Rex 121 sharpening finish?

JBoone

Gold Member
Joined
Dec 30, 2012
Messages
1,165
Just sharpened my sage 5 in Rex 121 on the wicked edge for first time. Was able to get a pretty consistent bevel on both sides at around 15 degrees. This seemed to mirror the factory bevel fairly well.
I used a sharpie to make sure I apexed and also worked through the grits to ensure I minimized the bur.
I know I need to get a loop to up my game and figure out what is truly going on.

I ended with 17 dps micro bevel. Still not very sharp - will cut paper but with effort (does not glide through).

For those with experience with Rex, what angles and finish are you using? Can you get this steel as sharp as most others? Polished vs course?

Edit: went back and took my time and got sharp. Stayed with 15 dps then a handful of passes at 18 dps at 800 grit diamond followed by stropping 1 micron diamond. The stopping was needed to bring it to sharp but I assume I had a bit of bur to get rid off. Shaving sharp now.
 
Last edited:
I have not messed with the stock angle on mine, and I'm able to get a very good edge for cutting paper and cardboard using a 1000 grit vitrified diamond stone, finishing with reduced pressure and edge-leading strokes, and doing a final strop on denim or kangaroo leather (it's thinner, so less chance of rounding the edge than with leather).

I think it's fair to say that what you describe is not typical for Spyderco Rex 121, and something is wrong with your edge. The question is what's wrong.

I assume you are using diamonds or CBN. If not, you definitely need to, with this steel.

Next check: do you have a clean apex? Look down on the edge with 8-12X magnification and a bright light. Can you see any spots reflecting back at you, where the edge should be? If so, you don't have a proper apex yet.

Next check: burr. By far the most common problem with an unsatisfactory edge. Move your most sensitive fingertip perpendicular to the edge, from spine to edge, in a few spots on each side. Do you feel anything, a little shelf of metal at the edge? If so, you have a burr. If not, you might still have a burr. Try stropping on denim or cardboard or your favorite stropping medium and see if the edge gets sharper.
 
Here yah go :
Link
Don't be afraid / go for it .
There is even a note somewhere there about Sal of Spyderco saying he immediately took his to 10 degrees per side .
 
I will spend some time on it tomorrow and work through methodically. Went a bit quick today but did most of the work for a fresh edge. Will concentrate on raising a burr. I thought I apexed today judging from the marker but very well could have fallen short as I never raised good, verifiable burs on each side early on (which was a mistake as I kind of went through quickly after finding good clamp position). My Diamonds go to 800/1000 combo a then 1200/1600(I think?) ceramic paddles. Not expecting the ceramics to do much on Rex. I have some diamond pastes from 5, 3, 1 and .5 so should be able to get where I need to be ultimately. Will try to polish as I can always reverse or rough up a microbevel.
 
Last edited:
I sharpened mine at a straight 17dps on a TS Prof. Ran it up to 2200 grit on the stones, then stropped with diamond compound down to 0.5 microns, so it's pretty much a mirror. It got extremely sharp. That was months ago, and it's still hair popping after plenty of use. I didn't have any issues with the burr. It came off beautifully, but I also didn't micro-bevel. That might be where something weird is happening or you.
 
I would guess it was the micro bevel, based on my experience. My experience is that when stropping diamonds tend to raise burrs, leading to much higher BESS scores. The only way to make diamonds work is to use very little so they don't do much. I prefer aluminum oxide for improving the keenness after my last stone, even on Maxamet. Yeah, totally against the trend here, but I can't argue with empirical evidence.
 
Just sharpened my sage 5 in Rex 121 on the wicked edge for first time. Was able to get a pretty consistent bevel on both sides at around 15 degrees. This seemed to mirror the factory bevel fairly well.
I used a sharpie to make sure I apexed and also worked through the grits to ensure I minimized the bur.
I know I need to get a loop to up my game and figure out what is truly going on.

I ended with 17 dps micro bevel. Still not very sharp - will cut paper but with effort (does not glide through).
For those with experience with Rex, what angles and finish are you using? Can you get this steel as sharp as most others? Polished vs course?

If you want to get the best out of a high carbide steel like Rex 121, then sharpen it to a fairly coarse edge.

Yes, you can polish it to a mirror and get it very sharp but that is not where a steel like this excels. Leave a coarse edge on it and it can hold up darn near indefinitely.

A super sharp hair whittling edge will disappear relatively quickly even on a steel like Rex 121, Maxamet etc and then you'll be left with a sharp edge that doesn't feel or perform as well as it could. There's a reason why the sharpest possible straight razor polished edges come from much more basic steels. High vanadium or tungsten carbide steels are not meant for such an edge. Yes, you can get them there but it's not where they win any awards.

If you like the polished look, mirror polish the bevel like you did, then raise your angle enough to create a microbevel back down to a medium-coarse stone.
 
Last edited:
If you want to get the best out of a high carbide steel like Rex 121, then sharpen it to a fairly coarse edge.

Yes, you can polish it to a mirror and get it very sharp but that is not where a steel like this excels. Leave a coarse edge on it and it can hold up darn near indefinitely.

A super sharp hair whittling edge will disappear relatively quickly even on a steel like Rex 121, Maxamet etc and then you'll be left with a sharp edge that doesn't feel or perform as well as it could. There's a reason why the sharpest possible straight razor polished edges come from much more basic steels. High vanadium or tungsten carbide steels are not meant for such an edge. Yes, you can get them there but it's not where they win any awards.

If you like the polished look, mirror polish the bevel like you did, then raise your angle enough to create a microbevel back down to a medium-coarse stone.
See my edit in original post. I ended with 800 grit micro bevel at 3 degrees more obtuse (18 vs 15) and finished with one micron stopping to get sharp. Seems I can never get decent edges without the final stopping (when finishing with medium grit) but should still technically be a course finish? Should be quite some time before I need to touch up depending on use.
 
Last edited:
Seems I can never get decent edges without the final stopping (when finishing with medium grit) but should still technically be a course finish?

Depends on what you define as a decent edge. Even a coarse, un-stropped edge on Rex 121 can be a very good all-rounder every day edge and can hold up well for a very long time.

A great every day use edge doesn't have to pop hairs or shave effortlessly.
 
Depends on what you define as a decent edge. Even a coarse, un-stropped edge on Rex 121 can be a very good all-rounder every day edge and can hold up well for a very long time.

A great every day use edge doesn't have to pop hairs or shave effortlessly.
Would not cleanly cut paper until I stropped. I assume I still had a bur remaining.
Spent some time with the stops and all good now.
 
Last edited:
If you want to get the best out of a high carbide steel like Rex 121, then sharpen it to a fairly coarse edge.

Yes, you can polish it to a mirror and get it very sharp but that is not where a steel like this excels. Leave a coarse edge on it and it can hold up darn near indefinitely.

A super sharp hair whittling edge will disappear relatively quickly even on a steel like Rex 121, Maxamet etc and then you'll be left with a sharp edge that doesn't feel or perform as well as it could. There's a reason why the sharpest possible straight razor polished edges come from much more basic steels. High vanadium or tungsten carbide steels are not meant for such an edge. Yes, you can get them there but it's not where they win any awards.

If you like the polished look, mirror polish the bevel like you did, then raise your angle enough to create a microbevel back down to a medium-coarse stone.
Would 325, 400, 600 or 800 grit be good for a long lasting edge? Would it still be good to strop them for bur minimazation ? I have had some longer lasting success with 325 blue DMT stone and then stropping a little. Would the other grits be just as acceptable? Thank you!
 
Would 325, 400, 600 or 800 grit be good for a long lasting edge? Would it still be good to strop them for bur minimazation ? I have had some longer lasting success with 325 blue DMT stone and then stropping a little. Would the other grits be just as acceptable? Thank you!

You could even stop at 400 or 600 for a nice every day use Rex 121 edge.
 
Would it also apply to magnacut? AEB-L? Carbon steels? Would those steels also last longer with the lower or medium grits? My apologies you all were talking Rex 121 but I dont have that steel yet.
 
Would it also apply to magnacut? AEB-L? Carbon steels? Would those steels also last longer with the lower or medium grits? My apologies you all were talking Rex 121 but I dont have that steel yet.

That's not easy to answer because it really depends on what those knives are being used for on a daily basis. If it's a hard working edge for real every day tasks (not just slicing thin paper or splitting hairs to show how off the edge on YouTube videos, but real world use), then I would say keep it coarse.

Typically for most every day carry and general use edges on my pocket knives, I prefer lower grit finishes. Most high vanadium or similar carbide steels excel at holding lower grit every day use edges.
 
Edit: went back and took my time and got sharp. Stayed with 15 dps then a handful of passes at 18 dps at 800 grit diamond followed by stropping 1 micron diamond. The stopping was needed to bring it to sharp but I assume I still technically have a course edge.[/B]

That works, I call that the "Simple Rick"

One stone, one strop

Execution and proper abrasives will be more important than pure stone progression and mirror finish anyways.

The secret has always been getting a crisp, low fatigue, burr free edge.

Like Burt said, whether that works for all steels depends on what you are trying to do.

One of my conversations with Murray Carter,
He told me "there are things you cut to keep and there are things you cut to throw away."

Things that you cut to keep for example, when you are shaving your face with a straight razor you want the edge to slide along your skin without irritating it and snagging into it.

The objective is to cleanly cleave the hairs off your face.

Keep your face; cuts to keep.

Or if you are making delicate cuts for sashimi, that is also an example of cuts to keep.


Cuts to throw away like tearing down cardboard. You're not so focused on the quality of the cut as much as the ability for it to slice and shred with low cut forces.

That's an example of cutting things to throw away.

As a sharpener, you are in control of teeth and angles.


So you can modify these behaviors to synergize the use case or preference.

As far as if specific steels require specific finishes or if one steel likes one finish or another,

My experience has been a lot of that specifically for matching finish to steel is at the mercy of the sharpening ability of the sharpener and their equipment, along with most importantly the heat treatment.
(HT is not in the consumer's control)

There is certainly a range of performance in sharpening behavior in the same steel depending on the heat treatment but that's another subject.

The end takeaway is that the higher the polish with a clean apex, the less force it takes for a pure push cut.

The coarser the edge, the less force it takes to slicing, saw like draw cut.

The pitfalls to a polished edge is it is extremely difficult to make a clean apex at high finish without the apex being rounded over microscopically resulting in a edge that has "no bite" and is completely slick with "no grab"

Folks have probably noticed they can have an edge that cuts receipt paper cleanly but does not grab or slice elastic material like tissue very well which by the way is perfect for face shaving.

The secret benefit to a polished edge is that it is more stable and durable since the stress risers from deeper scratches and deformation stress from coarser abrasive grains plowing through the steel have been removed.

A polished edge is a tougher edge.


A coarse edge (especially medium grit ) is easier to get to a crisp apex since it is less prone to burnishing and rounding over with more defined cutting from the coarse stone.

If we look at the work of Dr Todd Simpson he shows that we are essentially making a strong, straightened out residual burr at low grit which can be pretty effective depending on use despite being such a taboo. Of course, there are different kinds of burrs like explained by Dr Vadim (RIP) but that's another subject.


With a coarse edge, it will always take less force to draw cut and slice through things than it ever will for the most polished edge to.

It should also be noted that push cutting (cleaving) no matter how good or polished will always take more force than draw cutting (slicing) regardless.

That is a fundamental feature difference; drawing and sawing in a slicing motion will always take less force than pushing and cleaving regardless of edge finish.

It's just that the edge finish will maximize either feature better.

So, in use, there is certainly a pleasant experience with a coarse edge doing a light touch and draw whenever cutting with things and it will require the least amount of force to function Just as there is a pleasant euphoria in use with a very crisp, polished edge push cutting with quiet ease.

The main problem with coarse edges is that it is extremely difficult if not impossible to fully remove the burr like I mentioned above.


So, high sharpness coarse edge can be especially short-lived depending on how it's processed by the sharpener. However, hair shaving sharpness is fleeting regardless but it is certainly maximized with higher polish.

Coarser edges are also fundamentally more prone to chipping failure due to coarse scratches acting as stress risers and deformation buildup creating fatigue, especially if the apex is just a reinforced straightened out residual burr.



Which is best between coarse and polish?


You'll find folks on either end of the spectrum sometimes they are just trapped by their ability to execute.

For example.


Some people are stuck with coarse edges due to not being able to make a crisp polished edge due to lack of execution, equipment and understanding of how to avoid rounding over the apex.

"I can't get a sharp polished edge like I can with a coarse finish"

Or you will have people in the other camp who cannot make a coarse edge to save their life without massive floppy burr. This results in them relying on higher polish as a crutch in order to get a crisper edge and remove burr.

Avoid these camps of thinking and think of either option as a tool in your toolbox.

My general preference has always been a polished toothy edge like what Dave Martell and Eytan Zias taught.



So, IMHO the best of both worlds for general use is a medium grit edge with a 1 micron strop unless a specialized use dictates what is needed.

Keep in mind,
Geometry however is one of the greatest factors for performance.

You then tune the geometry to what you need.

If you want a ferrari go 15° per side.

If you want a monster truck 25° per side.

So, we don't want to be the guys whining about not having Ferrari performance because we were unaware we created a monster truck geometry and vice versa.

Mastering all of that and you can make your edges customized for whatever you need within reason.

Hope that was clear as mud.
 
Last edited:
Back
Top