Is your robot grinding to a halt? Have a door that makes an annoying SQUEEEAK every time you open it? Don’t reach for the WD-40 yet! In general, the most common application of a lubricant is to reduce friction between surfaces, but not all lubricants are equal. In this handy guide, we’ll go over a few of the most common lubricants, how they work, and when to use them.
Oils are thin liquids made of long polymer chains, with additives for various extra properties. Common additives include antioxidants to keep the oil from oxidizing, corrosion inhibitors to prevent parts from corroding, and detergents to keep deposits from forming. These long chains are hard to squeeze out from between surfaces, making oils useful as a slippery barrier between them. Oils come in different “weights” (such as 5W or 10W), which correspond to viscosity. The lower the number, the thinner the oil, and the more easily it will flow.
Uses: Hinges, bearings, tool maintenance, sharpening blades
Types: Motor oil, 3-in-1 oil, sewing machine oil, bar and chain oil
• You want to lubricate something without the resistance inherent in using grease
• You need lubrication to wick into a small space, without having to take anything apart
Don’t Use When:
• The surfaces being lubricated are exposed to dust or dirt, which can eventually gum up and cause more friction
• You need to keep things around the surfaces clean, because oils are low in viscosity and thus tend to drip and run
• The surfaces are exposed to water or anything that can wash the oil away. It won’t last long! (While oil can help make things water resistant, it can also absorb water over time. The more water that absorbs into the oil, the lower its adhesion will be, causing it to wash off of the very parts that need lubrication.)
Greases are made by using oil (typically mineral oil) and mixing it with thickeners (such as lithium-based soaps). They may also contain additional lubricating particles, such as graphite, molybdenum disulfide, or polytetrafluoroethylene (PTFE, aka teflon). Greases combine the lubricating properties of oils with added stickiness, allowing the lubricant to adhere to the surfaces better. Greases can even act as a barrier, protecting the surfaces from contaminants that can corrode or damage them. Like oils, greases come in a range of consistencies, from ketchup-thin to thick like cheddar cheese. One downside to grease is that because it’s so thick and sticky, it can cause resistance in small or fast-moving mechanisms.
Uses: Gears, bearings, chains, linkages
Types: White lithium grease, marine grease, silicone grease
• You need lubrication to stay put and stick to surfaces for a long time
• You want to seal out contaminants such as water or dust
• You use a machine so infrequently that you may forget to oil it
Don’t Use When:
• You have fine or fast-moving mechanisms where thick grease would create too much resistance
• You don’t want a mess. When parts move, they can fling grease all around, so it may not be the best option for keeping things clean
Any shade-tree mechanic would agree that these types of lubricants deserve their own special section. Penetrating lubricants are the saviors of many stuck-bolt combatants, loosening years of rust and debris in minutes. Contrary to the other substances covered here, penetrating oils are not designed for long-lasting lubrication. Instead, they are low-viscosity oils with additives that are specifically designed for one purpose: to infiltrate the tiny cracks between surfaces (such as screw threads), add lubrication, and break up rust.
There are a lot of different penetrating oils out there, but did you know that you can make your own low-cost penetrating oil that outperforms almost all of them? In an experiment conducted by Drexel University engineering students, they found that a mixture of vegetable oil and acetone works as well (or better) than WD-40 at loosening stuck bolts.
It’s easy to make! Just mix up a solution that’s 90% vegetable oil and 10% acetone, and squirt it wherever necessary. Be careful when mixing, as acetone is flammable, and will melt many plastic containers. If possible, use a glass or metal container to mix it, or buy an oil can to make things even easier. Also, be sure to shake the mixture before each use, as acetone and vegetable oil tend to separate over time.
Why Shouldn’t I Use WD-40 on Everything?
WD-40 actually stands for “Water Displacement formula 40,” and while it can help loosen rusty bolts, the film of oil left behind isn’t nearly enough for good, long-lasting lubrication. You might find that the troublesome squeak subsides for a little while, but soon enough you’ll have to go spray it away again. Using the right lubricant the first time will ensure that the problem is solved long enough for you to forget all about it. Save the WD-40 for what it does best: light lubrication, cleaning, and freeing stuck-together Lego bricks.
Dry lubricants are made up of lubricating particles such as graphite, molybdenum disulfide, silicone, or PTFE. At the molecular level, these particles are super slippery, so they reduce the friction between surfaces in contact with one another. It’s common to find these lubricants in spray form, where they are mixed with water, alcohol, or some other solvent that will evaporate away after application, leaving behind a thin film.
Uses: 3D printer rails, threaded rods, locks, hinges
Types: Graphite powder or spray, molybdenum disulfide spray, (dry) silicone spray, PTFE spray
• You have tiny parts that shouldn’t be gunked up by grease or oil that will attract dust
• You need to keep surrounding surfaces clean
• Your surfaces are exposed to extremely high heat or pressure, which would typically oxidize oils
Don’t Use When:
• Your surfaces are exposed to solvents or other liquids that can wash them away