Marking

The working lines for the drawing are to be marked on thework piece which could be either in already prepared conditionor as it is drawn from the stores. The marking will consists of lines, forms for further working with hand tools or machines.

The marking dimensions are to be as shown in the drawing. Do not measure from the drawing.

Correct and clear marking makes it easier to work on the job. The marking should be as accurate as possible and should be carefully checked before working on the job.

Preparation of the surface before marking:

·       Use marking chalk for caste iron and forged parts.

·       Use copper sulphate solution for steel.

·       Use marking ink for aluminium, copper brass and steel. Available in blue and red colour. Spirit can be used as thinner if required.

·       Before marking, two reference sides are prepared and marking is done with respect to these as references.

Marking Tools:

·      Surface plate

This is usually made of cast iron. Its surface is finished by scraping to a high degree of flatness.

Granite surface plates are also available.

·       Steel rule

Steel rule is used for approximate marking.

·       Scriber

           Scriber is used for scraping the lines on work piece. It is made of steel and point is hardened. Whenthe surface is to be absolutely scratch free, brass scriber is used.

·       V-Block

Used for cylindrical work pieces. The work piece can be fixed on the surface plate.

·       Trammell

              Trammell is used for measuring and transferring large dimensions. It can also be used for drawing circles and segments having large diameters.

                The scriber is to be moved in the marking direction.

·       Compass

Made of steel and have hardened points used for drawing circles according to required dimensions.

·       Dot punch

Made of steel and point is hardened. It is used tomake point marks on the scriber line for future reference.

·       Height guage with scriber

This is used with the surface plate for more accuratework. By moving it on the surface plate, horizontal line can be drawn and theheight can be adjusted on the vernier scale.

·       Try square

Made of steel. Used for marking on small work pieces. Lines can be drawn at right angles to each other.

·       Center punch

            Center punch is used for punching the marked centre point for drilling. That will guide the drill bit to the center. The point marked can also be used for the standing leg of the compass or divider head, when a circle is to be drawn.

Center punch is made of tool steel and the point is hardened. It is important that the point is ground on the center.

         Using the center punch:

·       A light punch mark is made first and checked whether the position is correct or not. If correct,a deeper mark is made. If not, it is to be corrected before the deeper mark is made.

·       Whenever possible, make inclined surfaces straight before punching.

Double punch

           Double punch is used for marking the centers of holes to be drilled at the same center distances.(3 or chain drilling).