Up-and-down motion mechanism for belt sander

An up-and-down motion mechanism for a belt sander including a continuous loop of sandpaper mounted on two end drums, comprising:

• a detachable worktable including an opening with the belt sander up-and-down moveably disposed therethrough, two bifurcations on an underside, a housing mounted to the underside, a chute disposed under both one drum and the opening, and two cylindrical columns extending downward from the underside of the worktable;
• a base including a plurality of posts releasably secured to the underside of the worktable;
• a control device mounted to the base;
• an electric motor disposed in the housing and including an upper motor shaft rotatably connected to one drum, a lower worm screw, two legs, at least one first hollow cylindrical member slidably put on one cylindrical column, and at least one second hollow cylindrical member slidably put on the other cylindrical column;
• and
• a transmitting assembly disposed in the housing and including a rotational shaft rotatably disposed through the legs, a worm wheel with the rotational shaft disposed through and meshing with the worm screw, two cams secured to two ends of the rotational shaft respectively, two links with the electric motor disposed therebetween, each link having one end connected to one arm and the other end connected to one bifurcation, and a biasing member having one end anchored at a bottom of the electric motor and the other anchored at the underside of the worktable.