How to check the straightness error of the horizontal milling head spindle axis when moving the working table of gantry milling machine?

Gantry milling machine method of checking for errors in the straightness of the horizontal milling head spindle axis when the working table is moved. When checking, fix the horizontal milling head in the position close to the working table, clamp the spindle sleeve, and adjust the milling head with rotating view point to zero. The working table moves to the guide rail base, that is, the place L/2 away from the main axis axis, and puts a special slide block in the t-shaped groove of the working table, so that the flange of the slide block is close to the surface next to the t-shaped groove of the base. Fix an Angle gauge bar on the spindle to make the top of the dial gauge on the side of the slider and take down the reading of the gauge. The slide block does not move, after moving the working table L length (L length is determined by the accuracy checking specification of the machine tool according to different specifications of the machine tool), place the main shaft 180° so that the contact of the dial gauge touches the side of the slide block again for checking. The difference between the two readings on the dial gauge is a straightness error.