There is no issue with the surface finish. The machining marks you see on the surface you will not be able to feel with your fingers, and will be removed by the sandblasting process for the group buy cases.
The straightness & flatness tolerance is the deviation from intended position over a defined length, i.e. a tolerance for deformations like bending and twisting.
Ah gotcha. Was it more on the side of machining error, or was it some kind of fundamental flaws associated with the chosen material that would make it susceptible to deformations?
Without being there, I wouldn't know for sure what is the exact cause of the slight deformation. Most likely a combination of material property, machining technique, cooling, part design etc.
If I had to take a guess, due to the poor thermal conductivity and poor machinability of 316 stainless steel, it's likely caused by localized heating of the cutting zone while milling the center cutout being the weakest spot, and the expansion of the material from the heat opened up the cutout slightly. Some adjustment to tool path, feed rate and cooling will most likely eliminate the issue.
Brass weights for the GB being a freeier machining material with good thermal conductivity, if my assumptions above are correct, will not have this issue.
TBH it's most probably just my specified tolerances being too stringent overall, and the factory overly cautious with me harping on about tight tolerances is priority...
