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 !!!

 

[OzarkChris]

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?

I wasn't suggesting you were wrong, but personally, I just pull out a measuring stick/tape, make a rough guess at corner to corner width, add 1/2-1" to each side of that value, pick the size auger closest to it that I have and call it a day. I don't normally have a calculator with me while I'm working - and no cell signal, so I don't carry phone. 2-way radio doesn't have apps like Calc either - actually it doesn't have any apps now that I think about it.

 

[OzarkChris]

How do you find the diagonal measurement?

If you are sinking posts, measure from either end. It's not like the post is already in the ground.

 

[sea2summit]

I wasn't suggesting you were wrong, but personally, I just pull out a measuring stick/tape, make a rough guess at corner to corner width, add 1/2-1" to each side of that value, pick the size auger closest to it that I have and call it a day. I don't normally have a calculator with me while I'm working - and no cell signal, so I don't carry phone. 2-way radio doesn't have apps like Calc either - actually it doesn't have any apps now that I think about it.

I didn’t have a 4x4 handy but was at a computer

 

[jimcrownover]

My PHD's are "Armstrong Type". I've always sized my holes with about 2" clearance around the post, whatever the size. That gives me clearance to use my busted sucker rod tamping bar to give a very solid fit. I don't use foam. A bull with an itch would dislodge the post before he got it completely scratched.

 

[tallyho8]

This is the way I always do my fence posts and ones I put in 30 years ago are still strong. Naturally, quality 4x4s that are treated with a good ground rating. This probably would not work in an area with much rock but here we have mostly clay and high ground water and lots of rain.

For a fence 4 1/2' tall i drill a 4" hole about 30" deep and then use my frontend loader to push the post down since the post is wider than the hole in the corners. Then I push or pound it down the rest of the way till it is 42" deep. If the ground is dry and hard I fill my bucket with dirt to give it the extra pressure it needs. This post will be very solid just like that but I fill the voids around the post with fine dirt or concrete with small aggregate. If your ground is very hard,
then you can drill the hole a little deeper than I do.

Putting the post in natural ground like that, the post will be much sturdier than if you dig a large hole and then try to pack dirt around it. The packed dirt will never be as hard as the natural ground already is.

 

[RandR10]

I suppose most of you guys have a tractor hitched auger but for anyone reading this from a search: I put in a property line split rail fence last year, number one son helped me with this. He's used a rental two man auger before so we went out to get one, old friend works there and said to get the self propelled wheeled machine, better for an old guy like me and not much more money. That machine is a jewel. Son was really surprised at how easy that machine bores the holes, especially in the pretty rugged area, no real lifting too. And I was thinking about hand digging? Might even be handier than the tractor hitch digger, and safer too I suspect. Highly recommended.

I've used both the single man hand held power auger and the one off the 3-point and unless I need a really big hole I prefer the hand one. Much faster to line up and easier to keep holes straight. If you know to keep it away from your body it doesn't beat you up too bad when it catches rocks and roots. If you stand close it'll pick you right up and spin you round. A lot easier to let it give if you hold it at arms length.

 

[tonynz]

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?

depends what size shovel you have really, it's digging out the dirt after you have bored the hole that matters' If you have a clamshell shovel probably 8 inch is good.

 

[revdoc]

When I build a wood fence, Use 1 1/2 inch clean crusher rock 4in on the bottom , set post, then add 3-4 inches of rock and tamp down hard, keep doing this until just above the ground....{always hard tamp] rock will go into the wood and the dirt..Post will last for years... My first fence I built in 1977 is still strong and steady... Just NO wood Rot... More work in the front door but worth it in the long run ...

 

[fritzp]

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?

Large enough to get the post in and plumb. The hole is easier to backfill and compact if it is a little larger.

 

[IndyJay]

I used an 8" auger. Still need to finish other side of road.