NAC Harmonic Gearing Technical Data

Assembly Considerations for Component Sets

Assembly Tolerances for Industrial Grade Component Set

Assembly Tolerances for Robotics Grade Component Set

Transmission Efficiency

  • Transmission efficiency of a harmonic gear drive is the ratio of the reducer’s output power to its input power. Many factors are affect efficiency, including output torque, temperature, lubrication, gear ratio, and speed. The efficiency of oil-lubricated reducers is shown in the following figures. The efficiency of grease-lubricated reducers is 5% to 10% lower than shown below.

Efficiency (%) vs. Gear Ratio

Efficiency (%) vs. Input Speed

Backlash – (Lost Motion)

Lost Motion is defined as the lag of the output shaft’s rotational angle when the input shafts position is altered, under no-load conditions. The allowable values are 6 (±3) arc-min for the industrial series, 3 (±1.5) arc-min and 1 (±0.5) arc-min for Robotics grade harmonic gears. Lost motion is the accumulated value of tooth backlash (zero for N-HDC and N-CSF series), wave generator coupling backlash (may be eliminated for critical applications) hysteresis, and torsional windup.

Transmission Error

  • Transmission error is defined as the difference between the output shaft’s actual position and its theoretical output position. This is measured in a unidirectional rotation. The allowable values are 6: ± 180 arc sec - Industrial Grade; 3: ± 90 arc sec - Robotics Grade and 1: ± 30 arc sec - Robotics Grade. Consult the factory for individual application needs.

No-Load Static Starting Torque

Overload Capacity

  • While a 250 - 400% overload capacity is generally available, NAC recommends momentary peak overload be limited to 100% over rated torque during acceleration or deceleration. Emergency stop conditions should be limited to less than 150% over rated torque for adequate safety margins. For information on higher overload applications, consult with the factory.

Torsional Rigidity / Inertia

Torsional spring rate over the torque range of 0% rated torque to 20% rated torque.  This range incorporates deflection due to backlash.   

Torsional spring rate over the torque range of 20% of rated torque to 100% rated torque.

Note: KA can be optimized to achieve a 50% increase 

Component Assembly

1. All components must be cleaned prior to assembly.
2. To assemble, slide the Wave Generator into the open end of the Flexspline.  Then slide the Circular Spline over the Flexspline (from the closed end, for cup-style sets) while slowly rotating Wave Generator.

3. During assembly, check the symmetry of the tooth engagement and be sure that all three components are concentric.  There should be an equal amount of space between the Flexspline and Circular Spline where the teeth are not engaged.  “A1” should be equal “A2”.  If the assembly is not symmetric, disassemble and start the assembly process again.

4. The Wave Generator must be fixed axially on the input shaft.  Failure to locate and maintain the input shaft at the correct axial location will result in damage.
5. The housing tolerances to ensure proper operation are shown in the prior section.
6. Coat all surfaces of each gear component with thin layer of lubricant to protect against rust.  Surfaces which constitute bolted joints should be kept clean and lubricant free.
7. The three gearing elements must be maintained as a matched set for “R” grade harmonic gears.
8) Dowel pin holes are provided in the Flexspline mounting boss.  The matching holes of the output shaft should be match-drilled.  Dowel pins should then be inserted.
9) A clamp ring must be used as part of the assembly to attach the Flexspline to the output shaft.  The outside diameter of the clamp ring must be less than the diameter of the Flexspline’s mounting boss.  The outer diameter of the contact surface must have a radius to protect the Flexspline diaphragm from damage. 

10. The housing must provide enough clearance from the outside surfaces of the Flexspline.

11. To ensure proper torque transmission of the bolted interface the following bolt sizes and tightening torque is recommended.

Service Instruction

Contact NAC Drive Systems for any questions regarding service and maintenance.

  1. Semifluid grease lubrication is used for sizes English Sizes 1C through 5C, and Metric Sizes 11 through 25.
  2. Oil lubrication is typically used for English Sizes 1M and above, and Metric Sizes 32 and above when the input speed is above 2000 rpm. Grease lubrication may be used when the input speed is below 2000 rpm. Please advise the company when ordering.
  3. An oil change is recommended after the first 100 hr of operation. Subsequent oil changes are recommended after each additional 1000 hr of operation
  4. An air vent must be used for oil lubrication when the unit is operated in a vertical (vertical axis of rotation) orientation.


1. The maximum permissible temperature rise is 60C from ambient.
2. Different oils and greases are available depending upon drive size and ambient temperature.  Contact NAC Harmonic Drive for recommendations and pricing.

Standard Configurations

To support our market, NAC offers modifications to our products which accommodate a wide range of generic applications. These modifications are available at an additional cost. Contact NAC Application Engineers for allowable modifications.

The following are product features which are available in various standard configurations.

 a)  Mounting Hole & Tolerance
 b)  Mounting Hole Configuration
 c)  Mounting / Pilot Boss & Tolerance
 d)  Addition of a Mounting Flange, Support Bearing, and Input Shaft
 e)  Other Simple Interface Dimension
 f)  Selection of Commercially Available Lubricants
 g)  Thread Specification
 h)  Bolt Size, Number, and Specification
 i)  Pocketing of Material for Weight Reduction Purposes
 j)  Corrosion Resistant Material or Coating
 k)  Marking
 l)  Packaging
 m)  Additional Testing and/or Furnishing of Test Data
 n)  Additional Screening and/or Furnishing of Screening Data
 o)  Minimum or Maximum Catalog Performance Level
 p)  Configuration Control
 q)  Special Quality Control or Quality Assurance Procedures

A suffix is typically added to the standard part number to document any standard configurations. The suffix is an incremental number beginning with “SP”.

Ordering Codes

N: NAC Drive Systems Product Code Suffix
AAA: Model
  • HDC
  • HDF
  • HDA
  • HDR
  • HDB
  • CSF
BBB: Size
CCC: Ratio: Wave Generator Speed (Input) / Flexspline (Output) Speed
DD: Configuration
  • E1: English Dimension Version #1
  • E2: English Dimension Version #2
  • M1: Metric Dimension Version #1
  • M2: Metric Dimension Version #2
E: Maximum Backlash (Total Lost Motion)
  • 6: ± 180 arc sec - Industrial Grade
  • 3: ± 90 arc sec - Robotics Grade
  • 1: ± 30 arc sec - Robotics Grade
F: Maximum Transmission Error
  • 6: ± 180 arc sec - Industrial Grade
  • 3: ± 90 arc sec - Robotics Grade
  • 1: ± 30 arc sec - Robotics Grade
SPXXXX: Special Ordering Code

Notice: All efforts have been made to assure that the information in this catalog is complete and accurate. However, NAC Drive Systems is not liable for any errors, omissions, or inaccuracies in the reported data. NAC Drive Systems reserves the right to change the product specifications, for any reason, without prior notice. Customers are responsible for determining product applicability to any particular application.

NAC Drive Systems - 4720 Salisbury Road - Jacksonville, FL 32256 - Phone: (904) 493-6496 - Fax: (904) 339-9241