Screw and screw selection Experiment 3 Screw and screw selection

Screws

Maximum shear theory Case 1 Case 2 Case 3

Square thread and Acme thread Square thread ACME

Power screw

Torque without friction efficiency Torque required to raising the load Torque required to lowering the load Torque due to collar

1 Slide 5.

1

1 Left figure

1

Joint- fastener stiffness

Joint- member stiffness

Bolt strength Table 5-9

Tension Joints- the external load For bolt with initial load Fi the force on the bolt Fb is The force on the member Fb is The stress in a bolted joint with preload Eq. 5-28

Statically loaded tension joint with preload Proof load 5-30 Fatigue loading of tension joints

Practice 1 A jack is shown as following:

If the dimension of each bar of the jack is 250mm If the dimension of each bar of the jack is 250mm. If this jack need to rise 10000N load and can self lock. Try to design this jack.

Practice 2 Determine the bolt size of the bicycle as shown.

D=25mm 200mm 280mm The dimensions of the handle bar of a bicycle are shown in figure. Try to design the screw of the clamp.