Synov wrote: ↑Sat Mar 21, 2026 7:33 am
Mage7 wrote: ↑Fri Mar 20, 2026 10:25 pm
That's just according to CATRA though. A box cutter blade that's too dull to bite into your finger tips will outcut an axe head that will shave your face in a CATRA test. Geometry dictates cutting ability, but sharpness doesn't necessarily dictate cutting ability.
But cutting ability is ultimately what we're talking about. You don't want to use an axe to cut cardboard regardless of how sharp it is. CATRA is the best proxy we have for determining edge retention in most common materials.
And I don't know why people would be worried about a thin 3V edge being unstable. There's a reason razor blades are not made from high carbide steels.
Let's say you cut up a few dozen boxes or something one day, and you go home and decide to touch up the edge because it doesn't shave arm hair or cut printer paper easily.
Did you just test its cutting ability or its sharpness?
The answer depends on whether or not it was still cutting the material you dulled it on. If it could, it still had the ability to cut what you needed it to cut, right?
On the other hand if it couldn't shave or cut printer paper, you would be focusing on sharpness rather than cutting ability.
Or it may have still been able to cut the material you cut to dull it, and still shaved and cut printer paper, but you wanted to touch it up so that the forces required to cut the same material the next day were as low as possible for a little while. In that context, what's making the force to cut lower, the sharpness or the cutting ability?
CATRA doesn't test edge retention, it tests cutting ability, and not in a way that reflects how many users try to optimize it. I would say that most users who touch up a blade at the end of the day, or even concern themselves with how long a knife will remain shaving sharp or paper cutting sharp, are not as concerned about pure cutting ability as CATRA measures it.
Let's talk about real steels and use for a second. I have Mules in 15V, K294, and T15. According to CATRA, 15V should stay sharper for much longer than either K294 or T15, but in my actual experience T15 holds a shaving sharp edge longer than either 15V or K294. However all three of them cut over half a mile of cardboard during testing without any indication that they wouldn't cut 2-3x that amount before they actually lost their ability to cut it. Except I don't usually spend all day cutting cardboard, so I still wanted them to have an edge sharp enough to cut other material easily too even though I could still muscle them through cardboard.
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As per your question about why people would be worried about it being unstable at thin geometries: Plastic deformation. Unless it was hardened to 65+ HRC then it will have a tendency to roll and dent more easily than high HRC steel, and especially at low edge geometry.
If you're asserting that razor blades don't roll or dent easily then I would encourage you to buy a few and use a laser goniometer to measure the edge angles and a pocket microscope to see the method of dulling. I'll save you the time and tell you that most are between around 24-34 degrees inclusive, and they dull from denting rather than chipping.
That may sound pretty acute but keep in mind that a straight razor would be 16-20 degrees inclusive. The reason DE razor blades are ground to a more obtuse angle is so they don't need to be hardened more to be able to resist plastic deformation, because then they'd suffer chipping more than denting. Chipping and fracturing tends to increase the edge apex radius a lot more rapidly than small dents do, which would more rapidly reduce their shaving ability.
3V would be great if it was left hard enough to perform the same way as razor blades, but lowering its angle would actually make it more prone to plastic deformation and require it to be harder to compensate. Then once it's harder it will lose its toughness advantage and be more prone to chipping and fracturing. I know that CATRA shows that thinner geometry means more cutting ability, but again that's not really a measure of sharpness as much as it is a measure of cutting ability. A very thin 3V blade will cut for a long time, but so would a moderately thin S110V blade. The S110V blade would dull by way of microchipping, but the 3V would dull by way of microdenting and neither one would be particularly sharp even though their cutting ability remained high.
Sorry for the long post, but I just really think people are misapplying the characteristics CATRA measures, especially in the context of edge geometry and sharpness.
