Cutting corrugated plastic

L

Lennyo3034

Joined
Nov 27, 2012
Messages
490
I was helping out at the local range this weekend by replacing the corrugated plastic target backers. They come in large sheets, and have to be cut down to size. I figured it would cut just like cardboard, and be no problem for my EDC knife. WRONG, it required a good amount of strength to push cut it, which was the only way to do it and keep straight lines. Because of the way the sheets came, I was cutting against the corrugations instead of with it.

I had actually stropped the knife that prior that morning to one that was just able to bite into a whittle a hair. Knife is a BM 710 in CPM-M4 sharpened on the edge pro. Primary bevel is around 30 degrees with a 38 degree microbevel. Knife was able to pop hairs easily after it was finished cutting boards for about an hour, but man did it take a lot of effort.

Is corrugated plastic board just that naturally difficult to cut? Or am I doing something wrong with the sharpening?
 
Corrugated plastic is a pain in the rear to cut. It is not nice to an edge, and is really hard to cut nice and evenly.

Best I can say is either go serrated on it, or break out the chain saw. Scissors (heavy duty ones) might actually yield an improvement. Tin snips can work in a pinch.
 
I've cut a lot of it, keeping a straight line is almost impossible. Nothing wrong with your sharpening, I would just recommend getting a utility knife if you plan on cutting anymore, they excel in cutting corporates plastic. :)
 
Lennyo3034 said:
I was helping out at the local range this weekend by replacing the corrugated plastic target backers. They come in large sheets, and have to be cut down to size. I figured it would cut just like cardboard, and be no problem for my EDC knife. WRONG, it required a good amount of strength to push cut it, which was the only way to do it and keep straight lines. Because of the way the sheets came, I was cutting against the corrugations instead of with it.

...

Knife was able to pop hairs easily after it was finished cutting boards for about an hour, but man did it take a lot of effort.

Is corrugated plastic board just that naturally difficult to cut? Or am I doing something wrong with the sharpening?
Click to expand...

YES, corrugated plastic IS that difficult to cut because of how stiff/strong it is. Once cut, the material does not split/bend/curl away but continues to apply pressure to the bevels of the blade. The BM 710 is hollow-grind and 0.115" thick at the spine. The grind improves penetration until it rapidly thickens, not an easy transition to follow for the material being cut. Standard "box cutter" blades are only 0.025" thick, potentially thinner than the BM710 at the shoulder of the edge-bevel! Once the plastic is cut, the thinner blade continues through the plastic with much less application of force.

The video above just places a thin blade on a special handle that allows comfortable use over extended periods. As for cutting a straight line, it's a LOT easier to follow the corrugations. Cutting across the corrugations in a deliberate line requires careful control of a lot of force. Use a thin blade (e.g. box cutter), insert to the hilt/handle, and push against the spine of the handle. OR use a saber-saw, cut-off wheel, etc. ;)
 
EDC, pocket knife sometimes is just not the right tool for the job. Never hurts to have a utility knife on hand. That corrugated plastic/fiber glass can be ARB to cut. Sometimes a good pair of shears is called for depending on the material to be cut. Now you know and will be better prepared next times. We have all been there at one time or the other.
 
chiral.grolim said:
YES, corrugated plastic IS that difficult to cut because of how stiff/strong it is. Once cut, the material does not split/bend/curl away but continues to apply pressure to the bevels of the blade. The BM 710 is hollow-grind and 0.115" thick at the spine. The grind improves penetration until it rapidly thickens, not an easy transition to follow for the material being cut. Standard "box cutter" blades are only 0.025" thick, potentially thinner than the BM710 at the shoulder of the edge-bevel! Once the plastic is cut, the thinner blade continues through the plastic with much less application of force.

The video above just places a thin blade on a special handle that allows comfortable use over extended periods. As for cutting a straight line, it's a LOT easier to follow the corrugations. Cutting across the corrugations in a deliberate line requires careful control of a lot of force. Use a thin blade (e.g. box cutter), insert to the hilt/handle, and push against the spine of the handle. OR use a saber-saw, cut-off wheel, etc. ;)
Click to expand...

That makes a lot of sense. It would also explain why the edge did not take much damage since it was friction on the sides of the coated blade that was making it difficult, not the edge's ability to separate material. The fact that its a coated blade with more friction didn't help. Although this particular one seems to be a saber grind. Not sure if that's the case for all 710s.

Here's a picture of the knife now. BK coating held up pretty well considering. I got this knife off the forum and I've seen pictures of this exact one floating around based on serial number. I'd imagine it's passed through a few hands, did anyone else own this one before? It's turned into a user now. Marks on the edge are just the light and reflection, I stropped it when I got home yesterday.
FF08E485-EA0F-4F8F-9A3E-F9F74A8F9210-325-000000DC0DBBA292_zpse83069db.jpg
 
Corrugated Plastic sucks. I don't use a knife for them, it's too much of a pain to deal with, and it takes forever. I use a Sawzall on it, much easier, and it actually happens without me needing to clear my schedule.
 
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