Boring Mills Process Description

What does it do? How can I use it? Why will it help me?

Boring mills, either vertical or horizontal, are the equivalent of turning lathes, but while lathes machine the outside diameter of a part, these cut the inside diameter. Boring mills are therefore often used to widen or finish a pre-existing drilled hole.

Boring achieves 3 things: proper sizing, straightness, and concentricity.

Unless the inside diameter is a “standard” size, drilling or reaming must be followed by boring to ensure proper sizing of the hole. Boring mills can be adjusted to any diameter within the machine’s work envelope. Usually, this envelope is far larger than can be worked on other machine tools.

Longer tools tend to wander or deflect, so boring can also ensure that the original hole is straight and true, since the cutting tool is moved straight along the ways, or the spindle itself might reach far into the cavity.

Finally, boring mills ensure concentricity between the inside and the outside of the part—making sure a cylinder is the same thickness along its entire length, for example.

For answers to your questions or more information on Extrude Hone machines call Liberty at 847-276-2761 or send us an email

Liberty Machinery buys and sells all types of  boring mills & turret lathes.

We are your trust source for high quality boring mills & other surplus machinery.

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Process: How does it work?

Boring works almost identically to turning, and can perform the same cutting processes. While many boring machines look complex, the machine movement is actually very simple. The spindle stock is mounted on ways that may themselves be able to move along other axes.

The layout of the machine differs based on the type of application needed. For instance, horizontal boring mills may be floor-type, bed-type, or ram-type. The shape of the part will determine whether a vertical or horizontal mill should be used.

Horizontal boring mills are more versatile since, while the work envelope is limited, the part itself may extend beyond the envelope. When a new section of the part needs to be worked, it can simply be moved along the table into the work envelope. On a horizontal boring mill, the workpiece is stationary and the spindle moves.

Vertical boring mills, also known as vertical turret lathes or VTLs, are basically lathes turned onto their sides. The rotating chuck that holds the workpiece sits on the ground and the spindle remains stationary.

Major manufacturers of boring mills

Bullard, Giddings & Lewis, Lucas, Okuma & Howa

Sell Your Boring Mill

Liberty is always looking for used boring mills to buy for inventory. Contact us and let us know what you have for sale. We’ll be happy to give you a free quote.

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  1. George Schneider, Jr., Cutting Tool Applications (Farmington Hills, MI: ASM International, 2002)
  2. Today’s Machining World, “Getting Bored.”