18-06-2012, 03:31 PM
Pillar type Drilling Machine
Pillar type Drilling Machine.docx (Size: 226.53 KB / Downloads: 49)
OBJECTIVE:
At the end of this exercise you shall be able to
1. Check the accuracy of the machine tool.
2. Use the following instruments — Straight Edge, Feeler gauges, spirit level, Dial Gauge, test mandrel.
3. Make the checklist for checking the different machine tools.
4. Justify the alignment tests to be performed on various machine tools.
THEORY:
The quality and accuracy of the finished work depends on the accuracy of the machine tools used in their production. The machine tools must be able to produce work pieces of given accuracy within prescribed limits consistently. It is for this reason the machine tools are tested at various stages, during assembly, after assembly, erection, repairs or overhauls as per accuracy test chart in order to determine whether it meets the requirement of specification or not.
The acceptance test of machine tool includes:
1. Alignment test or Geometrical test.
2. Performance test or practical test.
The alignment test is carried out to check the grade of manufacturing, accuracy of the machine tool. It consists of checking the relationship between various machine elements (such as bed table, spindle etc.) when the machine fool is idle and unloaded. Performance test consists of checking the accuracy of the finished components and is known as practical test. The performance test, therefore consists of preparing the actual test jobs on the machine and checking the accuracy of the jobs produced. Performance test is carried out to know whether the machine tool is capable of producing the parts within the specified limits or not.
ALIGMNENT OR GEOMETRICAL TESTS
Before conducting geometrical tests it is essential that machine is set up and principal horizontal and practical planes and axes are checked with spirit level etc. The various geometrical/alignment checks generally carried out on machine tools are
1. Straightness of guide ways and slide ways of machine tool.
2. Flatness of machine table and slide ways.
3. Parallelism, equidistance and alignment of the slide ways and axes of various moving parts with reference to some standard planes.
4. True running and alignment of shafts and spindle relative to other areas and surfaces.
5. The error of pitch or lead of lead screw.
6. Pitch errors of gears.
7. Dividing errors of dividing head/indexing devices.
8. Eccentricity, out of roundness, periodical axial slip. Main spindle is the fundamental element of machine and is tested for eccentricity, axial slip accuracy of axis and position, relative to other axis and surfaces.
EQUIPMENT REQUIRED FOR GEOMETRICAL TESTS:
The measuring equipments used for alignment tests are:
1. Dial gauges
2. Test mandrels
3. Straight edges and squares
4. Spirit level
5. Auto collimator
6. Waviness meter etc.
Dial gauges:
Dial gauges are widely used in alignment tests. The dial gauges selected should have measuring accuracy of 0.01 mm. The dial gauges must be mounted on robust and stiff base in order to avoid displacement due to shocks and vibrations. The initial plunger pressure should vary between 40 and 100 gm; for very fine measurement, a lower pressure as small as 20 gm is desirable.
Test mandrels
These are used for checking the true running of the spindle. Two types of test mandrels used are:
a) Mandrels with a cylindrical measuring surface and taper shank which can be inserted into the taper bore of the main spindle.
b) Cylindrical mandrel which can be held between centres. Test mandrels are hardened, ground and made to length that varies from 100 to 300 mm.
Straight edges and squares:
Straight edge of cast iron or steel should be heavy, well ribbed and seasoned. A square must have a wider bearing surface. Steel square is a precision tool used for laying out lines or for testing of squareness of two surfaces with each other.
The error at the top of Standard Square should be less than ± 0.01 mm, of a precision less than ± 0.005 mm.
Straight edge is placed on machined surfaces to check them for flatness or straightness.
Spirit level: -
Spirit levels are used for high-grade precision work. Spirit levels used are in the - shape of a bubble tube, which is mounted on a cast iron base. Spirit levels should have a sensitivity of about 0.04 to 0.06 mm per metre for each deflected division. Two main types of spirit levels used for acceptance test are:
(a) Horizontal spirit level (b) Frame spirit level,
MACHINE TOOL TESTS:
The tests applied for machine tools irrespective of type1 fall into well defined group which may be summarized as follows:
1. The level of installation of the machine in the horizontal and vertical planes.
2. Flatness of machine bed and straightness and parallelism of bed ways or bearing surfaces.
3. Test for true running of the main spindle and its axial movement.
4. Test for parallelism of spindle axis to guide ways or bearing surface.
5 Tests for the line of movement of various members e.g. saddle and table cross-slides etc, along their ways.
6. Practical test in which some test pieces are machined and their accuracy and finish checked.