When browsing specifications for a Linear Stepper Motor, you will often see specifications like “Tr8x8” or “Tr8x2.” Understanding what these numbers mean—and specifically the difference between Pitch and Lead—is critical for calculating whether the motor will meet your machine’s speed and precision requirements.
At AKT Motor, we offer a variety of lead options across our HSL series. This guide will help you do the math.
1. The Definitions: Pitch vs. Lead
The confusion often stems from the fact that for simple screws, pitch and lead are the same. But for efficient industrial motion control, they are often different.
- Pitch (P): The axial distance between adjacent threads. If you put a ruler on the screw, this is the distance from one crest to the next.
- Lead (L): The linear distance the nut travels for one full revolution (360°) of the screw.
- Starts: The number of independent threads running along the screw shaft.
The Formula:
Lead = Pitch × Number of Starts
- Example A (Single Start): Tr8x2 (Pitch 2mm, 1 Start). Lead = 2mm. (Slow, High Precision)
- Example B (Multi-Start): Tr8x8 (Pitch 2mm, 4 Starts). Lead = 8mm. (Fast, High Efficiency)
Takeaway: When calculating motion, always use the LEAD, not the pitch.
2. Calculating Resolution (Travel Per Step)
Most hybrid stepper motors (including our NEMA 8 to NEMA 23 series) have a step angle of 1.8°, meaning they take 200 steps to complete one full revolution.
To calculate the linear resolution (how far the load moves with a single step):
Resolution (mm/step) = Lead (mm) / 200 steps
Calculation Example: Let’s take an AKT 42HSL Series motor equipped with a standard Tr8x8 lead screw (8mm Lead).
Resolution = 8mm / 200 = 0.04mm per full step
Note: If you use a stepper driver with micro-stepping (e.g., 1/16), the resolution becomes even finer (0.04 / 16 = 0.0025mm).
3. Choosing the Right Lead for Your Application
Should you choose a high lead (e.g., 8mm) or a low lead (e.g., 1mm or 2mm)?
Scenario A: High Speed & Efficiency
If your application requires rapid movement—such as a pick-and-place machine or a fast axis on a CNC router—you need a High Lead.
- Why: A single rotation moves the load a considerable distance (e.g., 8mm). This allows the stepper motor to keep RPMs lower (where torque is higher) while achieving high linear speeds.
- Recommended Product: For high-speed applications requiring robust torque, the 57HSL Series (NEMA 23) paired with a Tr8x8 or larger lead is an excellent choice.
Scenario B: High Precision & Self-Locking
If your application requires fine positioning—such as focusing a microscope or a Z-axis that must hold position against gravity—you need a Low Lead.
- Why: A low lead (e.g., 1mm or 2mm) provides incredible mechanical advantage (force multiplication) and finer resolution. Additionally, screws with a lead angle of less than 5 degrees are typically Self-Locking, meaning the load won’t drop when power is cut.
- Recommended Product: The 20HSL or 28HSL series with Tr3.5 or Tr5 screws are standard for these precision tasks.
Conclusion
Selecting the right lead screw is a trade-off between speed and resolution.
- Need Speed? Go for a higher lead (e.g., 8mm).
- Need Precision/Holding? Go for a lower lead (e.g., 2mm).
For a complete list of available motor sizes and screw configurations, visit our Linear Stepper Motor Category. Our engineering team can also help you customize the screw length and lead to fit your specific project.