Yes, it is possible to CNC milling stainless steel that is very thin or very thick. However, there are some limitations to consider.

Thin stainless steel

Milling thinner stainless steel is more difficult because it bends and warps more easily than thicker stainless steel. Additionally, there's a possibility of chatter, which could result in a less flawless surface. CNC milling of thin stainless steel is only possible with a slow feed rate and a sharp end mill. The use of a support fixture might be necessary if you want extra defense against bending or warping.

Thick stainless steel

Compared to thin stainless steel, thick stainless steel requires more force and power during the manufacturing process. It is also more likely to produce heat, which could lead to warping or breaking of the part. Use a robust machine and a robust end mill when CNC milling thick stainless steel. Additionally, to keep the part from overheating, you might need to apply lubricant or coolant.

Generally speaking, it is best to avoid machine-finishing stainless steel that is thicker than 1 inch or thinner than 0.02 inches. However, with the right equipment and techniques, stainless steel of any thickness can be CNC milled.