the edge too much so 5mm seems about right.

sketchbag said:
I'd recommend practicing the whole thing on a cheap knife with softer steel.
Click to expand...
I have an Ontario SP8 thang (I can't call this "thang" a knife...) who just volunteered itself for me to practice on it... :D :D Trust me, I won't be sorry if I screw up on this one.

Right now I am convexing every kitchen knife I find at home and my SP8. Once I am done with them all I will go to the store and buy some coarser grit sandpaper. I will try to post some pictures of my RAT 7 BEFORE and AFTER convexing it.

Thanks for all the input.
Mikel
 
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