Friday, March 19, 2021


When you hear the word “bearings”, the normal prepper context is “a compass reading”. However, the other type of bearings that a prepper should know about are the mechanical ones that keep things spinning smoothly. Bearings are basically anything that separates moving parts, reduces the friction between them, and limits the direction of movement.

Knowing how to repair the things you use is part of prepping, so knowing a bit about bearings could be important.

Plain Bearings
A simple shaft or axle rotating through a hole, with some form of lubrication used to reduce friction and provide cooling; the lubrication itself is a plain bearing, which have been around for at least 2000 years and are still in use today because they're cheap and simple. Plain bearings provide fair performance at a low price, but are best used at low speeds and pressures. If you look at the wheels on a hand cart or child's wagon you'll see a plain bearing where the wheel is mounted on the axle. 

Discrete plain bearings are often found in older machinery; they look like a piece of pipe pressed onto the axle or shaft and are often made of bronze or some other soft metal. If you've ever rebuilt a car engine you've seen plain bearing where the piston rods connect to the crankshaft. “Babbitt” bearings are a plain bearing made by casting a soft alloy around a shaft where it passes through a mounting block, but working with molten metal might be beyond your abilities.

Packing boxes are a sub-set of plain bearings and provide pressure sealing as well as friction reduction. Where the shaft passes through a hole, a box or chamber is built around it. That packing box is filled with some form of fibrous material that has been infused with lubricant. A collar fitted around the shaft is attached to the packing box with threaded rods and as the threads are tightened, the collar compresses the packing around the shaft. Common in older boats for sealing propeller shafts, you'll also find packing box designs on high-pressure pumps.

Rolling Bearings
Both ball- and roller-bearings use a rolling part inside a fixed collar to reduce friction and limit the motion of a shaft. The fixed collar is called a “race” or “journal” and is pressed into a precisely bored hole in the block that the shaft passes through. The rolling element sits inside this race, and the shaft runs through the middle of the rollers. 

Ball bearings work well at moderate speeds and heavy loads, but require lubrication and maintenance for a long life. If you have a towed trailer, you'll have wheel bearings to inspect and lubricate. Boat trailers are notorious for consuming bearings because the axles get submerged in water every time you launch or recover a boat. 

Bicycles are another place where you'll find rolling bearings; I've seen both ball and roller versions in use. Automobiles have bearings all over them, with the wheels and U-joints on drive shafts being the most commonly repaired.

This is the type that I've been dealing with lately, rebuilding trailers and the various rolling mechanisms for agricultural equipment. Proper installation and maintenance makes them last a lot longer, but it's a dirty, greasy job that my predecessors neglected for several years. Common bearings aren't horribly expensive, but finding the proper ones can be a challenge; when things are measured in the thousandths of an inch, there is no “close enough”, it has to be exact. Have spares on hand if you're going to be doing your own work. 

Jewel Bearings
Old mechanical watches and clocks often used small chips of extremely hard jewels as bearings to support the end of a spinning shaft. Under very low load and at low speed, these bearings will last for decades or centuries; maintenance isn't an issue, as they either work or they don't. I doubt very many of us will have the time, training, or equipment to work on jewel bearings, but they are a type to be aware of.
Exotic Bearings
This is my classification for the “other” bearings in use today. Magnetic fields and fluid (gas or liquid) flow bearings are high-tech designs for very high-speeds (dental drills use air-bearings at 250,000 rpm) or extreme environments (the vacuum of space), and require no lubrication or maintenance while providing long life. I don't have the tools or training to work on exotic bearings and can't think of anything in my daily life that uses them, so they're an interesting topic of research but not something I worry about.

Next week I'll go through the process of maintaining and replacing a set of roller bearings. The process is the same on a bicycle, a car or truck, a trailer, and a 20-ton wagon, so it's good knowledge to have. We invented the wheel to make things easier to move, so keeping those wheels spinning makes our lives a lot easier.

1 comment:

  1. I think someone with more talent than I have could rework the song, "These are a few of my favorite things," into a version that names some of the types of bearings.
    I'll add tilting pad thrust bearings to the list.
    Really big thrust bearings that resist the push of an aircraft carrier's propellers.


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