How to Choose the Best CNC Screw Machine?

Decision Dimension	What to Define	Example Production Requirement	Machine Selection Implication
Part envelope	Maximum and minimum part diameter, overall length, and any features that must be machined from the bar.	A turned component with a 12 mm maximum diameter and a 45 mm finished length.	Choose a bar capacity and working envelope that accommodate the stock and finished part, while allowing for cutoff and workholding needs.
Material	Specify the exact alloy or material grade, condition, hardness, and whether the stock is bar, wire, or pre-cut blank.	Free-machining steel, stainless steel, brass, or aluminum bar stock.	Confirm spindle power, tooling, coolant, chip control, and cutting data are suitable for the material. Stainless steel may require different tooling and process settings than brass.
Part geometry	List turned diameters, shoulders, grooves, threads, cross-holes, flats, slots, and required back-working features.	A small shaft with two diameters, an external thread, and a cross-drilled hole.	Simple turned geometry may suit a basic configuration. Multiple side features or work on both ends may call for live tooling, a sub-spindle, or additional stations.
Tolerances and finish	Identify critical dimensions, geometric tolerances, surface-finish requirements, and inspection methods.	A critical diameter controlled to ±0.02 mm, with a specified surface finish on a bearing surface.	Assess machine condition, thermal stability, tooling, workholding, process capability, and measurement strategy. Confirm achievable capability with a production trial.
Annual and lot volume	Estimate annual demand, typical lot size, delivery schedule, and expected mix of part numbers.	200,000 parts per year in repeat production, or several smaller lots across a broad part family.	High, stable demand can justify investment in automation and dedicated tooling. Lower or variable demand may favor easier setup and flexible programming.
Cycle-time target	Define the required output rate and whether the target includes loading, inspection, tool changes, and downtime.	A target of 30 finished parts per minute, subject to validation on the actual part and material.	Compare complete process cycle times, not just cutting time. Simultaneous operations and reduced handling may improve output, but the result depends on part geometry and process conditions.
Bar capacity and feeding	Specify stock diameter, bar length, straightness, remnant requirements, and the planned loading method.	Continuous production from long bar stock with unattended running between operator checks.	Match the feeder to the machine's approved bar range and material. Consider floor space, bar support, noise, material handling, and safe replenishment.
Machine configuration	Determine whether the part needs single-spindle turning, multiple spindles, gang tooling, a sub-spindle, or live tooling.	A component requiring front turning, rear-end machining, and a radial milled feature.	Select the simplest configuration that completes the required operations efficiently. More axes or spindles can reduce handling but may increase setup and maintenance complexity.
Tooling and changeover	Estimate the number of tools, expected tool life, setup frequency, and need for quick changeovers.	Several part numbers share similar diameters but require different thread forms and groove locations.	Check tool capacity, adjustment access, presetting options, program management, and the time required to change between part families.
Quality and traceability	Define inspection frequency, critical-to-quality features, documentation, and any required lot or material traceability.	In-process checks for critical diameters, with recorded inspection results for each production lot.	Plan for suitable gauges or measurement equipment, process monitoring, sampling, and data handling alongside the machine purchase.
Factory requirements	Check available floor space, electrical supply, compressed air, coolant management, chip handling, and operator access.	A production cell with limited floor space and a centralized coolant and chip-management system.	Verify installation requirements and the full cell footprint, including the bar feeder, service access, chip conveyor, and material staging area.
Total operating cost	Estimate purchase and installation costs, tooling, maintenance, energy, labor, and expected uptime.	A comparison based on cost per accepted part over the planned service life.	Evaluate total cost of ownership and production risk, not purchase price alone. Include training, service availability, spare parts, and planned maintenance.