# Curved Slider Mechanism With Two Different Radii

I'm trying to make a slider mechanism that is guided around a curved rail that consists of two different radii. As you can see in the image, the section of the rail with a diameter of 120 mm requires the 3 circles to be spaced 9.615 mm apart, and the section of the rail with a diameter of 196.615 mm requires the 3 circles to be spaced 9.686 mm apart. This difference of .071 mm causes too much play between the slider and the rail, and I really need the slider remain as stable as possible. Any suggestions of how to design the slider in order for the slider mechanism to slide along the rail smoothly with the least amount of play?

• So rollers of diffent diameter that are fixed to each other to compensate the difference in radii... May 16 '18 at 4:37
• Can you add a spring to the rollers? May 16 '18 at 9:53
• Your question doesn't make any sense: change the dimensions of the triangle and the positions of the roller mounts until the roller surfaces mate to the inner and outer runs. There's no reason all 3 rollers need to operate at the same "rpm" . May 16 '18 at 15:45

You may need a five-wheel carriage.

Figure 1. Illustration of a possible solution using a five-wheeled carriage.

For ease of illustration I've used two radii - one of which is infinite.

• On the larger radius the inner centre wheel provides the accurate location.
• On the smaller radius the alignment is done by the previously floating wheels.

There are some details for you to work out:

• What exactly happens at the transition.
• The centre of the carriage has moved inwards a little on the curve.