polyethelene for handle material

[BayardStrachan]

i have access to a large supply of 10mm thick polyethelene plastic sheet offcusts, do you guys reckon that it would be a good handle material? 

[Irondragon Forge ClayWorks]

More than likely it will melt or catch on fire, I wouldn't use it.

[Frosty]

Handles for what? 

Frosty The Lucky.

[BayardStrachan]

ah yes sorry, i forgot to say, i was thinking mainly about knives

[Frosty]

It might be good for some, say kitchen knives where sterility is an issue. How are you going to attach it? What kind of adhesive is appropriate to glue it to steel? I'm ASSUMING you will pin the scales. However pins alone aren't likely to be enough.

Frosty The Lucky.

[Irondragon Forge ClayWorks]

My bad, I've been messing with hammer handles all afternoon and didn't notice you posted in Knife Making. If it is clear you would have to put some type of design under the scales to hide the tang, if opaque/colored then it would work. I saw a very good looking knife years ago that the builder made the tang with fancy stamping and engraving with clear scales. It looked very nice. It was a coffin handled Bowie with fancy pins, I think 8 of them.

[BayardStrachan]

yes the plastic is either black or blue, so having fancy designs wouldnt be an issue. as for fastening, i was just thinking of using a 2 part epoxy and some sort of pins. i saw some quite cool pins a while back on a YT video, i cant remember what it was called tho, they were ones that you counterbore a hole and then the pins screw into each other and lock very tight. kinda like this. if you know what they are called i would appreciate it if you could tell me. 

[Irondragon Forge ClayWorks]

I've heard them called Loveless Bolts, Corby Bolts or Cutler's bolts.

[Frosty]

Corby sounds like the name. Try searching on a knife supply site. If you use your preferred web search engine and add Iforgeiron to the terms it will search Iforge first and IFI has a large knife section. Unfortunately Iforge's search engine stinks LOTS. but that's the operating system, not Iforge.

You'll want to test the epoxy on your plastic and knife steel before risking it working on your knives. I'll have to search my bookmarks there was an extensive thread on a blade forum where guys did some serious and extensive testing on adhesives and different handle materials and some pretty brutal tests. a Dishwasher turns out to be one of the toughest tests. But a good hard slap on a hard surface is another tough test. I'll post it if It's still in my files.

It might not, my comp suffered the black screen of death a couple weeks ago and not all my data survived. I'm using a different version of Google Chrome and my email is a fresh blank slate. <sigh>

Frosty The Lucky.

[Bob Brandl]

They're corby bolts, and almost any epoxy will do fine for you. Just don't use five minute stuff. It would likely work, but I've had some of them fail me a few times over the years. Only once with a knife handle, but still.

Truthfully, a couple of plain old .125" stainless pins will do you just fine. Unless the look of the corby bolts is what you're after. Just dome/rivet the ends and you're good.

[Hefty]

Polyethylene is a tough material that should withstand the punishment handles can sometimes take and corby bolts should definitely help as a mechanical fixing, but gluing it is always a problem. It is almost as difficult to glue as polypropylene and PTFE. I am by no means an expert, but I'm not sure if even many of the high end epoxy adhesives would do it.

It CAN be glued, but you'll need to either research suitable adhesives or do some testing of your own. A quick search found a page with 3 recommended products: Gluesmith Repair Glue System, Permabond POP plastics primer and Tech Bond basic poly kit.

 

Hope this helps

Jono.

[BayardStrachan]

Ah yes corby bolts is the name, i like the look of them and they look a bit easier, but what would I know 

Yeah if you could find that thread frosty it could be quite interesting, I've only made one knife so far and it was pretty crude, I used some locktite 5 min epoxy and it seems to be holding up quite well. The knife was a sort of small machete that I got asked to make for cutting plastic off moulds, it gets a lot of abuse and is still quite strong,

Ok might be a little trickier than I thought then eh hefty I might have to do a bit of trial and error on some test pieces

Random idea, hear me out, what if I partially melted the back of each knife scale and then clamped it onto the knife steel with the pins through, it prolly wouldnt stick though, ill give it s go on another test piece 

[Hefty]

I honestly don't know if the melting would work. Maybe if you put some undercut grooves in the surface of the tang? The melted plastic might key into these undercuts and grip, but I don't know if it would be strong enough to grip well.

I had a similar thought about using epoxy with undercuts on the sides of the tang and the inside of the PE scales to lock them together. Again, no expert, just brainstorming.

[Frosty]

Giving the tang some "tooth" by grinding with a coarser belt than the blade gets so adhesive sticks better is pretty common practice. Melting the scales surfaces and pinning them to the tang would require almost inhuman speed. You aren't the Flash are you? Instead I'd drill the tang with smallish holes, say 1/4" for the purpose of this description. Then using a conical burr open them into tapered holes from ONE side per hole. Alternate tapered hole direction on the tang.

Test the plastic you have, it SHOULD start to melt around 300f. 300f shouldn't effect the temper of your blade so you can heat the tang and pin and clamp the scales. The hot tang will melt the plastic forcing it into the tapered holes and sticking to the other scale. 

As an alternative there was a pretty extensive and thorough study of adhesives on "The Knife Network" some years ago and it will tell you more about blades, adhesives and how brutally the guys tested them. There is so much more than just the adhesive involved it's well worth the hours it takes to read through the thread. They discuss plastic knife handle adhesives, glues and the testing done. It's an old (2005) thread and you might have to subscribe to read the whole thread.

http://www.knifenetwork.com/forum/showthread.php?s=97f704f8004c9e3f6bd59f8efeeb9a0d&t=27463

Frosty The Lucky.

Edited May 17, 2022 by Frosty
Correct the link

[JHCC]

IFI member (and Forged In Fire winner) TheoRockNazz had a number of blades that he made with cast-in-place epoxy handles. I wonder if one might similarly melt HDPE into a mold around a blade tang....

[BayardStrachan]

i had an idea, if i drilled a bunch of holes in a full tang knife and then melted the backs of the scales, the melted plastic would seep through the holes and fuse to each other. 

the plastic actually doesnt melt that fast if its melted enough, i have done quite a bit of plastic welding with polyethelene and when you get it melted enough it fuses together very very strong and you have about 2 mins of working time, which i reckon would be enough. i think what ill do is drill 10 holes in the tang and then melt the scales and stick them on and clamp them. once that has set ill get a drill bit and drill a couple of holes right through the plasctic and the tang and then put the pins in afterward. then grind the handle to shape and finish it. happy days an unbreakble handle ........... untill it breaks 

thats another idea john, i could use a plastic welder which puts out a thick stream of semi melted plastic and just slop it around a hidden tang knife, would probably have to make some small cuts in the tang so the pllastic would hold better