Mechanisms Flashcards
What is a lever?
A lever is a long, rigid object with a pivot somewhere along its length. The pivot is sometimes called the fulcrum
Class 2 levers
Class 2 levers have the load in the middle and the effort and fulcrum on the outside e.g a gardener lifting a wheel barrow
Class 3 levers
Class 3 levers have the fulcrum at one end, the load at the other and the effort somewhere in the middle e.g a fisherman catching a fish
Class 1 levers
Class 1 levers have the load at one end the effort at the other and the fulcrum in the middle e.g a work man pushing a trolley
Rack and pinion
The ‘pinion’ is the normal round gear and the ‘rack’ is straight or flat. The pinion rotates and moves the rack in a straight line another way of saying it is “rotary motion” changes to “linear motion”
Worm and wheel
The arrangement of gears seen left is called a worm. Which is like a screw and thread and only has 1 tooth. A worm wheel is like a normal gear or spur gear.
Beval gears
Beval gears can be used to change the direction of drive in a gear system by 90°. A good example is seen as the main mechanism for a hand drill as the handle of the drill is turned in a vertical direction the beval gears change the rotation of the church to a horizontal rotation.
Bund facer
The hand facer is used to smooth materials such as wood / plastics used to remove a small amount of waste material. It is. It’s a dangerous machine if safety is ignored.
Flat hand file is…..
Rectangular in section and are the most common file. The safe edge of the file has no teeth this is extremely useful when filing corners. This safe edge is placed into the corner because it is smooth and dose not damage the surface material.
Half round file
Used for filing curved surfaces. A normal hand file with its flat cutting edges is unsuitable for filing concave surfaces.
Round
Used for filing curved surfaces with holes
Smooth cut and second cut
Files are often graded according to the roughness/ smoothness of the cut.
Very little lines means it’s a rough file second cut with have a lot more lines but the file with the most lines close together is for a smooth finish
Butt joint
It’s when bits of wood are connected using nails.
Dowel joint
When dowels are used to connect wood together
Finger joint
The woods are cut like boxes in a flat line but alternating from side to side
Dove tail joint
When it’s like the fingers joint but at angles
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Where dose the strength of joints come from
The strength of a joint comes from the increase of surface area that the PVA glue can act on
What dose a cam do?
A cam changes input Motion which is usually rotary motion, to a reciprocating motion of the follower they are found in many machines and toys. A cam has two parts the follower and the cam profile
Key frases of the cam
One cycle- one rotation of cam
The rise. - part of cam that causes the follower to rise
Dwell. - when the cam rotate but the follower doesn’t rise or fall
What is the follower
There are different types of follower but they all slide or roll on the edge of the cam.
Name the for types of followers.
Flat follower.
Point/knife follower
Roller follower
Offset follower
Cam profiles
Cams can be shaped in any number of ways and this is determined by the way the follower is to move. The shape of the cam is called the profile.
Pear
Pear-shaped cams are used on the shafts of cars. The follower remains motionless for about half of the cycle of the cam, and during the second half it rises and falls
Eccentric cam
Circular cam, or a eccentric cams produce, a smooth motion these cams are used in steam engines
Heart shaped cams
Heart shaped cams allow the follower to rise and fall with ‘uniform’ velocity
Drop (snail)
It gives a drop and rise motion
What are the three main types of followers
Flat
Knife
Roller
What is a flat follower
Has a large flat surface on the base. Used when necessary that it follows a very precise cam profile. The cam will move in rotary motion while the follower will move in a reciprocating motion
What is a knife follower
Mainly used with heart shaped cams as they can follow very detailed profile. They normally have a hardened steel tip and are designed to go down into the right curves of the cams
What are roller followers
This type of follower has a small roller bearing at the end they are useful for reducing friction and wear between cam and the follower
The input
The input is usually a force and initiates the process
The process
The process will change the magnitude or direction of the force
Output
The output is what preforms a desired task
