Size of auger needed.

[TheMan419]

I need to plant some 6 inch round posts. What size hole do I need to dig?

 

[Shaneard]

I'd say a 12" bit would be just fine if your packing them or concreting unless you have something to mash them in with then a 4".

 

[CobyRupert]

Tempted to say 6", but I think the question becomes how much wiggle room do you need/want? 9" should be fine, 12" will be more than plenty.
If your dig isn't true vertical you want some more wiggle room, if auger bounced around on rocks on way down you might want some, if your knocking some dirt back in the hole when you drag the post over, a bigger hole won't fill back up as fast, etc...

 

[RPW]

I use a 9in. Seems to work for the vast majority of my needs

 

[atsah]

I put 30 6 inch posts for my dog yard a few years back, I used a 12 inch so that I could jam rocks on the sides of the post down 36 inches..

 

[CobyRupert]

I put 30 6 inch posts for my dog yard a few years back, I used a 12 inch so that I could jam rocks on the sides of the post down 36 inches..

I finally bought a "post hole digging/tamper bar". It's a serious 6 foot pry bar (weighs 20-30 lbs?) that I use for about everything else besides post holes, but it is great for tamping the dirt along the side of the post at every level as you fill the hole back in. Once your done the post is wicked solid compared to just stomping the surface level dirt around the post.

 

[atsah]

I finally bought a "post hole digging/tamper bar". It's a serious 6 foot pry bar (weighs 20-30 lbs?) that I use for about everything else besides post holes, but it is great for tamping the dirt along the side of the post at every level as you fill the hole back in. Once your done the post is wicked solid compared to just stomping the surface level dirt around the post.

Oh ya, if you're putting posts in you need a tamping bar for sure..

 

[QRTRHRS]

The secret to a solid post is a little bit of back fill and a lot of tamping. Two or three inches of space around the post works so for a six inch post you are talking about a ten or twelve inch auger. I use a couple of bars. One is just one inch around and the other has about a two inch head on it. I start with the smaller then take the larger one to it. Kencove.com has a tamper that looks kind of interesting. I might be inclined to buy one if I was planning on doing a lot of posts but I am getting away from doing that.

When I used to use concrete, I would use a 1/4 inch piece of rebar to settle the concrete

 

[TheMan419]

Looks like I can get a PhD w 8 inch auger at a good price. So looks like that should suffice.

Posts will have 1 bag quick Crete dumped in hole and then filled w dirt.

 

[EddieWalker]

If you want three posts to be in a perfect line, one of them is going to need some modifying with a clamshell digger. The more you put in, the more that you will need to modify. I have a six and a 12 inch auger. The six inch is worthless. Just realize that the smaller hole you drill with your tractor, the more work it will take to modify it so the posts line up by using the clamshell digger. Be sure to get the very best that you can find. My favorite one is all metal and twice as heavy as the wood handled one.

 

[Shaneard]

If you want three posts to be in a perfect line, one of them is going to need some modifying with a clamshell digger. The more you put in, the more that you will need to modify. I have a six and a 12 inch auger. The six inch is worthless. Just realize that the smaller hole you drill with your tractor, the more work it will take to modify it so the posts line up by using the clamshell digger. Be sure to get the very best that you can find. My favorite one is all metal and twice as heavy as the wood handled one.

I have an 8" and a 12", as far as I know the 8" has never been used.

A 6" post in an 8" hole isn't going to be much concrete and it will be hard to get all your post straight like Eddie said with only an inch of space all the way around.

 

[QRTRHRS]

Looks like I can get a PhD w 8 inch auger at a good price. So looks like that should suffice.

Posts will have 1 bag quick Crete dumped in hole and then filled w dirt.

Like I said, you need to "settle" the Crete, ie; get the air out of it. A piece of 1/4 inch rebar works great. You still need to tamp the backfill over the concrete.

 

[QRTRHRS]

If you want three posts to be in a perfect line, one of them is going to need some modifying with a clamshell digger. The more you put in, the more that you will need to modify. I have a six and a 12 inch auger. The six inch is worthless. Just realize that the smaller hole you drill with your tractor, the more work it will take to modify it so the posts line up by using the clamshell digger. Be sure to get the very best that you can find. My favorite one is all metal and twice as heavy as the wood handled one.

I set my corners then run a tight string to align the line posts to. I have had occasion to work with either a big dip or a big rise. For the dip, I hang a weight on the string then set a post or two somewhere along that row until I finally get them all aligned. For a rise, I find a long pole or pipe and temporarily secure it to a post so I can see over the rise. String or not, wood posts need a visual check as well. I will support an unbackfilled post then step away a couple of post spacings or so and do a visual. But then when it comes to fencing, I am fussy!

 

[747driver]

I use a 9" auger for 6" post. To big a hole and you end up using alot of concrete. The 9" gives you just enough wiggle room for concrete. I make a concrete mushroom at the ground level for water to drain away from the post.