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Elongated slots are recesses in workpieces which are made with a limited length in the form of the "elongation" of a workpiece bore hole by milling into a given direction.
Elongated slots can have a unilaterally or bilaterally limited length. Unlike the groove they completely penetrate the workpiece in full height, width or diameter.
Figure 28 - Elongated slot
(1) length unilaterally limited
(2) length bilaterally limited
(3) semicircular elongated slot
Elongated slots are produced mainly by plunge milling (plunge face milling). To do this, twist drill fluting cutters shall be used as milling tool.
Figure 29 - Plunge face milling
1 - workpiece
2 - twist drill fluting cutter
3 - plunging and cutting direction
When shank cutters are used, preliminary drilling with a drilling tool is necessary, as the face cutting edges of the shank cutter do not allow "plunging". The face cutting edges do not extend to the central axis of the cutter. Elongated slots are made with different accuracy specifications according to the application. When the workpieces are made of cast iron, the shape of the elongated slot has usually been cored with the necessary machining allowance.
Elongated slots can run in parallel to the prismatic or rotationally symmetrical outer surfaces of the workpiece. In few cases they are curved (semicircular), e.g. in the case of a change--gear quadrant.
Elongated slots frequently occur in the clamping means for milling (e.g. clamps, stop bars, etc.). For milling elongated slots the following milling machines are suitable:
- Vertical milling machines are mainly used. Depending on the geometrical shape and size of the workpiece as well as the position of the elongated slot in the workpiece, horizontal milling machines are also suited.- When large numbers of pieces are machined (medium and large series), groove and slot milling machines are applied.
- For making elongated slots of curved shape the circular dividing table on the vertical milling machine is used.
Milling of elongated slots is carried out in the following sequence of operations:
- Check the functionality and operational safety of the milling machine to be used (check oil level and lubricate).- Lay out the necessary workpiece clamping and tool clamping means as well as measuring and testing means.
- Fix, align and set the workpiece clamping means, clamp the work-piece, fix or chuck the milling tool.
- Mount the coolant system and the cutter safety guard.
- Bring the milling machine table into the working position in relation to the milling tool (X-Y-Z direction) and set the cutting values.
- Scratch and set the length of the elongated slot (stops at machine table), rough-mill the elongated slot.
- Carry out visual examination and dimensional check (length and width) and corrections, if necessary, and finish milling the elongated slot.
- Unclamp or remove the workpiece, deburr the cut edges and clean the workpiece. Make a visual inspection, dimensional check and surface examination according to the specifications.
What is the difference between a groove and an elongated
slot?
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What functions do elongated slots
have?
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