By Mike Smith, Product Manager – Reaming and EPB
Boring increases the inside diameter of a drilled or cast hole. Through boring, which includes roughing and finishing operations, you’re able to bring your hole to the desired size and finish as well as achieve hole straightness and concentricity. However, to ensure your boring process goes as smooth as possible, you need to have the right tools for your specific application.
Typically, boring tools consist of a holder, adapter and cutting unit such as a cartridge or slide. Although, when it comes to roughing versus finishing operations, there are certain boring head characteristics you must take into consideration to achieve the best results.
A rough boring head, also known as a twin bore, is going to involve two or more inserts (cutting teeth) to quickly remove a lot of material. Such a design proves to work best in shorter-reach, stable applications and those with larger hole diameters. A finish boring head, on the other hand, has a single tooth that removes less material, but provides a better finish as well as reduces cutting forces in longer-reach applications.
You’ll also find there are several different boring head styles on the market to accommodate different hole diameters. This includes cassette style boring heads for hole diameters that are generally over 0.700”. It is a style that allows you to switch between different grades and different chip breaker inserts, depending on your cutting material.
For smaller size diameters, it’s best to use a boring bar style with indexable inserts, similar to what’s used in turning operations. And for really small bores -- down to 0.012" -- non-indexable solid carbide boring bars with ground tips should be used. Keep in mind though, that with such a style of boring bar, it's possible to only go as deep as the bar is sticking out of the boring head. And the smaller the diameter boring bar, the less the tool will extend beyond the head. For example, when boring a 0.012" diameter hole, the boring bar used will not stick out very far, and it's safe to say that the maximum depth capability will be well below 0.047".
Because vibration is often a problem in boring operations, there are balanceable style boring heads that work well in high RPM and long-reach applications. There are also special vibration dampening systems, such as our Steadyline products, you can use behind the boring head to help reduce the vibrations. These dampening systems work by keeping any vibrations from reaching the machine’s spindle. Dampers prove really effective in large diameter bores that reach out between six and 10 times deep.
If you’re not using a dampening system and reaching out a long ways, you can experience unwanted chatter due to increased cutting forces. After all, when you put a lot of pressure on something, it tends to flex and create a significant amount of chatter. A twin-style boring head, because it relies on strong cutting forces to do its job, can create chatter in long-reach applications. At which point, you’re probably going to get better results with a single-tooth boring head because it requires less cutting forces.
For deep boring applications (like crank bores), it is a good idea to have a rotary bushing or some type of guide on your tool to stabilize it, preventing the unwanted pushing that occurs when cutting forces become so great.
Lastly, you must pay attention to the interface between your tool and spindle. When trying to determine your boring length-to-diameter ratio, do not factor in the maximum diameter of your boring head, look at the diameter of the shank of the modular connection behind the head.
Because this is only a snapshot into creating a smoother boring process, please feel free to contact me with any questions you have. Today’s boring heads and inserts are better than ever and there are a lot to choose from, which can be mind numbing. That’s why when you work with Seco, you can rest assured we’ll match you up with the right boring solution for your unique application.
About the Author
Mike is Seco's product manager for reaming and EPB tool holders, which includes EPB’s line of rough and finishing boring heads. In his spare time, Mike enjoys spending time with his wife and two daughters as well as running when he gets a chance. Contact Mike at email@example.com.