Better boring basics: People & Companies

You probably know that boring tools are used to bring holes to the desired size and finish, straighten drilled and cored holes and correct casting defects. But you may not know what to do — and what not to do — to get longer life and better performance out of boring tools, as well as improve the user experience. This knowledge falls into three categories: tool selection, best practices when using the tools, and developments that have had a positive impact on boring tools and processes.

When it comes to selecting the best boring tool for an application, some users are knowledgeable enough about the subject to request tools with specific
features and characteristics. For example, Scientific Cutting Tools Inc. in Simi Valley, California, normally makes boring tools with a 2-degree front angle across the face that facilitates efficient cutting, said Sales Director Todd White.

In some cases, however, “customers want to change that angle, so we make special tools for them based on their preferences and R&D that they have done,” he said. “For one customer, we make the front angle 8 degrees instead of 2 degrees because they find that works better for the materials that they cut.”

Good Guidance

Although some shops know enough about boring tools to make specific requests of suppliers, the majority rely to some extent on recommendations from toolmakers.

“Most of the time, when customers are looking at a finishing operation, they want a little bit of guidance,” said Natalie Wise, manager for finishing products at Allied Machine & Engineering Corp. in Dover, Ohio. The reason, she explained, is that “those are later operations in the manufacturing of their part, so it’s very critical that they get it right the first time. If something goes wrong with those finishing operations, they could be scrapping something very expensive that they’ve spent a lot of time on.”

To come up with the right boring tool for a particular application, White asks customers for basic information, such as the hole diameter, machining speeds and feeds and the part material. If the material is hard and abrasive, Scientific Cutting Tools can supply diamond- or CBN-tipped boring bars. Sometimes, however, he reports that customers dealing with such materials may start with conventional solid-carbide boring bars rather than pay extra for diamond- or CBN-tipped tools.

The 3E Tech digital display shows exact boring diameter adjustments. Image courtesy of Allied Machine & Engineering

“Then if they’re using them up too fast, they’ll call and I’ll say, ‘You should probably bite the bullet and get a diamond-tipped bar for those materials because they’ll last a long time,'” he said. “Even though they’re quite a bit more expensive, the (number of) parts you get out of them can be phenomenal.”

White said machine shops cutting very abrasive nonferrous materials might get through 5,000 parts with a diamond-tipped boring bar compared with 10 or 15 with a solid-carbide bar.

So even though a solid-carbide bar costs $25 and a diamond-tip option costs $150, “your cost per piece is going to be way less,” he said.

The same is true, White added, of CBN-tipped bars, which are suitable for boring hardened steel.

Once again, in these applications “a lot of people will start out with coated carbide, and if they have a short run, that will get them through and give them a good finish,” he said. “But if the volume is high, then CBN is something to look at.”

In some cases, White pointed out that price considerations lead shops to the least expensive option: an uncoated boring tool. But when those customers cut metals like stainless steel and Inconel, Scientific Cutting Tools urges them to think longer term and opt for a coated tool. He reports that his company has had “great success” with a high-performance AlTiSiN coating called nACo, which provides excellent wear resistance and lubricity.

“I know it’s a couple dollars more,” he said, “but it can make a huge difference.”

Going Deep

Another key factor that comes into play when choosing a boring tool is the ratio of hole depth to diameter. If that number is high, Scientific Cutting Tools can provide boring bars with a helical flute, White said, which minimizes deflection during the boring process.

For boring applications with depth-to-diameter ratios greater than 5-1, Allied Machine & Engineering offers Novitech, a mounted module that reduces vibration when machining hole diameters. Wise said this improves the surface finish of bored holes and increases tool life.

“The boring head is going to last a lot longer because it’s not vibrating,” she said, “so there’s not a lot of radial deflection or pressure.”

This lathe setup includes a solid-carbide boring bar in a toolholder. Image courtesy of Scientific Cutting Tools

Wise said Novitech also extends the life of machine spindles.

“When you have excessive vibration, it’s really hard on the customer’s machine as well,” she said. “So it’s a win-win when you include some type of vibration-reducing technology.”

On the downside, additional features, such as Novitech, increase the cost of boring operations.

But while shops always are concerned about price, “when customers come to us with a very
important operation like finishing, it’s more important that the tool does what we say it’s going to do,” Wise said, as long as the extra cost is “within reason.”

Best Practices

Once a boring tool has been acquired for a particular application, users should be aware of practices that will help get the most out of that tool. For example, Wise recommends that users make sure they’re removing enough material when boring to completely cover the nose radius of the insert. If this isn’t the case, she said, radial deflection or pressure will cause chatter, which in turn results in poor hole quality or surface finish.

In situations like this, she said shops can do two things. One is to make the pre-drill hole size a little smaller so more material is left for the finishing operation. If this can’t be done, the other option is to swap out the tool insert for one with a smaller nose radius while leaving everything else in the boring tool setup the same.