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****************** Recommended Reading: Manufacturing Engineering and Technology Marks' Standard Handbook for Mechanical Engineers ******************
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As mentioned briefly at the start of section 1.1.a) the fundamental principle of chip formation is identical for both turning and milling, to illustrate this the example of the single point tool of a planer can be used again. If the tool were to be placed in a rotating cutter block with the workpiece stationary as in fig 1.3.1. a concave surface would be produced. Fig 1.3.1
If the workpiece is now fed underneath the tool at a constant rate, the surface illustrated in fig 1.3.2. would be produced. Fig 1.3.2
It can be seen from Fig 1.3.2. that a flat but very uneven surface has been produced. To reduce the unevenness two options are available i) reduce the table field per revolution of the tool leading to the cuts intersecting at a lower height or ii) increasing the number of tools in the cutter block, thus increasing the number of scollops per revolution –Fig 1.3.3. Fig 1.3.3.
Click the image for full size picture This is the principle of the milling cutter, multiple cutting edges, or teeth, around a circular body. (Formulae for calculating spindle speed and table feed can be found in Appendix 1.2. - Calculating Milling Speeds & Feeds) It can be seen from Fig 1.3.1. that if this tool were rotated, the trailing edge, or heel, would contact the cut surface causing damage, it is therefore necessary to create further clearance, or a secondary clearance angle, on the tool Fig1.3.4. Fig 1.3.4.
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