Why do suppliers suggest ground ball screws when I mention low order quantities?

Fundamentally, this is a trade-off between "tooling constraints" and "machine tool flexibility."

For suppliers, producing **rolled ball screws** in custom sizes involves not only a bottomless pit of costs but also significant technical challenges; in contrast, **ground ball screws** inherently offer the flexibility required for made-to-order production.

The specific reasons can be broken down into four key dimensions:

1. Rolling is constrained by tooling; grinding is controlled by programming.

* **Rolled Ball Screws (Cold-rolled)**: The threads are formed by forcibly squeezing the material between a pair of massive, high-hardness rollers (dies).
* If a customer requires a specific lead, pitch, or non-standard outer diameter, the supplier must **redesign and manufacture a brand-new pair of rollers**.
* The cost of creating these roller dies is extremely high (often tens to over a hundred thousand yuan), and the development cycle is long. If the order quantity for a custom size is only a few or a few dozen units, the amortized tooling cost becomes prohibitively expensive.

* **Ground Ball Screws**: These are produced by grinding the material pass-by-pass using a CNC grinding wheel (cutting tool).
* For custom dimensions, engineers simply need to modify the wheel dressing parameters, tool path, and program settings on the CNC thread grinding machine.
* There is no need for expensive, custom-made dies; only the profile of a standard grinding wheel needs adjustment. Consequently, **the grinding process is viable even for a single custom-sized ball screw**.

2. Custom dimensions often entail "non-standard shaft ends" and "special geometric tolerances."

When a buyer requests a "custom size," it rarely involves just the threaded section; it often comes with additional requirements such as:

* Custom shaft-end stepped profiles (e.g., for mounting non-standard bearings).
* Extremely strict tolerances for coaxiality and total runout over the entire length.
* Excessive lengths or unusual length-to-diameter ratios. **Cold-rolling** involves continuous extrusion along a solid steel rod; this process generates immense internal stress, causing the leadscrew to undergo slight bending or twisting. For non-standard sizes with unusual length-to-diameter ratios, straightening becomes impossible after rolling, and form and position tolerances far exceed acceptable limits.
In contrast, **ground leadscrews** undergo precision machining (grinding) after heat treatment (quenching) and stabilization, while secured between centers. This process ensures perfect axial alignment, straightness, and geometric tolerances, even for complex structural designs.

3. Demand for special sizes cannot justify the "minimum rolling quantity" required for cold rolling

Cold-rolled leadscrews are **mass-produced, assembly-line** industrial products.

* The rolling equipment is massive; machine setup, trial rolling, and tool alignment consume significant raw materials and man-hours (machine setup alone can result in over ten meters of wasted steel).
* Consequently, cold-rolling facilities typically enforce strict "minimum rolling quantities" (MOQs).
* Market demand for special sizes (non-standard parts) is extremely low—often limited to high-end research institutes, automation R&D projects, or replacement parts for specialized machinery—with order volumes frequently in the single digits. Attempting to produce these via cold rolling would result in more material waste during setup than the actual quantity ordered by the customer.

4. Unwritten market rules: Special sizes often demand high performance

In the industrial sector, equipment requiring "special sizes" is rarely standard material handling or palletizing machinery; instead, it typically involves **highly customized precision instruments, aerospace components, semiconductor or medical equipment, or high-end military-grade machine tools**.
While these applications require specific dimensions, they also demand exceptional **rigidity, transmission efficiency, minimal backlash, and high positioning accuracy**. Since the equipment involves "high-end customization," the precision of cold-rolled C7-grade screws cannot meet the overall design specifications; only ground-grade screws (C3/C5) can match the performance standards of such specialized machinery. ---

> 🛠️ **In a nutshell:**
> **Rolling** is about mass production driven by tooling; changing dimensions requires a significant investment of time and money to create new molds. In contrast, **grinding** is akin to high-end customization driven by algorithms; changing dimensions simply requires adjusting the grinding machine's parameters. Therefore, when dealing with low-volume, high-precision, or non-standard dimensions, suppliers will invariably choose to produce **ground ball screws**.