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Grooves are milled recesses in workpieces which may have various geometrical shapes (prismatic, rotationally symmetrical) and sizes. We distinguish between the following kinds of grooves:
- rectangular groove
- T-slot
- dovetail groove
- fitting key groove
- radius groove
- tooth-shaped grooves (gullet and chip grooves).
Grooves are made with different accuracy specifications according to their application. Grooves for receiving objects or transmitting torques (fitting key slot/fitting key, disk key slot/disk key or T-slot/tongues) are made with small tolerances (permissible deviations from the nominal size) as fitting size (e.g. 20H7). The tolerances for fitting sizes shall be taken from corresponding standards or tables.
Figure 21 - Fitting key slot
Figure 22 - Disk key slot
Figure 23 - Tongues - clamping bolt
Figure 24 - Fitting size of a groove
Workpiece with groove: 1 fitting size 20H7 (upper deviation = 0.021 mm; lower deviation = ± 0; tolerance = 0.021 mm)
For milling grooves the following milling machines are suited:
- For rectangular grooves, radius grooves and tooth-shaped grooves mainly horizontal milling machines are used.- For T-slots and dovetail grooves horizontal milling machines are used for the first operation which is milling of the rectangular groove. For the second operation - milling of the undercut of the T-slot or milling of the dovetail - mainly vertical milling machines are used.
Figure 25 - T-slot and dovetail groove
(1) workpiece
(2) workpiece with rectangular groove
(3) workpiece with T-slot
(4) workpiece
(5) workpiece with rectangular groove
(6) workpiece with dovetail groove
- For fitting key slots either vertical milling machines, in few cases also horizontal milling machines or groove and slot milling machines are applied when large numbers of pieces (medium and large series) are involved.
Milling of grooves is carried out in accordance with the following working steps:
- 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.
- Align and set up the workpiece clamping means and 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.
If the workpieces are rotationally symmetrical, positioning, i.e. setting of the milling tool to the centre of the work-piece, requires special auxiliary equipment. For setting the cutter to the workpiece centre use a back square and corresponding slip gauges. The spacing between outer edge of the workpiece and outer edge of the milling tool, when measured from left and from right, must always be the same.
- Scratch, feed the cutting depth and rough-mill the groove.
- Check the dimensions, feed the necessary amount and finish milling the groove.
- Unclamp or remove the workpiece, deburr the cut edges and clean the workpiece. Check the dimensions and examine the surface.
Milling of small grooves (width) of large depth requires several working steps. When milling is performed in one working step there is the danger of overloading the milling tool which may result in breakage of the cutter, he dimensional check is made with the vernier caliper, with slip gauges or with a plug limit gauge according to the required dimensional accuracy.
Figure 26 - Checking with slip gauge
Figure 27 - Checking with limit gauge
If necessary, make corrections concerning the localization of the workpiece, the spacing dimensions in relation to the reference surfaces and the groove width. Put the dials of manual adjustment (knee and saddle) into the zero position and set up the necessary table dogs.
When changing the workpiece, make sure that the demands stipulated for clamping (freedom from burrs, cleanliness on the supporting and locating surfaces) are met. Regular checking of the workpieces as to meeting the quality requirements helps to prevent the production of scrap components (unserviceable work-pieces).
After having finished the milling of grooves, clean the milling machine, all tools used and the whole workplace.
What is a
groove?
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What are the basic kinds of
grooves?
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What has to be considered when milling
T-slots?
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