On face value you'd think the engine driven petrol Auger would beat the manual post hole digger hands down but after digging holes for the past few days to build a new fence I'm kind of surprised both have similar disadvantages, and in some ways I prefer to have the manual digger.
So I started with my manual post hole digger ($74) from Bunnings and found it did a pretty good job but it was really hard going and a very slow process. The soil I'm digging into is dry loam stuff and when wet it's like quick sand but when dry it's hard and compacted like road base. Then, at about half metre down the soil changes to heavy clay and in some places it's still wet clay and in others it's dry.
Bottom line is, my digging conditions are pretty awful! And after 21 holes with about another 40 to go I decided to hire a petrol post hole digger (one-man operation). The manual post hole digger would go through the crust fine but then hit the hard compacted stuff and spin making dust so I had to continuously break it with a crowbar to keep it digging down. Of course, once I hit the clay if it was wet the turning got a little tougher but at least it dug down.
Naturally, the clay stuck to the inside of the cylinder and even with the spring pusher it was a PITA to get out. I could imagine digging with this manual digger in predominately heavy clay soil would be really difficult (unless you just had a few holes to dig).
With these issues in mind my move to hire a mechanical digger seemed obvious - I was looking forward to standing by and letting the petrol Auger do all the hard work. When I picked up my Auger the hire guy said, "you'll notice a big difference using this machine over digging by hand" and that's what I expected...
I wish I could say the petrol Auger made hole digging a breeze; unfortunately, it still spun in circles on the compacted soil and required quite a bit of force to keep digging. When the drill hit clay it got clogged and stopped continuously so it needed to be withdrawn and the clay removed before continuing. If the drill hit even a small tree root it would get stuck.
The operating handle to turn the Auger was hard to hold in and grip - this was very annoying especially when downwards pressure was needed to be applied at the same time. Often my hand would slip and the drill would stop - it was poorly designed. Moving the digger around wasn't easy either and although with this particular design (motor balancing the Auger as a lift assist) it was still hard work getting it into position.
Nevertheless, with all these faults I managed to get the job done much faster than I could doing it manually. However, she was no piece of cake and after digging the remaining holes I was pretty buggered I have to say.
A one-man petrol engine Auger post hole digger would probably work totally fine in loose garden soil but if you are digging in heavy or compacted soils be aware you're still in for a tough day!
If I ever do a big digging job again in difficult soil conditions I will definitely get the holes dug by a Auger attached to a bobcat or mini excavator rather then the much less torque of a hand operated machine. As for my manual post hole digger, it's going to be handy to keep for those smaller jobs but anything over 10 holes and I'll be getting someone in with tracks or wheels to dig them for me...