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Conical bore holes are required if machine taper or taper pin connections shall be made. With large bore holes serial taper reamers cannot be used without special preparation; such bore holes must be cylindrically predrilled in steps. The calculation of the diameter of the drill is to be derived from the conicity:
Figure 14 - Taper bore predrilled in
steps
A conicity of 1:50 means:
Over a length of 50 mm the diameter changes by 1 mm.
Example:
A taper pin of a nominal diameter of 6 mm and a length of 50 mm has a diameter of 7 mm at its upper end.
With making a taper pin connection, step no. 7 - pinning and checking - is characterized by the preliminary fitting-in of the pin:
After reaming, the pin is pushed by the thumb into the cleaned bore hole. The upper edge of the pin roust project over the edge of the bore by an amount depending on the nominal diameter. If the measure achieved is identical with the empirical value (below table), the pin is driven in by two or three short strokes.
Empirical values for the preliminary fitting-in of taper pins of a conicity of 1:50
|
Nominal diameter of the taper pin (in mm) |
Measure for the preliminary fitting-in (in mm) |
|
5 |
3 |
|
6 |
4 - 5 |
|
8 |
5 - 6 |
|
10 |
8 |
The following condition applies to the length of the taper pin (illustration):
Figure 15 - Conditions of the fitting
in of taper pins
1 - Length of the taper pin
2 - Nominal diameter of the taper pin
3 - Thickness of the parts to be connected (total)
4 - Measure for prefitting
It must be 2 mm shorter than the total of the thicknesses of all parts to be connected.
If this condition is observed, the pin - after being driven in - sits in the bore hole in such a way that a drift can be applied from the opposite side in order to remove the pin. The upper edge of the pin is at level with the edge of the bore hole of the upper portion.
Plain pins and taper pins mostly consist of unhardened steel. Therefore, for driving the pins in, aluminium hammers or locksmith’s hammers are used in connection with a drift of non-ferrous metal.
Why must the locksmith’s hammer not hit the pin
directly?
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How can the pin connection be
undone?
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For making a taper pin joint, the length of the taper pin is important.
What condition must be observed when determining the
length?
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What instructions concerning labour safety have to be observed
with
reaming?
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