Bridgeport Machine Rebuilders

  • Increase font size
  • Default font size
  • Decrease font size
Home Bridgeport Machine Rebuilders Blog Bridgeport Machine Rebuilders Blog Hand Scraping Ways - Bridgeport mills, Harig surface grinders...

Hand Scraping Ways - Bridgeport mills, Harig surface grinders...

Bridgeport mill carriage & knee ways

We found the following information about "hand scraping way surface areas" floating on the web and thought it was interesting enough to share.  This is only a summary of the entire article.  It was written by Andrew Devitt.

Bridgeport Machine Rebuilders and the Harig Machine Rebuilders Division provided the pictures.


Harig 612 flat way hand scraped, Harig 612 flat way hand scraped

The first machine tools for cutting iron used wooden ways, but by the mid 19th century, cast iron became the material of choice for machine elements. It had the advantage of easy formability. Builders could produce it into shapes, cut it with the single point tooling of the time and hand fit it with a scraping operation. Few other options existed. When two scraped cast iron surfaces meet with a layer of oil in between, they slide rather well. For 100 years cast iron to cast iron plain slide ways were the state-of-the-art in way design. There is a good deal of art in the production of cast iron way surfaces. Historically, plain ways represented an important part of the value added by a machine tool builder. A highly skilled trade called "hand scraping" was, and still is, necessary to properly fit cast iron way surfaces and make a machine both geometrically correct and long lasting. But for years machine tool builders have tried to eliminate this labor-intensive manual scraping process.

Bridgeport mill hand scraped

Whether the count reaches ten points per inch or forty, the percentage of area in contact should be 50 to 60 percent. The spaces between high and low points provide oil reservoirs important to accuracy and long life. When bearing contact exceeds 80 percent there is an effect similar to the ringing together of joe-blocks resulting in "stick-slip" effects.

Harig 612 base ways hand scraped, Harig 612 base ways hand scraped.Thousands of high and low spots in a scraped surface provide evenly distributed oil reservoirs, and drains. As motion starts, oil is dragged between high spots across the whole surface. Perfectly flat surfaces (100%) at rest would with time squeeze out all oil and ring together. As this “sticktion” is overcome, the slide must move the distance between oil grooves to become lubricated. At that point, the slide rides up on a hydroplane of oil without the draining effects of the low spots in the scraped surface (like the thread of a tire), the slide rises up several thousandths causing inaccuracies.

Bridgeport mill hand scraped

Breaking up a bearing surface with a power flaker, which leaves a series of half-moon shaped marks on the ways, provides a quick fix for this problem. These spot or flaking marks are not to be confused with scraping. Developed as a cosmetic treatment, the marks give the surface a uniform appearance. Today, flaking provides relief in bearing surfaces that have lapped themselves flat by wearing through their relief. Spotting will not improve the straightness or flatness of a way surface, but it will help with stick-slip problems..


Rebuilt Mills for Sale

We sell Rebuilt Bridgeport Mills for approximately 50-60% of a new Bridgeport mill

We also offer an opportunity to trade-in your well used Bridgeport mill with a purchase of a rebuilt Bridgeport mill. Our rebuilt machines are guaranteed for a period of 1 Year, under normal use and proper maintenance.

Click Here to read more