CNC Graphics Tablet
CNC Hanging Plotter
I'd modify that like this:5a. Wrap the exposed cable's end in about 5-10cm of solder wire.5b. Feed it into the round half of the tube6a. Squash it gently with your mallet6b. Use butane torch or 100W soldering iron to melt the solder. Make sure you don't burn or melt remaining insulation on the cable. As solder melts, squash copper again to make sure cable is reliably held in place.This way you ensure that the connection will be reliable and won't heat under heavy load. Solder will prevent copper from corroding and increasing resistance on the joint.
Use $10 drill press from your local hardware store and a dremel: http://www.thingiverse.com/thing:1654673This allows perfect holes at 90-degree angle
Your build could have looked so much better if you have invested just about $2 in a cheap mixer for a hand drill (or, better, stronger mixer with SDS+ tip for power drill). It is almost impossible to mix concrete with a stick in large amounts - it is damn hard and takes too much labor. If you had used that, all surfaces would be so much smoother and concrete would be stronger.
Don't underestimate the weight of the concrete - it can break your styrofoam. Plywood is a smarter choice.
Simple 5V breakout board for ESP-01 (ESP8622)
The CNC Bubble Iris: A Computer Controlled Giant Bubble Machine
Duct Tape RC Airboat
Control your Tv, Dvd and Audio system with Arduino and Android