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Preparation of these techniques includes the following operations:
- Prepare in your mind the sequence of operations like
· choice of milling machine to be used
· choice of milling and clamping tools to be used
· choice of measuring and testing means to be used
· technological flow of milling operations for meeting the quality requirements.
- Lay out the necessary tools, measuring and testing means and auxiliary equipment while observing the basic rules for properly putting them down and securing them in position.- Check the functionality and operational safety of the tools and auxiliary equipment to be applied before using them. Sort out worn tools.
- Check also the milling machine to be used for functionality and operational safety. Check the oil level and lubricate the milling machine according to the lubrication schedule.
Clamping the workpiece for milling
There is a number of possibilities for clamping the workpiece to mill grooves, elongated slots and break-throughs. Their choice and application depend on the following factors:
- the geometrical shape and dimensions of the workpiece. The workpiece may have a prismatic or rotationally symmetrical shape. As far as the dimensions are concerned, lenght, width or diameter and height are to be considered.- the position of the groove, elongated slot or break-through to be milled on the workpiece;
- the accuracy requirements (dimensional and positional deviations as well as shape errors);
- the number of workpieces to be machined (single parts, small, medium or large series) and
- the workpiece clamping and auxiliary equipment available in the production department.
The most frequently used workpiece clamping equipment for milling grooves, elongated slots and braak-throughs are the following:
- machine vice of standard design
- machine vice with prismatic jaws
- shaft vice
- chuck (three-jaw and four-jaw chuck)
- clamping of the workpieces directly on the machine table or on a circular table
- work-holding fixtures
Figure 14 - Machine vice with
prismatic jaws
Figure 15 - Shaft vice
The workpieces are clamped mainly as individual parts. The application of auxiliary clamping equipment, e.g. stops, serves for determining the position in order to constantly reach a specified spacing from a given reference surface.
Figure 16 - Workpiece stop
1 - stop block
2 - workpiece
3 - reference surface
4 - spacing size
When clamping workpieces, take care to ensure that the bearing surfaces (locating and supporting surfaces) are free from burrs and clean. Impurities and burrs result in positional deviations during clamping and leave damaged spots (marks) on the workpiece surface.
When handling sharp-edged workpieces and tools (milling tools), wear protective gloves to prevent cutting your hands. Deburr the workpieces only with proper files (firmly secured and undamaged file handle).
- When clamping the workpieces in the machine vice, take care to ensure that the work locating and supporting surfaces (parallels and vice jaws) are clean and undamaged.
- Rotationally symmetrical workpieces are clamped in the prismatic vice or, when prismatic jaws are used, in the machine vice. For this purpose it is necessary that the prismatic jaws are without any impurities in their seats or guideways. Otherwise there will be positional deviations of the workpiece.
- When clamping the workpieces directly on the machine table, pay attention to the following:
· Determine the position by using tongues, stop bars, stops and other auxiliaries according to the accuracy requirements.· Fix clamping means (clamps, clamping bolts) at those points of the workpiece, where they do not hinder the milling operation (free space for milling tool and tool clamping means).
· Use appropriate stops to uniformly obtain the required spacing dimensions (dimensions from a reference surface) so that the determination of the position of the workpieces is clearly repeatable.
· When using workpiece clamping means be careful not to make any changes to the supporting or locating surfaces. Before mounting the means on the machine table or on the circular table, for example, clean the base surface of the fixture and the table surface.
Clamping of tools for milling
The tool clamping means for milling grooves, elongated slots and break-throughs include the following:
- cutter arbors (long and short)
- cutter chuck with collets (for cutters with parallel shank)
- adapter sleeves (for receiving shank cutters with taper shanks)
Work with extreme cleanliness when clamping the milling tools on the cutter arbor in the cutter chuck or when using adapter sleeves. This ensures thrust accuracy and concentricity of the milling tools.
For setting the tool clamping means use exclusively the corresponding tools like the pin spanner for the sleeve nut or the reducing sleeve with the corresponding taper (internal and external taper).
Regardless of the kind of workpiece clamping and tool clamping means to be used always pay attention to the labour safety requirements.
To prevent accidents and injuries, use the cutter safety devices according to their purpose. Use proper files for deburring the workpieces before clamping or before measuring and testing. To prevent hand injuries, move sharp-edged work-pieces and milling tools with protective gloves or a rag.
Choice and application of measuring and testing means
By measuring and testing a certain accuracy is to be reached in the milling process and dimensional and positional deviations are to be avoided.
The following measuring and testing means are used
- vernier caliper
- vernier depth gauge
- slip gauges
- back squares/dial gauge
- limit gauges (plug limit gauges)
Figure 17 - Vernier caliper
Figure 18 - Vernier depth gauge
Figure 19 - Slip gauge
Figure 20 - Limit gauge
Deburr and clean the workpieces before measuring and testing them. Use only serviceable and undamaged measuring and testing means. Send measuring and testing means for a regular check - depending on how frequently they are used (6 to 12 months' cycle) to the corresponding department of the factory. Do not use damaged measuring and testing means any more and send them to the repair shop immediately.
The life of measuring and testing means depends on how carefully they are handled and laid down at the workplace.
How can inaccuracies by avoided when clamping the
workpieces?
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What possibilities of clamping the milling tools for milling
grooves
exist?
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What must be done when a measuring and testing means gets
damaged during
work?
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