1.4 Machine Tool Basics -- Lathe Controls -- SMITHY GRANITE 3-in-1





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Published on May 15, 2010

http://www.smithy.com (see transcription of video below)

Learn about the basics of metal lathe operations using our Smithy Granite combo lathe/mill/drill machines. You can visit us at www.smithy.com for more information or send us any questions about your project. Our trained technicians will be glad to help you with your project.

"In general terms, all lathes have two basic groups of controls, the controls that govern the spindle speed and the controls that move the cutting tool. On combination machines, they use one motor to power both the lathe and the mill. There is a third control. This control is the clutch mechanism that transfers power to either the lathe or the mill. On this Granite 1324, the control lever for the clutch is here. On other machines, it's located inside the gear box on the end of the main drive pulley. These clutches can only be shifted when the motor is turned off and the machine is totally at rest.

Now, determining the correct spindle speed and RPMs depends on the type of metal you are cutting, the type of material the cutting tool is made of, and the diameter of the work piece you are cutting. Harder metals, metals that are tough to cut, are turned slower than those that are soft and easier to cut. Large diameters are turned slower than small diameters. Charts that outline the recommended cutting speeds for various metals can be found in a machinist's handbook.

The carriage assembly and the powerfeed system control the movement of the cutting tool. In a facing cut, the machinist will use the hand wheels on the carriage and cross slide to position the cutting tool to take the first cut.
The depth of the cut is then set by advancing the compound. Before the motor is turned on, the powerfeed system has to be adjusted so that the tool travels in the right direction and the right speed. The speed at which the tool travels is called the feed rate. When everything is set, the motor is turned on, and the cross slide is engaged to make the cut. Here we are cutting steel with a right-hand facing tool.

On a lathe, feed rates will vary, depending on the depth of the cut and whether you are doing a rough cut or a finish cut. In a turning operation, the depth of the cut can be set by advancing the cross slide. The carriage is then engaged to feed the tool along the work piece and then make the cut. For most lathe operations, the machinist will make a few rough cuts, to bring the material down to about 1/32nd of an inch of the final dimension. Rough cuts are usually heavy cuts, with no real concern for the finish of the part. The object is to remove as much material as possible, in the shortest amount of time. When the rough cuts are done, the dimensions are checked, then the machine is set to take the finishing cuts. Finishing cuts are usually done with a separate tool, designed just for that purpose. The depth of the cut is usually small and the feed rate is slow. The time it takes to make the cut is less important than the dimension and the finish on the part."


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