Plastic Gears, Good or Bad?

Plastic gears are a divisive topic. Some machinists love them, and some dislike them immensely. This issue is more nuanced than a simple good or bad declaration.

To give meaning to the topic, you must differentiate between Change Gears and Drive Gears. Most negative press around plastic gears center around Drive Gears, particularly the two-speed drive gear in the headstock of mini mills.

Fortunately, our HiTorque mills and lathes do not have Drive Gears. Our machines are powered by a brushless DC motor with a belt connecting the motor to the spindle.

Lathe Change Gears on the other hand are easily accessible from the side where you change their pairing to achieve different threading. These gears do not typically experience the same torque as drive gears. On a mini lathe we feel plastic gears have some benefits and here are the reasons:

Plastic change gears are quieter than metal gears. Metal change gears raise the sound level to an objectional level.
Our plastic change gears are made of high-quality thermoplastic which is durable and long lasting. With proper use gear damage should be minimal. See Polyoxymethylene Gears below.
Plastic gears are economical both in the initial cost and in replacement cost over the years.

Our larger HiTorque bench lathes, which are designed for larger work pieces, greater power, and more torque, have all metal gears as appropriate for their size.

Finally, a broken gear may serve as an indicator that the machine is possibly being used in a manner that is outside of its design parameters (or other underlying problems) and you should review your setup and operational practices. It's better to lose a gear than severely damage your lathe.

Polyoxymethylene Gears

It is important to understand that not all plastic gears are the same. The plastic gears in LittleMachineShop.com HiTorque mini lathes are made of Polyoxymethylene (POM).

Polyoxymethylene (POM), also known as acetal, polyacetal, and polyformaldehyde, is an engineering thermoplastic used in precision parts requiring high stiffness, low friction, and excellent dimensional stability. Polyoxymethylenes are manufactured by many different firms and sold under a variety of trade names including Delrin, Kocetal, Ultraform, Celcon, Ramtal, Duracon, Kepital, Polypenco, Tenac and Hostaform.^[1]

POM is characterized by its high strength, hardness and rigidity to −40°C. POM is intrinsically opaque white because of its high crystalline composition, but it can be produced in a variety of colors. POM has a density of 1.410–1.420 g/cm³.^[2]

Typical applications for injection-molded POM include high-performance engineering components such as small gear wheels...^[3]

POM gears are sometimes referred to as self-lubricating. This is not technically true. The reference is used because of POM's high abrasion resistance and a very low coefficient of friction. In normal mini lathe use, the POM change gears do not need to be lubricated. However, if you run your mini lathe at high speeds for prolonged periods of time, lubrication would not hurt and can even contribute to your gear’s longevity. If you want to lubricate POM gears, silicon-based or synthetic lubricants are recommended. We do not recommend lithium grease for this application as it is petroleum based and can be detrimental to plastics. In addition, lithium grease can pick up a lot of dirt and dust which should be minimized on your change gears.

If you would prefer metal Change Gears for your mini lathe, we sell a Metal Change Gear Set. See the compatibility tab on the product page to ensure that these gears are right for your machine.