How to use an engineer’s scraper?

29th February 2020


How to use an engineer’s scraper


	Shop for Engineer’s Scrapers


		Other equipment you will need
		In order to achieve the best scraping results you will need a few other pieces of equipment: Engineer’s spotting ink This is used to highlight the areas on the workpiece that have high spots which need scraping. There are many types of spotting ink that can be used in scraping, the most popular is Prussian Blue.

		Small roller A small rubber roller is best, although the foam sort you would use in decorating can also be used. This is needed to roll a thin, even layer of spotting ink.

		Reference surface plate Reference plates are used as a reference of a known flat surface, for transferring that accuracy to other objects. These can be made from either granite, cast iron or glass.

		Reference plates come in three grades of accuracy: Grade 0 Laboratory (Grade AA in America), Grade 1 Inspection/control room (Grade A in America) and Grade 2 Workshop/tool room (Grade B in America). A grade 0 surface plate 1000 x 1000 x 120 mm in size will have a flatness accuracy of 2µm between the highest and lowest part over the surface of the plate.

		Microfibre cloth The microfibre cloth lifts dirt from the surface of the workpiece, leaving it clean and ready to be scraped.

		Brush You will need a soft-bristled brush to clean off the scraped metal from your workpiece.

		Hand-scraping technique
		Step 1 – Find a comfortable stance Stand with your feet shoulders-width apart and one foot in front of the other. Hold the handle of the scraper in your dominant hand, and use your other hand to apply pressure at the tip of the scraper. The amount of pressure required varies depending on the type of metal you are scraping. The harder the material you are scraping, the more pressure you will have to apply.

		Step 2 – Begin scraping Push the base of the scraper handle forward with short, sharp strokes. Apply downward pressure to the tip of the scraper with the other hand and slightly rock your wrist with each pushing stroke. Rocking/twisting helps to take only the tops of the high spots from the surface and prevents the scraper tip digging into the workpiece.

		The scraping process
		Step 1 – Check and clean Begin by first checking that your workpiece and reference plate are clean. Use the soft-bristled brush to clear away dirt and then wipe over both the reference plate and workpiece with a microfibre cloth.

		Step 2 – Roll out spotting ink Place a small amount of spotting ink on the reference plate and spread it out with the small roller.

		You should spread out the spotting ink so that it creates an area larger than the workpiece, allowing you to move the workpiece around within the inked area.

		Step 3 – Place workpiece on inked area Carefully place the workpiece (highlighted in yellow) onto the inked area of the reference plate (highlighted in green), then move the workpiece around within the inked area. This process is called rubbing.

		Step 4 – Remove workpiece from inked area Carefully remove the workpiece from the reference plate and secure it in a position where it’s comfortable to work on the face being scraped (highlighted in yellow).

		What is a false rub and how can it be avoided? A false rub is one that may give an inaccurate impression of where the high spots are on a workpiece. As the workpiece is dragged off the side of the reference plate, or moved outside the inked area, the spotting ink is rubbed off some areas and pushed onto others, giving a false reading of where the high spots are.



		Step 5 – Remove first set of high spots At this stage, you should have a few large spots of ink on the workpiece; these are the areas that need scraping. Only scrape the areas highlighted by spotting ink.

		Step 6 – Scrape in parallel lines Scrape away the inked high spotted areas on the workpiece, in a series of close, straight parallel lines. Only scrape the inked areas.

		Step 7 – Second scraping pass Repeat step 6, going back over the same area, but at a right angle to the previous lines.

		Step 8 – Clean workpiece Clean off the workpiece with a soft-bristled brush to remove any dust created in the scraping process. Then wipe the workpiece over with a microfibre cloth.

		Step 9 – Repeat ink rubbing and scraping Repeat steps 2, 3 and 4. Each time you roll out an area of spotting ink on the reference plate, try and make it slightly thinner than the previous time. This will help to highlight smaller high spots on the workpiece. At the end of this, the high spotted area marked with ink should be larger than the first time.

		Step 10 – Continue until flat Repeat steps 5, 6, 7, 8 and 9 until the entire surface of the workpiece is evenly covered with high spots, at which stage the workpiece is flat and ready to be frosted/flaked if required.