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Chapter 1. Basic Machining and Tips


Marking-off Tools

Marking-off is the process of drawing lines on the raw stock corresponding to the dimensions on the plan. Figures 1 to 6 show the tools used for the marking off.

Determining the Need for Accuracy

In the case of preliminary cutting or "roughing-out" it is satisfactory to mark-up using generally accurate measurements however, when finishing or high precision is needed, then it is essential that utmost care be taken to mark-up the work piece with extreme care and attention to detail.

When working in a commercial environment, there needs to be a balance between achieving the desired quality of workmanship with that of the time taken to complete the work.

Fig. 1, Marking-off Scribe
A marking-off scribe is used for drawing lines on material. Its point is sharp, and is tempered to ensure that point is maintained.

Fig. 2, Steel Rule
The steel rule is used for measuring-out and drawing lines. A good quality steel rule is a good investment in achieving accuracy.

Fig. 3, Steel Compas
A compas is used for drawing circles or an arc. Its points are also sharp and hardened.

Fig. 4, Center Punch and Hammer
A center punch is used for marking an "indent" before a hole is bored with a drilling machine. The point is usually set to the point of intersection between two marking line.

Fig. 5, Block and Flat Table
Generally, the marking process is done on a flat table, called a marking-off table. The block with a V-shaped slot, as shown in the above photograph useful when marking our round or irregular objects.

Fig. 6, Height Gauge
The height gauge as shown in the above photograph can measure with the accuracy of 1/100 mm. The point of the gauge is also a marking scribe, so that it can be used for drawing accurate lines by sliding the gauge on the flat table while at the same time scribing along the work piece.

Marking-off and Drilling

The procedure of making holes in a simple mechanical process and is presented as follows.

(1) Drawing of the Horizontal Center Lines
Touch the material to the block, and slide the hight gauge.

(2) Drawing of the Vertical Center Lines
Rotate the material to 90 degrees. And draw the vertical lines.

(3) Set the Point
After marking the center point with the center punch, set the drill.

(4) Drilling
Drill a hole with the drilling machine.

(5) Drilling
It may be necessary to withdraw the drill from the work piece to remove any swarf that may otherwise clog the drill bit

(6) Completion
When drilling is completed it is usually necessary to remove any burrs as previously discussed.
Fig. 7, Flow of Markings and Drillings

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