Selecting a Shaft Collar
There are a variety of factors that determine which collar is ideal for an application. It is important to carefully identify your system's relevant requirements, parameters, and limitations before selecting a shaft collar.
clamping, set screw, thin line, standard clamp types, double wide, heavy duty, threaded/bearing locknut.
In many applications, holding power is the key performance factor designers seek. It is affected by a variety of collar specifications and affects the collar’s . A holding power is dependent on how much the screw can impinge into the shaft, which is a function of the relationship between the screw and shaft materials.
Bore size and concentricity influence the holding power of , however the importance of fastening hardware cannot be understated. The size and quality of hardware, namely thread quality, tensile strength, and size tolerances, affect how much torque the screw can transmit to the collar. Forged screws are generally superior to broached screws as they are more consistent and are less likely to ream out. Likewise, the collar itself must be manufactured from a material strong enough to withstand the recommended screw torque, or else it may crack or deform.
cut to increase clamping efficiency in small size shaft collars.
Small bore (1-5/8” or 38mm and under) are often machined with a back-cut opposite to the clamp cut. The back-cut reduces the cross-sectional area at the hinge point of the collar lowering the force required of the screw to clamp the collar around the shaft. This allows the screw to use more of its seating torque for holding power. As one-piece collars move up in size, the size and strength of the screw increases to a point where the back-cut is no longer needed. reduce the amount of material that must be bent around the shaft and have the added advantage of a second screw to transmit torque. Even with these benefits, holding power only increases by about 5%. The choice between a one-piece or two-piece design largely comes down to convenience and the disassembly requirements of an application.
Surface Treatment & Stick-Slip
The surface treatment on a shaft collar and its screw(s) is another factor that contributes to holding power. Shaft collars and their screws are most frequently steel with either a black oxide or zinc plated surface finish. Black oxide enhances holding ability and helps keep the torque rating of the screw within its design parameters. Zinc plating is more corrosion resistant but reduces the collar’s friction coefficient, reducing its holding power.
Black oxide is effective largely because it is an anti-stick slip compound. Read more about stick-slip .
Screw treatment is equally important for stainless steel collars. If screws are untreated before installation, galling will occur as the material of the collar and screw are the same. This can make the collar harder to disassemble and may only allow one use. If disassembly is required, the screw may be bound to the collar in such a way that it can not be taken out, complicating removal. Treatment can be done using off-the-shelf thread coatings; however, Ruland treats all stainless hardware with a proprietary formula that provides the necessary dissimilar material to prevent galling.
Precision Facing
Face-to-bore perpendicularity is another key performance feature of shaft collars, especially when used as a load-bearing face or to align or locate components on a shaft. Precision facing ensures squareness of the collar face with the bore, allowing for even pressure at the interface between the collar and mounted component, eliminating spot loading, which can shorten the life of the assembly.
Designers are often looking for shaft collars with low TIR (<= .002” or .05mm) for high-leverage applications such as the collar being used as an axial stop in a pneumatic cylinder application or seated against a precision bearing. When face to bore relationship is not controlled, displacements such as shifting or tilting relative to the shaft axis can occur. An axial stop application may cause the collar to “walk” down the shaft because the axial force is not even distributed across the shaft collar face.
Installation & Disassembly
While it is important to understand how effective a shaft collar will be in an application, many assemblies benefit from or require a specific style. Some applications require infrequent adjustment or disassembly after installation of the shaft collar. In this case, a one-piece clamp type or set screw shaft collar may be suitable, as either can be installed quickly and easily. In other assemblies, the collar needs to be frequently disassembled, and other difficult-to-remove components are installed on the shaft. In this case, a two-piece style is beneficial as it can be installed and removed without disturbing other components.
Quick clamping shaft collars with a or are ideal for applications that require frequent axial adjustment along the shaft. By skipping the manual torquing of the screw, adjustments with this style of collar are several times faster and more convenient.
Other applications, such as packaging, printing, medical, and food, may have space or weight restrictions but low holding power requirements. In this situation, a may be suitable due to their reduced width, weight, and screw size. Conversely, large shafting may require high axial loads that a standard style can not accommodate and a would be preferred.
Material
Material can significantly impact the performance of a shaft collar in a given system. Since the strength of the screw itself has a dramatic effect on the collar’s holding power, the strength of the screw material to that of the collar is important. Generally, the manufacturer will offer the appropriate screw for the collar. However, it may be sensible in some applications to use a non-standard screw, understanding it could adversely impact collar performance.
Aluminum shaft collars are lightweight and have good holding power, making them a common choice in many applications. Steel shaft collars possess the highest holding power and some corrosion resistance but have higher mass than aluminum collars. The steel grade can impact collar performance depending on the application. While 12L14 is easier to machine than 1215, it is not well suited for applications where the collar will be welded to another component due to the lead content. Stainless steel collars have increased corrosion resistance over aluminum and steel types, however they have reduced holding power compared to shaft collars that use steel hardware. Stainless steel collars are commonly found in 303, 304, and 316 stainless steel. Designers must consider the material of the shaft collar and screw before selection. For example, manufacturers may offer a 316 stainless collar with an 18-8 stainless screw. While the shaft collar will be able to withstand the harsh environment, the screw will not, leading to reduced performance and premature failure.
Although most shaft collars are manufactured from aluminum or steel varieties, some are made of less common materials. Plastic shaft collars are lightweight and inexpensive as an alternative to stainless steel types but have greatly reduced holding power. Titanium collars are lighter than aluminum, have good holding power, do not outgas (useful for cleanroom environments), and can tolerate extreme temperatures. However, they are only used if the application absolutely requires these properties due to their prohibitively high cost.
Types of Shaft Collars
Set Screw Shaft Collars
Set screw shaft collars are the most common style of shaft collars. Their relatively low cost and ease of installation make them a starting point for many designers. They have limitations, including low holding power, inability to adjust/reposition, and can only be used on unhardened shafts. Our image above demonstrates how a set screw shaft collar must permanently mar the shaft for proper use. Other than being aesthetically displeasing, this also causes potential functional problems. The impingement of the screw causes an eruption of material around the screw point resulting in a raised burr, making it difficult to remove the collar or further refine its position. Small angular and lateral adjustments are nearly impossible to make since the screw point will always be drawn to its original location.
Clamp Style Shaft Collars
Clamp style collars solve many of the problems that exist with set screw collars and are available in One- } and designs. They utilize compressive forces to lock the collar onto the shaft. Since this does not damage the shaft, clamp style collars are easily removed, indefinitely adjustable, and work well on virtually any shaft. In addition, when the clamp screws are tightened correctly, the clamping forces are distributed uniformly around the circumference of the shaft. This is significantly more secure than the point contact of set screw collars, as much as doubling the holding power.
Quick-Clamping Shaft Collars
New to the shaft collar market, operate similarly to other clamping collars and do not mar the shaft. The advantage of quick-clamping shaft collars over standard clamping styles is that they do not require tools to install or remove, making them well-suited for quick adjustments. The primary drawbacks are they have less holding power than traditional shaft collars and should not be used in rotating applications. They are traditionally offered in two styles, with a cam lever and a clamping lever.
are operated with a low profile lever that controls their clamping forces. When installed, the integral handle sits flush with the outside diameter and can be finger-actuated without tools for quick installations and adjustments. Quick clamping shaft collars with cam levers have a tension-adjustment screw which makes the collar compatible with slightly wider shaft tolerances than standard shaft collars and allows for a range of holding power. The screw comes preset from the factory to a torque in the middle of the tolerance range and never needs to be adjusted unless the user desires it. They are available in one-piece style in anodized aluminum. The lightweight, compact design aids in the ease of installation and repositioning.
offer similar functionality and benefits but make use of an adjustable, removable lever that replaces standard collar hardware. With a ratcheting action, the user can lift the handle and twist it 40° to lock it in a new position. This feature allows the user to turn the lever until they reach their desired torque in space-constrained environments. Quick clamping shaft collars with clamping levers are available in and clamp styles in steel, 303 and 316 stainless steel, and aluminum. The range of styles and materials contrasts the cam lever style, giving users a quick clamping alternative for most applications.
Both quick clamping shaft collars are ideal for light-duty applications requiring frequent setup changes or adjustments. Since they can be tightened or loosened very quickly, quick clamping shaft collars are particularly useful in the printing and packaging industries, where they will not impede frequent item changeouts or regular setup adjustments.
Heavy Duty, Thin Line, and Double Wide Shaft Collars
Application requirements and limitations sometimes necessitate variations in the non-bore dimensions of a shaft collar. In high axial load applications where threaded shafting is not possible or on large shafts over 3” (75mm), wider, stronger shaft collars should be used as space allows.
have greater widths and outer diameters to take advantage of the increased torque of larger screws. When increasing the outer diameter is not an option, increasing the width of the shaft collar enough to support additional screws is also an effective way of increasing holding power. have similar advantages to stacking several shaft collars and can increase holding power up to 25%.
In space or weight-restricted applications such as encoders, with reduced widths, outer diameters, and screw sizes are often the correct choice. Ultimately, an unnecessary excess of holding power also means an unnecessary excess of width, outer diameter, and weight.
Threaded Shaft Collars & Bearing Locknuts
A popular shaft collar variation is the . They are typically manufactured in one- and two-piece clamp styles because they do not permanently damage the shaft, can be repositioned, and are simpler to remove when compared to set screw collars. Threaded clamping shaft collars are particularly useful in applications with high axial loads and applications requiring fine location or preload adjustments.
In high axial-load applications, threaded instead of round shafting may be desired. Round bore collars rely on friction to resist axial loads, making them susceptible to movement when shocked. Threaded collars create a positive mechanical stop through the interface of the threads on the collar and shaft. This makes it nearly impossible to move the collar axially without breaking the shaft itself.
Clamp-style threaded collars also make it easier to perform fine adjustments and preloading of components such as bearings. The collar can simply be threaded into the location and locked in place by tightening the screw to proper torque levels.
are threaded collars made to AFBMA standards and specifically designed to mate with high precision spindle bearings commonly found on CNC mills and lathes. They have more precise TIR than standard shaft collars to ensure even pressure on the entire bearing face and precise preload control. Spanner wrench slots are machined into the outer diameter, allowing for easy access and fine preload adjustment. As with other threaded shaft collars, once the preload is established, the locknut can be secured by tightening the clamp screw.
Hex and D-Bore Shaft Collars
Not all shaft collars are manufactured with round bores. are designed to fit hex shafting. This allows for higher torque capabilities when used in positive drive applications (assuming the shafting is not over or undersized). have a single flat in the bore and can be used in place of set screw shaft collars, which are commonly used with d-shafting. When used on appropriate shafting, they offer higher holding power, more even surface contact, and will not mar the shaft.
Mountable Shaft Collars
either have flats and holes in the outer diameter or face holes through the collar. in the outer diameter allow the shaft collars to be easily mounted to each other, sensor brackets, or metallic plates with no significant detriment to holding power. are typically offered with threaded or through holes giving the user flexibility to use the hardware or mounting option of their choice. They are commonly used to mate with sprockets, pulleys, metallic plates, or other components.
Deciding On A Shaft Collar
Despite being somewhat simple components, shaft collars can be complicated and critical to the performance of an application. Designers have many factors such as style, material, bore size, and shaft geometry to consider before a selection can be made. This article, along with performance and sizing information available on the website, should help users make a more informed decision. If additional help is needed, the user can always contact the manufacturer directly to help with selection.