Hand scraper

Three different engineering hand scrapers

Hand scrapers are single edged tools used to scrape metal from a surface. This may be required where a surface needs to be trued, corrected for fit to a mating part, needs to retain oil (usually on a freshly ground surface), or even to give a decorative finish. They are single edged cutting tools.
The task of scraping has been the bane of most engineering apprentices however it's versatility and appropriateness far outways the hard work it requires, or is perceived to require. It's effective use requires skill and concentration.
An often overlooked advantage of scraping is the ability to take the tool to the workpiece. When the workpiece weighs several tons and towers head and shoulders over you, the apprentices solution of chucking it on t'e mill is impracticable, if not outright impossible. A skilled craftsman can wield a scraper and turn out work that is the envy of his peers, it just takes more time than the usual methods.
Surface plates were traditionally made by scraping. Three raw cast surface plates, a flat scraper (as pictured at the top of the image) and a quantity of bearing blue were all that was required in the way of tools. Methodology, skill, patience and tenacity was to be supplied by the tradesman.

The scraper in the center of the image is a three corner scraper and is typically used to deburr holes or the internal surface of bush type bearings. Bushes are typically made from bronze or a white metal.

The scaper pictured at the bottom is a curved scraper. It has a slight curve in its profile and is also suitable for bush bearings, typically the longer ones.

With precision ground surfaces, any oil film applied to the surface will lack the means to adhere to the surface, especially between two mating parts of exceptional finish. The oil film will be swept away leaving nothing but bare metal and the risk of seizure. Scraping the surface carefully will leave the original high quality surface intact but provide many shallow depressions where the oil film can maintain it's depth and surface tension.

Scraping can leave an attractive pattern on the surface and was in fact, the physical evidence of a craftsmen built machine. It is therefore still treated as evidence of craftsmanship by the astute buyer, or the more market savvy machine builders.