2.4 Machine Tool Basics -- Milling Controls -- SMITHY GRANITE 3-in-1





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Published on Aug 20, 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.

"Now lets look at the controls on the machine and run through a few simple milling and drilling demonstrations. In a simple milling operation, the head is positioned over the table and securely locked in place. The depth of the cut is then set using the fine-feed mechanism on the quill. Here we're cutting steel with a half-inch end mill. As a general rule, the depth of cut for an end mill, cutting steel, should not be greater than one-half the diameter of the tool. The quill is then locked and the width is set. For this job, we're advancing the cross slide to make this adjustment. The cross slide is also locked so the setup has as much rigidity as possible. The power feed system is then adjusted so the milling table moves in the right direction and at the right speed. After this is set, the motor is turned on, and the carriage is engaged to start the first cut. Standard end mills are right hand cutters, meaning that they cut when rotated clock-wise over the workpiece. Feeding the work into the mill against the rotation of the tool, as we're doing here, is called up-milling. This is the recommended feed direction on the Smithy. In milling, just as in lathe work, the machinist will make a few rough cuts to bring the material down to size, then set up the machine to make the finishing cuts. Finishing cuts are always shallow cuts with a slower feed rate, in order to produce a fine finish on the surface of the part. Before we leave our milling demonstration, lets talk about spindle speeds and feed rates when it comes to milling and drilling.

In general terms, the same basic metal cutting principles we talked about for lathe work also apply to milling and drilling. To find the correct spindle speed, again, start by finding the recommended cutting speed, based on the type of metal you are cutting, and the type of material the mill or drill is made of. Then convert cutting speed to RPMs with the formula: cutting speed multiplied by 4, and then divide that number by the diameter of the cutting tool, either the mill or drill, to get your RPM.

Now, determining the correct feed rate for a milling operation depends on a number of variables, the number of cutting edges on the mill, the use of cutting fluid, the depth of the cut, and especially the rigidity of the setup all have to be taken into consideration. You can turn to the charts in the machinist's handbook for guidance, but only for guidance. The truth is, there really is no right feed rate that you can work out on paper. Every situation will be different because so much in milling depends on the rigidity of your setup. My suggestion with end mills is to start with a conservative depth of cut and a modest feed rate. You can always increase the depth of cut after you see that the setup is working out.

Let's look at drilling. On a Smithy machine, and really all manually fed drill presses, you have to watch and feel the progress of the drill to determine the correct feed rate for what you are doing. You should be looking for even chips as the drill goes into the work. Remember that the flutes of the drill are designed to carry the chips up and out of the hole. As the hole goes deeper, the possibility of the chips clogging in the flutes and causing the drill to bind increases. This is especially true with small drills. Using cutting fluid and frequently removing the drill to clear the flutes can prevent the flute from jamming.

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