Khavaran Sanat Pasargad


spindle in Cnc machine and differentiation among them, built-in, direct drive, gearbox type, belt-type.

 spindle types in Cnc machine and differentiation among them, built-in, direct drive, gearbox type, belt-type.

Initially we explain the meaning of spindle and in continue will explain its role in cnc machines and its differences.

The spindle of each machine is truly the heart of it which includes the rotating part (cartridge) which the ability of clamping the tool on it. Motors are the transmitters of power in vary types which would cause the spindle to move. You can find the spindle details as the shape below:




Choosing the appropriate spindle and compatible with your necessities would lead you to cost-effective and more proper situation in production. Spindles must be considered based on power and torque. The crucial points of selecting the spindle for our machine, is pay attention to power requirements and relevant weight of that. In the overall view we will see no special role for spindle, tools cut metals, table moves, control system coordinate the movements and software run all of these together and spindle is just the holder of tools which rotates it by means of motor. But the importance of spindle is far more than the above statement because the final accuracy and the machine`s level of efficiency is mainly related to spindle, truly spindle is the heart of a cnc machine tools.


Bearing systems in spindle:

Bearings are made of stainless steel in accordance to maintaining the internal and external races. Operation temperature, amount of vibrations and the longevity of spindle is very related to the material. Utilizing the combined bearing (hybrid) as ceramic bearing definitely far better than the steel.

The lighter mass roughly around 60 percent lighter than the steel ones. That is very crucial to consider, all bearings are all the time rotating and specially in the higher speed the centrifugal force would pressurize the bearing against to the outer race can would cause the friction and eventually deformation and continuously the breakout fast. Because the ceramic bearing are lighter they would be even faster 30% more in comparison with steel bearings. Ceramic bearing neutralize the destruction factor called Adhesion. One of the main factors in destruction of bearings is Adhesion factor. This issue occurs when due to shattering the surface of metal, micron adhesion and continuous movement of bearings will make the rough surface which eventually with increasing the temperature will destruct totally. Just due to the stated reason the ceramic bearings would produce less temperature in longer period and last more. Test proven that the spindles utilize the ceramic bearings are more rigid and have less resonance there are more sensitive to vibrations and longevity is more.

Bearing mechanism in spindle:

Apart of the type of bearing materials as well as steel or ceramic. Bearings basically are designed to tolerate difference pressures. utilizing the bearings with angular contact in axial and radial pressures in high speeds are common. This type of angular contact provides more accurate, more tolerance capacity and applicable speed for machining process. Bearings in the inner race are located in a way which create The most stable geometrical state.


Bearing and spindle lubrication:

This issue is the most important factor to be considered for machine tools manufacturers which includes different types as well as, oil-jet, oil-air, oil-mist and some others.


Study of different spindles:


Spindles based on their functions and requirements are divided into some types:

1-    Belt –type

2-    Direct drive or DDS type

3-    Gearbox

4-    Built-in

5-    HF or high frequency spindles

Each of the above cases have some advantages and some disadvantages

1-   Belt –type spindle: this type of spindle calls for power transmission by means of the belt from motor to the spindle



  • Easy and cost effective maintenance
  • Lower cost


  • More vibration
  • Loader noise compared to DDS and built-in
  • Less longevity and destruction
  • Unable to reach high speed like more than 12.000 rpm
  • Less positioning and repeatability accuracy which results the lower quality in surface roughness
  •  Mass compensation of pulley by motor
  • More friction and lower efficiency

1-   DDS spindles: this type power transmission from motor to spindle is without any intermediaries and motor is directly coupled to spindle.


  • Increasing the efficiency without losing the energy
  • No necessity of mass compensation by motor so all power will directly transmit to spindle
  • Lower noise VS belt type
  • Longer longevity
  • More torque in low speeds
  • Higher speeds and more positioning accuracy ad reaching the speeds more than 12.000 rpm


  • The main disadvantage in these types utilizing the bigger size motor so it would limit the area for machine producer on specific area.
  • Higher price
  • Weight of spindle is more because it has to carry the motor with it
  • Lower torque VS built-in

1-    Gearbox: in this type the power transmission is made by gears which would cause the greater torque for very rough machining processes.




  • More torque
  • More capability of cutting


  • High cost maintenance
  • High price
  • Low speed

1-    Built-in: this type power transmission is by integrated motor inside the spindle there are some other names as motorized spindle, electro-spindle and integrated spindle




  • Low weight
  • Reaching the high speed like 35.000- 50.000 rpms
  • Producing the huge torque with dual winding motors
  • Lower noise VS belt, gearbox, DDS
  • Lowest the energy waste


  • High price
  • High costs for maintenance

The important factors which needed to be considered in spindle manufacturing:

  • Spindle body machining process
  • Grinding
  • Assembly



Above article is just the little explanation of spindle; we would definitely elaborate more on stated matter.


The article is prepared in Ksp-group R&D unit