The Cut Scene: The Finer Details of Large-Format Machining

Barbco Inc. produces trenchless boring equipment at its main facility in East Canton, Ohio. This equipment includes large boring machines, guidance systems and drill heads meant to bore holes through earth and rock without disturbing the ground above it (for example, when drilling to install pipes for utilities under a major thoroughfare, or under railways). Doing so requires highly rigid and accurate machine tools. One of the company’s latest parts, a collapsible drilling head, has tolerances of 0.005 inch for most surfaces — with some holes requiring even tighter tolerances, at 0.001 inch.

The company primarily uses a Johnford DMC-4100PH double-column bridge mill to perform both roughing and finishing on its large parts, producing smaller parts on a Hurco VM20i vertical mill and a DMG MORI NLX 4000|750  lathe. The company then welds these together to create its collapsible drill heads. Even after welding, small details and features on these parts are vital to successful operation of the drill head:

1. The Central Pillar. The hexagonal central pillar of the drill head is designed to better withstand the stresses of horizontal drilling. To create it, the company pre-drills six points, then uses an end mill to peck around the OD before machining the interior. For this part, the company uses alloy steel to ensure the torque load does not strip out the hex. Barbco also creates larger versions of the part with six- and seven-inch edge-to-edge diameters using the Johnford DMC-4100PH, but this (relatively) smaller version was machined on the shop’s Hurco VM20i.
2. Wing Cutter Bolt Holes. Barbco uses a bolt through the upper and lower holes here to attach its “wing” cutter. This is the same as the cutters on the rest of the drill head, except the wing cutter starts at a 90-degree angle to the spokes of the drill and can rotate 100 degrees on a pin to extend the effective cutting diameter beyond the casing diameter. Barbco drills and taps holes both to secure the cutter and to ease access to the pins for end-of-life replacement.
3. Varied Cutter Configurations. To ensure full drilling coverage of the hole, Barbco uses three configurations of cutters with different bit angles. Staff marks numbers on the in-process part to indicate which style of cutter to weld onto each space. In addition to the cutters welded onto the head, the central pillar will play host to a either a pilot drill or a tri-cone arrangement of three cutters.

To learn more about the machines that make this part, read “Three-Axis Bridge Mill Opens New Doors for Construction OEM.”