Should I bore or ream my holes

Departments - Mike’s Tooling Insights

May 23, 2022

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Recently I was in a manufacturing shop and one of the machinists asked me, “How do I know if I should ream or bore these holes?” That’s a very good question that can be answered based on the print dimensions and tolerances.

Let’s look at some possibilities of how to differentiate. If you’re sizing a diameter and the tolerances aren’t restrictive, reaming may be your best option. In most cases reaming is faster than boring. Using reamers to open holes and control the diameter is a very good use of this tool. Reamers come in a variety of flutes, giving you options to how much feed rate you can use on the tool.

When should I bore a hole? Boring is used in many cases to ensure dimensional tolerances are held. One such area is if you had an absolute position from the center line of your diameter to a datum point of the part. Boring is also a good option when producing large diameters. Boring tools also come in different configurations. Many have two or more cutting tools mounted to the bar, allowing you to increase feed rate and improve cycle time.

As with everything in machining, there’s no one answer for when to ream versus bore. However, smaller diameter holes lend themselves to reaming more than boring. That only applies when the part tolerance permits. Reaming in many cases will also give you a better surface finish versus boring. There are also tools that ream and burnish, allowing you to obtain a burnished finish and producing very fine surface finishes. Use boring when part tolerances and dimensional accuracy applies.

As always, work with your favorite tooling supplier and make sure you have the most efficient tool available that allows you to produce the finest quality part at the least possible cost.

CMR Consultants

Do you have specific topics you would like addressed or cutting tool challenges? Email me so I can address them in a future column.

Mike Ramsey, president of CMR Consultants, retired from Kennametal Inc. as vice president, global machine tool industry sales, after 39 years of service in sales and marketing. He can be reached at