| 摘要 |
A speed-changing device for a machine tool spindle comprises two driven gears of different diameters secured to the spindle, two driving gears for meshing with respective ones of the driven gears and angularly fixed relative to each other, the spindle being orientable in a predetermined angular position. The driving gears are axially slidable with respect to the driven gears for selecting which of the two pairs of driven and driving gears is in mesh. The gear ratios are such and the fixed angular relationships between the driven gears and between the driving gears are such that one gear of each said pair has a tooth aligned exactly with a space of the other gear of the pair. The two driving gears have an overall axial length greater than the axial clearance between the other two gears whereby, when changing speed, one pair of gears commences to mesh before the other pair has ceased to mesh. |
