Where should the oil level be in lubricating a ball bearing with a bottle oiler?

When lubricating a ball bearing with a bottle oiler, the recommended practice is to maintain the oil level at the middle of the lowest ball. This position allows for adequate lubrication to the rolling elements while avoiding excessive oil that could create a hydraulic pressure situation or lead to foaming.

Having the oil level at the middle of the lowest ball ensures that the lubricant reaches the contact points between the balls and the races, providing effective lubrication and prolonging the life of the bearing. It also helps to ensure that the oil can maintain proper viscosity at the operating temperature, facilitating smooth operation without risk of under-lubrication or over-lubrication.

Positioning the oil level in other suggested ways, such as halfway up the bearing or at the bottom of the bearing race, may lead to insufficient lubrication or compromise the bearing's performance. Flooding the housing could result in excessive oil that might cause the bearings to operate inefficiently, introduce contaminants, or increase the risk of leaks.