The physics of digging a post hole

physics post hole boring digging Upper Hutt Hire Kenards kennards Hirepool

The physics of digging a post hole

It seems there are quite a few fencing projects around Upper Hutt. Our one-man Tanaka post hole borer has been popular since we opened for business but perhaps a little lightweight for some jobs. A couple of years back we bought a digger attachment for our 1.7MT excavator, but the excavator + attachment was probably a bit too much for other projects (great for a long line of post holes but). We had an equipment gap somewhere in the middle.

Enter our new ‘Digga’ 9HP post hole borer, purchased at Fieldays last month.

This machine utilises a cantilever system and petrol-driven hydraulic power to turn the augers and dig the hole. It’s an elegant way of getting the job done with minimal fuss. But if you stand back and look at it, there’s a physics lesson wrapped up in how it works:

1. Newton’s third law. Newtons third law states that ‘For every action, there is an equal and opposite reaction.’ It sounds rather dull and mundane, until you hit something with the one-man post hole borer, and find yourself rotating around the auger pulling 10 G’s. You’ll probably send someone else off in fits of laughter and perhaps get yourself immortalised on YouTube, but it can be rather dangerous. Lets try and stay in one place. It’s safer.

2. The power required to turn an auger increases exponentially. Double the diameter and you’ll need roughly 4x the torque to turn it. A high-torque situation is ideal for an electric motor, but there usually aren’t a lot of power points where most post holes need to get dug. Instead some decent four stroke torque should be enough to get the job done, especially when trying to turn a 300mm auger. That’s why we like the availability of 9HP of hydraulic power.

3. Dug dirt needs to be lifted. The cantilever system makes the removal of the earth easier, without having to lift the dirt + machine & auger.

As you can probably gather, we like the design of this piece of kit. Whoever designed it didn’t sleep through a lot of those high school science lectures.

If you’re interested there is more information at http://bit.ly/UHH9HPPosthole


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