Serrations for cutting hard plastic?

[Road Tripper]

I'm giving thought to picking up a Salt knife to keep near the bathroom. I'd be using it for opening packaging, but particularly for cutting the hard plastic pump bottles where it is so challenging to get the last bit of product! I'm leaning toward a Dragonfly or Delica size, but am wondering if serrations or plain edge would work better for the use case?

Thanks for any thoughts.

[blueblur]

Both edge types will work but the se will make that type of cut easier and faster.

[JD Spydo]

I have two old school Spyders I frequently use for those types of cutting jobs (serrated blades). And those two blades are two of my favorite blade steels for serrated blades. One I use the most is my old trusty stainless RESCUE model which is out of the ATS-55 era ( late 90s). The other is my older Spyderhawk model (first run) with a VG-10 full SE blade.

Many of the blade steels I find to be good for full SE blades are some of the older steels. However I do find ATS-55 and VG-10 both to be really decent steel for both edge types. I've never ever chipped a serrated blade with ATS-55 blade steel. That's noteworthy because I use that Stainless RESCUE model on some really brutal cutting jobs.

And VG-10 is just a real work-horse type blade steel that you can depend on. Two additional older steels I also like for serrated blades are AUS-8 and GIN-1. I'm anxious to see where this thread goes.

[JRinFL]

I find that SE starts the cut easier, but PE does not steer in the cut. If you need a quick cut use SE, if you need an accurate cut use PE. In my opinion, at least. Either D'fly or Delica. Both are excellent choices.

[Wartstein]

..., but am wondering if serrations or plain edge would work better for the use case?
...

No surprise, but my vote goes to SE.

- With PE you often will find it much easier to initiate the cut by piercing with the tip of the blade first, but with SE and its "spikes" you can just start to cut the hard plastic with any part of the edge

- SE will give you effectively more edge than PE in the same blade. Not totally unimportant especially in the small size you're looking at.

- SE will stay sharp longer, especially when cutting tough stuff (as said: Effectively longer edge= dulls slower, and the edge in the scallops is protected by the spikes when initially breaking the surface).

-SE will still rip through plastic when already dull, while dull PE more or less glances off.

- SE is a bit easier to sharpen in my experience

[ladybug93]

I find that SE starts the cut easier, but PE does not steer in the cut. If you need a quick cut use SE, if you need an accurate cut use PE. In my opinion, at least. Either D'fly or Delica. Both are excellent choices.

i was going to say this too. se is great and i really like it for emergency use, but it more rigid materials, it's hard to keep it from traveling with the chisel grind. i'd go with pe for the application you're talking about and keep se for softer, fibrous materials like line and webbing, etc.

[Wartstein]

JRinFL and Ladybug93 do have a point here - SE chisel grind tends to "steer" a little bit in hard material.

But I just compared SE and PE in the application you (Road Tripper) mentioned and really had to focus on just that to perceive that tendency to "steer".
I personally also think that if your goal is to just somehow cut the plastic pump bottles apart in order to get to the last bit of product, it probably does not matter if the cut is not totally perfect, right? That´s not the goal here and you´ll throw the bottle away then anyway.

Otherwise I found again what I mentioned already above:
With SE one just puts the cutting edge on the bottle and starts to cut - the spikes of SE will puncture the surface and initiate the cut easily.
If one wants to do so with PE (and not puncture the plastic with the tip first) I think the knife should be always very sharp and ideally have a very coarse edge, otherwise it could "glance off" to easy.

Overall just to me SE would be more convenient and less "maintenance intensive" ( less sharpening needed) in that particular application. Actually it is even one (application) where SE can really shine (just roughly separating hard, man made material)

[mongo1958]

I'm giving thought to picking up a Salt knife to keep near the bathroom. I'd be using it for opening packaging, but particularly for cutting the hard plastic pump bottles where it is so challenging to get the last bit of product! I'm leaning toward a Dragonfly or Delica size, but am wondering if serrations or plain edge would work better for the use case?

Thanks for any thoughts.

If the knife is strictly for indoor use only and will be exposed to possible harsh chemicals then why limit it to a small folder?
Why not go with a fixed blade like this fish hunter.

[JoviAl]

I find that the difference between PE and SE in this application is less noticeable than blade shape and thickness. My little Wharncliffe K390 dragonfly utterly violates plastic bottles when I’m making stuff with my kids (pretend suits of armour, weapons, space helmets, etc), whereas blade shapes with more belly tend to skitter about a bit and stab in less willingly for the initial cut. The Salt 2 Wharncliffe would be a delight for the OP’s task IMO, in either PE or SE depending on which they find easier to sharpen.

[standy99]

I use a PD1 for the exact reason and it works a treat. PE is better in my view as it’s a cleaner cut

[dull&blunt]

I use a PD1 for the exact reason and it works a treat. PE is better in my view as it’s a cleaner cut

This is my thinking as well. Cleaner cut and easier to stab into the bottle to begin the cut.

[Road Tripper]

OP here; thanks for the feedback, everyone. To add a little more detail, the plastic I'm cutting is about 1/8" thick, and more rigid than, say, a typical shampoo bottle. I usually pierce the bottle, and then cut around the circumference.

I was thinking that a serrated knife might trap the material in one of the scallops and act as a recurve. I've found when cutting with a plain edge that it takes a good bit of pressure and I need to angle the knife as I would when cutting thick cardboard.

[James Y]

I think my favorite knife for cutting things like tough, plastic clamshell packaging is my SS SE Harpy. It also feels the safest, because due to the blade shape and the serrations, it offers me more control, with less chance of slippage. Of course, I don't saw with it, and I always cut away from myself, but still...

Jim

[SaltyCaribbeanDfly]

Either one will do the job

[Wartstein]

OP here; thanks for the feedback, everyone. To add a little more detail, the plastic I'm cutting is about 1/8" thick, and more rigid than, say, a typical shampoo bottle. I usually pierce the bottle, and then cut around the circumference.

I was thinking that a serrated knife might trap the material in one of the scallops and act as a recurve. I've found when cutting with a plain edge that it takes a good bit of pressure and I need to angle the knife as I would when cutting thick cardboard.

You´re thinking is correct - sharp SE can act just that way (trap the material in a scallop and easily cut it).

The folks recommending PE over SE for your particular demands certainly have their points and know their stuff, but I personally still would prefer SE.
It WILL make very clean cuts when the material is "trapped in a scallop" - and if not, just for separating a plastic bottle to get to the remains in it, the cleanest cut in the world is not really necessary ,right?

Plus: I think for a utility knife kept in the bathroom it is a nice thing not having it to sharpen it to often. And SE stays sharp longer than PE and will still do the job (just separating a plastic bottle you´ll throw away then anyway) when actually "dull" already (when a PE knife would have a hard time)

Just my 2c of course, but coming from real experience (which I have some, but others will certainly have more).

[Cl1ff]

You could probably get away with it just fine using a Salt Ladybug or Dragonfly (especially the hawkbill versions).
I would, personally, definitely prefer serrations at the smaller sizes.

Any of them will work, so it’s mostly about what you prefer and value more.

If I were grab a knife and go cut something like that in my bathroom right now, it would be my serrated UKPK Salt that’s right next me as I’m typing this.

Or my Spy27 Mule Team 2 with a coarse edge that’s also within reach.

[Surfingringo]

I’d favor a pe wharncliffe for that job. I often cut two liter bottles in half to make water scooped for the boat and kayak. PE makes a cleaner straighter cut. And if it’s sharp it actually makes a more efficient cut than se on that material. If your knife is sharp you shouldn’t need to be “sawing” material like that. Just my 2 cents.

[vivi]

for 1/8" thick I'd definitely go with PE.

- Sharpened to a thin, coarse edge, it will nullify nearly every advantage of SE for this application, and retain the upsides of PE. You can slice into the sides of plastics just fine with one, though I'm like you and prefer to initiate these sorts of cuts with a puncture.

- I've broken serrations on things PE has handled without issue. If you go way back in my post history you'll read about me snapping serrations off a CE Manix 2 back when they used 154CM. What abusive task did I do to damage the edge? Sliced the bottom of a 2 liter in half while breaking things down for recycling. 1/8" thick plastic will be much harder on the apex than a 2 liter.

- No steering issues with PE. This is a big one for me cutting thick plastics. Even back when I EDC'd a SE Pacific Salt, if I were at home with access to my PE knives, I've choose one of those instead.

All that being said, wouldn't it be far less work simply tilting the bottles upside down and letting gravity do its thing?

[Wartstein]

.....

All that being said, wouldn't it be far less work simply tilting the bottles upside down and letting gravity do its thing?

... good point!

(but I admit: I, too (like the op), prefer the "cut the bottle" method occasionally - just cause I am "desperately" looking for cutting tasks in my life )

[Road Tripper]

OP here again... I ended up getting a Dragonfly Salt serrated edge, and can confirm it works well! The blade tip is great for piercing, and the serrations work well for the cut. I did find some issues with blade steering, but was able to manage it.

For this application, plain edge may well be preferable, but it seems that H1 holds an edge longer when serrated from what I've read so I went that way. I also wanted to try Spyderco's serrations (so far I'm impressed; I'll have to try some other SE knives).

As Vivi mentioned, I could let gravity do its thing with the bottle contents, but where's the fun in that? :)

Kudos to the team in Seki City. The Dragonfly was well-built and finished, with even seams on the FRN and a nicely ground blade.

Thanks again for all the feedback!