|Centring, Drilling Counterboring and Countersinking, Reaming and Tapping on the Drilling Machines - Course: Techniques for Machining of Material. Trainees' Handbook of Lessons|
Clamping the workpieces
Work-holding devices have the following special functions for machining on drilling machines:
positioning - fixing of the workpiece position in relation to the tool
clamping - neutralization of cutting forces during the machining operation
The clamping elements to be used must both neutralize the cutting forces (feed and speed) and hold down the workpiece during the machining operation.
Especially when drilling is made with twist drills the torque caused by the cutting force is of great importance for a safe clamping of the workpiece. The torque subjects the tool to torsion and simultaneously tries to drag along the workpiece.
Therefore, greatest importance shall be attached to a firm, job-related workpiece clamping according to labour safety regulations.
The choice of the respective clamping equipment depends on
- the shape, size and number of workpieces to be machined
- the number of bores in a workpiece and their size
- the angular position of the bores
- the cutting forces acting on the workpiece
- the type of drilling machine to be used
- the position, direction and necessary quality of the bore.
There is a great number of variants of the various clamping elements and fixtures.
As main variants for clamping workpieces, the following ones are applied:
Clamping against a stop
for loose workpiece clamping with medium-sized and bulky workpieces as a safeguard against displacement and distortion.
1 stop, 2 table, 3 work-holding bolt, 4 workpiece
Loose vice clamping for quickly fixing the workpiece's central positions in single-piece production or at low cutting pressure. Firm vice clamping with determination of fixed position in series production or at high cutting pressure.
1 vice, 2 workpiece, 3 parallels
for clamping rotationally symmetrical workpieces and machining of their end faces.
1 tool, 2 workpiece, 3 chuck
Clamping by means of clamps
for clamping large or bulky workpieces on the table. We distinguish between flat, U-shaped, fork-shaped and cranked clamps of fixed and adjustable design.
1 clamp, 2 support, 3 work piece
Make sure by means of supports that the clamps are arranged horizontally.
Clamping in fixtures
for clamping workpieces which due to their geometrical shape can not or only with considerable effort be clamped with usual clamping equipment such as vice, stop and clamp. This is the safest kind of clamping ensuring high quality. It is, however, dependent on the specific workpiece and construction of the fixture.
1 tools, 2 drill bushes, 3 fixture, 4 workpiece
In addition to this, angle-plates, parallel clamps and toe dogs can be used.
Clamping of tools
The following tool holders are applied:
for tools or tool holders with taper shank and for compensating different tapers per inches between drilling spindle and tool taper.
for chucking tools with parallel shank or cylindrical tool holders.
for chucking tools by friction. It makes a quick change of the clamping of different tools possible and is applied when work-pieces have different hole contours and hole qualities.
for drilling of tapped holes with safety clutch preventing breakage of taps by interrupting the operation when 2/3 of the ultimate torque of the tap are reached.
What function do work-holding devices
What kinds of vice clamping can be