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

[Doz]

I’ve pulled out treated 4x6 post that where in the ground for 18 years with concrete poured around them busted the concrete off them and reused at my house been in the ground for another 10 years still standing strong just packed the soil back around them the second time.

 

[kenhar]

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 hole needs to be big enough to allow at least 2" of packing material on each side of your post. Concrete around any treated wood will void the warranty on treated lumber. The ash in the concrete will rot the wood in a few years. People do it every day but read the warranty on your treated lumber. A hole 36" deep with play sand and water works pretty well.

 

[aircommuter]

If you want a long lasting one just get some Sono tube and rebar, just drill the hole and set tube on top and fill it up. If it’s for a building then concrete in the ground and steel frame above.

 

[OzarkChris]

a^2+b^2=c^2

4"^2+4"^2=c^2

16"+16"=c^2

32"=c^2

sqrt 32"=c=5.65"

So you need a 5.65" hole minimum. If you're using material to anchor it like concrete or phone you need to determine how much of an ancohor you need for your soil conditions.

I am sort of curious why you are using the pythagorean theorem, which is used to figure out the value of the hypotenuse in a right triangle, when calculating for a 4x4.

 

[sea2summit]

I am sort of curious why you are using the pythagorean theorem, which is used to figure out the value of the hypotenuse in a right triangle, when calculating for a 4x4.

Hmmmm, I'll turn that question around on you. How would you determine the minimum radious of a hole required to fit a square 4x4 into?

 

[charlessenf]

Hmmmm, I'll turn that question around on you. How would you determine the minimum radious of a hole required to fit a square 4x4 into?

Well, isn't the High Pot and use = 2 the diagonal measurement on a 4x4? And if you wanted to leave room for a minimum of X" of setting material like concrete or foam - wouldn't that diagonal measurement determine the minimum diameter of the auger required?

Or. you could simply measure across the 4 x 4 I suppose, add 2X". divide by 2 to get the radius, then multiply by 2 to get the diameter and go buy (or rent) the auger.

 

[sea2summit]

Well, isn't the High Pot and use = 2 the diagonal measurement on a 4x4? And if you wanted to leave room for a minimum of X" of setting material like concrete or foam - wouldn't that diagonal measurement detrmine the minimum diameter of teh auger required?

How do you find the diagonal measurement?

 

[Gord Baker]

Streetcar,

Several huge differences in what the power company is probably using for urethane foam and what guys walking into the local hardware are going to be able to purchase. I spent 20+ years in advanced elastomers and there are many grades of urethane for many different applications. I could bore ( pun intended ) your with the details but finished cured urethane can range from glass like to foamy elastic stretchy sponge just by changing the polymerization components/ ratios.
Power company is also sinking that power pole a min of 10 feet and probably closer to 15-18 feet into the ground and they are probably using a very small overbore tolerance which all produces a tight fit and very little foam gets used.

I use the hole spoil for the most part, tamping every 6". Some stone if available is good. Crown the hole around the post at the surface as they rot at grade level due to surface moisture. I soak posts in used oil if available. The power company would not be sinking holes more than 8'.

 

[Flogger]

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?

My standard is 9". I have a 24" for corners.

 

[zzvyb6]

I see presumptions here that the goal is a long lasting pole that doesn't rot away. Around here, you can repair a fence with 6" posts and the next day a 12pt buck will charge thru the fence and break posts just because you blocked his path. So, I install posts with quick change in mind. My posts don't ROT off, they RUT off !!!