There are several popular used-secondhand CNC Boring Mill Machine brands, including:

1. Giddings & Lewis: Giddings & Lewis (G&L) is an American manufacturer of CNC boring mill machines. Their machines are known for their high precision and reliability.
2. Toshiba: Toshiba is a Japanese manufacturer of CNC boring mill machines. Their machines are known for their durability and high accuracy.
3. Doosan: Doosan is a Korean manufacturer of CNC boring mill machines. Their machines are known for their reliability and affordability.
4. Wotan: Wotan is a German manufacturer of CNC boring mill machines. Their machines are known for their high accuracy and productivity.
5. Union: Union is a German manufacturer of CNC boring mill machines. Their machines are known for their precision and versatility.
6. TOS Varnsdorf: TOS Varnsdorf is a Czech manufacturer of CNC boring mill machines. Their machines are known for their precision and high performance.
7. Scharmann: Scharmann is a German manufacturer of CNC boring mill machines. Their machines are known for their high accuracy and advanced technology.

These are just a few of the many popular used-secondhand CNC Boring Mill Machine brands available on the market. When looking for a used machine, it’s important to research the specific model and its history to ensure it’s in good condition and meets your needs.