Page 87 - Mechanical Engineer's Data Handbook

76 MECHANICAL ENGINEER’S DATA HANDBOOK

Effective coefficient of friction (vee thread) po = p sec fl Acme thread
where: fl- half angle thread.
Used for power transmission. Has greater root
Vee thread strength and is easier to machine than the square
thread. Used for lathe lead screw.
The vee thread is used extensively for nuts, bolts and
screws. The thread may be produced by machining but
rolling is much cheaper.

0.137P

0.64P

Buttress thread
Whitworth thread
A power screw with the advantages of both square and
Acme threads. It has the greatest strength but takes a
large load in one direction only (on the vertical face).

f

Multi-start thread

This gives a greater pitch with the same thread depth.
The nut advance per revolution (lead) is equal to the
pitch multiplied by the number of ‘starts’.
Square thread i Lead 1
-
Used for power transmission. The friction is low and
there is no radial force on the nut.

.-

. P ,I%. ’ Ball-bearing power screw

The friction is extremely low and hence the efficiency is
high. The power is transmitted by balls between the