| A hand scraper is a single-edged tool used to scrape | | | | on the work piece will be colored by the dye on the |
| metal from a surface. This may be required where a | | | | standard. These high spots are scraped off and the |
| surface needs to be trued, corrected for fit to a | | | | process repeated until there is an even spread of high |
| mating part, needs to retain oil (usually on a freshly | | | | spots which total about 60% or more of the surface |
| ground surface), or even to give a decorative finish. | | | | area. If desired the surface can then be |
| Surface plates were traditionally made by scraping. | | | | “Frostedâ€. A surface prepared in |
| Three raw cast surface plates, a flat scraper (as | | | | this way is superior to any machining or grinding |
| pictured at the top of the image) and a quantity of | | | | operation, although lapping can equal it. Grinding and |
| bearing blue were all that was required in the way of | | | | machining stresses the metal thermally and |
| tools. Methodology, skill, patience and tenacity was to | | | | mechanically, scraping and lapping do not. |
| be supplied by the tradesman. | | | | Although well done scraping provides an extra |
| The scraper in the center of the image is a three | | | | measure of accuracy, for most applications it does not |
| corner scraper and is typically used to deburr holes or | | | | matter. A ground lathe bed or milling machine ways |
| the internal surface of bush type bearings. Bushes are | | | | are perfectly adequate for almost all types of work. |
| typically made from bronze or a white metal. | | | | With precision ground surfaces, any oil film applied to |
| The scaper pictured at the bottom is a curved | | | | the surface will lack the means to adhere to the |
| scraper. It has a slight curve in its profile and is also | | | | surface, especially between two mating parts of |
| suitable for bush bearings, typically the longer ones. | | | | exceptional finish. The oil film will be swept away |
| The task of scraping has been the bane of most | | | | leaving nothing but bare metal and the risk of seizure. |
| engineering apprentices, however its versatility and | | | | Carefully scraping the surface will leave the original |
| appropriateness far outweighs the hard work it | | | | high quality surface intact, but provide many shallow |
| requires, or is perceived to require. Its effective use | | | | depressions where the oil film can maintain its depth |
| requires skill and concentration. An often overlooked | | | | and surface tension. When a scraping is used for this |
| advantage of scraping is the ability to take the tool to | | | | purpose it is more accurately called "Frosting", |
| the workpiece. When the workpiece weighs several | | | | "Spotting" or "Flaking" as opposed to actually fully |
| tons and towers head and shoulders over the worker, | | | | scraping an accurate surface. Typically a scraped |
| the apprentice's solution of chucking it on the mill is | | | | surface is scraped to highly accurate flatness and then |
| impractical, if not outright impossible. A skilled craftsman | | | | "frosting" is applied over it for oil retention. The |
| can wield a scraper and turn out work that is the envy | | | | advantage of this oil retention "frosting" is debatable. |
| of his peers; it just takes more time than the usual | | | | Scraping can leave an attractive pattern on the |
| methods. | | | | surface and was in fact, the physical evidence of a |
| The man who scrapes is called a "hand". It is done by | | | | craftsmen built machine. It is therefore still treated as |
| using a precision surface such as a surface plate or a | | | | evidence of craftsmanship by the astute buyer, or the |
| straight edge as a standard (a straight edge in this | | | | more market savvy machine builders. Even machines |
| context is not a ruler it is a miniature surface plate of | | | | that have been ground and not scraped often have |
| extreme accuracy). A professional scraping tool will be | | | | frosting applied. Presumably this is at least partly to fool |
| a special made tool, not an old file. The standard is | | | | the unsavvy buyer into thinking the machine was truly |
| coated with a very thin coating of some material such | | | | hand scraped. That this frosting is applied not only to |
| as Prussian blue. The work piece and standard are | | | | way surfaces but also to table tops and other non |
| touched together by gravity alone and the high spots | | | | bearing areas shows that it is ornamental. |