Permissible Rotational Speed
Critical Speed of the Screw Shaft
When the rotational speed reaches a high magnitude, the Ball Screw may resonate and eventually become unable to operate due to the screw shaft’s natural frequency. Therefore, it is necessary to select a model so that it is used below the resonance point (critical speed).
Fig.13 on Permissible Rotational Speed Diagram shows the relationship between the screw shaft diameter and the critical speed.
If determining the critical speed by calculation, it can be obtained from the equation (7) below. Note that in this equation, a safety factor of 0.8 is multiplied to the result.
DN Value
The permissible rotational speed of the Ball Screw must be obtained from the critical speed of the screw shaft and the DN value. The permissible rotational speed determined by the DN value is obtained using the equations (8) to (17) below.
| Model No. | Permissible rotational speed determined by the DN value N2 |
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|---|---|---|---|---|
| Precision | Caged Ball | Models SDAN-V and SDA-V | Standard lead/ Super lead |
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| Model SBK (Medium) (SBK3636, SBK4040, and SBK5050) |
Large lead |
 |
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| Model SBK (Medium) (Other than the above model numbers and the small size model SBK) |
 |
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| Model SBK (Small) |
 |
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| Models SBN-V (Medium), HBN-V | Standard lead |
 |
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| Models SBN-V (Small), HBN, and SBKH |
 |
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| Models HBN-K and HBN-KA |
 |
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| Full- Complement Ball |
Models SDAN-VX and SDA-VZ (shaft diameters ø28 to 63) |
Standard lead/ Super lead |
 |
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| Model SDA-VZ (shaft diameters ø10 to 25) |
 |
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| Model WHF | Super lead |
 |
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| Model WGF |
 |
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| Models BNS-V and NS-V | Large lead |
 |
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| Models BLW, BLK, BLR, BNS-A, BNS, NS-A, and NS |
 |
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| Models BIF-V (Medium), BNFN-V (Medium), and BNF-V (Medium) |
Standard lead |
 |
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| Models BIF-V (Small), BNFN-V (Small), and BNF-V (Small) |
 |
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| Models BIF, DIK, BNFN, DKN, BNF, BNT, DK, MDK, MBF, BNK, and DIR |
 |
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| Full-Complement Ball (DIN Standard Compliant) |
Models EPB-V, EBB-V (2806 to 8020) | Standard lead |
 |
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| Models EPB-V, EBB-V (1605 to 2512) |
 |
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| Rolled | Full- Complement Ball |
Models WTF and CNF | Super lead |
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| Models BLK and BLR | Large lead |
 |
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| Model BTK-V | Standard lead |
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| Models JPF, BNT, and MTF |
 |
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N2 : Permissible rotational speed determined by the DN value (min-1)
D : Ball center-to-center diameter
(indicated in the dimensional tables of the respective model numbers)
When considering the rotational speed, the permissible rotational speed is regarded as the lower of the following rotational speed guidelines: the critical speed of the screw shaft (N1) or the permissible rotational speed determined by the DN value (N2).
Refer to the dimensional tables of the respective model numbers for the permissible rotational speed.
If the service rotational speed exceeds the guidelines for maximum rotational speed, contact THK.
Point of Selection
- Conditions of the Ball Screw
- Conditions of the Ball Screw
- Estimating the shaft length
- Selecting lead･Selecting a shaft diameter
- Method for Mounting the Ball Screw Shaft
- Permissible Axial Load
- Permissible Rotational Speed
- Selecting a Nut
- Calculating the permissible axial load
- Studying the Service Life
- Studying the Rigidity
- Studying the Positioning Accuracy
- Studying the Rotational Torque
- Studying the Driving Motor
