Question about dulling during use.

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NateHodge

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Apr 30, 2018
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Hey guys, I experienced something yesterday that Ive never had happen and was hoping I could get some feedback. I was slicing some window tint on top of a glass sheet using an M4 blade. I noticed that the knife stopped slicing pretty fast and thought that was pretty bizarre considering all I was cutting was film and paper. When I finished, I noticed that there was a burr on one side just as if I were sharpening. Is it because I was using glass as a cutting board? I stropped it and it came back to shaving sharp pretty fast, but Im amazed at how fast the M4 lost its cutting edge and it has me baffled as to why. TIA
 
Yes, a glass cutting board will dull an edge in a heartbeat. Glass is usually harder than the matrix steel in most cutlery, so a knife edge will either roll, flatten or chip if cutting against glass. This is also why fiberglass is notorious for dulling edges very quickly.

If cutting against a firm backing, I always prefer to use something in wood or plastic as the backing, for this reason.
 
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Obsessed with Edges said:
Yes, a glass cutting board will dull an edge in a heartbeat. Glass is usually harder than the matrix steel in most cutlery, so a knife edge will either roll, flatten or chip if cutting against glass. This is also why fiberglass is notorious dulling edges very quickly.
Click to expand...

Note to self. Break out the box cutter to finish my project! Stropping after every other cut is going to get old real fast haha
 
Yeah glass will dull an edge very quickly ... I don't know if you have ever seen or heard or tried it ...

but if you roll the window of your vehicle down part way you can put a nice sharp edge on your knife using the top edge of the window ... just as you can sharpen on the ring of a ceramic mug ... you can probably find videos on youtube showing it ...
 
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JJ_Colt45 said:
Yeah glass will dull an edge very quickly ... I don't know if you have ever seen or heard or tried it ...

but if you roll the window of your vehicle down part way you can put a nice sharp edge on your knife using the top edge of the window ... just as you can sharpen on the ring of a ceramic mug ... you can probably find videos on youtube showing it ...
Click to expand...


Yeah, as a young teen and a broke 20 year old, I actually used to sharpen my knives this way because I didnt have money for good stones. I just didnt expect the flat side to have the same effect as the rough cut edge.
 
The wonderful Science of Sharp blog shows what happens when an edge meets glass. I recommend you get a snap knife and use the point of the blade to cut the film; the point will instantly dull, but the edge right behind it will still be sharp and will still cut the film. When the tip becomes too messed up you just snap off that section and repeat; this is both faster and less expensive than replacing entire blades in a basic box cutter.

rolled.jpg
 
NateHodge said:
Note to self. Break out the box cutter to finish my project! Stropping after every other cut is going to get old real fast haha
Click to expand...
Cutting against glass will dull everything pretty quick, as will cutting glass fiber, such as air filter material.
If you want to get a few more cuts in before sharpening, try maxamet.

IMG-6944.jpg


None of my m4 blades will do this.
 
I didn't tested much against glass before. So did a test to sort of answering my own curiosity.

Test cutting paper; leather against glass/pyrex backing

CPM M4 67rc, HT 2.5
15 dps, 600 grit diamond plate finished.

 
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