I prefer Dura-Bar - It doesn't have a rough finish like a sand casting. It doesn't have hard spots especially on this corners from heat treating. Here is the last order I made 2 years ago. I use these plates for my practice plates when teaching. I have the host mill them.
1 0.750"H X 3.625"W X 72.000"L 2 52.3 lbs 105 $137.644/EA $275.29 GRAYIRON G2 IRON CUT PLATE Offering plate Material finish .625"X3.5" Lead time 3 days (This size was approx.$2.00 a foot)
2 Shipping & Handling 1 0.0 lbs 0 $127.19/EA $127.19
I will order some square material and have them saw it corner to corner, mill them and sell it on here. I am sure I can sell them cheaper then one can have a casting made.
If you are having trouble with castings having hard spots on the corners, you are using castings from an incompetent foundry. There are ways to use proper feedstock, melting, and casting techniques to prevent such problems. As part of my quality control I have three methods of testing for uniform softness. I use a Leeb Hardness Tester or a Wilson harness tester on every casting that leaves my foundry. In addition, I machine about 1/3 of my castings and can tell on the first cut if the casting is uniformly soft. That is the "final word" on uniformity.
Secondly, proper thermal stress relieving a casting does NOT induce corner hardness. The correct stress relieving temperature is 1150 F (I think some heat treaters might use 1200). To get to the transformation temperature of cast iron a person should have to raise its temperature to 1350F or greater and then quench it. I think it is unform practice by any heater to then slowly cool from 1150 (1200) to room temp. So, for stress relief, the part would not ordinarily be raised to the transformation temperature of iron and it sure wouldn't be quenched. And to anneal cast iron I follow the common practice of raising its temperature to 1750 and slowly cooling it. Done correctly, that guarantees the softest casting possible.
Today I will stress relieve my new Featherweight Parallel/Level casting pictures of which I posted in a parallel thread. When I do so, I will put in a scrap of iron and pull it from the oven and quench it to see if that will harden it. I don't think it will. But, let's answer the question---easy enough with the right equipment.
Rough finish is a relative term, of course. But, if a foundry is using good sand with proper additiives and proper pouring technique, a relatively smooth surface will result. Here is a pic of the casting I poured for the first time yesterday. I think you can see it has a fairly smooth surface as cast---enough so that you can see it glistens.
Added: Oh, since you mentioned the feel of a casting in the hand, the above casting with its oval "windows" really feels nice in the hand.