LIBRARY | START | BACK | NEXT 8-Engine Lathe -Speeds and Feeds To efficiently machine various types of materials, hold tight tolerances and produce good surface finish , the spindle RPM must be properly selected. Selection of spindle speed is accomplished by manipulating the appropriate levers. Speeds are calculated by formulas. Nearly every gear head engine lathe uses a method similar to this video for setting spindle speeds. First you will have to locate the spindle speed read out on the machine. Now select an RPM from those available. In the video 370 RPM is selected which requires the two levers shown to be in the correct position. The next speed selected is 36 RPM. As with spindle speeds, correct feed rates must also be calculated. Feed rates can be set by locating the settings panel (index plate) on the lathe. In this video 0.002 per revolution is selected. Four levers and one dial must be set to A E V 3 X. The next feed rate selected is 0.040 per revolution which requires a setting of B E R 7 X. Both feedrates were with the same spindle RPM. Changing spindle RPM does not change the feed rate. The correct RPM is calculated from a known cutting speed (CS) for the specific material being machined in Feet Per Minute (FPM). The formula for RPM is RPM = (CSx4)/diameter. Typical CS for aluminum is 250 and for mild steel it is 80. Therefore a 6" dia bar of mild steel should be turned at (80x4)/6= 53 RPM. This is a simple forumlae that you will use thousands of times once remembered.The correct feed rate in Inches Per Revolution (IPR) is calculated from chipload. Chipload is the amount the cutter is buried into the part and varies from tool to tool on all materials. R.S. Do not confuse feed "speed" with feed "rate". Feed rate is the amount the tool moves for each revolution of the spindle. If the spindle is turning very slowly the tool feed "speed" will be slow. If the spindle is turning very fast the tool feed speed will be very fast. In both cases the tool feed rate is identical. R.S. LIBRARY | START | BACK | NEXT