MODULE 3: M

ARKING OUT

AND HAND TOOLS

ME C H A N I C

A L WO R K S H O P

MODULE OBJECTIVES

After the completion of this module, student should be able to: Identify different marking out tools and their usage. Select the appropriate tool required for marking out. Mark out work-pieces according to the dimensions given in engineering

drawings. Distinguish the different hand tools and their uses. Select the correct tool for the task. State the care and safe use of hand tools.

3.1. INTRODUCTION TO MARKING OUT

Marking out is the process of transferring a design, layout or dimensions from the drawing to a work-piece, and it is considered as the first step in the manufacturing process.

COMMON MARKING OUT TOOLS 1- Scriber

2-Marking blue3-Punch

4-Engineer’s square5-Surface plate6-Surface gauge

7-Angle plate 8-Vee block

9-Spring dividers10- Ball peen hammer

1- SCRIBER Scribers are used in metalworking to mark lines on work

pieces prior to manufacturing. They are used instead of pencils as the marks from pencils can rub off easily. Scribers consist of a rod of steel that has been sharpened to a point at one or both ends and they are used to draw shallow scratches on the surfaces of the work pieces.

There are 2 types of scribers 1- One-end scriber 2- Double-end scriber

2- MARKING BLUE. Marking blue is a dye used in metalworking to aid in marking out. It is used to paint a metal object with a very thin layer of dye that can

be scratched off using a scribers to show the bright metal underneath.

The advantages of using the marking blue are:

The existing scratches are covered with the dye. The new lines have a contrasting background.

3. PUNCH

The punch is a hard metal rod with a shaped tip at one end and a rounded butt at the other end, which is usually struck by a hammer.

The most commonly used ones for marking out are:3-1-Center punch:

It is used as an aid to drilling operations. The center punch forms an indent in which the tip of the drill fits. A center punch has a point angle of 90°.

90°

3-1-Prick punch :It is used to produce a smaller indentation than a center punch,

which acts as a useful datum (standard) point in layout operations. A prick punch has a point angle of 60°.

60°

3-3- Letter stamps or number stamps:

These are used to print a letter or number into a work piece.

4. ENGINEER’S SQUARE

The engineer’s square is used for checking the straightness of a work piece. It can also be used for marking perpendicular lines onto a work piece.

DIFFERENT USES OF ENGINEER’S SQUARE Marking on Edges Marking on a side Checking outside corner

DIFFERENT USES OF ENGINEER’S SQUARE Checking inside corner Checking flatness Measuring short

distances

5. SURFACE PLATE The surface plate has a high degree of flatness. The flat surface is

being used as a datum surface for marking out and for measuring purposes. It is also called surface table if it can stand on the floor.

5.1 MAINTAINING THE SURFACE PLATE You should

1- Keep the surface in a good condition.2- Keep the surface lightly oiled to prevent corrosion.3- Take care when placing marking out tools on the surface.

You should not1- Place anything on the surface that would damage it.2- Drop tools on the surface.3- Hammer on the surface.

6. SURFACE GAUGE

A surface gauge is used on surface plates for scribing lines on work pieces and checking parallel surfaces and heights.

The surface gauge is used also in finding the center of a cylinder and determining whether a plane's surface is truly horizontal.

Checking parallel surfaces and heights

In the example shown the tilt screw was used to set the indicator reading to zero on a gage block (not shown) of 0.375 inch thickness. The gage block is then removed and the black part shown is pushed forward so that the indicator stem rides up over it. If the indicator reads zero then the part thickness is exactly 0.375.. If the indicator reads -0.002 then the part is 0.373 thick. If the indicator reads +.002 then the part is 0.377 thick.

7. ANGLE PLATE

The angle plate is used to assist in holding the work piece perpendicular to the table. The angle plate is provided with holes and slots to enable the secure attachment, clamping and adjusting of work pieces.

8. VEE BLOCKThe Vee blocks are generally used for holding circular work pieces for

marking out or machining.

9. SPRING DIVIDERS

The spring divider is used for scribing arcs or circles. The below figure shows a circle that was marked by a spring divider onto a work piece.

10. BALL PEEN HAMMERThe ball-peen hammer is shown in the figure. The crowned, or rounded,

edge (hemispherical head) works metal smoothly without marking it. The other end of the hammer can be used to strike punches and chisels