Speed change control mechanism of a vertical milling machine

A speed change control mechanism installed in a milling machine for high/low speed transmission control, comprising a motor for power output, a main shaft, a belt transmission mechanism driven by said motor to turn said main shaft, a gear box disposed at one side of said main shaft, said gear box comprising a gear shaft, a small gear slidably mounted around said gear shaft and stopped from rotary motion relative to said gear shaft, said small gear being moved into engagement with a big gear which is fixedly mounted around said main shaft, wherein a bearing means is fixedly secured to said small gear, a rack is fixedly mounted on said bearing means and meshed with a toothed shaft, said toothed shaft being rotated to move said small gear between the operative position, in which said small gear is engaged with the big gear of said main shaft for permitting the output power of said motor to be transmitted through said gear box to said main shaft for a low-speed milling operation, and the non-operative position, in which said small gear is disengaged from the big gear of said main shaft for permitting the output power of said motor to be transmitted through said belt transmission mechanism for a high-speed milling operation.