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Looking for a hard durable plastic......

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Sailor3

Sailor3

Coastal
Sep 21, 2009
5
Hello everyone,

I have been looking for a hard durable plastic for a few weeks now searching the internet and calling a few places and noone has been able to fully answer my questions so I figured I would try to pick your brains for a while.

What I want to build is an auger out of plastic that will be used to drill into sand by hand, simular to the one pictured below. I want it to be strong, stiff, and maybe a little flexable. I do not want it to be able to shadder, I would rather it flex and bend than shatter.

This will about a 5-6 foot shaft about 3"-4" in diameter with "threads" or "blades" like an auger on three feet of one side of the shaft. The auger "blades" will be about 4" wide and will be about 1/8" thick near the end tapering to about 3/8" where it spirals around the shaft.

It will be used to be temporarily set in the sand and will be spun by hand, only about 3'-4' of the shaft will be going down into the sand. The plastic needs to be durable enough to be able to drill though sand. If the ground is hard packed dirt or clay then the product should not be used in it.

From what I have learned so far I think I would prefer a thermaset plastic? (so that I do not have to heat it and pour it in)

Or maybe some sort of epoxy? Not sure about epoxy, because the epoxy that I have used (to build a small wooden sailboat) was very hard and didn't have any flex to it.

What I hope to do is make a mold of a current metal auger out of a silicone rubber like GI-1000 ( Then use that rubber casting as a form to pore my plastic/epoxy into to make my plastic auger.

So can anyone give me a suggestion or point me in the right direction?
Any advice or guidance would be greatly appreciated!
 
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Take a look at what plastics they use in similar applications such as plastic Garden Tools, I believe some are ABS.

Posting guidelines faq731-376 (probably not aimed specifically at you)
What is Engineering anyway: faq1088-1484​
 
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The best material will be cast nylon. Nylon 6 can be cast from caprolactum and can be moulded by pouring into cheap moulds. Glass reinforced cast polyurethane might be another option. Controlling the glass fibre placement during curing will be a problem.


Regards
Pat
See FAQ731-376 for tips on use of eng-tips by professional engineers &
for site rules
 
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pat,

Thank you very much for your reply. Just did a quick search on Cast Nylon and I find that it doesn't do well fully submerged. For my application the plastic auger will probably be sumbmerged a pretty good deal. It states that it can swell as much as 5% in fully submerged applications.

Not sure if this is a problem or not, does it loose it's strenght when it is swollen?

Also where I find it, it can only be puchased in a solid state. Not in a liquid so that it could just be poured into a mold and a hardener be added. I would like to try and avoid having to heat the material in the process.

When you say it may be a problem controling the glass fiber placementduring curing, do you mean that the strengthening particles in the mixture may settle to the bottom?

Thanks again pat.
 
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KENAT,

I seemed to have missed your post when I was scrolling down the page (I am new to this forum layout). I will check out garden tools, great suggestion.
 
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ABS cannot be cast. You would need an expensive mould.

The submerged thing is a new twist that seems to have been overlooked in your previous posts.

Nylons absorb water and swell and soften and toughen. They absorb a fixed amount then stabilise so long as the humidity remains constant. The absorption process is quite slow with thick section. Some glass fibre can offset the change of properties.

I still think cast nylon 6 is your best bet, unless you have another surprise announcement.

Regards
Pat
See FAQ731-376 for tips on use of eng-tips by professional engineers &
for site rules
 
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I'm trying to imagine anyone using a hand auger to dig into sand 5-6 feet. If I tried that at the beach, I might get 1-1.5' down before it gets really tough to move. the first 6-12" isn't bad at all, but once you dig down pressure makes it a bitch. And if I could apply enough force, I can't think of any plastics that wouldn't eventually break under the stress.

Dan - Owner
Footwell%20Animation%20Tiny.gif
 
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I think that is the last surprise.

The auger wouldn't be left in the water for any more than 24 hours and would normaly be left in the water/sand for 4-6 hours.

pat, you said that nylons absorb a fixed amount then stabilize if the humidity remains constant. So lets say one day the auger was left in the water/sand for 6 hours and then again the next day for 4 hours. Would cast nylon 6 still be strong enough. Also, do you know about how much strength would be lost when the nylon absorbs it's maximum amount of moisture?

macgyvers,
You could be 100% correct. I intend to try it with a metal auger by hand before the plastic one is made. Good point.
 
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The design of 4-5 inch auger that is intended to penetrate into the sand 4 feet and made entirely out of plastic will be difficult. The size of the shaft will have to be much thicker than an equivalent steel auger. Therefore, the resistance to turning will be much higher. I am not sure you will be able to do it by hand. I would suggest you try to prototype it at a professional prototype house using cast urethane and conduct beach test before you go much further.
 
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"Would cast nylon 6 still be strong enough"

How long is a piece of string?

You haven't really provided enough information on the loading etc to really tell you that.

(Pat, Nylon was my first guess but then I searched hand tools and the first few I found were ABS but your point on manufacturing is well taken)

Posting guidelines faq731-376 (probably not aimed specifically at you)
What is Engineering anyway: faq1088-1484​
 
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Why not just make a cheap mould and cast one in nylon. Cast nylon is substantially stronger than injection moulded nylon.

I agree the shaft will need to be thicker than if it were steel. I can't comment on the force required to turn the auger.

Another option is to have a steel shaft with small arms sticking out then casting over that.

I presume you want plastic rather than metal is so that it does less damage to the boat if it is dropped or handled roughly against the deck or hull or people for that matter.

Regards
Pat
See FAQ731-376 for tips on use of eng-tips by professional engineers &
for site rules
 
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I was thinking he wants plastic so as to avoid corrosion concerns in having a steel anchor embedded in gritty, salty water for long periods of time.

But, it seems we must play guessing games.
 
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I'd be barefoot at the beach long before specifying a plastic as screwing anything 4ft deep into sand by hand will be next to impossible. Most have a hard enough time getting a spiked umbrella pole to stick in deep enough to keep it from blowing away or tipping over. Good luck.
 
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I want plastic so that hopefully it would be lighter than metal. A metal auger banging around the boat and such would scratch things up a bit. Yes, plastic also to avoid corrosion.

I have used small augers that drill into the sand for umbrellas and they went in without a whole lot of effort. So I figre is something that small can be driven into the sand then why not a larger one where you could put a bit more power behind it if needed.
 
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You should make a few prototypes, you might start by testing a manual post hole digger that is about the correct size.

The plastic one will be harder to drive as it will have a thicker shaft and blades

Regards
Pat
See FAQ731-376 for tips on use of eng-tips by professional engineers &
for site rules
 
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Sailor3 said:
I have used small augers that drill into the sand for umbrellas and they went in without a whole lot of effort. So I figre is something that small can be driven into the sand then why not a larger one where you could put a bit more power behind it if needed.
Click to expand...
Unfortunately, things rarely scale up that nicely/linearly, particularly when energy/force is involved. Ask the guys who mixed their reagents in a 1 Liter container without issue, then decide to do it with 1,500 gallons at a time... KABOOM!

Dan - Owner
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