Smithy Midas 1220 XL - Manual (Page 97)

the backlash problems associated with it.
Feed rates. Your feed rate should be as high as your machine, cutting tool,
workholding method, and workpiece can tolerate while giving a good finish. Feed rate is
usually given in inches per minute (ipm). You determine feed rate by the speed of the
cutter in rpm and the number of teeth in the cutter.
There are many factors to consider in selecting the feed per tooth, and there is no easy
formula to follow. Here are several principles to guide you:
• Use the highest feed rate conditions allow
• Avoid using a feed rate below 0.001” per tooth
• Harder materials require lower feed rates than softer materials
• Feed wider, deeper cuts more slowly than narrow, shallow cuts
• A slower feed rate gives a better surface finish
• Never stop the feed before finishing the cut
If you know the feed in inches per tooth, use this formula to calculate table feed rate in
inches per minute (ipm):
Ipm = ipt x N x rpm
Where ipt = inches per tooth, N = number of teeth in the milling cutter, and rpm =
spindle speed of the milling machine.
Figure 22.1 In up milling (left), the workpiece feeds into the cutter in the opposite
direction of the cutter’s revolutions. In down milling (right), the workpiece
feeds into the cutter in the same direction as the cutter is turning.
Up
Milling
Down
Milling
Feed Direction Feed Direction
Speeds and Feeds for Milling
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