Mini Type SFK Series Ball Screw

Main Technical Parameters and Design
Precision Manufacturing: The grinding of the ball screw shaft raceway, the processing of the nut, and the assembly of tiny steel balls (with diameters possibly less than 1mm) require extremely high manufacturing precision.
Structural Innovation: May employ end-cap circulation or special miniature recirculators to accommodate the extremely small internal space.
Materials and Heat Treatment: High-strength alloy steel is often used and subjected to special heat treatment to ensure sufficient strength and wear resistance at miniature sizes.
Accuracy and Performance: Available in C5, C7, and even higher precision grades. Due to its extremely small lead, it can often achieve sub-micron precision displacement control.
Specifications and Selection: Offers extremely small shaft diameters from φ3mm to φ10mm, with leads typically of 0.5mm, 1mm, 2mm, etc. Users need to carefully calculate load, speed, and lifespan.

Applications
The Mini type SFK series ball screw is the ideal power source for the following miniaturized and lightweight cutting-edge equipment:
Micro-automation and Robotics: Desktop micro-robotic arms, micro-motion platforms in chip packaging equipment, joint drives for bionic micro-robots.
Precision Optics and Instruments: Fiber optic alignment equipment, micro-adjustment axes for laser engraving machines, automatic focusing mechanisms for microscopes.
Medical and Laboratory Equipment: Cell manipulators, gene sequencers, precision feeding mechanisms for microfluidic chips, fine end-effectors for surgical robots.
High-end Consumer and Model Products: High-precision 3D printer nozzle lifting, professional camera sliders, rudder control for high-end model aircraft.

The Mini type SFK series ball screw is an outstanding representative of precision engineering's advancement into the microscopic realm. It breaks the limitations of "efficient and precise transmission being difficult to achieve in small spaces," condensing the essence of ball screw technology into a compact design. Choosing the SFK series means equipping your miniaturized innovative products with professional-grade, highly reliable core motion components, which is key to creating differentiated competitiveness and a superior product experience.

_Parameters

_Drawings

_{Supports Product Combination Selection}

_{Production Capacity}

Cyclone Milling Machines LWN160-6000mm Leistritz Cyclone milling machines imported directly from Germany, the ball screw shaft precision can be C3, C5, and C7 the max length can be 7000mm

Rolled Thread CNC Machines ST-20.2 and ST-347.7 rolled thread ball screw machines from TaiWan. The ball screw shaft precision can be C7 - C10

Ball Screw Assembly Workshop We conduct nut assembly in a constant temperature workshop,  all workers having decades of work experience and zero clearance between the screw and nut.

Ball Screw Assembly Workshop One ball screw shaft matches one ball screw nut. Because each ball screw shaft has a very tiny different tolerance. There are dozens of different ball sizes for different screw shaft. Our ball screw shaft and nut can be interchanged with the Taiwan TBI ball screw shaft and nut very well.

_{Model Code Explanation} 

_{Design Accuracy}

1-1-1 Lead/Travel Accuracy

According to the standard of JIS,we classified our lead accuracy through E,e,e3oo and e2m four main regulations.As figure 1.1.1～1.1.3 shown in below, all the definition and tolerance are specified.To test the accumulated travel deviations for grade C7 and C10, the tolerance wll be chosen in random 30omm of useful length and evaluated if it is qualified with the e300 table of 1.1.3.

Fig 1.1.1 Diagram of Lead Accuracy

Terms	Reference	Definition	Allowable
Travel Compensation	T	Travel compensation is the deduction between specified and nominal travel in the useful travel. A slightly smaller value compared with nominal travel is often selected by customer, to compensate for an expected elongation caused by temperature rise or external load. Therefore"T "” is usually a negative value. Note:if no compensation is needed,specified travel is the same as nominal travel.	Table 1.1.2
Actual Travel		Actual travel is the axial displacement of the nut relative to the screw shaft.
Mean Travel		Mean travelis the linear best fit line of actual. This could be obtained by the leastsquares method. This line represents the tendency of actual travel.
Mean Travel Deviation	E	Mean travel deviation is the deduction between mean travel and specified travel within travel length.
Travel Variations	e	Travel variations is the coverage of 2 lines drawn parallel to the mean travel. Maximum width of variation within the travel length. Actual width of variation for the length of 300mm taken anywhere within the travel length. Wobble error, actual width of variation for one revolution (2πt radian)	Table 1.1.2 Table 1.1.3 Table 1.1.3

Table 1.1.2 Mean Travel Deviation (±E) and Travel Variation (e) (JIS B 1192)

Table 1.1.3 International standard of accuracy grade for ball screw

Grade	C0	C1	C2	C3	C5	C7	C10
	3.5	5	7	8	18	50	210
	2.5	4	5	6	8

1-1-2 Axial Play

Axial play of WANGONG's precision ball screw is shown below:

Table 1.1.4 Classification of Axial Play

Excessive preload increases the friction torque and generates heat which wll reduce the life expectancy. However, insufficient preload will reduce stifness and increase the possibility of lost motion. WANGONG recommends that the preload applied on CNC machine tools should not heavier than 8% of the dynamic load; 5% for industrial automation X-Y table.

Table 1.1.5 The reference spring force of (P2)

Table 1.1.6 Axial Play (Po) Clearance in the Axial Direction of Rolled and Grind Ball Screw

1-1-3 Definition of Mounting Accuracy and Tolerance on Ball Screw

The main items of the mounting accuracy of ball screw are listed in below.
(1) Periphery run-out of the supporting part of the screw shaft to the screw groove.
(2) Concentricity of a mounting portion of the shaft to the adjacent ground portion of the screw shaft.
(3) Perpendicularity of the shoulders to the adjacent ground portion of tha screw shaft.
(4) Perpendicularity of the nut flange to the axis of the screw shaft.
(5) Concentricity of the ball nut diameter to the screw groove.
(6) Parallelism of the mounting surface of a ball nut to the screw groove.
(7) Total run-out of the screw shaft to the axis of the screw shaft.
All WANGONG ball screws are manufactured, inspected and guaranteed to be within specifications.

Fig 1.1.2 Mounting Accuracy and Tolerance

1-1-4 Preload Torque
As figure 1.1.3 shown in below, it specified allthe type of preload torque generated by rotating a preloaded ball screw.

Fig 1.1.3 Descriptions of preload torque

Glossary

1. Preload
To generate the inner force inside the ball screw to decrease the
clearance and increase the rigidity, a set of one gage ( approximately 2μ) larger steel balls is filled inside the nut or two nuts which are executing mutual displacement in axial direction.
2. Preload dynamic torque
The dynamic torque required for continuously rotating the screws shaft or the nuts under unload condition and the preload has applied to the ballscrews.
3. Reference torque
The targeted preload dynamic torque Fig 1.1.3-(1)
4. Torque variation values
The variation values of the targeted preload torque variation rates are specified.Take a positive or negative value relative to the reference torque.
5. Torque variation rate
The variation ratio of reference torque.
6. Actual torque
The actual measured preload dynamic torque of the ball screws.
7. Average actual torque
The arithmetic average of the maximal and minimal actual
torque values measured when the nuts are doing reciprocating
movements.
8. Actual torque variation values
After the nut doing reciprocating movements on the effective
length of the thread, the biggest variation tested will be the actual
torque variation value, which is covered between the positive and negative minimum value relative to the actual torque.
9. Actual torque variation rate
The rate of actual torque variation values in relation of the average
actual torque.

Table 1.1.7 Permissible ranges of toque variation rates

Remarks: 1. Slenderness is the value of dividing the screws shaft outside diameter with the screws shaft threading length.

_{Testing Equipment}
WANGONG has a comprehensive quality control management system and advanced testing instruments.

Profilometer Test and inspect the contour, two-dimensional dimensions, two-dimensional displacement, and contact angle of the ball screw nut.

Hardness Tester Used to measure the surface hardness and core hardness of ball screw materials.

Roundness Measuring Instrument Used to measure the roundness, cylindricity, coaxiality, concentricity, flatness,parallelism,verticality, radial deviation, thickness deviation, radial runout, radial total runout, diameter measurement, straightness, inclination, taper, diameter contour tolerance, straight contour tolerance, etc. of nuts.

Roughness Measuring Instrument The roughness measuring instrument can measure the surface roughness of various machined parts, including flat surfaces, inclined surfaces, cylindrical surfaces, curved surfaces, small holes, grooves, and axles.