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Auger Flights


tentman
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Gidday Guys

 

I'm wondering if there's any rule of thumb for selecting an auger size to predrill post holes in hard clay, posts driven down the hole after pre-drilling.  Working in fairly tough clay, currently lots of (good) posts getting smashed with a 340 kg monkey.

 

I was hoping to get away with buying one 100mm flight but do you use a different size for strainers??

 

Thanks

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Really you need different sizes for different scenarios and different types of ground. If your drilling really hard ground or rock you might want auger just slightly smaller than the post. If your just using a 4" you've only got the benefit a rockspike could do.

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A 4 inch auger will be more beneficial than a rockspike because it actually removes the material from the hole- a spike will just compact the side of the hole further- this is why in my opinion augers are better for hard/compacted ground and spikes are better when things need shattering- i.e. Rocks and concrete/tracks etc.

I tend to use an auger 2 inches smaller than the post if it's hard ground. I have a 4" 6" and 12" which covers most scenarios.

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A 4 inch auger will be more beneficial than a rockspike because it actually removes the material from the hole- a spike will just compact the side of the hole further- this is why in my opinion augers are better for hard/compacted ground and spikes are better when things need shattering- i.e. Rocks and concrete/tracks etc.

I tend to use an auger 2 inches smaller than the post if it's hard ground. I have a 4" 6" and 12" which covers most scenarios.

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I would agree with using a narrower auger in clay. As mentioned in another thread dug in posts are not as secure and need little effort to pull out. Whereas driven posts require alot more force to extract.

In clay which expands and shrinks with water content a tight fit is required.

A pre drilled hole the force of going in should compact the sides for a snug fit.

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I also think it's far better to get a post deep by pre drilling with an auger than to get a post not so deep but no predrill. When I started I only had a 100kg monkey on my post driver- on its own it was pretty **** in hard ground but if I predrilled with an auger 2" narrower it was surprising how deep I could a big post in even pretty hard ground.

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