Topics about "Scraping" No.1

What is "Scraping"?

Scraping is work in which the surface of a casting is cut away with a chisel-shaped tool known as a scraper. Scraping is preformed on sliding surfaces (the parts of tables or columns that move), surfaces where two objects contact each other, and tables or pallets. The amount that is trimmed off by each movement of the scraper is around 1-3µm and therefore it is possible to create any desired shape or form. Skilled workers can realize degrees of flatness, squareness and straightness not possible with machines.

Why is "Scraping" Required?

The simple answer is "You cannot make a better child than the parent".

For example, if Machine A is able to achieve a flat surface for Machine B with a flatness of 10µm, objects processed by Machine B will not be more precise than 10µm.. However, scraping can enable Machine B to be more precise than Machine A through corrective measures done by solely by hand. Mitsui Seiki s corporate an ideal lies in this concept called "monozukuri" manufacturing.

The Basis of Scraping is "Rubbing"

When scraping, the flat plate known as the "rubbing jig" is set as a standard and is made using the "Three-surface Rubbing" technique The surface produced by scraping will have minute irregularities with high parts and low parts. By painting vermillion onto the surface and rubbing the Rubbing Jig over the surface, the vermillion on the areas that stick up will be rubbed off. Where the vermillion has rubbed off, the he scraper is used once again to trim the excess sections. Flat surfaces are created by continuously repeating the process of painting vermillion and rubbing the jib.


How Can We Make a Flat Surface? - "Three-surface Rubbing"

Making a flat surface is fundamental to scraping. Here we explain how scraping is used to make a flat surface using the "Three-surface Rubbing" technique.

As the name makes apparent, three surfaces are involved in this process. But, why three surfaces?


For example, take the case where scraping has been used to make three flat surfaces in the forms shown in Diagram 1.

As shown in Diagram 2, plates "1" and "2" and plates "2" and "3" each match surfaces are a perfect fit. On one hand, if plates "1" and "3" do not match, this entails that one or more of the surfaces are not flat. On the other hand, if plates "1" and "3" do match, then all three surfaces are flat. As seen with this example, all three combinations must be successful to prove whether the surfaces are flat or not.

▲PageTop