Every machine shop wants to get as much material removed as quickly as possible without any tool failure. Unfortunately, standard slotting will often cause issues such as excessive heat, chip packing and a large amount of gullets due to the cutter being fully engaged within the workpiece. However, using Trochoidal Milling can help with this issue. Using the correct cutter, such as a STS Endmill, will provide a strong tool path with lots of gullets and resistance to heat. This guide is designed to explain this in simple terms.
What Is Trochoidal Milling?
Trochoidal milling is a toolpath strategy where the cutter moves in a series of small circular or looping arcs while it travels forward. This is different from conventional slotting, where the tool cuts with its full diameter in a straight line.
In a trochoidal path:
- The cutter touches only a small part of the material at any moment.
- The tool uses its full flute length (deep axial depth of cut).
- The radial engagement stays small and constant.
- The tool gets a short time out of the cut on every loop, which lets it cool.
This approach is also called dynamic milling or high-efficiency milling (HEM), and it is common in modern CAM software. It works best on CNC machines with good rigidity and a stable spindle.
Why Material Removal Rate Matters
Material Removal Rate (MRR) is the volume of material removed in a minute. It is most commonly calculated using radial cutting width, axial depth of cut and feed rate.
A higher MRR will reduce cycle time and reduce the per part cost. However, increasing MRR in a traditional slotting operation can be very risky. If cutting at full width you will be experiencing high cutting forces, increased temperatures and poor chip evacuation. This will cause vibrations, tool wear and sometimes sudden tool failure.
Trochoidal Milling increases MRR by cutting deep with low cutting widths. Due to a low radial engagement you can increase feed rate significantly and a higher axial depth. This will increase the volume of material removed per minute whilst keeping the load on the tool under control.
The Role of a Solid Carbide End Mill
Trochoidal toolpaths need a cutter that can handle deep cuts, high speeds and repeated entry and exit from the material. This is where a solid carbide end mill performs better than high-speed steel.
Carbide offers:
- High hardness that keeps the cutting edge sharp at high temperatures.
- High stiffness, so the tool bends less under load.
- Good wear resistance, which is vital in stainless steel, alloy steel and titanium.
Trochoidal milling uses the whole length of the flutes. That puts the entire cutting edge to work and spreads wear evenly instead of concentrating it at one point near the tip. A quality carbide end mill is made to take advantage of this.
How a Well-Designed Cutter Improves Material Removal
A tool made for high-efficiency milling improves results in several practical ways. The following points explain how an STS carbide end mill supports each stage of the process.
1. Strong Core and Flute Geometry
A good cutter balances flute depth with core strength. Deep flutes carry more chips, but too much material removed from the core makes the tool weak. A well-designed STS endmill keeps a sturdy core while still offering enough chip space, which allows heavy axial cuts without excessive deflection.
2. Better Chip Evacuation
In slotting, chips get trapped between the tool and the walls of the slot. In trochoidal milling there is open space around the cutter, so chips can leave more easily. Polished flutes and the right helix angle help chips slide out smoothly. Clear chips mean no re-cutting, which protects both the tool and the surface finish.
3. Controlled Heat
Because the cutter spends part of each loop outside the material, heat is carried away by the chips and the air or coolant. A heat-resistant coating, such as AlTiN or TiAlN, adds another layer of protection. This keeps the carbide hard and slows down thermal cracking on the edge.
4. Reduced Vibration
Many cutters use variable pitch or variable helix designs. These break up the rhythm of the cutting forces and reduce chatter. Less chatter means a better finish, longer tool life and the ability to run at higher feeds.
5. Consistent Edge Quality
Accurate grinding and a sharp, well-prepared edge help the tool cut cleanly from the first loop to the last. Uniform edge quality is important because trochoidal paths make thousands of small entries and exits.
Key Features to Look for in a Carbide End Mill
Choosing the right tool matters as much as choosing the right toolpath. Look at these points before you buy or program:
- Number of flutes: Four to seven flutes are common for trochoidal work in steel and stainless steel. More flutes allow higher feed rates, but chip space gets smaller, so match the flute count to the material and the engagement.
- Flute length: Choose a length that fits your planned axial depth. Do not use a longer tool than you need, because extra stick-out reduces stiffness.
- Corner radius: A small corner radius makes the corners stronger and reduces chipping.
- Coating: Pick a coating suited to the work material. Hard, heat-resistant coatings work well for steel and stainless steel, while polished or specialty coatings suit aluminium and non-ferrous metals.
- Shank tolerance and runout: Low runout spreads the load across all teeth. Poor runout makes one tooth do most of the work and shortens tool life.
- Hardness rating: Match the tool to the workpiece hardness, such as 55 HRC or 65 HRC grades for harder steels.
Cutting Parameters: A Simple Starting Guide
Always follow the tool maker’s cutting data first. The points below are general guidelines used in many shops, not fixed rules.
- Radial engagement: Usually about 5% to 15% of the tool diameter for trochoidal paths.
- Axial depth of cut: Often one to two times the diameter, or more if the setup is rigid and the tool is designed for it.
- Step-over of each loop: Keep it small and constant to avoid sudden load spikes.
- Feed per tooth: Because of chip thinning, the real chip thickness is smaller than the programmed feed per tooth. When radial engagement drops below about half of the diameter, you can raise the feed to bring the chip thickness back to a healthy level.
- Cutting direction: Climb milling is preferred, as it gives a cleaner cut and less heat in the tool.
- Coolant: Use air blast, mist or through-coolant to push chips away and keep heat low.
Start at a conservative setting, listen to the cut, check the chips, and then increase feed in small steps.
Understanding Chip Thinning
One reason for the effectiveness of trochoidal milling is chip thinning. With a small cut made by the tool, the chips produced are very thin. Thin chips remove less heat from the tool. If the feed is too low, rubbing can occur.
This can be overcome by increasing the feed rate during programming. Many CAM packages will do this automatically. This results in a high MRR for the tool as it is cutting with a carbide end mill which has strong edges. The tool will also run cool.
Best Materials for Trochoidal Milling
Trochoidal toolpaths are useful in many materials, especially the difficult ones:
- Stainless steel: It work-hardens and holds heat. Light, constant engagement avoids both problems. A sharp STS carbide end mill with a suitable coating can keep the cut stable.
- Titanium and heat-resistant alloys: These conduct heat poorly, so the heat stays at the cutting edge. The short contact time of trochoidal cuts helps a lot here.
- Hardened steel: Lower radial loads reduce the chance of chipping the edge.
- Alloy and tool steels: Deep slots and pockets are removed faster and with less tool wear.
- Aluminium: It can be milled very fast, but needs a cutter with polished flutes to prevent chip welding.
Common Mistakes to Avoid
Even the best cutter cannot fix a poor setup. Watch out for these frequent errors:
- Feeding too slowly. This causes rubbing and heat instead of clean cutting.
- Using a long tool when a short one will do. Extra length increases deflection.
- Sharp direction changes in the toolpath. Sudden changes spike the load. Use smooth, rounded transitions.
- Ignoring runout. Check the holder and collet before you blame the tool.
- Poor chip clearing. Re-cut chips destroy edges quickly.
- Skipping tool-wear checks. Inspect the edge regularly and replace the tool before it fails.
Tips to Improve Tool Life
- Use a rigid, balanced tool holder and clean collets.
- Keep the workpiece clamped firmly.
- Use the full flute length so wear spreads along the edge instead of concentrating at one point.
- Keep the engagement angle steady, since sudden jumps in load cause micro-chipping.
- Record your tool life and cycle times, then adjust settings based on real shop results.
Frequently Asked Questions
1. What is trochoidal milling used for?
Trochoidal milling is used to cut slots, pockets and deep cavities in tough materials. The tool moves in small looping arcs with low radial engagement, which reduces heat and cutting force. It allows deeper cuts and higher feed rates, giving better material removal rates and longer tool life than conventional full-width slotting.
2. Why is a carbide end mill better for high-efficiency milling?
A carbide end mill stays hard and stiff at high temperatures, which suits fast feed rates and deep cuts. It resists wear better than high-speed steel, especially in stainless steel, titanium and alloy steel. This stability helps maintain accuracy, surface finish and tool life during long trochoidal cuts that use the full flute length.
3. How does an STS endmill help in trochoidal milling?
An STS endmill with a strong core, good flute geometry and a heat-resistant coating can handle deep axial cuts and light radial engagement. Its design supports smooth chip flow, lower vibration and steady edge wear. These features allow higher feed rates and more consistent material removal during dynamic toolpaths.
4. What radial engagement should I use?
For most trochoidal toolpaths, radial engagement of about 5% to 15% of the cutter diameter is a common starting range. The best value depends on the material, machine rigidity, tool length and coolant. Always check the tool maker’s cutting data and increase settings slowly while watching chip shape and sound.
5. How can I make my end mill last longer?
Use low runout holders, keep tool stick-out short, and choose a coating that matches the material. Maintain smooth toolpaths without sharp load changes, and use the full flute length. Clear chips with air or coolant. Inspect the cutting edge regularly and replace it before heavy wear causes poor finish or breakage.
Conclusion
Trochoidal milling changes the way machinists think about slotting and pocketing. By cutting light and deep instead of wide and shallow, it lowers heat and force and raises material removal rates. The results depend heavily on the cutter, so choosing a strong, well-ground STS endmill with the right flute count, coating and geometry is just as important as writing a smart toolpath. Pair it with correct feeds, stable holding and good chip control, and you will see faster cycle times, better surface finish and longer tool life.
If you are looking for a dependable source for cutting tools, Jaibros offers a wide range of carbide cutters, endmills, holders and measuring instruments for CNC work.