Criminal that you don't have more views on this. I've been trying to figure out for a week or more how to make a DIY SPT or CPT to check my soil type/psi at 4' frost line depth. Using HD black iron was one way I was going to make a load tester with a 6x6' plate on it, which 1/4sqf. However I'm going to make one like this, only 4' long. Pound it to depth, remove handle and push out the plug. It'll be a little compressed, however I can take the bottom 4-5", throw it in a jar of water, shake, and let it settle for a day and get a good idea from separation lines of the % of clay, silt, sand, etc. It kinda funny how many people build their decks just using the local rule of thumb of x inches deep and a 12/16" pier.
Thank you for your efforts! What was the dimensions of the cut? Based on the video the length was 8 inches, specifically what was the dimensions cutting down into the metal? Was it a 1/4"? Thank you again for motivating me to do this project. I bought and pieced the black metal at the store and even the employees said it was a great idea!