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View Full Version : Need Suggestions: Which type Plastic should I use?



KevinWilkins
05-23-2008, 01:03 AM
I hope this is the best place for this question, so here goes!

I am looking at having grips injection molded in two parts for a military knife I have designed with another knifemaker. The grips would still be removable and held in place with screws. You can see pics of the handmade version of the knife ere: http://www.wilkins-knives.com/utility_e.html The injection molded grips will have a slightly different texturing, but you get the idea. The grips shown are machied from G-11 or Micarta.

Obviously we need a plastic for injection molding that is grippy when wet, impact resistant, heat resistant, etc. Probably some type of glass or Kevlar filled?

What would you folks suggest that would make a nice knife grip?

ImanCarrot
05-23-2008, 10:26 AM
Just curious.. this aint my field, but always curious here:

Why not wood handles?

Grippy, not slippy.

KevinWilkins
05-23-2008, 12:16 PM
You can't injection mold wood...

airpro_1
05-23-2008, 01:19 PM
I would suggest going with nylon. It's easily moldable and extremely tough so it could take all of the environments your knife would be in.

I do Injection molding as my trade and nylon is probably our most used material it's just extremely rugged.

KevinWilkins
05-24-2008, 03:13 AM
A glass filled nylon is one option we're talking about...

Jim Estes
05-24-2008, 11:05 PM
I would recommend fiberglass filled nylon also. Just be sure that your molds are built tough enough for the fiberglass.

Jim

KevinWilkins
05-25-2008, 02:31 AM
Thanks Jim, It doesn't look like I'll be making the molds myself, I have a pretty good quote from one company here in Berlin and will get another from a company in Istanbul who do a lot of work in the firearms industry.

The knife in question is the Jordan/Wilkins Military knife which you can see pics of here: http://www.wilkins-knives.com/utility_e.html

plasticpeter
05-27-2008, 12:05 PM
Another alternative (but expensive) is to have the grips two-part moulded in glass-reinforced nylon with some of the outer surface overmoulded in a more grippy thermoplastic elastomer material.

You see this often on good quality hand tools and it really does make for a superior product. I'm not an expert on this but I think you are looking at adding something like 30 to 40% to your costs.

airpro_1
05-27-2008, 12:18 PM
I don't know that glass fill is really necessary and you could go with a outer surface of neoprene as in some of the higher end hand tools. We have worked with neoprene on several of our products and you can get it in several grades, colors, etc. Glass fill would be great if you were building a structural part but just to have as an exterior surface i feel would would be adding expense and pretty unnecessary not to mention having to have a coated/hardened mold to keep the glass fill from removing the surface of your mold. Our nylon parts with glass fill are extremely durable but you tend to crack or chip them when hit just right. Nylon 6 by itself remains tough but flexible and tends to lend itself to abuse a little better in an application that not structural.

Just my 2 cents. Hope it helps

Boots
05-27-2008, 02:29 PM
Have you considered Polycarbonated Plastic? The stuff they make lenses out of for eye glasses and it is also used for windshilds in our Fighter Aircraft. It's very strong,clear and will take a heck of a wack to break it.

airpro_1
05-27-2008, 02:41 PM
Polycarbonate is an outstanding choice but again a bit overkill for handles-the pricing of polycarbonate is very expensive. I think the last time we purchased PC it was over $5(US) per pound- nylon is closer to $2(US) per pound. Also PC when it is stressed (i.e. using a bolt to retain it) if it is tightened to much you will get stress cracks (crazing) radiating from the bolt hole which will cause brittleness in your part and make it easier to break if it were wacked.

If this part were to be structural I would definately say go with fiber reinforced nylon you almost can't beat it in rugged tests. If it was to be an injection molded single part then I would go with the PC.

But i would say your best bet for hand grips is a textured mold with Nylon.

KevinWilkins
05-28-2008, 01:32 AM
Thanks for the info!

I don't think PC would be a good choice for the grips but I'll try and find out more. Nylon – whether with or without fibres – is looking more like it.

Does anyone know what types of plastic are used for pistol grips on modern pistols?

airpro_1
05-28-2008, 09:50 AM
was looking through the latest 'General' catalog- It appears ABS and Glass filled Nylon are used quite a bit in handgrips

plasticpeter
05-28-2008, 02:19 PM
Neoprene grips would probably mean that you could get away with a cheaper resin for the main body (ABS?) as the rubber would absorb any blows. It looks a weighty piece of steel to be throwing around so this is probably a critical consideration. Coring out the design would reduce the risk of sink marks that you wouldn't get with a reinforced nylon.

I agree with the comments on Polycarbonate - it is a quality material but resin/processing costs will be high and it is hygroscopic, which could lead to the stress cracking.

ImanCarrot
05-29-2008, 05:30 AM
http://findarticles.com/p/articles/mi_m3197/is_n2_v34/ai_7423593

It seems they can be made of anything!

Search for Bill Jordan grips, they're moulded plastic from Pachmayr who usualy make rubber grips.

robinhood2b
06-01-2008, 06:12 PM
HI i was involved a few years back in the SA80 rifle project that was and i believe still is atandard issue weapon to the uk armed forces.
the handle on that weapon was moulded in glass filled nylon and the rifle butt end that sits against the shoulder was moulded in polyurathane which was for recoil absorbtion reasons as it is a very spongy rubbery material.
the grip on the handle came from the shape and the coarse spark eroded finish that was moulded on it.
regards
mark from the good old UK

KevinWilkins
06-02-2008, 01:23 AM
That's great info! Thank you. I hope to have to drawings ready this week to get some quotes.

jetski
06-14-2008, 07:36 AM
Nylon is the best choice we make lots of things that, well let just leave it at go bang. Nylon is by far the best choice, 2nd choice for grips is abs. I would stick with nylon 6/6. Dont spill anything like acetone, gas, or lighter fluid, on all of the other choices (including the abs). Nylon will not care what you spill on it. hope this helps (from a grip maker).

KevinWilkins
06-14-2008, 09:48 AM
That's really helpful info! Much appreciated.

What type wall thicknesses are good for Nylon 6/6?

Here's a rendering of the grips as redesigned for molding. The original, milled grips can be seen on my website:http://www.wilkins-knives.com/utility_e.html

jetski
06-16-2008, 07:21 AM
.090 inches or 2.25 mm. is pretty standard. You can go thicker any you can go thinner depending on design issues. Shrink will be about .018 inches per inch. By the way Nice looking knives on your web site! The best way to help you out is, go to the mateial supplier and get thier information design guides. Hope this helps.

Moldmaker*1
06-18-2008, 08:15 PM
I'm guessing $3500 US for a steel mold and $.50US per set to run in low volumes.
Am I close?

Stu_M3
06-19-2008, 07:59 AM
My own suggestion would be to abandon the project altogether and not add to the growing knife problem.

bloefeld
08-22-2008, 01:35 PM
These are easily made with thermoplastic or thermo-set urethane. What you use depends on the volume you are going to need.

I would suggest molding the grippy part with a 60A durometer urethane and then molding the attachment section in 75A urethane.

Go to Chemtura and check out Adiprene and Vibrathane for thermo-set material. Reinforce the 75A with functionalized Kevlar particles from Inhance, although I doubt you can break the virgin material with an axe.

Nylon's, even long-fibre reinforced nylon is too brittle and too expensive for this type of project.

Make the tools yourself out of aluminium. If you go it alone you will need a curing oven and a method of heating the components. If the volume is small enough that can mean a kitchen stove or two with a really good fume hood. The tools have to be pre-heated but that is about 10 minutes in the oven.

Even in units as low as a few hundred the cost of the handles should be less than a couple of bucks each.

Cheers,

Bloefeld

jetski
08-22-2008, 01:51 PM
I would ask stu m3 what he is using to cut his been sprouts with. Or how do they cut their pasifist buddie down from the haning tree. Wow! Growing knife problem? When knifes are outlawed only outlaws will have knifes, oh and me too. Never brought a knife to a gun fight. Any way sorry for the side track. Your mold from an injection moldling shop like our (45.00 per hour rate), would be more like 10,000 to 15,000 for a 2 cavity tool made from H-13. Run full automatic with sub gates. Kevlar is over kill (Sorry stu m3) Nylon 6/6 would be what the military uses in the product we mold (it goes bang), Don't let Stu m3 read that. And for all you scoff laws just remember lighter are on the list right after knives. Sorry I got off the subject. We any way it is time for the head count here in D block talk to you later, got to go make a shive to stick the guard with. Just having fun. pretty soon the government will want to register your full automatic knives. And don't even get me started on what they will need to do to the good old Swiss Army Knife. Sorry Stu M3 just had to have fun. By the way those damn leathal tooth picks are next.

jetski
08-22-2008, 01:59 PM
Dear Bloefeld, You would not want to run Kevlar in an aluminum tool, unless you wanted less than 50 to 100 pieces. It is so tough it will roll the parting line in an injection mold tool. Nylon 6/6 is a military specification for alot of product. Kevlar cost to nylon cost will be a bunch different. I believe GE sells both of these materials. If you want to see some more nice looking knifes go to seldom seen knives he is out of Yellowstone Steve has some nice stuff. Not to piss of STU m3 but Steves knives will cut stuff.

KevinWilkins
08-23-2008, 05:00 AM
We have had very positive feedback from military purchasers of these knives.

It does look like I will continue to mill the grips from glass fibre plastic. Costs for a steel mould were around $9,000 allthough I did get one figure that was less but I have doubts about the ability of the company to actually come through on the deal.

Right now I am working on a moulded sheath system for the knives. It seems the sheath system is going to be very important as it should be mole compatable and heat resistant.

Thanks to all those for the positive suggestions.