Polyhedral Tungsten Carbide

[tgbto]

Guys, I must confess I've fallen for it out of curiosity again.
I was looking for a nice pocket knife and stumbled across this one. It's supposed to be 71 HRC and "flexible", and pure polyhedral tungsten carbide... I wanted to see for myself how sharp it really is and if I would be able to improve sharpness with the Tormek Diamond stones... I'll keep you posted!

Cheers,

Nick.

[micha]

Nick,

you may already have come across this, too: https://knifesteelnerds.com/2019/11/18/sandrin-carbide-what-is-it/
I'm looking forward to reading about your results.
Mike

[tgbto]

Hey Micha,

I hadn't come across this information yet, thanks a bunch !

I don't expect being able to do an outstanding job when sharpening it, but it ought to be fun...

[tim]

Just a heads up about carbide. Nickel is the "glue" carbide needs to hold together. Chlorine in tap water breaks nickel down. As a toolmaker I`ve seen solid carbide tooling in stamping dies come apart. Use distilled water in your tormek for carbide.

[tgbto]

Thank you for the advice, I appreciate it!

I was wondering whether the anti-corrosion additive for Tormek Diamond wheels (the obvious wheel choice for such hard material) would help as well ?

And I think the incredibly detailed paper provided by Mike mentions Cobalt being used as cement, with a minimal amount of Chromium Carbide... I don't know if Cobalt has the same issue as Nickel, but I guess distilled water won't hurt anyway...

[tim]

I wish you luck with the carbide experiment. Surface ground carbide years ago and one of the frustrating things I noticed was fractures throughout the ground surface. Used diamond wheels with no coolant.
Check the chemicals in the tormek water additive and make sure there wont be a reaction with your blades.

[tgbto]

Well, I just received it yesterday, and haven't decided to sharpen it yet, as I want to see how it performs before I ruin it ^^

I took an out-of-the-box BESS measurement, which came out at 150. I usually get around 50-80 BESS for standard steel knives with SG-> SJ -> PA-77@+2°, and around 80-100 with DF -> DE -> composite wheel @+2, we'll see how it goes!

[tgbto]

Well, I've used this knife very little.

Yet when I measured it before sharpening, it came out @320BESS. Why it lost 170 BESS after having cut maybe 40 times is beyond me, especially for a knife advertising a huge edge retention. Does it bang against the handle when folded ? Anyway...

In terms of sharpening, It was kind of weird. I used distillated water with the anticorrosion additive, I don't know what's inside and if it could damage cobalt, which is the cement for this blade. I started with the DF-250, using very low pressure, the marker trick, and I was amazed by how quickly it would grind the blade. There was a tiny bit of a burr, that I could barely feel under my fingers and hardly see under a standard microscope.

In terms of movement I had to do a double backward pivoting ^^ : one to grind the heel, one to grind the tip. The standard draw&lift motion resulted in too wide a bevel.

When I was sure I was hitting the edge on both sides (with a combination of sharpie and microscope) I switched to the DF-250, then honed on the felt wheel with 1 micron diamond spray @+1 dps, and finished on the leather wheel with .25 spray just for the show.

The result was unexpected, I will try to take a picture somehow and upload it : the apex itself was burrless, very clean, very straight, but the edge was full of tiny scratches, about 0.5 to .2 millimeters apart. Maybe the diamond wheel tore the hard carbides apart from the soft cobalt. I didn't look at the edge under the microscope out of the box, but it looked quite scratchy already. In my experience it is common for factory-sharpened blades.

And the blade came out @130 BESS. Marginally better than out of the box, taking into account the standard deviation on such measurements. So all in all it seems that this is not the best way to sharpen such a blade, and I am not quite sure the edge retention is any better than a 25€ Opinel...

[tim]

Hone more to remove scratches? Carbide cutting tools when they are new are not a sharp to the touch as new high speed steel ones. Wonder if it is the same with blades? Carbide needs a higher pressure to cut where steel ones need to be very sharp to work.

[tgbto]

Actually the scratches can go the entire height of the bevel, so I'm not sure honing would make much of a difference...

[cbwx34]

...
In terms of sharpening, It was kind of weird. I used distillated water with the anticorrosion additive, I don't know what's inside and if it could damage cobalt, which is the cement for this blade. I started with the DF-250, using very low pressure, the marker trick, and I was amazed by how quickly it would grind the blade. There was a tiny bit of a burr, that I could barely feel under my fingers and hardly see under a standard microscope.

...
When I was sure I was hitting the edge on both sides (with a combination of sharpie and microscope) I switched to the DF-250, then honed on the felt wheel with 1 micron diamond spray @+1 dps, and finished on the leather wheel with .25 spray just for the show.

...

Just for clarity... 

[tgbto]

...
In terms of sharpening, It was kind of weird. I used distillated water with the anticorrosion additive, I don't know what's inside and if it could damage cobalt, which is the cement for this blade. I started with the DF-250, using very low pressure, the marker trick, and I was amazed by how quickly it would grind the blade. There was a tiny bit of a burr, that I could barely feel under my fingers and hardly see under a standard microscope.

...
When I was sure I was hitting the edge on both sides (with a combination of sharpie and microscope) I switched to the DF-250, then honed on the felt wheel with 1 micron diamond spray @+1 dps, and finished on the leather wheel with .25 spray just for the show.

...

Just for clarity... 

Right, sorry. It was first DF-250 then DE-250.

[cbwx34]

Right, sorry. It was first DF-250 then DE-250.

Thanks.  (I was curious, because if you used the coarse wheel, thought that might be an issue).