REX121 Madness: .009" Behind Edge, ~12° Per Side, Mirror.

[Wowbagger]

PS: I realize this belongs in maintenance; just wanted to leave a flag here in General before it gets moved.
thank you mods.

Turns out with the right tools this stuff was crazy easy to reprofile.
I'm still pinching my self !
No pics ( but it happened ). Maybe pics later / tech wise I'm very limited right now.
Come on, you can imagine a big wide polished edge on a Sage.

Equip. =
Old Edge Pro Apex
Lots of spare blank aluminum plates like for putting polishing film on

First plate / grit was a section of a sanding belt (cut it well short of the ends of the plate, don't ask why just be glad you didn't have my F'up). Cut to length by folding belt in two and ripping ( =super easy). Norton BlueFire Zirconia Alumina 1inch wide 60 grit. Held to plate with side by side strips of 1/2" double back tape.

All the other stuff I put on the other blank plates was ditto.

Atoma 140 for E.P.A.
Venev Diamond plate C 100% F60 250/200 for E.P.A.
DMT plate for the Aligner, (has the round holes in the steel plate) Blue 325 mesh 45 micron, stuck on E.P.A blank.
DMT plate for the Aligner, (has the round holes in the steel plate) Red 600 mesh 25 micron, stuck on E.P.A blank
DMT plate for the Aligner, (has the round holes in the steel plate) Green 1200 mesh 9 micron, stuck on E.P.A blank
******WARNING ! WARNING ! WARNING ! ******** wrap or tie thick rubber bands on sliding rod for stops so you don't have these short aligner stones flail off the edge of your knife; or better yet use longer / proper stones for the guided sharpener you are using. I'm just saying what I patched together.

Edge Pro Diamond 4000 "Diamond Matrix" stone . Seems to be grit in resin; off white color. This stone is scarry to use because it seems to be only for trailing edge (stropping like motion). Going edge leading seemed like the edge would just cut into the resin matrix.

At this point I was somewhat tree topping sharp but with a super small bur edge.
I attenpted to take off the bur using a solid steel plate with metal bonded diamond going edge leading . . . the stone is a P.D.T. , Premium CBN, 15,000 grit No912 for Edge Pro.

The edge bevels got prettier but the bur remained. I then went both directions (leading and trailing) to abraid the bur off. Still hung on.
I increased the sharpening angle; twice !!!!!
Still there !
I banged my head on the wall. That didn't help either.

I finally resorted to using a rather tired and cut up cow hide strop, I had pre mounted on one of the aluminum blanks, finished side, that long ago I loaded with 50,000 diamond paste.
That pretty much did it.
It's crazy sharp and pretty. I'm not happy with it because of those half assed final steps but . . .
if it had been M4 my Norton 8000 water stone would have taken care of that bur, hell there probably wouldn't even have been a bur with M4.

My hand kept reaching for that little magic yellow Norton 8000 but my brain kept telling me how stupid that would be for REX121.

The edge was fantastico off the Green 1200 Aligner stone, I don't recall a bur at that point and the bevels were getting pretty shinny.

The main thing is she's thin, layed back and SHARP ! (all that's an understatement)

Now we will see how long super thin will hold up.
Was I a wimp; should I have gone for .006" behind the hedge ? .004" ?
Hey, I'm not Shawn Houston or Phil Wilson , OK ! ? !

edits for spelling.

 

[patrickguignot]

Take a very low toughness steel like Rex121 and put a super fragile edge (12° per side) on it.
What could go wrong?

 

[Diemaker]

Edge Pro Diamond 4000 "Diamond Matrix" stone . Seems to be grit in resin; off white color. This stone is scarry to use because it seems to be only for trailing edge (stropping like motion). Going edge leading seemed like the edge would just cut into the resin matrix.

The edge cutting into the stone is user error and a sign your angle is off. It not only is hard on the stone but the knife edge as well.

Softer abrasives work well to deburr due to what the burr consists of.

 

[elevator man]

So did you reprofile, thin out, the main bevels of the blade, to make it thinner behind the edge? Or just reprofile the edge. Pics would be awesome.

I have a 15v paramilitary2 that is pretty thick behind the edge that in the near future I'd like to regrind the blade to thin out the stock /thinner bte and remove finger choil. The bevel on it is almost twice as wide as my endela and both are same edge angle. I was planning on using a belt grinder though instead of by hand.

 

[elevator man]

Never sharpened 121, but on my 15v and k390 I have good success deburring by doing edge leading strokes only on the last 2 diamond stones, followed by stropping on denim with diamonds

 

[Kryme]

Never sharpened 121, but on my 15v and k390 I have good success deburring by doing edge leading strokes only on the last 2 diamond stones, followed by stropping on denim with diamonds

How does 15V compare to K390? I find K390 an absolute joy to sharpen, but I haven't had the need to touch up my 15V Manix yet, but it's gonna need some reprofiling. I reprofiled my Maxamet PM2 a few weeks ago and that's the only steel that comes close to Rex 121. I've only had my Sage with Rex 121 for a few days but already put it through some abuse (beer cans and tomatoes) and so far it hasn't even lost its "bite" let alone dulled. Luckily it's a pretty thin knife so I won't have to remove much material, but something tells me I'm gonna be spending some time on it, even with diamond plates.

 

[elevator man]

I use DMT plates to sharpen. It's pretty similar to me between the 2. I find them both easy to sharpen with diamonds, i would agree enjoyable. If your doing a big reprofile it won't move super quickly though. Thankfully for me I like 30 degrees and spyderco is right around there on the factory edge.

 

[elevator man]

Suprised your cutting beer cans with your rex 121. To be honest I'm waiting for the chipping pictures to start popping up in general with that steel as more folks get to using it. Somewhat like the snapped maxamet blades

 

[Wowbagger]

Take a very low toughness steel like Rex121 and put a super fragile edge (12° per side) on it.
What could go wrong?

One of my favorite movie quotes :
We need someone who can bind an elephant with a spider's web ; not stun him with a kick.
(Bruce Lee wrote the screen play )

How does one know where the boundaries are without pushing on 'em
I haven't broke a knife yet and have lots of regrinds. Some sub 2mm at the spine.

 

[Wowbagger]

The edge cutting into the stone is user error and a sign your angle is off. It not only is hard on the stone but the knife edge as well.

Softer abrasives work well to deburr due to what the burr consists of.

THANK YOU.
I realize this is your wheel house for sure, for sure.
You have given me the confidence to give 'er another go tonight; edge leading. I didn't say it was tending to dig in but feared it wouldn't take much error on my part to go there. I do use the Edge Pro stone thickness compensator stop so the angle is pretty darn predictable.
Thanks again !

 

[Wowbagger]

So did you reprofile, thin out, the main bevels of the blade, to make it thinner behind the edge? Or just reprofile the edge. Pics would be awesome.

I have a 15v paramilitary2 that is pretty thick behind the edge that in the near future I'd like to regrind the blade to thin out the stock /thinner bte and remove finger choil. The bevel on it is almost twice as wide as my endela and both are same edge angle. I was planning on using a belt grinder though instead of by hand.

Just laid back the edge bevels.
Yes I use power for the full main bevel work. That could turn into real work / time and as Patrick said might be a bad idea with 121.
. . . though I might be OK taking .5mm or .8mm off the spine . . .

 

[Wowbagger]

beer cans

Aluminum will put zero wear on that edge. Cutting aluminum is about like cutting wood; perhaps less abrasive because wood has mineral deposits where as alu. is cleaner.
Little known fact : one can cut thick ( 1/2" or 3/4" solid plate ) aluminium on a table saw with a rip blade.

Steel cans . . . now thasss a different planet . . .and why we have Cold Steel brand knives, right ?
I took a couple of my 4" XHP TiLites sub 2mm at the spine, full flat grind !

They wouldn't mind a bit of steel can work
I have a Razelized 6" XHP TiLite at work I regularly use to debur mild steel ( and aluminum ) ; it's about a 3" blade now with lots of handle for two hand control.

PS : I intentionally shortened the blade way up before putting the razel end on there. The above work was the original purpose for this knife. I have reason to cut dings and spot burring off machine parts in my day job.

 

[Wowbagger]

The edge cutting into the stone is user error and a sign your angle is off. It not only is hard on the stone but the knife edge as well.

Softer abrasives work well to deburr due to what the burr consists of.

YUUUUUUUP !
Oh hell yes ! ! !
Diemaker, I'm so happy !
Just as you say.
I set the angle back to my original (rather than the couple of degrees steeper I had to cut off the bur last time).
Then backed up to coarser grit beginning with the :
DMT Aligner, Blue 325 mesh 45 micron then
DMT Aligner, Red 600 mesh 25 micron then
DMT Aligner Green 1200 mesh 9 micron

then the devine . . .
Edge Pro Diamond 4000 "Diamond Matrix" stone first trailing edge (stropping like motion) to varify my angle, then both ways to polish up the bevel faces and refine the edge.
At this point there was basically only the hint of a bur here and there along the edge.
I steepened the angle a micro amount (sorry, I don't have a digital angle cube) just to be sure I was right down there on the entire apex. I went back and forth edge leading and trailing each stroke.
Then I went just edge leading super lightly and one or two strokes per side alternating.
BAM !
Somewhat tree topping, super easily hair splitting and whittling; zero bur.

I stopped there !
No reason at all to strop.
I hate stropping and will avoid it when ever I can.
Sure, I studied all about it in Science Of Sharp and agree that there is a place for it (mostly it seems with stainless that is softer than it could be no matter how many letters and numbers they put in it's name) (yuck).

Years ago I made up a denim strop and a finish side cow hide strop with 50 thou diamond on blanks for my Edge Pro. They work !
I still prefer my final edge to be off a stone because of my experiences planing bevel up on bubinga wood; stropping was detrimental.
Old dogs, tricks etc.

I'll probably dream about splitting atoms while I sleep tonight.

 

[Kryme]

I would have called it a day at 1200. Heck I don't go over 600 on the KME anymore, just finish off with really really light strokes alternating sides, then a few strokes on the strop. Gives a really aggressive edge that bites into material like crazy. Nearly chopped off my ring finger's tip when I tried to close my Mordax and didn't pay attention to my fingers. Used to go all out with fine stones then progress through lapping films up to 0.1 micron, but I've found that polished edges just don't last as long, since there's no teeth in their bite. Since Rex 121 is more "chippy" I'll probably go to 1200 and leave it there.

I use DMT plates to sharpen. It's pretty similar to me between the 2. I find them both easy to sharpen with diamonds, i would agree enjoyable. If your doing a big reprofile it won't move super quickly though. Thankfully for me I like 30 degrees and spyderco is right around there on the factory edge.

I use KME plates, so I should be good to go then.

Suprised your cutting beer cans with your rex 121. To be honest I'm waiting for the chipping pictures to start popping up in general with that steel as more folks get to using it. Somewhat like the snapped maxamet blades

I do it fairly often, to make cups because I'm too lazy to walk to the store and get plastic ones. It's not as bad as it sounds, aluminum is fairly soft so a knife with a thin profile will go through it with relative ease.

 

[elevator man]

I would have called it a day at 1200. Heck I don't go over 600 on the KME anymore, just finish off with really really light strokes alternating sides, then a few strokes on the strop. Gives a really aggressive edge that bites into material like crazy. Nearly chopped off my ring finger's tip when I tried to close my Mordax and didn't pay attention to my fingers. Used to go all out with fine stones then progress through lapping films up to 0.1 micron, but I've found that polished edges just don't last as long, since there's no teeth in their bite. Since Rex 121 is more "chippy" I'll probably go to 1200 and leave it there.

I use KME plates, so I should be good to go then.

I do it fairly often, to make cups because I'm too lazy to walk to the store and get plastic ones. It's not as bad as it sounds, aluminum is fairly soft so a knife with a thin profile will go through it with relative ease.

I do it to, to make cups to spit sunflower seeds in. Just no experience with rex121 and in my mind it's delicate like glass so hearing folks using it is surprising.

I still use fine diamond plates to sharpen, xf and xxf. Not so much for a finer edge, I can shave with the blue coarse plate. But more for removing the burr. From what I'd read on science of sharp, the finer the grit, the less pressure it takes to cut the steel. So I can achieve cutting of the steel/burr with far less pressure so I can cut it off without pushing it to the other side. At least that's my theory

 

[WóðanaZ]

Take a very low toughness steel like Rex121 and put a super fragile edge (12° per side) on it.
What could go wrong?

I reprofiled mine to ~6-8° per side (shallow convexed) and micro beveled at ~16° per side so toughness isn’t a problem. The reduced secondary significantly improves cutting performance while the micro retains the toughness it already had. The edge isn’t fragile; it’s all about reducing the behind the edge thickness to minimal (what it can handle) to increase performance. The only part of the edge that needs to be stout it the apex itself (which is very small) and with a reduced secondary bevel angle less force is required to initiate a cut and thus less force is put into the apex itself.

With such geometry the very apex sees less forces than a V grind with a well defined transition into the secondary because there’s basically nothing to wedge. Micro bevels truly are king but only when the secondary bevel has been reduced in degrees.

The micro bevel degrees should always be your intended angle and the secondary reduced to allow it. Some people grind the secondary as fairly normal (15-20° ps) and then micro bevel, this defeats the purpose of adding a micro as it just makes the geometry obtuse and simultaneously requires you to place more force into the apex to initiate the cut.

 

[patrickguignot]

I reprofiled mine to ~6-8° per side (shallow convexed) and micro beveled at ~16° per side so toughness isn’t a problem.

Interesting. Could you show a picture of the edge?
The reprofiling of a Rex121 blade must be difficult.

 

[Wowbagger]

Interesting. Could you show a picture of the edge?
The reprofiling of a Rex121 blade must be difficult.

Not to be redundant . . . first few lines from OP post =

Turns out with the right tools this stuff was crazy easy to reprofile.
I'm still pinching my self !

right tools are listed
YMMV
. . . carry on . . .

 

[WóðanaZ]

Interesting. Could you show a picture of the edge?
The reprofiling of a Rex121 blade must be difficult.

It’s not hard and as usual there’s a lot of hype and misunderstanding around high carbide steels used in cutlery which were never really intended for cutlery. If you have no problems grinding Maxamet or S110V then you’ll have no problems doing the same with Rex121. You’ll notice the hardness and wear resistance of it, most definitely; but it’s nothing diamonds can’t easily handle.
It does feel glass-like but diamonds still grind it no problem.

Atoma #140 (a well used one at that) made quick work of it; Atoma #400, DMT #600, #1200 to clean it up a bit.

The above grit progression never touched the apex, only the bevel. Finally, DMT #600 to apex a micro, and a well used DMT #1200 to refine with ultra light passes.

It took 14 minutes to reprofile from stock to ~6-8° ps. Less than 1 minute to apex. (All freehand, I don’t use jigs)

I’ll see if I have time to get a photo for you later (it’s 8:30am here). I’ll quote you again when I can.

 

[Wowbagger]

Take a very low toughness steel like Rex121 and put a super fragile edge (12° per side) on it.
What could go wrong?

Thought you might want to share your views on REX121 with Sal over in the Spyderco forum.
He just posted and I quote : "I've been maintaining a very coarse edge (CBN Gauntlet Vivi style) at 10 DPS with no problems so far."

You probably better enlighten him before something bad happens .

I only use those dummo polished edges around 12° and never venture into "toothy" 10° edges so I don't feel equipped to advise him.