What size earth auger bit do you use for a 4x4 fence post?

[Bison]

I Hammer them in with a tamper plate vibrator on my Tracksteer

 

[Cougsfan]

After reading this thread, along with my lifetime of experience of putting in posts, I am convinced there is no single proper way to put in a post. It depends on your soil, your moisture and drainage conditions, what you have for equipment to work with, and the kind of post material. What will last 50 years at one location may last only 5 years at another. I am also very aware that some pressure treated posts are much better than withstanding rot than others, even if they appear to be identical.

 

[Buchanan]

I've seen 3x the size online but nobody seems to do that in real life. What size bit would you use for a 4x4 post? I will use either concrete or the foam stuff, probably the foam, so maybe the hole should be smaller diameter?

The hypotenuse of a 3.5" x 3.5" post is 4.95" so you would need a 5" auger. A actual sized 4"x4" size requires 5.66" or 6" auger.

 

[charlessenf]

24' long laminated posts

Huh!? Burying laminated stock? Where'd you get the stuff? Any articles on it? What were the posts for?

 

[charlessenf]

"roofing cement"

I put a spigot in the bottom of a six-gallon plastic pail (like the ones Drywall Mud comes in) some screening to prevent blockage, roofing shingles and diesel fuel to the top. After weeks, months, (even years by now!), i drain some of the liquid into an appropriately-sized container and set my 4x4 post into this 'sauce' and let it absorb all it might. I also liberally brush it above - coating all that will be buried. Lately, I've been adding the chips of creosote that come off our fireplace insert innards to the 'stew.'

 

[charlessenf]

expanding foam


View attachment 782731

 

[MH8675309]

Ive set hundreds of posts with and without an auger. We never use concrete or foam. Just pack the dirt or maybe pea gravel in the hole first (bottom 6" or so) then pack the dirt. Use a dirt packer - 5 foot 3/4" steel rod with a 3" round steel cookie welded to the packing end. It will firm up those posts nice. Also are you using 4x 4 treated posts? A 5 or 6 " round treated post is much more suitable and sturdy for a fence.

 

[CobyRupert]

Agree that having a 6’ - 7’, 18lb post hole digging/tamping bar is handy for post holes, especially when soil isn’t perfect and you may encounter a stone or two, three. Even for loose dirt, I think a bar is good for packing the soil denser than undisturbed surrounding soil. Perhaps this keeps moisture away from post for a season or two.

A true 4”x4” has a diagonal of around 5-5/8”. So why not the use round if you drill the hole round?
A 2-1/2” operator err adjustment factor on each side and you’re quickly up to over 10”.
I use a 12”, because it’s what I have and works. It’s easier to backfill a bigger hole you needed than trying to shave off another 1” or 2” after the fact.
…of course it means you need a larger obstruction free diameter too.

 

[MapleLeafFarmer]

Huh!? Burying laminated stock? Where'd you get the stuff? Any articles on it? What were the posts for?

maybe a language difference here.
I have always just made my own but can buy them from lumber yard pre-made as well. Menards carrys them.
When we build a pole shed we would take 2*8's and nail 5 together to make a 5 ply laminated post.
PWF below grade and regular non treated above grade.

then set 36' rafters on top of each post spaced 4' apart help together with 2x6 purlins and girts 2' apart.

here is a pic I grabbed from the Menards website showing the top part of the post that is not PWF though use PWF for portion in ground. 24' laminated post lets me build a 16' clear span building having about 7' of the post in the ground.

 

[mediplt]

I use a 6" PTO auger. Then turn around and use the bucket to push the post in the hole. Takes 2 people but the post don't move. I'm putting the posts in red clay. Very hard ground