Operation of Lathe Machine(Face Turning)

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. Don't worry too much about determining the correct cutting speed: working with the 7x lathes for hobby purposes, you will quickly develop a feel for how fast you should go.
Until you get a feel for the proper speeds, start with relatively low speeds and work up to faster speeds. One of the great features of the 7x is that you can adjust the rotational speed without stopping to change belts or gears. Most cutting operations will be done at speeds of a few hundred RPM - with the speed control set below the 12 O'clock position and with the HI/LO gear in the LO range. Higher speeds, and particularly the HI range, are used for operations such as polishing, not cutting.

Preparing for the Facing Cut

First, make sure the tumbler gear lever on the back of the headstock is in the neutral (middle) position so that the leadscrew does not rotate. This is very important since you will clamp the half nut on the leadscrew during the facing operation to keep the saddle from being forced back away from the end of the workpiece by the force of the cutting operation.
Clamp the workpiece tightly in the 3-jaw chuck. To get the work properly centered, close the jaws until they just touch the surface of the work, then rotate the workpiece by hand in the jaws to seat it; then tighten the jaws. It's good practice to tighten the jaws from all 3 chuck key positions to ensure even gripping by the jaws.
Workpiece should not extend from chuck jaws by more than 3x its diameter
Choose a cutting tool with a slightly rounded tip. A tool with a sharp pointed tip will cut little grooves across the face of the work and prevent you from getting a nice smooth surface. Clamp the cutting tool in the tool post and turn the toolpost so that the tip of the cutting tool will meet the end of the workpiece at a slight angle. It is important that the tip of the cutting tool be right at the centerline of the lathe; if it is too high or tool low you will be left with a little bump at the center of the face.
Clamp the toolpost in place and advance the carriage until the tool is about even with the end of the workpiece. Make sure that the compound is not all the way at the end of its travel towards the chuck; about midway in its range of travel is good.
Set the lathe to its lowest speed and turn it on. Make sure the leadscrew is not turning. Turn the lathe off and press the half-nut lever down to engage the half-nut with the leadscrew. When properly engaged, you should feel the lever click into place in a nearly horizontal position. You may have to work the carriage handwheel back and forth a little to get good engagement. Locking the half-nut to the leadscrew will prevent the carriage from moving back away from the workpiece during the facing operation. If this were to happen, the end of workpiece would be a slight cone shape instead of perfectly flat - or the tool might stop cutting entirely. A much better way to lock the carriage in place is to add a carriage lock to your lathe as described on Varmint Al's site and on my mini lathe mods page.