Quick answer: A thread mill must be smaller than the thread it produces. If the cutter is too large relative to the thread, the helical toolpath can create a deviation in the thread profile. The suitable cutter diameter depends on the thread diameter, cutter diameter, profile angle and pitch. Use SmiProg, the SmiCut Catalogue or the THREAD MILL SELECTOR to confirm that the selected tool is suitable before machining.
Why Tool Diameter Matters in Thread Milling
When thread milling, the tool diameter must be smaller than the thread diameter. This is because the thread has a helix angle, while the cutting profile of the tool is straight. If the tool diameter is too large, it will cause a deviation in the thread profile.
The size of this deviation depends on several factors:
- Thread diameter
- Cutter diameter
- Profile angle
- Pitch
Deviation increases when the cutter diameter is large compared to the thread diameter, when the profile angle is small, and when the pitch is large.
However, an unnecessarily small cutter may reduce tool rigidity, cutting performance and process stability. The best choice is therefore the largest cutter diameter that is suitable for the thread diameter, pitch and profile.
SmiCut provides three methods for choosing the correct thread mill diameter. See below for more information.
SmiCut Catalogue
In the catalogue you can see which coarse or fine threads each thread mill can produce. Please note that a thread mill can always produce a larger thread than the one specified, provided it has the same pitch and profile.
Use the SmiCut catalogue to find the most suitable thread mill.
SmiProg – Software for Thread Milling
Use SmiProg to enter thread diameter, pitch and thread length. You get a list of suitable thread mills with the correct diameter for that thread. Select the thread mill to also receive recommended cutting data and a CNC program.
➜ SmiProg – Software for Thread Milling
Use SmiProg to find a suitable thread mill for your thread.
→ THREAD MILL SELECTOR
Go to the SmiCut Online Store and open THREAD MILL SELECTOR. There you can choose the thread you want to produce and get a list of all suitable thread mills with the correct diameter for that thread.
Example: M12
- Select THREAD MILL SELECTOR on the left.
- Select M – metric coarse thread.
- Select M12.
- Choose the type of tool you want, for example without internal coolant.
You can now see all solid carbide thread mills without internal coolant that can machine an M12 thread reliably.
THREAD MILL SELECTOR is a useful tool for finding recommended thread mills that can produce a thread within the required tolerance.
