Not to speak for others, but I have been following 100model for at least 10 years, and so know a few things about what he does.
Correct me if I am wrong, but 100model has spend at least 20 years mastering the art of "green sand", which is sand mixed with clay and other additives such as coal dust.
There is an absolute art to making/mulling good green sand (a muller is a larger mixer for foundry sand).
Too much or too little sand/clay/coal/water, etc. can be the difference between a successful iron casting and a total casting failure.
I tried a few castings with green sand, and realized just how tricky that can be.
My solution to mastering green sand it to not use it (I use resin bound sand).
But green sand is reusable, and is what most backyard casting folks use (along with Petrobond, which is similar to green sand, but uses oil instead of water).
All of 100modeler's impressive iron melts and excellent pour temperatures would mean nothing if he did not have superb green-sand molds.
And so the moral of the story is there there are many facets to a successful gray iron casting process, including the green sand, the burner, the furnace and its mass, gating/risering/runner configuration, etc.
Its about getting a complete mold fill without having defects in the castings, having a good surface finish, and creating strong cast parts that retain their machinability.
Not to put words in 100model's mouth, but that is what I have observed over the years while watching him, and that is basically what he has told me.
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