CPM REX 45 | Edge Performance

[Albatross]

What's everyone's favorite edge finish on rex 45?

Lately I have been experimenting with DMT coarse through EF, followed by a series of strops, ending at .25 micron. I've used my Rex45 knives to cut leather and this finish works very well for making clean, quick cuts. Previously I had finished with a DMT fine, followed by a 1 micron strop and was happy with that.

[Karl_H]

Has anyone experimented with thinner primary bevel grind (reduce thickness behind the edge) or more acute edge grind (secondary bevels).

I am hoping to turn my my Rex 45 Native 5 into a pocket scalpel. So, I am wondering if anyone has found any practical limit on how him REX 45 can be ground for straight draw and push cuts in relatively soft materials (no twisting, torquing, prying, scraping, etc.), without excessive deformation or chipping.

I was thinking of going for a zero grind (no secondary bevel) or keeping a 15 dps microbevel (~0.005” BTE).

[GarageBoy]

Now that more of the sprints are out, anyone have good results (good fine edge holding) with finer diamond stones? I remember hearing that rex 45 has finer carbides vs m4, so it should be better in that aspect, right?

[GarageBoy]

Also, the manix 2 and native 5 are thinner than the para 3, correct?
Figured if I'm going with a fancy steels, I'd get one with the best cutting geometry

[Sharp Guy]

Also, the manix 2 and native 5 are thinner than the para 3, correct?
Figured if I'm going with a fancy steels, I'd get one with the best cutting geometry

Blade stock thickness on the Para 3 is .145"/3.7 mm. Native 5 and Manix 2 are .125"/3.2 mm. So they're a little thinner but I have noticed much of a difference in use

[Karl_H]

I am going to necro this thread. Hopefully, this will prompt others to provide their preferred edge geometry and finish for REX45 and possibly provide some feedback to Spyderco regarding the heat treatment.

I reprofiled the edge bevel to 15 dps. I finished sharpening on a 800 grit diamond stone and used a 1 micron diamond strop to deburr. I experienced significant chipping when slicing rubber inner tubes. Carving wood also produced extensive chipping along the entirely of the edge that was in contact with wood, but the chips were not as deep as the ones that occurred from cutting rubber.

I have yet to ever roll the edge. With the current heat treatment, it seems like the edge will always fail by chipping, before rolling. I haven’t measured the hardness of my blade. However, based on my experience, I would be willing to sacrifice a bit of hardness to increase the toughness.

Based on my limited experience, I wouldn’t recommend reprofiling the edge to less than 17 degrees, unless you also put a more obtuse microbevel on the edge. Finishing on higher grit and polishing the edge should also help reduce chipping. If you want a low grit, toothy edge, increasing the edge bevel angle might help avoid chipping. That being said, I think K390, M4, and Maxamet are generally preferable for toothy edges and REX 45 / HAP 40 is better suited for finer edges.

Fortunately, Larrin did some testing on REX 45, which can be found here: https://knifesteelnerds.com/2021/05/10/ ... 15-rex-76/

When Larrin tried to replicate the Spyderco heat treatment, he got a an impact toughness of what appears to be 6 to 7 ft-lbs. I personally feel like the sweet spot for toughness is probably closer to 15 ft-lbs (per Larrin’s test method). I would suggest that Spyderco consider revising the heat treatment for REX 45 to try and achieve an impact toughness of 10-15 ft-lbs, which would likely require reducing the hardness a bit.

[Accutron]

PM2 and Chief, KME diamond at 15DPS with a 1500 grit finish, deburr with my thumb. I've never had any significant chips or rolls, with 3+ years of use. I've cut hardwood, cable ties, small gauge copper wire, scraped paint off aluminum surfaces, etc.

I am firmly *against* any lowering of the Rex 45 heat treatment. High hardness is the critical factor which sets it apart from M4. As ran by Golden, Rex 45 has far better edge stability, and is more capable of supporting low bevel angles. Lowering the HRC nullifies that advantage.

[TkoK83Spy]

I've taken 2 of my 3 Rex45 knives down to 17dps. Neither over 600 grit finish. I cut mostly warehouse type of stuff (miles of cardboard, braided tape, rope, plastic strapping) I've only received the tiniest ding in my Manix edge one day. Still cuts great so I'm just leaving it as is until the next session.

I've been very impressed with every factor of Rex45 in terms of edge stability, wear resistance and sharpening. Top 2 steel for me and my uses.

[tomhosangoutdoors]

PM2 and Chief, KME diamond at 15DPS with a 1500 grit finish, deburr with my thumb. I've never had any significant chips or rolls, with 3+ years of use. I've cut hardwood, cable ties, small gauge copper wire, scraped paint off aluminum surfaces, etc.

I am firmly *against* any lowering of the Rex 45 heat treatment. High hardness is the critical factor which sets it apart from M4. As ran by Golden, Rex 45 has far better edge stability, and is more capable of supporting low bevel angles. Lowering the HRC nullifies that advantage.

100% agree with this. Without that additional hardness, it's basically M4 at that point. Lowering the hardness will definitely affect edge retention as well. Arguably worse than M4 in that regard at the same hardness.

[JRinFL]

It looks like high hardness is all Rex 45 has over M4. The better toughness of M4 with very similar edge retention is an appealing combination. However, M4 has pitted on me and Rex 45 has not yet done that in my use.

[RustyIron]

I am going to necro this thread. Hopefully, this will prompt others to provide their preferred edge geometry and finish for REX45 and possibly provide some feedback to Spyderco regarding the heat treatment.

My observations with REX45 are not unlike to your own. I get a lot of microscopic chipping through normal use. It's not so terrible that it renders the knife unsuitable for use, in fact the blade can remain usably sharp despite the chipping. When I sharpen, I'll usually leave a couple divots in the edge just because getting rid of them would remove more blade material, and I'll just get new chips the first time I use the knife. Despite this, I still prefer REX45 over SV30, VG10, etc.

I'm not knowledgable enough to suggest how to make REX45 better... other than maybe forgetting it and getting the knife in K390. I suspect that the boys and girls at Spyderco didn't just randomly settle upon a specific heat treatment, and there are some good reasons why they did what they did. Such things are really outside my area of expertise.

You asked how I sharpen REX45. I always sharpen it to 26 degrees, 13 per side. Sometimes I'll stop at 250 or 650 on my CGSW stones. More often I'll take it to 4k, and often I'll strop it with some 1 micron or 0.25 micron diamonds. I don't get too fixated on any single finish, as I enjoy sharpening and seeing how cutting performance changes. My finished edges need to be able to give a close, clean shave ( I wouldn't actually DO that, I'm speaking metaphorically). Once the edge can do that, I'm happy. If it can't, then I can never be happy with the edge.

Here are a handful of REX45 sprints that are in the desk drawer right now.

[Accutron]

If anybody's interested in trying Rex 45 with a lower heat treatment, Bradford makes a Guardian 3 at 64-65, and a fillet knife at 58-60 with a spring temper.

https://www.gpknives.com/catalogsearch/result/?q=rex+45

https://bradfordknives.com/gatsby/521-1 ... knife.html

[Snacktime]

If anybody's interested in trying Rex 45 with a lower heat treatment, Bradford makes a Guardian 3 at 64-65, and a fillet knife at 58-60 with a spring temper.

https://www.gpknives.com/catalogsearch/result/?q=rex+45

https://bradfordknives.com/gatsby/521-1 ... knife.html

I shouldn't have clicked the link to the fillet knife, that is one sexy knife.

I keep my REX45 at 20-25, I tend to get big chips when I hit something or put lateral pressure on the edge (scaping). I would give up some edge on my rex45 for some durability for my use. I will say chipping has slowed down as I have taken more steel off. I have really become a fan of the Chief with rex45 the thinner leading edge is much easier to maintain!

[tomhosangoutdoors]

Screen Shot 2021-10-20 at 12.19.50 PM.jpg

It looks like high hardness is all Rex 45 has over M4. The better toughness of M4 with very similar edge retention is an appealing combination. However, M4 has pitted on me and Rex 45 has not yet done that in my use.

That's not exactly a perfect comparison as that M4 was tested at roughly 61 and REX45 was at 67.5. 61 for M4 is a bit low to what we've seen from Spyderco (62-65) and the REX45 was higher than what we've seen (65-67). I bet if you bumped the M4 to what Spyderco runs it at, the toughness would drop pretty significantly and also become less stable at the edge. M4 gets a little wonky at the higher end of its hardness range when paired with lower edge angles. REX45 has the stability at the higher hardness to support the lower edge angles. As always, edge angle should be based on what you're using it for and it's going to vary from person to person. I've never experienced any chipping on REX45 at 15dps in my use, but I could definitely see it happening depending on the use.

[Karl_H]

I have pulled REX45 and M4 hardness measurements from the HRC Database: viewtopic.php?t=83847

REX45 Military - (66.3 - 67) HRC
REX45 Paramilitary 2 - (65 - 66.7) HRC
REX45 PM2's @ 66.7
REX45 Para 3 - 64.7 HRC
#40. P3 Lwt-rex45-65.2
#41. P3 G10 B. Orange rex45-66
#42. P3 C-shoppe blue-rex45-66.4
#43. P3 C-shoppe green-rex45-66.75
#44 Manix 2-G10 rex45-66.9
#45. Shaman rosewood-rex45-67.1

#34 Shaman Bhq-dlc-M4-63
#38 P3-BHQ- M4-64.7
#39 Pm2 BHQ-dlc M4-65
M4 Paramilitary 2 - 64.3 HRC
M4 Manix 2 - 64.2 HRC
M4 Shaman - (63.9 - 64) HRC
M4 Shaman @ 64HRC
M4 Gayle-Bradley 2 - 63.2 HRC
M4 Para 3 - 63 HRC
M4 Mule - (60.8 - 62.5 HRC)
M4 Gayle-Bradley 1 - 62.5 HRC

I also looked Tom Hosang's spreadsheet: https://docs.google.com/spreadsheets/u/ ... I/htmlview . Tom's spreadsheet might be using some of the same values, and so I am not sure if any of those datapoint are independent from the ones listed above.

I also looked at the Crucible data sheets for CPM REX45 (http://www.crucible.com/PDFs/DataSheets ... v12010.pdf) and CPM M4 (https://www.crucible.com/PDFs/DataSheet ... 202010.pdf)

If one assumes that Spyderco is using the same heat treatments that Crucible used to create these datasets, then the c-notch charpy impact toughness range for Spyderco's REX45 and M4 knives can be inferred from the Crucible data set:

Toughness Range for CPM REX45 Reported By Crucible
- 15 ft-lbs (at 67 HRC)
- 20 ft-lbs (at 65 HRC)

In the hardness range from 67 to 65 HRC, the change in toughness of REX 45 can be estimated to increase by 25%. This essentially covers the entire hardness range measured in Spyderco's knives.

Toughness Range for CPM M4 Reported By Crucible
- 20 ft-lbs (at 65.5 HRC)
- 28 ft-lbs (at 63.5 HRC)

In the hardness range from 65.5 to 63.5 HRC, the change in toughness of CPM M4 can be estimated to increase by approximately 28%. This essentially covers half the hardness range measured in Spyderco's knives (~ 62 to 65 HRC, if you exclude the mules).

I thought it was interesting that the toughness of M4 at 65.5 HRC and REX45 at 65 HRC were the same (20 ft-lbs).

While the hardness ranges for each steel may seem to be insignificant, you can see the potential for huge swings in toughness. Obviously, these inferences would be totally invalid if Spyderco's heat treatment differs significantly from Crucible's.

[Wartstein]

If anybody's interested in trying Rex 45 with a lower heat treatment, Bradford makes a Guardian 3 at 64-65, and a fillet knife at 58-60 with a spring temper.

https://www.gpknives.com/catalogsearch/result/?q=rex+45

https://bradfordknives.com/gatsby/521-1 ... knife.html

I shouldn't have clicked the link to the fillet knife, that is one sexy knife.

I keep my REX45 at 20-25, I tend to get big chips when I hit something or put lateral pressure on the edge (scaping). I would give up some edge on my rex45 for some durability for my use. I will say chipping has slowed down as I have taken more steel off. I have really become a fan of the Chief with rex45 the thinner leading edge is much easier to maintain!

You mean per side of course, right?

So that means that actually some of your REX 45 knives are sharpened to 50 degrees inclusive??

If you are talking about Spyderco folders this really surprises me. As said once more in Larrins latest article: More obtuse angle means a rather significant decrease in edge retention. So if your knives need to be sharpened up to 50 incl. in order to avoid chips, the very good edge retention of REX 45 would be pretty much annuled by that and it would have no real advantage over steels with nominally less edge retention, but the potential to be sharpened to a more acute edge..

[R100]

I am really surprised and disappointed by the accounts of Rex45 chipping. It has put me off a purchase I was considering. I have a number of S30v knives taken back very thin behind the edge and given a 30 degree microbevel. I have not experienced chipping with fairly heavy use unless I hit steel or rock or do something stupid. The only conclusion I can draw from this thread is that Rex45 is a long way behind S30V as an edc steel and I would be crazy to use it. What am I missing?

Dan

[TkoK83Spy]

I am really surprised and disappointed by the accounts of Rex45 chipping. It has put me off a purchase I was considering. I have a number of S30v knives taken back very thin behind the edge and given a 30 degree microbevel. I have not experienced chipping with fairly heavy use unless I hit steel or rock or do something stupid. The only conclusion I can draw from this thread is that Rex45 is a long way behind S30V as an edc steel and I would be crazy to use it. What am I missing?

Dan

I really hope you're joking?? This post is making me twitch.

[The Meat man]

I am really surprised and disappointed by the accounts of Rex45 chipping. It has put me off a purchase I was considering. I have a number of S30v knives taken back very thin behind the edge and given a 30 degree microbevel. I have not experienced chipping with fairly heavy use unless I hit steel or rock or do something stupid. The only conclusion I can draw from this thread is that Rex45 is a long way behind S30V as an edc steel and I would be crazy to use it. What am I missing?

Dan

If you look back a few pages, you can see where I used my CPM REX 45 Military to cut through rope, cardboard, thin and thick copper wires, and a steel can. I thought the steel did very well. It's definitely stronger than CPM S30V, much stronger.

[Sharp Guy]

I am really surprised and disappointed by the accounts of Rex45 chipping. It has put me off a purchase I was considering. I have a number of S30v knives taken back very thin behind the edge and given a 30 degree microbevel. I have not experienced chipping with fairly heavy use unless I hit steel or rock or do something stupid. The only conclusion I can draw from this thread is that Rex45 is a long way behind S30V as an edc steel and I would be crazy to use it. What am I missing?

Dan

I really hope you're joking?? This post is making me twitch.

Haha! That's the way the internet works. Tons of people praise these Spyderco REX45 knives and then a couple people come along and say they've had chipping and suddenly it's no good