Page 1595 - MISUMI Thailand Economy Series

[Technical Data]
Selection of Ball Screws 1

3. Axial Clearances of Ball Screws
Axial clearance does not affect positioning accuracy if the feed is unidirectional, but will generate backlash and negatively affect on
positioning accuracy if the direction or the axial load is reversed.
■Types of Rolled Ball Screws ■Types of Precision Ball Screws
Accuracy Screw Lead Screw Shaft Length(mm) Axial Clearance Accuracy Screw Lead Screw Shaft Length(mm) Axial Clearance
grade Type shaft dia. (mm) min. max. (mm) grade Type shaft dia. (mm) min. max. (mm)
08 02 100 400 08 02 210
02 02 100
10 600 10 315
04 0.05 or less 04 0.008 or less
04 04
12 500
12 05 800 10
10 150 05 150
05 15 10
C5 C－KBS
10 0.1 or less 20
15 1200
16 05
C－TBSE
C7 C－TBSB 20 20 10 200 900 0.015 or less
05 20
20 10 0.15 or less 05
20 25 10 300
2. Ball Screw Lead Accuracy 05 200 25
Ball screw lead accuracy is defined by JIS Standards property parameters (ep、vu、v300、v2Q).
Parameter definitions and allowable values are shown below. 25 10 2000
In general, a ball screw lead accuracy grade is selected by evaluating if the Actual Mean Travel Error of a candidate is within the allowable positioning error. 25
■Table 1. Positioning Screw (C Class) Actual Mean Travel Error (±ep) and Variation (u) allowances Unit : μm 05 0.2 or less
Thread Effective Length (mm) Accuracy Grade 32 10 300
C5
over or less Actual Mean Variation 32
Travel Error
315 23 18
315 400 25 20 Selection Example of Lead Accuracy Selection Example of Axial Clearance
400 500 27 20
500 630 30 23 <Requirements> <Requirements>
630 800 35 25 · Ball screw diameter F15, lead 20. · Ball screw diameter F15, lead 5.
· Allowable backlash Ú0.02mm
· Stroke 720mm
800 1000 40 27
1000 1250 46 30 · Positioning accuracy Ú0.05mm/720mm <Selection Details>
1250 1600 54 35 <Selection Details> When the screw shaft diameter is F15, C5 grade with axial clearance
■Table 2. Positioning Screws (C Class) variation per 300mm (300) Variation per rotation (2π) standard values Unit : μm Select an appropriate lead accuracy grade based on the application below 0.015mm can meet the condition of allowable backlash amount
Ú0.02mm.
requirements.
Accuracy Grade C5 C7
Parameters V300 V2π V300 (1) Evaluating the screw thread length
Stroke＋Nut Length＋Margin＝720＋62＋60＝842mm
Standard Values 18 8 52 * The Margin shown above is an overrun buffer, and normally
determined as 1.5～2 times the screw lead.
Lead 20×1.5×2 (both ends)=60
(2) Evaluating the lead accuracy
P.1589 Table 1. is referenced and an Actual Mean Travel Error
±ep for 842mm ball screw thread.
C3 · · · Ú0.021mm/800～1000mm
C5 · · · Ú0.040mm/800～1000mm
(3) Determining the lead accuracy
It can be determined that a C5 grade (Ú0.040/800～1000mm)
ball screw can satisfy the required positioning accuracy of
Ú0.05/720mm.

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