|Operations with Shaping Machines - Course: Mechanical woodworking techniques. Trainees' handbook of lessons (Institut für Berufliche Entwicklung, 18 p.)|
Arc-likechipping ensues through milling with a shaping machine, moreover in a similar manner to level milling, thickness milling and circular sawing. Thereby one differentiates between climb-feed and counter-rotational cutting in line with the chipping direction vis-a-vis the direction of feed.
Figure 12 - Types of tension
(1) climbfeed cutting,
(2) counter-rotational cutting
Given climbfeed cutting the cutting elements along with the feed force motivate in the same direction. The processed faces are extremely clean, however given manual feed the workpiece can be pulled away from the hands.
Given manual feed, climbfeed cutting is forbidden because of the considerable accident risk!
In the case of counter-rotations cutting the cutting forces operate against the feed force. Consequently safe manual feed becomes possible. Chipped edges along the processed surfaces of slotted and milled cuts may result during counter-rotational milling. This occurs because of the unfavourable cut direction of the tool cutters vis-is the grain direction of the work-piece.
Figure 13 - Cutting force
(1) cutting force at great cutting depth
(2) cutting force at small cutting depth
1 feed force, 2 cutting force, 3 chipped edges
Why is climbfeed cutting so prone to
The tool cutters been arranged in a knife cutting circle. As cutting ensues, given an even workpiece feed, a wavy processed surface results. These waves are known as cutter blows. The nature of the waves, resp. the cutter blow depth, depends on:
- the number of tool cutters
- the tool diameter
- the rotational speed of the tool spindle
- the rate of feed of the workpiece
Figure 14 - Chip formation through milling
1 direction of feed, 2 cutting direction, 3 tool radius, 4 cutter feed, 5 engagement size, 6 knife cutting circle of cutting edge one, 7 knife cutting circle of cutting edge two
In order to ensure sound cutting it is necessary that all the cutters of a tool rotate through the same knife cutting circle, that is to say equidistant from the tool exis. This requirement should be especially heeded during tool maintenance. An extremely wavy or carelessly milled workpiece face can prove a hindrance during subsequent top surface processing and precondition extensive reworking.
What is the effect of using blunt tools for million