# Robotdigg linear guide not smooth motion

I recently bought the MGN12H linear guide and rail from robotdigg, which is supposed to be the copy of the Hiwin. I have noticed that the motion is very smooth when moving fast, but if I move it very slowly, it gets stuck and the motion is not smooth at all. I think this will cause problems on my prints once I assamble the printer. Am I missing something? Should I put some king of oil on the balls?

• Yes, you may need to clean and lubricate the rail, some times this parts get some dust or the initial oil gets a little hard due lack of usage. Apr 22 '18 at 18:24

Difficult to say with the given data, but here are a couple of ideas:

First theory:

The belt is too thin/flexible for the linear guide.

Linear guides remove the backslash by adding quite some pressure in the ball system: The block is slightly too small (compared to the rail) and thus it compress the balls and rail. The backslash is avoided until you reach this force.

This pressure require a little bit of force to move the block along the rail, so if your belt is too thin or flexible, the belt will start to move until the elasticity of the belt reach the force required to move the block, then the block move a little bit and stop again.

In a fast movement, your block never get to stop, while in a slow movement, it has time to start and stop. Maybe what you feel like "not a smooth movement"

If you identify this case, I suggest you the following solutions:

• Lubricate correctly the guide, this could be enough to reduce the issue to an acceptable level.
• Change the belt to a larger one, with fibre glass inside (not only rubber).
• If I am correct, the "H" of your MGN12H stand for the pressure of the block. H is for high pressure, switching to a C is far enough for a 3D printer and will reduce the drag.

Second theory: (Thanks to FernandoBaltazar)

You got some dust, rust inside

Remove the belt and move the block with the hand, if you are able to feel the movement is not smooth, then it's probably this case.