## 1 Introduction
This is due to the variability of ways to define these parameters, the units used and the different nomenclatures, which generate an important focus of problems when approaching the study, understanding, choice and definition of parameters, and application of calculations. This makes it difficult and even prevents in many cases comparability between different studies and the reproducibility of the tests. Therefore, at the same time it is proposed to establish a common nomenclature to avoid the ambiguities and difficulties that arise in this regard (Table 1). The difficulties found are associated with the kinetics of the process. In helical milling, the holes are obtained through the combination of the rotation movement of the tool together with its translation along a helical trajectory (feed rate). At the same time, the movement of the tool on the helical trajectory is a relative movement between the tool and the part that can decompose into a circular movement on the work plane and an axial movement perpendicular to it (generating the tangential and axial feed rate) (Figure 1). \begin{table}
\begin{tabular}{l l l} \hline \hline
**Parameter** & **Nomenclature** & **Units** \\ \hline Cutting speed & V\({}_{\text{c}}\) & m\(\cdot\)min\({}^{-1}\) \\ \hline Feed rate & V\({}_{\text{f}}\) & mm\(\cdot\)min\({}^{-1}\) \\ \hline Tangential speed & V\({}_{\text{fht}}\) & mm\(\cdot\)min\({}^{-1}\) \\ \hline Peripheral speed & V\({}_{\text{f}}\) & mm\(\cdot\)min\({}^{-1}\) \\ \hline Axial speed & V\({}_{\text{fha}}\) & mm\(\cdot\)min\({}^{-1}\) \\ \hline Tangential speed per tooth & f\({}_{\text{zt}}\) & mm\(\cdot\)tooth\({}^{-1}\) \\ \hline Axial speed per tooth & f\({}_{\text{za}}\) & mm\(\cdot\)tooth\({}^{-1}\) \\ \hline Ramp angle & \(\alpha\) & degrees \\ \hline Pitch per helical revolution & a\({}_{\text{p}}\) & mm \\ \hline Bore diameter & D\({}_{\text{b}}\) & mm \\ \hline Tool diameter & D\({}_{\text{t}}\) & mm \\ \hline Helix diameter & D\({}_{\text{h}}\) & mm \\ \hline Spindle speed & n & RPM \\ \hline Tool teeth & z & Units \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Proposed Nomenclature for kinematic parameters of the helical milling process. In this sense, three aspects have been detected as sources of imprecision, in addition to the variability of nomenclature used. First of all, the \"Sense of rotation\". This parameter is a categorical variable that makes it necessary to duplicate experimental tests, and although the importance of the machining direction (up milling, down milling) is known in conventional milling [24; 25; 26], there are many helical milling research works in which there is no reference to this parameter. It is considered absolutely necessary to identify this parameter in the process in order to correctly evaluate and compare the results. Secondly, there are the parameters that define tangential feed rate and the units used. There is a problem associated with the difference between orbital or tangential speed (V\({}_{\text{fht}}\)) (speed developed by the centre of the tool while describing the orbit), and peripheral speed (V\({}_{\text{ft}}\)) (described by the main cutting edges of the mill). Figure 2 shows the tangential and peripheral speed of the tool in its translation movement. \[V_{fht}=\frac{V_{ft}\cdot(D_{b}-D_{t})}{D_{b}} \tag{2}\]  
\[V_{ft}=f_{zt}\cdot z\cdot n \tag{3}\]  
The units must be correctly defined, the feed per tooth must be referred to the hole perimeter, which is related to the peripheral speed, as defined by [PERSON] and [PERSON] in their respective  
Figure 1: Kinetic decomposition of helical movement. Figure 2: Tangential and peripheral speed. papers [17; 27]. From Equations (2) and (3) essential information for the calculations is identified and must be defined. Table 2 shows in blue the values provided in the papers, in orange the values calculated, and in in grey where there is a different result for each spindle speed, highlighting those that are not reproducible because of an absence of information.