Right tool to drill a 3 to 4" diameter hole approximately 3ft deep through remnants of a ground up tree stump

Question

I'm installing a very basic fence with welded wire mesh that will be fastened to galvanized steel T-posts. But I've run into a snag. At the very end of my run on one side I cannot dig into the ground. This is because there used to be a very large 40ft tall horse chestnut tree. Most of the stump was ground away. Unfortunately, it couldn't be done as thoroughly as we all had hoped because the base of the tree was growing right up next to a cement wall that is our neighbor's garage. My T-posts are 10ft tall that have been dropped into the ground at about 3ft. I'm not dead center on where the tree trunk was but I'm about a foot over. This is where my last post will go. However, the trunk was approximately 20" or so in diameter. Even though I'm off to the side a bit I'm going to guess that the area I want to insert my T-post will be solid root.

If successful, my plan is to drill a hole large enough to drop the T-post in, use a cement or some type of epoxy (or I'm open to suggestions) to adhere the T-post in place inside the hole. Then I'll use braces to help secure it along the run of my fence and then another one that will run perpendicular into our yard to help secure it in place. See the link for the braces/ enter link description here

Those braces will help keep it secure.

My question is, what type of drill bit can I use. In addition to drill bits I was looking at extensions to help me get down deep and am a bit overwhelmed with what to use.

Anyone have any suggestions/recommendations?

Answer 1

The amount of torque it would take to auger even a 3 inch hole in a tree root would be way beyond what you could safely do with a hand drill. You might be able to rent a gas powered 2-man well drilling auger with as small of a bit as they have for it, then wedge sticks or something in with your post before pouring epoxy resin in it, otherwise you may end up needing a gallon or more of resin.

But... Anything you do here is only going to last until the tree root fully rots away, then you will have to replace that entire post setup. Once you drill into it, it may accelerate the process and you could be looking at a couple of years max. The "geometry" option seems better to me; just add a post before and after the stump and angle that corner to go around it.

Another option would be to forestall the fence post installation a bit and either use a chemical stump remover (potassium nitrate) now, or drill a hole in the root and burn it out when the weather is dry.

Answer 2

I think that you will end up chiseling and chipping, rather than drilling. I would be very difficult to hold a tool by hand and drill a hole that size into hard wood.

I would consider renting (or buying) a chipping hammer and use a chisel bit:

Answer 3

An auger bit would work very well for this situation. It has a threaded tip so it self drives and no downward force is needed, just insert and go. Also, it won't spin in the chuck under high stress, the end that inserts into the drill is hex instead of round. They come in some pretty large sizes. Be careful because the self driving feature also means that the bit is in constant drive mode and therefore, unlike regular bits, there is always a torque on the drill and the only way to stop that is to let go of the drill trigger (stop drilling). If you use a 'hole hawg' or other larger and VERY POWERFUL drill it is very possible to break a wrist.