开云体育Good advice. ?I agree that - in general - three jaw chucks are less accurate than four jaw chucks. ?It is important to note, however, that the question of accuracy is related not to the number of jaws but to the mechanism by which those jaws are actuated. ?Almost all three jaw chucks are simple scroll chucks, in which all jaws can be moved simultaneously by a single pinion. ?Convenient and quick, but as stated they are usually off by several thousandths when new, and with wear can get worse. ?The great majority of four jaw chucks have each of the jaws controlled independently. ?Work held in one of these - even in an old and worn chuck - can be dialed in to run perfectly concentrically with the spindle. ?Less convenient and much slower, but for fine work much more accurate. There are, however, some important exceptions to this. There are three jaw scroll chucks of the Adjust-Tru type, in which the chuck body can be shifted slightly on the backplate after tightening on the workpiece. ?Convenient and quite accurate when used with workpieces of the same size, although they may require re-adjusting for different sized workpieces due to manufacturing inaccuracies in the scroll and to wear. As noted, there are some four jaw scroll chucks around which are scroll chucks. ?Convenient and quick and hold a bit better than three jaw chucks, but subject to the same inaccuracies as all of the scroll chucks. And then there are the combination chucks. ?I have an ancient Skinner combination chuck - four jaws that can be adjusted independently or that can be controlled simultaneously by a ring and pinion mechanism as can a scroll chuck. ?Once the jaws are individually adjusted, it will be reasonably accurate over a range of sizes. ?More common years ago, these are tough to find new these days. Exceptions to every rule. On Dec 20, 2024, at 12:03 AM, rfmarchi1 via groups.io <rfmarchi@...> wrote:
|
