Lathe Operations: Facing

Facing Operations Facing is the process of removing metal from the end of a workpiece to produce a flat surface. Most often, the workpiece is cylindrical, but using a 4-jaw chuck you can face rectangular or odd-shaped work to form cubes and other non-cylindrical shapes.

When a lathe cutting tool removes metal it applies considerable tangential (i.e. lateral or sideways) force to the workpiece. To safely perform a facing operation the end of the workpiece must be positioned close to the jaws of the chuck. The workpiece should not extend more than 2-3 times its diameter from the chuck jaws unless a steady rest is used to support the free end. Cutting Speeds

If you read many books on machining you will find a lot of information about the correct cutting speed for the movement of the cutting tool in relation to the workpiece. You must consider the rotational speed of the workpiece and the movement of the tool relative to the workpiece. Basically, the softer the metal the faster the cutting. D…

What is fiddle-bow lathe?

Fiddle-Bow lathe was used mostly for small work, generally metal work, was called a "fiddle-bow lathe," on account of the method of driving it. In this lathe, which is shown in the figure below.

Fiddle-Bow Lathe

The same idea of propulsion is used, that of a cord passing around either the piece to be turned or a rotating part of the mechanism by which the piece was revolved. In this case, however, instead of the resistance of the flexible limb of a tree or of a "spring pole" acting to keep the driving cord taut, it is held in that condition by the flexible bow F, which is bent to the form shown by the driving cord D. The engraving is an exact reproduction of a lathe, the bed A of which was about twelve inches long and it had a capacity of about two inches swing, that was made by an older brother for the use of the author when he was nine years old, and in the use of which he became quite a boyish expert in turning wood and metals. The head-stock B, and rest C, were formed of bent pieces of wrought iron, and the "spur center" was formed upon the main spindle, the point being used as a center for metal work.

Lathes driven in this manner are still in use by watchmakers and jewelers and a great deal of very fine hand work is performed with them.

The main features in this lathe was, first, to suspend the work to be done, or the piece to be operated upon, between two fixed pivots or centers; second, to revolve it by means of a cord wrapped around it, or some part of the machine fixed to it, and kept tightly strained by means of some kind of a spring, as an elastic piece of wood; and third, to reduce the piece to be oper­ ated upon by means of a tool having a cutting edge which was held tightly against the material to be operated upon, thus reduc­ ing it to the circular form required; fourth, that to accomplish this it was necessary to revolve the piece to be operated upon, first towards the cutting tool for a certain number of revolutions , then by a reverse motion of the taut cord to reverse the circular motion, at the same time withdrawing the cutting-tool for an equal number of revolutions . By this method one half the time was lost, as no cutting could be done while the work was running backward.


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