Общий каталог Tungaloy 2020 - 2021 - страница 1630

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Fundamentals o f screw threads

Relationship between lead, lead angle and pitch Thread angle Pitch P (large)

1. Lead is the axial distance a screw advances in one rotation. In single Thread height Pitch P (small) = lead

start screw, the lead is equal to the pitch. 2. The inclination angle of a threaded groove is called lead angle. In screws of the same diameter, the lead angle increases as the pitch increases. 3. The side face of a completed thread groove is called fl ank. The distance

Lead angle

between the crest and the root is called thread height.Flank(large)
Lead angle (small)
Single and multi start thread
1. The single start thread has a single groove. Two start thread or threeLead

start thread has two grooves or three grooves respectively. Two start thread Pitch

2. The pitch of multi start thread is the distance of adjoining groove. 3. When viewing the section of the multi start thread, the pitch is same as that of the single start thread. The lead of the two or three start thread is twice or three times the pitch. The multi start thread is mainly used for

trapezoidal threads.

Tolerance class of threads

Tolerance classes of screw threads are expressed as follows:cutting or rolling, are generally used. 5H- and 4h-class
Metric coarse external thread: 6h, 6g Metric coarse internalthreads (former JIS first class) are generally finished by
thread: 5H, 6H grinding.
These classes are ranked with tolerances of thread diameter,For example, M8-6g means metric coarse external thread of
pitch, thread angle, etc. For fastening applications, 6H- and6g tolerance class.
6g-class (former JIS second class) threads, manufactured by
TAC threading insert
Diff erence between full-profi le and partial-profi le insert
Full-profile insert
In the full-profile insert, the major diameter of the thread isthread as shown in Figure below, these portions must be
fi nished by the profi led fi nishing edge as shown in Figure below.fi nished by another tool later.
Therefore, about 0.1 mm of fi nishing stock must be left on theFull-profi le insert could produce no burr and good thread by the
outer surface of the workpiece before threading. In trapezoidalprofi led fi nishing edge.

threads, since slants of 15º to 30º are left on the crest of the When machining trapezoidal threads: Partial-profile insert Full-profile insert Trapezoidal thread

Thread Thread Thread height Full-profile 15° ~ 30°

Partial-profileCrest (finishedSurface turnedinsertCrest (finished
insertin precedingin precedingwith threadingPortion to be
operation)operationFinishing stinsert)finished later

Partial-profile insert For example Partial-profi le inserts can not be used for fi nishing of the Insert radius

DesignationPitch (mm)TPI
crest, but can be applied to a wide range of pitches.RE (mm)
16ERA600.5 ~ 1.548 ~ 160.06
16ERG601.75 ~ 314 ~ 80.22

Corner radii of inserts are fitted to the thread of the smallest pitch. Diff erence between external and internal use inserts In full-profi le inserts for metric and unifi ed threads, the corner radius and thread height diff er from those for the external and internal use insert respectively. Therefore, the right hand insert for external use and the left hand insert for internal use are not the same tool.

Since the rake angles of toolholders are -10º for external toolholders and -15º for internal toolholders, the external / internal toolholders can not be used for machining internal / external thread. In Whitworth thread, though the external thread and internal thread have the same thread form, the external and internal toolholders are incompatible because of the diff erent rake angle. For example

DesignationApplicable insertsInsert radius R RE (mm)Thread hight (mm)Rake angle of holders
16ER20ISOExternal0.251.52-10°
16IL20ISOInternal0.141.3-15°