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Straight reamer:
It consists of a cutting portion with axial, straight or spiral-fluted peripheral cutting edges and the shank which is equipped with a square (for being received by a tap wrench).
The end of the straight reamer is tapered - the taper lead. At the taper lead, the greatest quantity of chips is taken off. The nominal diameter is at the straight part of the cutting portion.
Figure 6
1 - Effective length of cutting portion
2 - Taper lead
For better guiding and aligning of the reamer in the bore hole, the taper lead is longer than that of a machine reamer the guiding of which is guaranteed by the machine spindle.
Conclusion:The hand reamer can only be used with through holes, because a blind hole cannot be completely cylindrically reamed due to the long taper lead.
Taper reamer:
It consists of a long, conical cutting portion of a certain conicity (for instance 1:50); the shank is equipped with a square so that it can be received by a tap wrench. The nominal diameter is at the beginning of the cutting portion. Taper reamers belonging to a set (serial taper reamers) have differently shaped cutting portions with special chip-breaking grooves, because they must be abler to remove great quantities of chips. Only the finishing reamer leads to the required surface quality.
Figure 7 - Comparison of reamers in
use
a straight reamer
b machine reamer
c Taper reamer
1 Taper lead
2 Cutting portion
3 Neck
4 Shank
5 Square
6 Nominal diameter
What is the task of the taper lead at the straight
reamer?
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Why must the straight hand reamer have a relatively long taper
lead?
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Why is the straight machine reamer allowed to have a relatively
short taper
lead?
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Why can the straight hand reamer be used only with through
holes?
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