One of the key parameters in metal cutting applications is the “Chip-Load Per Tooth” (CPT). CPT is the average chip thickness that is removed with each cutting-tool tooth per one 360° cutting-tool turn. Producing the right CTP will result in increased tool life, better surface quality and cutting geometries.
In order to achieve optimum CPT, the Toodle™ must rotate in a specific rotation speed and a specific linear feed-rate. These two parameters must be optimized with reference to several conditions. These are machine condition, the material being machined, and spindle condition.
The work conditions affecting the feed-rate are:
- Spindle output power
- Spindle rigidity
- Tool-holder rigidity
- Tool edge dynamic-runout
- Tool sharpness
- Tool cutting angles
- Depth of cut/axial depth of cut (ap)
- Width of cut/radial depth of cut (ae)
- Clamping rigidity of the work material
- Machine rigidity
- Machine output power
It is important to note that high rotation speed and relative low feed-rate will deliver small chips – dust; whereas low rotation speed and relative high feed-rate will deliver larger chips.
For initial calculation of the feed-rate, one should use the following equation:
FR = N x CPT x S
- FR = Feed Rate [mm/min];
- N = Number of teeth;
- CPT = Recommended chip size [mm/tooth] and
- S = Toodle rotation Speed [rpm]
Each material to be processed has its own recommended CPT. Typically, for high-speed Toodle milling, CPT should be between 0.02 to 0.05 [mm/tooth]. It is relevant in this context that tool diameter has a direct influence on the CPT size: small tool diameter leads to smaller CPT. Also relevant is that the Toodle rotation speed is typically a function of the emulsion pressure, while the number of teeth is a function of the tool selected.
You may calculate the average chip thickness by using the following SFI web calculator:
For soft materials (e.g., Aluminum) increase the CPT. For hard materials (e.g., Steel) decrease the CPT.
While there are formulas for calculating feed-rates. optimum feed-rates are usually determined through trial and error.
When using the Toodle for high-speed milling applications, one should initially optimize the procedure according to CPT, using relatively small tool penetration (ap and ae) and high feed-rate.
Toolmakers normally recommend initial cutting speeds – Vc. Based on Vs it is possible to calculate the feed-rate.
Note that only the end-user is aware of, among other matters, its spindle condition, its machine accuracy, or its dynamic runout. Therefore, and since each and every machine has its own history (which affects its machining condition), and since no two machines perform exactly the same, the operator should take machine-specific conditions into account.
Due to the fact that the Toodle has a relatively low dynamic-runout and relatively low vibration-rate, one can operate the Toodle at higher cutting speeds than recommended by the tool-makers.
When using the Toodle it is best to increase the Vc and maintain low CPT by decreasing ap and/or ae.