Circular-Arc Contact Groove vs Gothic-Arc Groove

October 25, 2018

THK's LM Guides utilizes an ideal four raceway, circular-arc groove, two point contact structure which results in a self- adjusting capability that is unique to THK's LM Guides.

LM Guide

  • The material stress for the LM Guide load is reduced and the total load capacity is increased resulting in circular arc contact. Due to this, the use of raceways with a ball bearing which is slightly smaller than the base results in a larger contact patch, which spreads the load over a large area.
  • The LM Block is able to absorb light distortion of the mounting surface. This is due to the elastic deformation of the ball bearings and the contacts point moving to ensure smooth, unforced motion. A resilient mounting base with high rigidity and accuracy for machinery such as a conveyance system is removed.

Gothic-Arc Design

  • Ball bearings with a gothic-arc design has a high differential slip which creates a change from rolling to sliding under load conditions, high friction, a short service life, low long-time accuracy, a higher energy consumption and a lighter preload.
  • The gothic-arc groove is void of a self-adjust capability. It prevents deformed elasticity and moving contact points as each ball contacts the groove at four points. Therefore, absorption of a slight mounting surface distortion or a rail bed accuracy error is not possible. A smooth motion is also not possible. Therefore, a higher rigidity mounting base has to be machined and a high precision rail needs to be mounted.