Mastering Tungaloy Helical Milling: Optimize Tooling Strategy

Have you ever needed to machine a hole or pocket where a drill was not the right diameter, or where a large-diameter hole needed more flexibility? In such cases, helical milling, in which a milling cutter follows circular interpolation while feeding in the Z direction, can be a highly effective option.

Helical milling is useful for opening holes without a pilot hole and for machining large holes that are difficult to cover with drills. A key advantage is that one cutter can often cover multiple hole diameters. This can help reduce tool inventory and simplify machining processes.

On the other hand, once you start setting actual conditions, many checks are required: which cutter diameter is suitable for the target hole diameter, how large the helical pitch can be, whether the ramping angle is within the tool specification, and whether feed correction is needed. In other words, helical milling is very useful when applied correctly, but easy to get lost in when selecting tools and conditions.

This article explains the fundamentals of helical milling, the tool-selection flow, ramping-angle and pitch calculation, and key machining cautions in a practical order. It also introduces an in-page calculator and a separate tool selector that helps find candidate Tungaloy cutters from your input conditions.

What Is Helical Milling?
Helical milling is a machining method in which the tool follows circular interpolation while feeding in the Z direction at the same time. Instead of plunging straight down, the tool moves downward little by little while drawing a circle, creating a helical tool path.

This method is used for holemaking, pocket-entry machining, counterboring, and opening holes without a pilot hole. It makes it easier to machine hole diameters larger than the cutter diameter, and the same cutter can often be used for multiple hole sizes.

However, in helical milling the tool is always entering the workpiece at an inclined angle. Unlike ordinary side milling or slotting, you need to check the ramping angle, helical pitch, tool-center path, and feed correction.

In helical milling, any cutter that fits inside the hole diameter is not automatically suitable. You need to confirm whether the tool supports helical milling, whether the hole diameter is within the minimum and maximum supported helical-hole range, and whether the pitch and ramping angle are within the tool specifications.

Types of Cutters Used for Helical Milling
The main candidates are shoulder milling cutters with ramping capability and high-feed cutters with ramping capability. For both types, confirm whether the tool can be used for helical milling, what the maximum ramping angle is, and whether the target diameter falls within the minimum and maximum helical-hole range.

For Roughing, High-Feed Cutters Are Usually the First Choice
When helical milling is used as a roughing process, it is reasonable to start by considering a high-feed cutter. Although high-feed cutters may have a smaller maximum depth of cut APMX, they can often apply a higher feed rate, which is advantageous for productivity.

Depending on the machining distance and tool-center path diameter, the maximum ramping angle of a shoulder cutter can become the limiting factor, preventing the cutter from fully using its available APMX. Therefore, a high-feed cutter can be advantageous even when its APMX is smaller, because it can apply higher feed conditions.

Where Shoulder Milling Cutters Are Effective
There are also cases where shoulder milling cutters are advantageous. Consider a shoulder cutter when workpiece rigidity is low or when the appearance of the machined hole wall is important.

This section outlines the practical flow for selecting a milling cutter for helical milling. First, set the candidate cutter diameter and confirm whether the tool can cover the target hole diameter. Then the flow branches depending on whether you decide the helical pitch first or the ramping angle first.







Method 1. Decide the Helical Pitch First
When deciding the helical pitch first, check whether the pitch exceeds the tool's APMX. If it is acceptable, apply that pitch and calculate the ramping angle from the tool-center travel distance and pitch.




Method 2. Decide the Ramping Angle First
When deciding the ramping angle first, check whether the angle exceeds the candidate tool's maximum ramping angle. If it is acceptable, apply that ramping angle and calculate the helical pitch from the tool-center travel distance and ramping angle.




Because the tool enters at an angle while moving along a circular path, helical milling requires more condition checks than ordinary side milling. In particular, always check ramping angle, pitch, feed correction, and chip evacuation.

Do Not Make the Ramping Angle Too Large
As the ramping angle increases, the load on the cutter shoulder and insert increases. Even when the angle is within the maximum ramping-angle limit, chatter or chipping can occur depending on work material, machine rigidity, and overhang length.

Keep the Helical Pitch Within APMX
Helical pitch is the amount of Z-axis depth per revolution. If the pitch is too large, it may exceed the tool's APMX and lead to chip clogging or chatter.

Be Careful: Tool-Center Travel and Cutting-Edge Travel Are Different
In helical milling, NC commands are based on the tool-center path. However, the actual cutting occurs at the tool periphery.

In internal helical milling, the tool-center path diameter is smaller than the machined hole diameter. Therefore, the travel distance of the tool center and the travel distance of the cutting edge are not the same.

If catalog feed values are commanded directly as tool-center feed, the actual feed at the cutting edge may become larger than expected. Check the tool-center command feed and feed correction so that the feed at the cutting edge does not become excessive.

As described above, helical milling requires checking the hole diameter, cutter diameter, pitch, ramping angle, and feed correction in sequence. The formulas themselves are not difficult, but doing the calculations manually every time is time-consuming. If APMX or maximum ramping angle checks are missed, the condition may exceed the tool specifications.

For this reason, using a calculator that automatically calculates ramping angle and pitch is an efficient way to review helical milling conditions. The calculator below can switch between pitch-to-angle and angle-to-pitch calculation modes.

After calculating ramping angle and helical pitch, the next question is which cutters can be used under those conditions. In helical milling, the hole diameter, cutter diameter, APMX, maximum ramping angle, and min/max helical-hole range must be checked together, which can make catalog-based searching time-consuming.

To support this check, a separate tool selector is available for finding candidate Tungaloy cutters from your input conditions. By narrowing down candidate cutters in the tool selector, you can review helical milling conditions more smoothly.

Summary
Helical milling is a machining method in which the tool follows circular interpolation while feeding in the Z direction. It is useful for large holes that are difficult to machine with drills and for pocket-entry machining, but incorrect condition setting can increase tool load significantly.

In helical milling, calculations and tool selection should not be considered separately. It is important to check hole diameter, cutter diameter, pitch, ramping angle, feed correction, and tool specifications as one continuous workflow.

Calculate ramping angle and pitch.

www.tungaloy.com