How to use an engineer’s straight
edge when scraping

Shop for Engineer’s Straight Edges

Other equipment you will need:

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 used to roll a thin, even layer of spotting ink.

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.

Engineer’s scraper

An engineer’s scraper is used to scrape off and remove high spots from the surface of a workpiece, making it flatter.

Begin work

Step 1 – Clean

Begin by first checking that your workpiece and engineer’s straight edge are clean.

Use the soft-bristled brush to remove any dirt and then wipe over both the straight edge and workpiece with a microfibre cloth.

Step 2 – Spread out spotting ink

Place a small amount of spotting ink on the straight edge’s working face and spread it out with the small roller.

Step 3 – Rub straight edge in spotting ink

Carefully place the straight edge onto the surface of the workpiece, then move it across the surface. This process is called ‘rubbing’.

Step 4 – Remove straight edge

Carefully remove the straight edge from the surface of the workpiece.

Step 5 – Reveal areas to be scraped

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 high spots

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 – Scrape again

Repeat step 6, going back over the same area, but at a right angle to the previous lines.

Step 8 – Clean

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 inking and rubbing

Repeat steps 2, 3 and 4.

Each time you roll out an area of spotting ink on the engineer’s straight edge, 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 – Repeat scraping

Repeat steps 5, 6, 7, 8 and 9 until the entire surface of the workpiece is evenly covered with high spots, at which stage it is considered to be flat.