Make an auger

not worth the time, only 16.95

Such things already exist , they are called Ground Anchors,

Put Ground Anchor into a google search and click images and you will get loads of examples.

As the name implies they are for anchoring things to the ground such as rotary washing line poles etc. As such they won't be that easy to pull out of the ground and I think you have underestimated how much effort you will need to pull out a soil core unless your garden soil is very light and sandy anyway, but you may find a way to use one.

G.Harman

I did once hire a manual one. It was not a success, but that might be because the soil I was trying to make make a hole in is very stony.

or "post hole borer"

Fair comment ... maybe I'll buy wife one for Xmas

If you really want to make one for the fun of it, you cut a number of circles with a hole in the centre, then one cut from centre to outside,then weld one of those straight cuts to one on the next disc, and so on then stretch and weld to a pipe,

Google "Soil sampling auger" for small diameter augers.

Just buy a few tons of sharp sand, spread it and dig it in if your soil is heavy. Footling around with holes is a waste of time.

I bought one on ebay for around £16. Stones can be a problem but it was a useful tool for the majority of the post holes. I went down 24 inches but if the soil is softer it will go further. Better to just do a few turns and pull out and keep repeating because once you `screw` it in too far you will never pull it out and have to `back screw` to free it. When I did it the soil was quite wet though. Mine had a 24 inch wooden crossbar. If you want more leverage it would be easy to make a longer crossbar..

serious gauge metal there - obviously not a hand operated auger bit :-)

I just bought a Draper model ...seemed sturdier than some (we will see)

I only got 4" diameter .... suits my purpose.

What I have is parts of my ground don't drain and waterlogged. Going to try series of holes .... and fill the holes with sharp sand This will give better drainage ... almost like vertical land drainage.

Then after a few months .. when sand has migrated into the surrounding soil Rotovate the top layer .. and repeat (maybe several times)

I guess I could add compost to the sand as I fill holes - undecided on that yet.

The ground is awful .... so anything I can do to assist will help.

In some areas I dug down 2m and installed drainage crates .... but can't do that everywhere - takes a huge amount of effort ( and cost)

Both but made to fit hand held petrol auger motor