Written by John Winkler CEO, Office of the President
There are few other machine components that seem more elementary than a knob. Yes, those handles that allow users to firmly and comfortably grip an area of machinery to open, operate, or control it.
These devices may seem simple, but they are often essential, practical, and imperative to good design. Knobs are used to transmit a force between a person’s hand and an object. There are many possible configurations for this simple part, and choosing the right type is key to the optimal function of the machine. For example, knobs may be axisymmetric, multi-lobed, spherical, or T-shaped.
Ultimately, a knob must have a sufficient area and ergonomic shape to transfer the force comfortably into the user’s hand — typically through a range of angles when the handle is moved. The right choice of knob provides this ergonomic interface.
When deciding on a style, consider the type and material used for the knob based on the application and environment it will be used in. Moisture, for example, may affect the user’s grip on certain types of knobs and this could be a safety issue. Also, ask about the knob’s metal insert, which is molded into the knob material during manufacturing. It’s this insert that provides the knob its strength, which in turn enables the maximum torque.
Here are a few different types of knobs, including certain advantages and disadvantages, so you can select the ideal one for your application.
Ball knobs. Ideal for applications that require movement in any and all directions. Ball knobs typically offer a comfortable to grip and are easy to wipe down and keep clean. However, avoid ball knobs in applications that deal with moisture or grease because the knob will become slippery and tough to handle.
Control knobs. These knobs are specifically used for the fine control or adjustment of devices and may be referred to as instrument, electronic, or electrical knobs. Basically, control knobs allow for precise positioning of equipment or machines. They come in a variety of styles, and may include a revolving handle or scale markings for measurement.
Knurled knobs. This group encompasses a variety of knob styles (round, push-pull, clamping, mushroom, tapered, etc.) but always includes ridges or knurls at the rim to provide a non-slip grip. The knurled rim is the answer for greasy or wet environments where slipping is unacceptable or a safety concern. The knurled ridges mean sacrifices to easy cleaning, so this may be a problem in clean room and food applications for example.
Pointer knobs. This is a type of control knob but in a pointer shape. The design makes it easy to operate with a thumb and finger. It works well when the application involves a few options or repeated settings (such as off/on, open/closed, etc.). It’s also ideal when the application requires a sort of scale marking.
Prong or multi-lobed knobs. The protrusions on a prong knob are longer (certain star knobs may also fall in this category), increasing the leverage of the operator’s fingers. This means they’re ideal for higher torque requirements. In lighter torque applications, one finger may be all that is required to turn a prong knob. The downside of this style is an increased surface area, which makes it a bit more difficult to clean. Also, if steady, unbroken turning is required, go with a crank or handwheel.
Push-pull knobs. These simple knobs vary in style but are typically easy to operate and control because of a larger head. Solid push-pull knobs are simple to clean — unlike open-backed styles, which collect dirt or other contaminants. If the application involves a lot of use or stress, opt for a type made of metal or with a metal insert. Push-pull knobs can also get quite slippery to grip, so you may want to consider a style that is knurled at the rim.
Tapered knobs. The length of these knobs makes them ideal for side-to-side or up and down movements. They are particularly good for applications that operate by grasping and rotating from a 90-degree angle. This means they work well as the handle grip at the end of an operating lever, gear stick, or handwheel. But bear in mind that unless fluted or knurled, tapered knobs can be slippery in wet or greasy environments.
T-handle knobs. The two-lobe design of these knobs provides for an easy grip, allowing for optimal leverage and control in in-and-out operations or rotating ones. T-handle knobs also offer a strong clamping force, however, avoid using too much torque (as it might twist the insert out of the knob). If your application involves a limited space where only one hand can reach, these knobs work well. If the user is at an awkward angle, a prong knob might be preferred.
Wing nuts or screw knob. Essentially, these knobs are a two-pronged knob that are designed for frequent tightening and loosening. They typically function in applications where the operator needs to apply torque using a thumb and finger only, and fit well in confined spaces. Metal or metal-insert wing nuts can achieve a good clamping force.