Use a horizontal boring mill (HBM) for parts requiring an accurate bore in addition to the drill hole. In boring, a drilled hole is enlarged during the machining process using a single-point cutting tool using an internal turning operation. An internal surface can be roughed or finished using boring typically maintaining a tolerance of between ±0.0020″ to ±0.0005″. (“How It Works – Getting Bored”)
Image: (“Horizontal Boring Mills”)
Productivity Features
There are two primary benefits to using a horizontal boring mill over a horizontal machining center.
- They have a larger configurable work envelope so you can easily machine very large parts, which are those with dimensions greater than about a 60′′ envelope.
- They have a quill that advances out from its headstock, allowing you to reach into small cavities. The quill keeps the tool short between the workpiece and the spindle to minimize tool deflection. The quill is built rigidly so it can extend into the workpiece with minimal deflection, whereas long boring bars would sag or deflect much more at their farther reach due to cutting forces.
(“How It Works – Getting Bored”)
Horizontal Quill
HBMs have a vertically-traveling Y-axis and a horizontally-traveling X-axis. The Z-axis also moves horizontally. The quill moves in the same horizontal direction as the Z-axis, but is labeled the W-axis. The quill extends and the spindle rotates within the quill.
Image: (“Johnford FBMC Series – Floor-Type Horizontal Boring Mills”)
When boring, just like when milling, it’s important to evacuate chips. The horizontally-oriented spindle permits the chips to fall away from the workpiece. Chips do not accumulate on top of the workpiece and risk interfering with subsequent operations.
Work Swing and Height
The work swing and work height specifications define the cylindrical volume handled by the HBM. Several factors depend on the swing and height dimensions, such as the tallest possible workpieces and workholding, the reach of the axes, the diameter swung by the B-axis, and finally the swapping capacity of the pallet changer, if equipped.
Common Choices
Rotating B-Axis
HBMs pallets rotate around the B axis and, depending on the HBM, in 1 or 0.001 degree positions. The B-axis permits machining, boring, and drilling on multiple sides of the workpiece.
The positioning you’ll need depends on your workpiece. If the workpiece needs machining on sides with 30 and 45 degree angles, the 1 degree positioning option will do.
Linear Guide Type
See linear guide types, which include ball bearing guides, roller bearing guides, and box ways.
Sources
“Horizontal Boring Mills.” Hurco, https://www.hurco.com/en-us/products/horizontal/Pages/HBMX-horizontal-boring-mill.aspx. Accessed 12 January 2023.
“How It Works – Getting Bored.” Today’s Machining World, 8 April 2009, https://todaysmachiningworld.com/magazine/how-it-works-getting-bored/. Accessed 12 January 2023.
“Johnford FBMC Series – Floor-Type Horizontal Boring Mills.” Absolute Machine Tools, https://absolutemachine.com/product/johnford-fbmc/. Accessed 12 January 2023.
