Smithy Midas 1220 LTD - Manual (Page 34)

Table 7.1 Cutting Speeds and Feeds for High-Speed-Steel Tools
In everyday lathe operations like thread cutting and knurling, always use cutting oil or
other lubricant. On such work, especially if the cut is light and lathe speed low, dipping
a brush in oil occasionally and holding it against the workpiece will provide sufficient
lubrication. For continuous, high-speed, heavy-duty production work, however, especially
on tough alloy steels, using a cutting oil or coolant will increase cutting efficiency. It's
essential if you're using a non-HSS cutting tool.
When you use coolant, direct it against the cutting point and cutter. Consider installing a
coolant system if you don't have one.
Table 7.1 lists cutting speeds and feeds for HSS cutters so you can set up safe rpm rates.
The formula is as follows:
rpm=CSx4 / D"
where:
CS = cutting speed in surface feet per minute (sfm)
D" = diameter of the workpiece in inches.
To use this formula, find the cutting speed you need on the chart and plug that number
into the CS portion of the formula. After calculating the rpm, use the nearest or next lower
speed on the lathe and set the speed.
If you were to make a finish cut on a piece of aluminum 1" in diameter, for example, you
would see the desired sfm per Figure 7.3 is 300. Then:
rpm = 300 sfm x 4 / 1
rpm = 1200 / 1
Low-Carbon
Steel
High-
Carbon
Steel
Annealead
Alloy Steel
Normalized
Aluminum
Alloys
Cast Iron Bronze
Speed (sfm)
Roughing
Finishing
90
120
50
65
45
60
200
300
70
80
100
130
Feed (ipr)
Roughing
Finishing
0.010-0.202
0.003-0.005
0.101-0.020
0.003-0.005
0.010-0.020
0.003-0.005
0.015-0.030
0.005-0.010
0.010-0.020
0.003-0.010
0.010-0.020
0.003-0.010
Midas 1220 LTD Operator’s Manual
7-2
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