KTR Corporation | 122 Anchor Road | Michigan City, IN 46360 | T 219-872-9100 | F 219-872-9150

FAQ - Frequently asked questions

Zero-backlash couplings

Backlash-free servo couplings ROTEX GS by KTR Systems GmbH

1. Which data do I require for selecting a coupling?
To support you optimally, we need to know from you details about the kind of application, the torque to be transmitted and the shaft diameters to be connected. Please also advise specific ambient conditions such as temperatures or contact with aggressive media. We will be pleased to provide you with questionnaires we have prepared. For that purpose please contact our application consultants.

2. Is it possible to select a coupling based on bore diameters?
We strongly recommend NOT to do so. For an optimum selection of a coupling other parameters are decisive, see question No. 1. The only exception to the rule are applications on shaft encoders. In this case, the couplings are selected according to shaft diameters. Suitable for such applications are our miniature couplings COUNTEX®, ROTEX® GS and TOOLFLEX®.

3. How do ROTEX® and ROTEX® GS couplings differ in their function?
The only difference is ROTEX® GS jaw couplings have zero-backlash. They are used on such applications that require positioning of drives.

4. How can I recognize if a ROTEX® or ROTEX® GS spider is laying in front of me?
There are two visual features in which the spiders differ from each other: On the one hand the ROTEX® GS spider has a straight tooth from a radial view, while the ROTEX® spider has a crowned shape. On the other hand, the ROTEX® GS spider has a web on the inside diameter (illustration on the left: ROTEX® GS spider, illustration on the right: ROTEX® spider).

Explanation gear by KTR Systems GmbH

5. My coupling hub looks like the one in the illustration shown in the company catalog, but it has a different number of jaws. Can I order it like that?
The number of jaws depends on the coupling size. The products shown in the catalog are only a part of our portfolio. That is why it is possible that the number of your jaws differs from that presented in the catalog.

6. Does the bore diameter of the clamping hub have to have the same size as the shaft diameter?
Yes, it does. The clamping hubs are able to compensate for differences in diameter within the tolerance range, but the nominal size should be the same.

7. Does the bore diameter of the clamping ring hub have to have the same size as the shaft diameter?
Yes, it does. The clamping ring hubs are able to compensate for differences in diameter within the tolerance range, but the nominal size should be the same. If your shaft tolerance deviates from the shaft tolerance specified in the catalog, please speak with our application consultants.

8. Which shaft tolerances does KTR recommend?

The shaft-hub-connection basically has to be reviewed by the customer! With frictional connections, please observe the transmittable friction torques specified in our assembly instructions and catalogs.

9. How do the kinds of spider hardness of ROTEX® GS differ
We provide the flexible spiders in five different kinds of Shore hardness. Scale A is used for softer nylon, while scale D is used for harder nylon.

Shore hardeness

To facilitate the identification of the spider hardness, our spiders are molded in different colors.

Varaition of gears by KTR Systems GmbH

10. Is it possible to combine the different types of hubs?
Yes, it is. The different types of hubs can be combined with each other within one coupling size.

11. Why may it be difficult to plug in the spiders/coupling hubs of ROTEX® GS or are they available easy to plug in as an alternative?
The zero-backlash feature of the ROTEX® GS coupling is based in the prestress between spider and coupling hub. The force required for plugging depends on the coupling size and spider hardness. It can be reduced by lubricating or greasing the spider or hub. For that purpose, please make use of oils and greases on a mineral oil basis without any additives, lubricants on a silicon basis (e. g. Optimol Optisil WX) or Vaseline. Another option to reduce the force applied is our patented procedure of thermo calibrating. For that purpose please contact our application consultants.

12. Can I install a mixture of ROTEX® and ROTEX® GS components in one coupling?
Yes, you can, but not for zero-backlash applications.

13. What is the difference between TOOLFLEX® M and TOOLFLEX® S?
The difference is the number of layers and the resulting length of the bellow. The TOOLFLEX® Design M has six layers and is able to compensate for large displacements subject to its length. In contrast, Design S has only four layers, is consequently shorter and has a higher stiffness.

14. Where can I get 3D data from?
A large number of our 3D data is available in the KTR 3D-SpaceCenter. If the data you require is not included, please send an email to one of our application consultants.

15. When will you send me my password for the KTR 3D-SpaceCenter?
We will not send you the password. With your initial registration, you will define your personal password at that time. As soon as you have registered and defined a password, you will have immediate access to our 3D data.

16. Where can I find the coupling description on the coupling or which description do I use for ordering spare parts?
Our couplings are always marked with coupling type and coupling size (e. g. www.KTR.com - ROTEX® GS 28). The type of hub or bore diameter is not part of the marking on the coupling and has to be measured. Our application consultants will assist you with the identification of the type of hub.