Page 989 - MiSUMi FA Mechanical Components Economy Series

3. Axial Clearances of Ball Screws
Axial clearance does not aff ect positioning accuracy if the feed is unidirectional, but will generate backlash and negatively aff ect 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 20 20 10 200 900 0.015 or less
CTBSB
05 20
20 10 0.15 or less 05
20 25 10 300
200
05 25
25 10 2000
25
0.2 or less
05
32 10 300
32
Selection Example of Lead Accuracy Selection Example of Axial Clearance
<Requirements> <Requirements>
· Ball screw diameter F15, lead 20. · Ball screw diameter F15, lead 5.
· Stroke 720mm · Allowable backlash Ú0.02mm
· Positioning accuracy Ú0.05mm/720mm
<Selection Details>
<Selection Details> When the screw shaft diameter is F15, C5 grade with axial clearance
Select an appropriate lead accuracy grade based on the application below 0.015mm can meet the condition of allowable backlash amount
requirements. Ú0.02mm.
(1) Evaluating the screw thread length
StrokeNut LengthMargin7206260842mm
* The Margin shown above is an overrun buff er, 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.985 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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