Machinist

[Lawrence London <lfljvenaura@gmail.com>]

http://www.okuma.com/handscraping

Hand Scraping FAQs

• Is hand scraping a lost art?

  No. While some machine tool builders have eliminated this practice due to cost, Okuma CNC machines continue to be built using this tried-and-true craftsmanship to achieve unparalleled accuracy and longevity.

• What does hand scraping actually do?

  Hand scraping creates contact points and oil pockets (high spots and low spots) on surfaces that are to be mated together. For moving parts, this allows the two surfaces to glide across each other without sticking. For bolted parts it creates a tighter bond which is less likely to separate during material expansion, contraction and flexing that occurs during CNC machining.

• Can’t the skill of hand scraping be replicated by a machine, with greater efficiency and accuracy?

  No. While it may seem counter-intuitive that a human can actually achieve better accuracies than a machine, the craftsmanship involved in hand scraping involves using human senses (see, touch and feel) to accommodate for inherent differences in the metal castings and other key components. The process of hand scraping involves one part at a time, encompassing multiple steps and checks to achieve the perfect surface mating – something that just can’t be achieved by a machine.

• How does hand scraping add accuracy and longevity to your machine tool?

  When it comes to your machine tool, there are a few components that should be hand scraped: the base, headstock, tailstock, tailstock base, cross slide, saddle, and gibs. Hand scraping these critical parts helps ensure that the mated components are matched perfectly – one part and one machine at a time. This allows the CNC machine to start with a strong foundation so that it maintains a high level of accuracy, and lasts as long as possible.

• Is hand scraping only for the surfaces of sliding parts?

  No. Anywhere you have parts that need to be mated—whether they’re bolted together or sliding against each other—hand scraping ensures that they’re paired together perfectly. Starting with a strong foundation means mating key components with handcrafted attention to detail. That way, you get the most out of your CNC machine over its long and healthy lifespan.

• Do you take care of hand scraping here in the Americas?

  Yes. While the majority of this work takes place in Japan during the machine building process, we do hand scrape here in the Americas when we “configure to order” (provide machine options based on customer requirements) and when we supply replacement components for customers’ machines that may have been damaged or worn out.

• Does hand scraping enhance the life and long-term value of the machine tool?

  Yes. While many companies forgo hand scraping due to the labor costs of employing skilled craftsmen, at Okuma we believe our investment in hand scraping is an investment in the longevity of your components and your machine tool. A CNC machine that lasts longer is always of greater value—and saves you precious dollars over time.

• Is hand scraping a full time task for a certain department at Okuma or is it another part of the assembly process?

  Hand scraping is a full-time task for certain departments. Although it is a finishing process for mating parts, there are Okuma members whose job it is to scrape cross-slides, saddles, or tailstock bases and do it 8 to 10 hours a day.

• What surface area can a trained craftsmen scrape per hour?

  There are a lot of factors that go into calculating how much surface area a trained craftsman scrapes in one hour. It all depends on the size of the part, of course. Let’s take for an example a gib for a cross-slide that measures 1.5” x 18”. In one hour, he should have taken up to 540 square inches off that gib, given that all other factors are correct. Scraping is just like any other job, if all factors are correct, it will take less time to scrape, but if there is one factor that is not correct then it could take up to several hours to scrape that same gib.