Tips for Machining Large-Diameter Holes

Helical interpolation with indexable high-feed tooling

Hole making is both a time- and tool-consuming process for many shops. Helical interpolation with indexable tooling is a great way to tackle this challenge quickly – and it's an especially advantageous approach when creating larger-diameter holes.

Although you can helix with a variety of tool types, high-feed takes its benefits to another level. Here, we'll machine a 4" diameter hole in 2.5" thick 4140 PH steel on a 40-taper machining center. Total cycle time? Just two and a half minutes, running somewhat conservatively.

Benefits of high-feed helical interpolation

Helical interpolation offers a crazy-fast way to machine holes, but there are benefits beyond your cycle times.

Low tool pressures
Very easy to program, especially on newer CAM packages
Create many hole sizes with a single tool by simply updating your program
Utilizes low horsepower, so both small- and large-diameter holes can be made quickly and easily on even a 40-taper machine
Eliminates the need for time-consuming starter holes and step cuts

While high-feed tooling will generate a scalloped wall finish, it provides the shortest cycle times by far, and it works very well in more challenging long-reach scenarios.

Learn more about our indexable high-feed tooling.

Tips for hole helixing

Choose a cutter that can handle your hole size without leaving material at the center, and that will leave the desired wall finish
The insert must cover the hole's center line, or you'll need to drill a start hole first
Recommended minimum 1/2 insert IC for center overlap
Maximum hole size = 2xD (for single pass)
Position the tool at the 3 o’clock position over the hole to be machined, .100” above the part to start, with the OD of tool at the ID of finished hole size
Execute G02 (CCW arc), with I-value = interpolation radius, Z-value = pitch; repeat the number of times necessary to reach bottom
Add a straight G02 pass (no Z-value) for flat-bottom hole
0.5 to 1.0 degree ramp angles are typically recommended, depending on hole size – more important is to specify a depth per hole revolution (pitch) that will allow good chip evacuation
Feed rate does not typically need to be adjusted, unless chip evacuation is an issue
Excellent air blast or high-pressure coolant is necessary for chip evacuation, especially on VMCs

Have questions about implementing this approach?

Contact an applications specialist

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