What are the parts of a sprue cutter?
The handles of sprue cutters are made from steel, which is often covered with a sleeve made of PVC (polyvinyl chloride) or TPR (thermoplastic rubber), to provide more comfort and a better grip.
On smaller, thinner sprue cutters designed for cutting plastic, the end of the steel handle is shaped to form the jaws and cutting edge.
The handle sleeves of a sprue cutter can serve several purposes. However, their main function is to give the user a better grip and provide a more comfortable way of holding the sprue cutter for use over longer periods of time.
Other roles performed by the handle sleeves include protecting the handle from damage and helping retain the ends of some types of return spring. The handle sleeve is made of plastic. For more information see
The pivot point is the point around which the jaws pivot as they are opened or closed. Some heavy duty sprue cutters may have two pivot points, one for each jaw.
The return spring opens the jaws of the sprue cutter once the user releases the pressure on the handles. There are three types of spring commonly used on sprue cutters:
Dual leaf springs
Dual leaf springs are two thin pieces of metal attached to the handles just behind the pivot point (fulcrum) of the jaws. As the handles are pressed together the two leaf springs come into contact with each other and are pushed together. Once the force on the handles is reduced, the leaf springs push the handles back, opening the jaws.
Dual leaf springs provide the least resistance of the three spring designs, so less effort is required on the part of the user, avoiding fatigue when the cutter is used for long periods. However, if the cutter becomes stiff due to corrosion or dirt, dual leaf springs may not provide sufficient force to open the jaws.
Multi coil spring
Multi coil springs are either located just behind the pivot point (fulcrum) of the jaws like dual leaf springs or further down between the handles. It is possible to achieve a wide range of sprung resistance with multi coil springs by varying the spring size, coil thickness and position of the spring.
Small multi coil springs positioned close to the jaw pivot point will provide the least resistance while larger, thicker coiled springs, positioned further down between the handles, will provide the most.
Single coil spring
This type of spring looks like a keyring with two arms attached to it. The two arms of the spring are attached to the handles in one of three places.
With the arms of the spring attached to the handles just behind the pivot point of the jaws, the keyring-like spring sits between the two handles. This attachment position provides the least resistance to the user, and so will result in less fatigue during long periods of use.
With the arms of the spring attached midway down the handles, the keyring-like spring sits just behind the pivot point of the jaws. With the spring arms attached to the handles in this position, much of each arm is often covered by the handle sleeves or handles themselves.
With the arms of the spring attached to the ends of the handles, the keyring-like spring sits further behind the handles. This attachment position provides the maximum resistance possible with this type of spring.
The toggle joint is not found on all sprue cutters, only those which have a compound lever action, also known as multi-leverage (see). The toggle joint is the pivot point of the handles, but not the jaws. Instead the ends of the handles attach to the jaws at the secondary lever point.
Secondary lever point
The secondary lever point is where the handles attach to the jaws of sprue cutters with a compound lever action. This is what turns the output lever force from the handles into the much greater input lever force for the jaws, creating the compound lever action. The secondary lever point is not found on sprue cutters that do not have a compound lever action.
The jaws are the parts of the sprue cutter that cut the moulded parts from the sprue. On many sprue cutters designed for use only on plastic sprues, the ends of the handle are shaped to form the jaws of the cutter. This allows them to be thinner to reach into smaller spaces for more delicate work.
On some models that feature a compound lever action the jaws can be replaced once they become blunt or damaged. The jaws on these sprue cutters can have either one or two pivot points.
Jaws that feature two pivot points have an upper and lower flat bar or plate connecting the two halves of the jaws. The two pivot points are positioned at each end of the flat plates connecting the two halves of the jaws. This type of jaw construction is most commonly seen on large, heavy-duty sprue cutters with replaceable jaws.
The thickness of sprue cutter jaws varies depending on the thickness and type of material they are designed to cut. The jaw thickness is usually given in millimetres. However, it may also be seen in fractions of an inch on sprue cutters sold in the U.S.
Thicker jaws will be stronger and so able to cut through thicker sprues or ones made of harder materials. However, thicker jaws are less able to get into tight spaces so are not suited for removing small, intricate parts from a sprue. Generally, thinner jaws are found on single action sprue cutters designed for use with plastic model making. Thicker jaws are found on compound lever sprue cutters designed for use on metal by jewellers.
The jaw width of a sprue cutter is the measurement of the distance between the outsides of the two jaws. Sprue cutters with a greater jaw width will have stronger jaws that are better suited to cutting through thicker, harder material. However, sprue cutters with a greater jaw width will not be able to access and remove parts from a tightly packed sprue, or small delicate parts.
Longer jaws have a greater reach for getting in and removing parts from a tightly packed sprue. However, the cutting ability of the jaws is vastly reduced further away from the jaw's pivot point. Short jaws have more strength and cutting ability at their tips.
Some sprue cutters feature jaws that are angled. This can help the jaws to gain access to tightly packed sprues or removal of small delicate parts from sprues. Jaw angles can range from no angle at all (0 degrees) up to nearly 90 degrees.
The cutting edges are the inside edges of the jaws that actually perform the cutting of the sprue. The angle or bevel placed on the cutting edges will determine the quality of the finish achieved on the cut of the part by the sprue cutter.
What is a bevel?
The bevel has an acute angle (less than 90 degrees) which forms the cutting edge of the jaw. The jaws of sprue cutters may have one or two bevels placed on their cutting edges. For more information on bevels see our page