Mike,
Check out <A target="_blank" HREF=http://www.tractorbynet.com/forumfiles/33-157058-auger.jpg>this</A> auger Don (centex) purchased for cutting rocky soil.
When I bought my tractor I put my money in adaptors. I bought some and I made more. I can use about any auger available. But my Lowe machine uses a two inch hex male pin on the auger motor.
I have adaptors for all the round sizes, the one and five eighths hex and the two inch square.
This makes life easier.
The auger bits you show in your picture are like hubcaps on a tractor needing a wheel.
Something most folks miss out on is the importance of the pilot bit. I've learned about this over the years using manual operated power augers like Ground Hog, General, and Little Beaver.
Your pilot bit does much more than just center the auger in starting a hole.
If it's designed and working properly it's performing two functions. It's locating the auger by centering a pilot hole. But just as importantly it's initiating the drilling process by pulling down the bit into contact with the earth, rock in your situation./w3tcompact/icons/laugh.gif
I don't know if you've ever used a brace and bit to drill a hole in a wood post. The flights on the bit can be sharp enough to want to marry off to your favorite daughter. But when that puppy puts the pilot through the wood you'll notice them sharp flights don't want to cut. With your auger it isn't as important for the pilot to pull the flights into the cutting the dirt. But it is important that the pilot is cutting it's own way through with ease.
That point in your picture couldn't locate a blond in a beauty pageant much less move dirt.
Now let me give you something else to consider. Think about the action that is happening when you are using a round rod coming out of the auger motor and a pipe on the auger itself.
The forces are operating against the bolt pure and simple. The glitch that'll bite you in the butt until you'll find standing your preferred position for rest is if the bolt is hardened it's gonna eat the pin and the pipe.
I mean heck they're going cheap and we know that because it's the cheapest way to connect the auger to the motor. We know they ain't gonna spend to have the pieces hardened or use tool steel.
If you use mile steel bolts they are gonna be like shear pins.
But consider what's happening with the hex or square system. The forces are working against the shoulders. The bolts or pins are just for vertical locating of the auger to the motor shaft, no real serious stuff when you think about it.
Your system would work for most folks for most of the time. But with your conditions you need serious tools.
I'd consider ordering a hex shaft auger with a Pengo system cutting head. I'd see what it would take to replace or modify the output shaft on your auger motor to take the hex shaft auger.
Then I'd drill holes and pat myself on the back for being so darn smart.
