MARKING & MARKING TOOL (ITI THEORY) PART 1

MARKING MEDIA 

THE LINES DRAWN ON THE METAL ARE NOT VISIBLE PROPERLY, FOR THIS, SOME MARKING MEDIA APPLIED ON THE JOB.

TYPES OF MARKING MEDIA :-

1.  WHITE WASH - IT IS APPLIED TO ROUGH FORGING & CASTING SURFACE. WHITE WASH IS NOT RECOMMENDED FOR WORK PIECE OF HIGH ACCURACY. IT MADE OF CHALK POWDER WITH WATER, CHALK MIXED WITH METHYLATED SPIRIT OR WHITE LEAD POWDER MIXED WITH TURPENTINE.
2. PRUSSIAN BLUE - THIS IS USED ON FILLED OR MACHINED FINISHED SURFACE. THIS WILL GIVE VERY CLEAN LINE BUT TAKES MORE TIME FOR DRYING THEN THE OTHER MARKING MEDIA.
3. COPPER SULPHATE (BLUE VITROL)- THE SOLUTION IS PREPARED BY MIXING COPPER SULPHATE IN WATER AND FEW DROPS OF NITRIC ACID. COPPER SULPHATE IS USED ON FILED OR MACHINED FINISHED SURFACE.
4. CELLULOSE LACQUER- THIS IS EASILY AVAILABLE MARKING MEDIA. IT IS MADE IN DIFFERENT COLOURS & DRIES VERY QUICKLY.  

SURFACE PLATE :-

1. IT IS ESSENTIAL TO HAVE A DATUM PLANE WITH A PERFECTLY FLAT SURFACE.
2. SURFACE PLATE ARE GENERALLY MADE OF GOOD QUALITY CAST IRON, GRANITE OR CERAMIC. (GRANITE IS A DENSE & STABLE MATERIAL)
3. THE WORK SURFACE IS MACHINED & SCRAPED. THE UNDERSIDE IS HEAVILY RIBBED TO PROVIDE RIGIDITY.
4. A THIN COATING OF RED LEAD MIXED WITH OIL IS SPREAD EVENLY OVER THE SURFACE PLATE.
5. THE SURFACE PLATE SHOULD BE SUPPORTED ON THREE LEGS FOR AVOIDS ROCKING & TWISTING.
6. SURFACE PLATE ARE FOUND IN THREE GRADES- 1,2,3
7. THE WORKING HEIGHT BEING ABOUT 800 MM FROM THE FLOOR.
8. ACCURACY OF SURFACE PLATE USED IN WORKSHOP IS 0.025 MM, INSPECTION SURFACE PLATE IS 0.0025 MM, MASTER SURFACE PLATE IS 0.00025 MM.

SPECIFICATION OF SURFACE PLATE

SPECIFIED BY THEIR LENGTH, BREADTH, GRADE & THE INDIAN STANDARD NUMBER. FOR EXAMPLE- CAST IRON SURFACE PLATE 

                                     2000 x 1000 GR.1 I.S 2285

MARKING TABLE:-

1. IT IS MADE OF CLOSE GRAINED CAST IRON.
2. THE MARKING TABLE PROVIDE A ' REFERENCE PLANE ' ON WHICH THE WORK & THE MARKING OUT TOOLS STAND.
3. THE WORKED BEING MARKED MUST BE PLACED AT 90 DEGREE TO THE REFERENCE PLANE.
4. THE MARKING SHOULD BE PROTECTED BY WELL FITTING WOODEN COVER, WHEN NOT IN USE.
5. PARALLEL LINES ARE ENGRAVED IN BOTH DIRECTION AT A SET DIRECTION, THESE LINE SERVE A GUIDE FOR POSITIONING THE COMPONENTS WHILE SETTING AND MARKING.
6. HEIGHT FROM THE FLOOR IS 75-90 CM.

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