AUS-8, D2 and VG-10 Deerhunters on cardboard

Cliff Stamp

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I intended this to be a simple test, cut cardboard until it became too difficult with each blade. Then look at each blade under a couple of sharpness tests to evaluate just how much of a difference in blunting was induced, and a few sharpening methods to see how the blades responded. In theory it seemed sound, but in practice it didn't go as planned.

I was cutting 1/4" double line-ridged cardboard, through the ridges using the entire blade length on a slicing pass. This was the critical mistake. Slicing is a very poor way in general to test for sharpness as it "smears" the cut out so much that blunt spots can be hidden, and in general a blade can be far blunter and still slice something that what is required to do a push cut. In retrospect the cutting should have been done with a push cut, and all cuts done on a very small area of the blade. This would have also allowed a quick and easy comparison of before and after sharpness as much of the blade would still be at full sharpness.

The result : each blade cut all the cardboard at hand, ~600 feet total. I could not tell the blades apart by feel in use. I then did some cuts measuring the amount of force required. The blades would cut into the cardboard with less than a pound of force, however to push the blades through the cardboard required ~25 lbs. Thus the effect that sharpness had on the cutting ability was very small. For example if the AUS-8A blade had degraded twice as much as the other knives, the total effect on the force increase would be just ~4 percent. Thus in other words it was impossible to judge the sharpness of the blades by the amount of force of the cuts.

Inspecting the blades under magnification revealed another side to the picture. The AUS 8A blade had much more extensive wear, it was missing pieces of blade about twice as deep as the other steels [2.5 mm chips, with patches of wear up to 1 cm long [x20 mag]) and as much or more in total amount of wear. Thus there was no doubt that the AUS-8A blade blunted much more than the others, which isn't surprising. The VG-10 and D2 blade were very close, it would be difficult to judge which was more worn, but the D2 blade would probably be given the nod.

I then stropped each blade, five passes per side on CrO. The AUS-8 blade jumped back immediately back to hair shaving ability and was now sharper than the other two. Under magnification though the more extensive edge damage was still there, the edge had just been more responsive to the aligned and light polish of the very edge. However when the edges were restored fully using SiC sandpaper, the AUS-8A blade took about three times as long to have all the damage removed. This is a rough estimate as I was only checking even 10 passes, this was all that was required for the VG-10 and D2 blade, but the AUS-8A one took two more runs of 10 passes.

No real surprises in the above, the harder and more wear resistant blades take less blunting in the cutting and take less effort to restore on an abrasive as the damage isn't as extensive. The softer blade is however more responsive to the stropping. Geometry is also shown to be much more key in determing the cutting ability of a knife when cutting thick and binding materials than the actual sharpness of the edge.

-Cliff
 
The cardboard provides reasonable low impact abrasion. Doing thread cutting tests should help quantify how much the edges are dulling. If you want a sharpness test that covers a wider area of the edge you could supplement your thread test with a ribbon cutting test. Quarter inch wide christmas ribbon would probably work and keep the forces within instrumentation scale.
 
Jeff Clark :

Doing thread cutting tests should help quantify how much the edges are dulling.

Yes, I somewhat indented to do this, but instead just went by feel to see if the difference in edge retention would show itself on that scale, to answer the basic question could you actually tell the knives apart in basic usage. I figured I had easy enough cardboard, which I would have been true if I did the cuts in the correct manner. I have a 3/8" hemp rope cutting trial planned in which I will do sharpness testing during the cutting, hopefully this weekend.

If you want a sharpness test that covers a wider area of the edge you could supplement your thread test with a ribbon cutting test.

That is an excellent idea, the probelm of the thread being so isolated had been bothering me for some time, that is an obvious solution which I missed. I had been using 1/4" poly for large edge areas, but it is slicing and not push cutting so it measures a related but not identical property.

Eric, there was no significant difference in the behavior of the D2 and VG-10 blades in the above, note however that the effects were looked at in a very gross way.

D2 and VG-10 in the Deerhunter are at 59/61 RC. The AUS-8A blade is spec'ed at 57/59 RC. All blades were honed to a fine shaving finish before the cuts, and the edge geometry and edge angle on all blades were very similar, 0.010 - 0.020" thick, at 12-14 degrees per side.

-Cliff
 
Ressurecting this topic since it seemed closer to my question than your rope cutting experiment. Have you tried these blades in the kitchen to see if there is a noticeable difference?

These are designed as hunting knives. That largely involves work on hide, meat, and sinew. Working on chicken and meat with bones would give some sense of how the blades work on the subtle end of the job. I wondered whether you would notice a difference between AUS-8 and D2 in real application. I would expect VG-10 to be very similar to AUS-8. These knives work well in the kitchen.
 
The blades when freshly sharpened, have near identical cutting ability as the profiles are very similar. Since foods in general are very soft and not abrasive, the edge holding is near infinite on such materials even with cheap knives, so you can't tell a difference there either. The only thing that comes to mind that might be able to separate the knives in that regard would be peeling vegetables that were not cleaned, but you would need a fair amount of them [or if you process a lot of shark or lobster etc. on a regular basic]. However the knives may have large difference in performance in regards to corrosion resistance, and edge durability [tossed in the skink, scraping, cutting on plates etc.] . Corrosion resistance should be trivial to test, just soak in lemon juice , wait, and then test sharpness. Impact testing could be looked at without undue difficulty as well.

-Cliff
 
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