Hi Keld
Just seen your video on the machining of your aluminium bars, and you seem despondent, and believe it is not worth while. I cast my own bars then machine them on the vertical mill, using a round nose cutter in a fly cutter, using no cutting fluid. The bars up to 250mm are placed on parallels in a 150mm vice, and I achieve an excellent finish.
I only use metal ingots that I have previously cast, that are free from any inclusions. The sand I use around the pattern is always new for approx. 10mm, then backed up with used sand. This gives a much better finish. To avoid shrinkage I use a runner and riser one at the ends of the bar and a feeder channel. For longer bars I use an additional riser. a cup shaped reservoir, is made at the top of the runner and risers, to ensure there is no shrinkage.
Somewhere along the line you have problems that are solvable. If you need any help please ask.
Cheers David