CPM-M4 at low angles. My experience recently.

Chris "Anagarika";16565087 said:
Jason, Chuck,

I don't get it.

For same final apex bevel, say 12° per side. On thicker blade (primary grind) this results in wide bevel, say 0.4" before it transition to the primary grind. At this point, the shoulder thickness is say 0.03". If the primary is thinned down so this bevel now is only 0.1" wide, the thickness right behind the new shoulder is same as old bevel when bevel width is 0.4". However, the stock (now new primary grind) at 0.4" from apex is thinner (assuming 0.02") as it's now the new primary grind after being thinned down.

Why it is now better handling the chipping by lateral forces with less material at say, 0.4" from apex?
Click to expand...

Chris, I have no idea but I would consider that a 12dps bevel is still on the saner side. I was talking about taking down 3mm thick stock to less than 10dps bevels. I find that I like the performance of knives that are made from thinner blade stock with less acute bevels than with thicker knives taken down to very thin bevels. I have a locally made 52100 knife that's around 2 mm thick and I really like how I can use it for all around tasks including wood working and still zips through thick media like cardboard. I can keep the bevel angle of this knife to around 13-14dps and it'll still work better for me than say a 3mm knife taken to lower angles.

That however is just my preference. It's probably a YMMV thing.
 
Chuck,

Thanks. Yours is easy to understand. Perhaps I misunderstood Jason's comment, as Marthinus actually reground the GB primary bevel. Does it mean he keeps the previous chipped bevel or the robust one he used to fix the chip?
If the latter, then It is same as your sample case. If the previous one, then I'm confused as on why thinning the primary helped the chipping if the final bevel is kept at the chipped one :confused:
 
Chris "Anagarika";16567591 said:
Chuck,

Thanks. Yours is easy to understand. Perhaps I misunderstood Jason's comment, as Marthinus actually reground the GB primary bevel. Does it mean he keeps the previous chipped bevel or the robust one he used to fix the chip?
If the latter, then It is same as your sample case. If the previous one, then I'm confused as on why thinning the primary helped the chipping if the final bevel is kept at the chipped one :confused:
Click to expand...

I still maintain the GB at around 10-12 dps even with the regrind. It is the angle I end up freehand sharpening most of my knives and have had no issue with even higher carbide steels at those angles.

I will have to carry the GB again to get some pictures, most of its use these days are in the shop deburring titanium and cutting sandpaper. At a recent get together someone had a newer GB 1 and we compared it to mine. Mine is about 2mm shorter at the tip and even more so at the belly area, but pictures do not really reflect that.
 
I will try and explain better,

When the ground bevel is very large like you see on page 1 you have multiple facets from Shoulder to Apex. Having multiple points of contact on such a large bevel and trying to make it very acute tends to leave you with a bevel that is heavily tapered behind the apex... imagine a water droplet upside down.

The main issue becomes thickness and contacting surface area. The GB from page 1 has a cutting apex supported by a large bevel where the reground GB has a small bevel supported by the primary grind. The difference as Brock-O-Lee explained is the amount of force exerted on the apex. With the thicker bevel the support of the apex is so far away from the apex that all the pressure from cutting is transferred directly to the apex. With the reground blade you have a much smaller bevel with more consistent angles and less surface area. This allows the edge apex to initiate the cut without the bevel binding in the material and transfers the forces into the primary blade grind which keeps the pressures low at the apex.
 
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Chris "Anagarika";16575748 said:
Nice!

It seems a new generation of patina is forming [emoji51]
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Jip. The GB1 remains one of the best workhorse folders I have ever bought.
 
Very cool!

I have a kitchen knife in CPM M4 at 64 HRC that experienced micro-chipping at 13 DPS per side when used on a walnut cutting board. I am running it now at 17 degrees per side and quite pleased.

M4 edge stability and resistance to wear is well know. I do not believe these properties translate well to toughness in thin cross sections.

Use is certainly a consideration. I chopped alot of salsa... with great passion.
 
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