Cutting Plastic Bags & Wrappers

rhino

rhino

Joined
Dec 30, 2000
Messages
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Lately I've noticed that some of my knives don't do well cutting plastic bags or wrappers. The most trouble is with very thin and very thick plastics. Other knives I have slice through them like a zipper.

My Spyderco Endura (VG10) doesn't do well, even after I sharpen it so it pops hair from my arm. My Buck 110 made from 420HC goes to town, even when it doesn't feel sharp.

I know part of it is edge geomtry, but I've got the Endura about as thin as physically possible without redoing the entire hollow grind.

I normally use progressively finer diamond tools for sharpening.

Do I want a toothy edge for cutting plastic bags smoothly? Or do I want an ultra polished edge?

Do I just need to be more aggressive about setting a microbevel on the VG10 Endura?
 
rhino said:
My Spyderco Endura (VG10) doesn't do well, even after I sharpen it so it pops hair from my arm.
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Sounds less than ideal for the job at hand. Try getting it that sharp and then taking a few passes over a coarse stone to get some bite.
 
It is easier with a more coarse edge, very easy if the blade has a recurve or similar dropped profile like the Persian where the blade and handle are angled to induce the same effect, fairly trivial with something like the Dodo, fairly hard with something like the Pelican.

-Cliff
 
Serrations would probably help. PE tends to slip on the plastic, serrated edges catch the material as it passes by.
 
I use the empty plastic bags to test sharpness. I put a little weight in the bag then put the blade through the bag handles to see if it cuts through when I lift up.
 
I would suggest a serrated knife as this is exactly why I carry one in work. A hawkbill could also be a good idea as in my experience they work well for this kind of thing.
 
Interesting ... thanks!

I do note that my Cold Steel Voyagers also sail through plastic wrap and bags like it's not there, at the same approximate level of sharpness as my Endura. Maybe the AUS8A is a little "toothier" than the VG10 after I sharpen them?

I did a little experiment last night (maybe it was early this morning). Instead of lightly stroking the microbevel (on the Endura), I layed it down on the primary bevel that I established (long ago) and used a little more pressure on the diamond rod until the both side "met" again. It slices through the plastic quite a bit better now.

Along these lines, is there a substantial difference in the kind of edge you want to cut synthetic ropes and cords vs. natural fibers? I'm thinking polypropylene rope or even nylon 550 cord vs. sisal and hemp. Or do you want toothy/grabby and aggressive for anything fibrous, regardless of its origins?
 
You want toothy/grabby and aggressive for anything fibrous, regardless of its origins. That's why serrations are best on fibrous materials. But a toothy edge is OK, especially if the fibers are fine. Cold Steel serrations are a good compromise, also.
 
I cut plastic all night long at work.A fine smooth edge is the best for all the plastics I've ever cut,plastic straps,plastic wrapping both thick and thin,packaging ect.I personally use a Fallkniven F1 but that's just me.
 
rhino said:
Or do you want toothy/grabby and aggressive for anything fibrous, regardless of its origins?
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It depends on how they are being cut. Push cuts on rope work better with a polished edge, and if the edge is thin and acute enough there is no need for a slicing action and the blade will travel little when force is applied as the knife will go straight through the rope, thus a high polish is prefered.

-Cliff
 
That makes sense. I used a small, hollow-ground, plain edge Cold Steel tanto folder at work. I cut A LOT of plastic bands and sheeting. The edge was slightly coarse, and worked all right.

I also had an ER-1, a strange Cold Steel out-the-front manual sheepsfoot with their tiny serrations, and that zipped through the plastic with no effort at all.

But very little of what I cut was accessible to push cutting.
 
I'm a little confused: doesn't a box cutter or razor cutter work well here? What would a razor's edge be considered, polished? Or is it not an appropriate measure due to the geometry and thiness of the razor...?
 
Use a very very fine but slightly toothy razor edge, basically the same kind of edge you have on a new utility knife blade. The knives I carry to work usually get touched up on a 1200 grit dmt and stropped a couple times on each side, and it just glides through everything from the plastic wrap on our truck shipments to heavy wire insulation.
 
JohnG said:
...doesn't a box cutter or razor cutter work well here?
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Yes.

What would a razor's edge be considered, polished?
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Highly, and yes the very thin and acute profile allows push cuts with no draw, very efficient cutting knives can do the same. In general it is just more demanding to do a push cut than a slice.

-Cliff
 
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