17 Deg. (Per Side) M4 vs. 180 Grit Sandpaper: Sandpaper Won

stabman said:
You can definitely screw up the heat treat with grinders/belts.

While doing the machining course in college, we ground our own cutting bits for the lathe from pre-hardened high speed steel blanks.
It was VERY easy to overheat while doing that...and you found out when you went to cut steel on the lathe, and the tip/cutting edge went busting off (or wearing off...either way is bad).

Heat can build up really fast in small sections.
Reality doesn't care if you believe the argument or not. ;)

(Oh yeah, we were holding the blanks with bare hands to better tell the heat...still easy to screw up in a matter of seconds)
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Yes , you can definitely screw up the heat treat with grinders/belts IF you do not know what you're doing :) If you know you can grind even Gillette :D
 
Scissors are a way better tool to cut sandpaper with, than a knife. Cutting those 3M green pads can dull the edge on a knife as well. Ah, you'll just have more opportunity to sharpen your sharpening skills.
 
I used to work at a place where I had to sharpen the circular knives for 3M on a tool and cutter grinder. About 80-100 every two weeks. I don't know what kind of steel they were, but they would come back extremely dull and chipped. When I was FINALLY done sharpening, I would drive them over to 3M and drop them off and I saw that they were cutting the paper from the back side.
I certainly would call it abusive!
 
danbot said:
I used to work at a place where I had to sharpen the circular knives for 3M on a tool and cutter grinder. About 80-100 every two weeks. I don't know what kind of steel they were, but they would come back extremely dull and chipped. When I was FINALLY done sharpening, I would drive them over to 3M and drop them off and I saw that they were cutting the paper from the back side.
I certainly would call it abusive!
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Of course that they were cutting the sand paper from back side , that way blade PUSH aside grains . . . . even when edge/apex ? make contact with grains there is not enough resistance to stay on way of edge so , in one way when you cut sandpaper you sharpen edge :D
 
As a rule you only cut sandpaper from the back side and just barely cut it then fold on the line and it will separate along the line nicely.
 
TIL that I'm not supposed to cut sandpaper with my pocket knife

Do we have a comprehensive list of things we're not supposed to cut?
 
GermanyChris said:
TIL that I'm not supposed to cut sandpaper with my pocket knife

Do we have a comprehensive list of things we're not supposed to cut?
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Rocks, metal, other knives, cats, dogs, children, adult children, boat hulls, yourself, myself, ourselves. Atoms...more rocks.
 
dirc said:
Very good point, I think it really is the aluminum oxide (https://en.wikipedia.org/wiki/Corundum) with a mohs hardness of 9.0 that kills it.
If the m4 was hardened past 60 (which should be the case for any decent m4), and the sandpaper only had silica (mohs 6.0), it should have been fine, right?
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Nah--you'd still be blunting your edge. Abrasive wear does occur to the abrasive, not just to the workpiece. That's why really hard stones will eventually glaze and start burnishing instead of cutting. The abrasive grains blunt and just rub at that point.

The Moh's scale sucks and is non-linear. Vickers, Brinell, and Knoop are better scales to use.
H
Fig1.JPG


ceramics-49-638.jpg


Chromium carbide is about 1735 KH
Vanadium carbide is about 2660 KH
Silicon dioxide is about 790 KH
Iron carbide (cementite) is about 1025 KH

But even in high-vanadium steels, the edge isn't 100% vanadium carbide and vanadium carbides are tiny (about 3µ) and so are easily scooped out of the steel matrix by sufficiently large abrasive grains.
 
Tearing sandpaper along the 12" leg of an 8 x 12 carpenters' square gives clean-edged, measured and square pieces and spares your Rockstead edge for vegetables.
 
Relatively speaking M4 isn't tough, though. It's "tough for a high speed steel", which is to say still not very tough. What you're asking is unreasonable for any knife, I think.

Your results using Maxamet or Rex-45 would have been even worse, I'd bet.
 
bluntcut said:
I'm curious, so I made a few cuts onto grit-face of 150 grit sand paper, here is the edge afterward

v9lSyTB.jpg


yt video: youtu.be/T5VBl9BBavA
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Well , I cut 40 grit spare sandpaper for one of my disk sander ...from back side and blade cut easy paper after that .But when I cut 40 grit zirconia sandpaper for my disk sander / same sandpaper as for belt grinder,backed with cloth / there was damage even I cut from back side ... Probably because bonding resin is much stronger on that sandpaper then one on sandpaper with only paper behind grit + cloth make it more rigid so grit don t go aside ......... :)

M35 HSS steel

tth5ZS1.jpg
 
I trim disc sander on the backside as well. To preserve the edge, usually I push, lift a little then pull before push forth again. It actually worked well on cloth-backed paper too. M35 HSS covers the tough side with lower carbon than T15, good stuff.

Natlek said:
Well , I cut 40 grit spare sandpaper for one of my disk sander ...from back side and blade cut easy paper after that .But when I cut 40 grit zirconia sandpaper for my disk sander / same sandpaper as for belt grinder,backed with cloth / there was damage even I cut from back side ... Probably because bonding resin is much stronger on that sandpaper then one on sandpaper with only paper behind grit + cloth make it more rigid so grit don t go aside ......... :)

M35 HSS steel
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dirc said:
Very good point, I think it really is the aluminum oxide (https://en.wikipedia.org/wiki/Corundum) with a mohs hardness of 9.0 that kills it.
If the m4 was hardened past 60 (which should be the case for any decent m4), and the sandpaper only had silica (mohs 6.0), it should have been fine, right?
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Don't confuse silica with silicon carbide. Silicon carbide is much harder than silica.
 
Eli Chaps said:
Don't confuse silica with silicon carbide. Silicon carbide is much harder than silica.
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I keep forgetting we've had silicon carbide sandpaper since 1921... (aka 3m wet'n'dry) ... thanks!

edited to add: no, I'm not old enough to remember the time before it existed... it's just something that wasn't really common growing up either
 
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