How to Use a Boring Bar on a Lathe

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The lathe is an incredibly versatile power tool with many different functions. One such function is to take an existing hole and make it bigger. To enlarge an existing hole using a lathe, you need to use a boring bar. Use these step-by-step instructions on how to use a boring bar on a lathe and familiarize yourself with the process. 

What Is Boring? 

Boring is the process of making an existing hole bigger. It is similar to drilling but produces a much more accurate hole.

Lathe boring a metal rod

Boring bars are a tool used in lathework to enlarge existing holes. They are usually used to make holes in metal, although it is possible to bore using a lathe into wood, as well. 

Boring bars are attached to the tool rest, which slides along the lathe carriage. When the boring bar encounters the spinning workpiece, it removes material from the inside of the workpiece. 

Boring bars are usually made from one of three materials: 

  • High-Speed Steel (HSS) boring bars are the least expensive option.
  • Brazed Carbide boring bars are more expensive, but they cut much faster than HSS, and tend to stay sharper for longer. 
  • Indexable Carbide boring bars have removable/replaceable tips and are more versatile than HSS or brazed carbide. 

Using a Boring Bar on a Lathe

Follow these instructions for a step-by-step guide on how to boreholes using a lathe and boring bar. 

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  1. Attach the workpiece to the lathe. Use a device such as a chuck or a collet to attach the workpiece to the headstock of the lathe. Spin the workpiece by hand to ensure it doesn’t hit the lathe carriage or rails. 
  2. Choose a boring bar. Boring bars are subject to stress from multiple directions, for safe boring, the bar should be as thick, short, and rigid as possible for the size of hole you’re trying to make. 
  3. Confirm clearance. Hold your selected boring bar up to the existing hole, and make sure it fits inside. 
  4. Set the depth. Measure out the depth of your hole, and mark it on your boring bar using a piece of masking tape. If your lathe is equipped with a depth stop, you can also set that to the desired depth of your hole. 
  5. Attach the boring bar to the tool post. Place the boring bar in the tool post and raise it until the tool is close to center. Tighten the grip of the tool post so it holds the boring bar firmly in place. Don’t expose more of the boring bar than necessary for the depth of cut you’re making. 
  6. Set the spindle speed. The appropriate spindle speed depends on the kind of metal you are boring and your experience level. In general, slower spindle speeds work better for boring. If your lathe starts to vibrate or chatter, your spindle speed is too high.  
  7. Lubricate. Drip some cutting fluid into the hole to keep your tool and your workpiece lubricated. This will keep things cool, make cutting easier, and produce a smoother finish. 
  8. Start the lathe. Move the tool rest along the carriage, inserting the boring bar into the hole. Slowly introduce the boring bar to the material. Listen for any chattering as the lathe cuts through the material. Be prepared to stop if necessary. 
  9. Stop to clean. After boring for no more than one inch, back the boring bar slowly out of the hole and turn off the lathe. As you bore, metal chips are going to build up inside the hole. These will put extra wear and tear on the boring bar, and make your job more difficult. Stop frequently to clear out waste material from the hole. 
  10. Continue boring. If everything is going well and your hole is clean, add more lubrication and continue boring. Stop every inch to remove waste material. Watch as the masking tape or depth stop approaches the entrance to the hole. Stop boring when you reach the appropriate point. 

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Conclusion

Boring is one of the many functions you can accomplish using a lathe. Choosing an appropriate boring bar is key to success. Boring should always be done on the slowest possible spindle speed. Work in small increments to avoid the build-up of metal chips inside the borehole. 

Ellenkate grew up on job sites run by her family’s construction company. She earned her theater degree from The Hartt School, a prestigious performing arts conservatory in Connecticut. Her design and DIY work from her Chicago loft was featured in the Chicago Reader and on Apartment Therapy.