Machining Practice

The session started by the facilitator going through the terminology of machining and these included;
# Milling - which means taking some materials off a certain piece done by machine like the CNC machine which are programmed to manufacture the required shape.
#Grinding - this is a process of rubbing off some materials to reduce size or diameters like crankshafts.
#Stamping - which is basically shearing the materials like sheets of metal to make holes through instead of using drill bits. Below is a picture of a bracket i stamped after cutting it on the Guillotine and then bending on the Sheet bender before cutting off excess length using a hand bench snipper.

In actual fact safety comes first, every machine has safety rules and regulations to follow before, during and after use. The facilitator then demonstrated with a round piece of polythene, by using the lathe to reduce the diameter of the rod and making fine threads on it. it was drilled on the other side which was not supported and the tail stock the supported the loose end when the length was increased from the chuck side. The tool post is where the cutting tools are mounted and it can be rotated so that different angles of cutting can be achieved.

                                                        Lathe Machine          

                                            Guilotine Machine.

This is the machine that i used to cut the required piece of metal sheet to stamp and bend to make a bracket shown above. The machine is foot operated to cut off the pieces. safety is to be observed not to place the fingers under and beyond the guard. The sheet to be worked on has to be marked so as not to waste material and right sizes to be achieved.

DC motors.

I learnt about parts of a direct current motor, which include Shaft, armature, windings, bearings, commutator and brushes as the picture below;

A DC motor converts electric current into mechanical movements, i.e Rotational movement known as torque or turning effort therefore can be used to drive a number of systems. One example is a starter motor which drives the car Engine to start or a window winding motor to close and open car windows.

Brushes are always in contact with the commutator which is attached to the ends of the individual windings around the armature which are insulated to avoid short circuits. The commutator is a split slip ring so that when the motor is running, it should not produce reverse current to induce drag against direction of rotation.
Bearings hold the shaft in a true rotational position to avoid it touching the outer casing and magnets.

When the motor is given current the armature becomes an electro-magnets which react to the permanent magnets on the casing and this causes rotation of the armature shaft which can drive any desired component. When there is no current flow, electro magnetic force collapses and the motor stops. To change the direction of rotation only polarity of the current is reversed and the more the current the more the speed of the motor. the relationship of speed and torque is that torque is maximum at start and continues dropping as speed increases, But as current is increased torque increases. Efficiency on the other hand increases sharply after idling speed and starts dropping slowly as speed continues to increase.

Nowadays motors are driven electronically from pulse generators which operate transistors which in turn switch the motor ON and OFF at a high frequency, this allows a small current to be used in the control circuit and to vary the speed only the switching time is varied. This allows the system to be automated and self monitoring.

Control Systems.

The facilitator led us through the components of any control system, which include Sensors which collect data from a physical system and send signals to the  decision making part (Micro processor) or computer which looks at the preset rules it was given beforehand to use in deciding what command to give to the Actuators to perform a certain function within the physical system again. One of the examples of such systems is the operation of the electric cooling fan in a car, The Temperature sensor sends a signal to the computer box indicating that the engine is hot, the microprocessor then commands the fan switch to close the circuit to the fan, to allow current to flow and the fan will run. when the temperature is low, the sensor sends another signal to the microprocessor which commands the switch to open the circuit to stop current flow to the fan, therefore less air will cool the radiator.

We had examples of sensors, mostly switches which are normally open and some are normally closed. We looked at single pole, single throw and double pole double throw as shown in the pictures below.

ingle Throw Switches

This is about the simplest switch--it makes or breaks a contacts between two lugs.

You would typically use this for a power switch.

Dual Throw Switches

This is the most common family of the mechanical switches, dual throw means you are switching one or more lugs between two positions.

  We them started to set rules which would be given to the decision making component of a system but i ended up not able to test them on the actual system..

Engineering report writing.

I learnt about report writing as a way of communicating information in a comprehensive way and it is structured as stipulated below;

The Title page.
This gives information of who wrote the report, the date and any relevant information identifying the module covered. the report is manly presented in a past tense.

Abstract
This is a brief summary of the report which indicates the scope and breath of the activity done.

Table of contents
This shows where specific things are found in the report.

List of figures and tables or Attachments.
Here there is a list of figures and tables included in the report so that they can be distinguished easily.

Main body
Here every detail of the process is described in full length, how the activity was done, key features, what was found, problems encountered and remedies.

Conclusion
This details the importance of the activity and what was learnt and recommendations.

References
This tabulates where external information was sourced from.

Safety and usage of wood working machines.

We were taken through the safety aspects in the Wood workshop by the technician, Showing us how to operate each machine, from switching ON to finally switching OFF after use. This included how to set them for correct use without compromising safety.

They are categorized into three classes, which are differentiated by color codes, which are Green, Amber and Red. These groups are used as follows;

Green labelled machines can be used by students without supervision and can ask for for from the workshop technician if need be.

Amber labeled ones are also used by students only under the supervision of the technician.

All the Red labelled ones are for staff usage only.

In the afternoon, it was our turn to demonstrate to use some machines, the facilitator cut equal pieces of boards for each learner, we were given a drawing that we had to mark on the piece and use machine to cut it out. Below is the facilitator cutting out pieces for us while demonstrating how to use the machine safely as seen using the push stick and holding the longer side of the bigger board.

The picture below shows the drawing i was given, the board piece and the final product i made using machines. Even though i managed to cut out the shape required, i exceeded the measurement from the inner shape during cutting, but i leveled the curve with a hand file.