I. What are some common machining precision issues in the market?
Many people think that “a difference of two or three micrometers doesn’t matter,” but this is not the case for drone motors. Common problems fall into these categories:
Misalignment between the stator housing inner hole and the bearing position:The inner hole houses the bearing, while the outer diameter positions the stator core. Misalignment leads to uneven air gaps, with one side larger than the other.
Excessive runout of the rotor housing end face: The rotor housing holds the magnets; excessive runout causes the magnets to oscillate, resulting in magnetic field fluctuations.
Insufficient cylindricity of the bushing: When the bearing is pressed in, it either deforms and jams or is too loose and wobbles.
Misalignment of the threaded hole position: Screws are tightened too much, causing stator housing deformation or uneven surfaces.
Substandard surface roughness:The bearing position roughness Ra is greater than 1.6, causing surface scratches during press-fitting and resulting in fit failure.
The root causes are not complex: unreasonable process design, insufficient equipment precision, and perfunctory quality control.
II. What impact do these problems have on the final product? Take a 3115 drone motor (air gap 0.3-0.5mm) as an example: a concentricity deviation of 0.05mm results in only 0.25mm on the smallest side of the air gap. The consequences are:
Increased torque pulsation → aircraft hovering and shaking
Increased eddy current losses → severe motor overheating and decreased efficiency
Limited maximum speed → originally 20,000 RPM, actually only 15,000 RPM
Sharpened bearing life → from thousands of hours to tens of hours
Interference with the flight control IMU → jelly effect in aerial photography, even crashes
Poor consistency → assembly line requires individual screening, leading to exponentially higher after-sales costs
Conclusion: Substandard CNC part precision directly leads to a collapse in motor performance.
III. Observation: Our Machining Experience and Customer Cases
1. Choosing the right material is half the battle.
Stator housing / Motor Cap: 6061-T6 or 7075-T6 are recommended. Ordinary 6061 is too soft; stress release after machining will cause dimensional drift of 0.01-0.02mm. 7075-T6 has high strength and is suitable for heavy-duty motors.
Rotor Housing : 7075 is commonly used, but thin-walled parts (1-1.5mm thick) must be rough-machined with allowance → allowed to rest for 24 hours to release stress → finish-machined. Otherwise, it will become elliptical as soon as the clamp is released.
Sleeves/Holders /Shaft: 303/304 stainless steel or SUS420 is recommended. 45# steel will rust, and drones often fly in humid environments.
Real Case: A customer of an agricultural drone experienced a rotor housing roundness change from 0.01mm to 0.08mm. Several companies tried different dynamic balancing services without success. We used 6061-T6 with a stress-relief process, stabilizing the roundness at 0.012mm, and the dynamic balancing passed on the first try.
2. Cutting Parameters and Clamping Method: Use PCD or single-crystal diamond tools for finishing. Aluminum alloy tools tend to stick to the tool, while ordinary tools quickly produce built-up edge.
The cutting fluid must be a high-concentration aluminum alloy-specific fluid. Insufficient chip removal and lubrication will cause dimensional inconsistencies.
Thin-walled part clamping: Use flexible chucks or soft jaws to avoid triangular shapes caused by three-jaw gripping the inner hole. For wall thicknesses <1mm, even use low-melting-point alloy filler for support.
FPV customer case: A 40,000 RPM motor previously had a roundness of 0.03mm, requiring repeated dynamic balancing. We switched to soft jaws + stress relief, achieving a roundness of 0.008mm and achieving G0.4 grade dynamic balancing in one go.
3. Temperature control is an invisible barrier. Aluminum alloy has a thermal expansion coefficient of 23ppm/°C. A 30mm diameter part with a temperature difference of 10°C results in a dimensional change of 0.007mm, while bearing fit tolerances are only 0.005-0.015mm. Therefore, our workshop maintains a constant temperature of 20±2°C, and parts are kept at this temperature for at least 30 minutes before measurement. During a winter night shift without air conditioning, all parts were found to be 0.01mm smaller than expected, leading to returns by the customer’s IQC.
4. Surface treatment can alter dimensions. Ordinary anodizing involves pickling, which slightly reduces dimensions; a thicker hard oxide film actually increases the dimension on one side. We will confirm the final treatment method with the customer before processing, allow for oxidation allowance, and protect precision holes with rubber plugs.
IV. Solutions: How does Kzron ensure precision and stability?
We manage it through five stages.
🔧 Stage 1: Process Review (Proactive Optimization)
After receiving the drawings, we conduct a manufacturability analysis. For example, if a customer specifies a minor dimension of ±0.005mm but omits the critical perpendicularity, we proactively offer suggestions to help the customer relax non-critical tolerances and tighten critical ones. We once improved a customer’s assembly yield from 92% to 99%.
🏭 Stage 2: Equipment and Capabilities
We possess 3/4/5-axis CNC milling and turning equipment. Key specifications:
Motor Housing: Critical dimensional tolerance ±0.01mm
Motor Mount: Flatness ≤0.01mm
Motor Shaft: Concentricity ≤0.003mm
Annual Production Capacity: 5 million units
Materials include 6061/7075 aluminum alloy, stainless steel, and titanium alloy. Surface treatments include sandblasting and hard/colored anodizing.
📋 Step 3: Process Control (SPC)
First piece 100% inspection → Only qualified pieces are batched.
During production, 3 pieces are randomly selected from every 20 pieces, and a control chart is created.
If a dimensional drift trend is detected (e.g., 5 consecutive points deviating from the upper tolerance) → immediately stop the machine, adjust the tool, or replace the tool.
Critical dimension Cpk requirement ≥ 1.33
🔬 Step 4: Pre-shipment Inspection
Bearing seats, bushing inner holes: 100% 100% inspection (pneumatic measuring instrument)
General dimensions: AQL sampling 0.65 or 1.0
Geometric tolerances: 5-10 pieces are randomly selected from each batch, measured with a coordinate measuring machine, and a report is generated.
All data is archived and traceable.
📄 Step 5: Shipment Report
Provided with the shipment:
Measured dimensional data
Cpk value
Processing equipment number, tool information
Measurement temperature
Dimensional comparison before and after surface treatment
Quality commitment: If the problem is confirmed to be ours, we will unconditionally rework or refund the product, and bear the emergency air freight costs.
V. Action Call: How to Choose a Supplier? Why Choose Kzron?
✅ Six Points to Consider When Choosing a CNC Supplier:
Thin-Wall Parts Experience: Directly ask, “What is the consistent roundness?” Be wary of suppliers answering 0.02mm; those achieving within 0.01mm demonstrate true expertise.
Constant Temperature Workshop:Without temperature control, dimensions will change between winter and summer.
Inspection Equipment: At least one coordinate measuring machine (CMM). Replace suppliers with only calipers and micrometers as soon as possible.
Sample Production Capability: Suppliers willing to produce 5-10 samples and help optimize your process are long-term partners.
Mass Production Cases: Suppliers who have produced similar motor parts and continue to place orders are reliable.
Surface Treatment Experience:Able to explain how to reserve oxidation allowance and protect precision holes.
💡 What Can Kzron Offer?
Focus on the Motor Industry: We only manufacture stator housings, rotor housings, motor end covers, motor mounts, shafts, stator cores, bushings, etc., not miscellaneous items.
15 Years of Experience: Over 5000 customized solutions, 5 million units delivered, serving FPV, industrial, agricultural, and eVTOL clients.
One-Stop Service: From prototypes and small batches to large volumes, 24-hour quotes and manufacturability analysis.
Transparent Data: Publicly available Cpk and dimensional distribution reports for each batch.
Flexibility + Batch Size: Supports multi-variety small-batch production, as well as large orders of 5 million units per year.
Rapid Response: 24-hour drawing review, 5-7 day delivery for urgent orders.
Finally, a word of advice: In the early stages of setting up a factory, entrust CNC machining to professionals and focus your energy on magnetic circuits, drives, and overall machine testing. Only consider buying your own machine tools when you achieve monthly sales of tens of thousands of units.
If you are looking for suppliers of CNC motor components for drones, or have drawings that require a quote, please visit our website: www.Kzron.com
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