A round part does not always require a three-finger gripper, and a two-finger model does not necessarily mean lower positioning accuracy. The choice depends on how the workpiece enters the working area: whether it needs to be moved horizontally, fed into a chuck, installed in a fixture, rotated, or accurately aligned with the machine axis.
For a round bar, bushing, flange, cylindrical housing, or ring, it is important to define the gripping method before selecting a model. A mistake at this stage can lead to part slippage, misalignment during feeding, longer cycle times, and overload of the custom fingers.
A pneumatic gripper for round parts is selected based on five key parameters:
- workpiece diameter and length;
- gripping method: friction-based or form-fit;
- required part position after gripping;
- length and weight of the custom fingers;
- loads during movement, acceleration, braking, and rotation.
When a two-finger parallel gripper is needed
A two-finger parallel pneumatic gripper is suitable for external gripping of a round part by its side surfaces. It is selected when the workpiece needs to be moved horizontally, transferred between operations, loaded into a machine, or removed after machining.
This solution is often used for:
- round bar stock;
- pipes;
- cylindrical workpieces;
- bushings;
- rollers;
- parts with two convenient opposite gripping areas.
The jaws of a parallel gripper move toward each other simultaneously. The custom fingers are designed according to the shape of the part: with a radius cutout, support surface, form-fit stop, or another contour that reduces the risk of displacement.
For typical automation tasks, parallel pneumatic grippers of the VGTR series with T-shaped guides are suitable. If higher loads, longer fingers, or increased resistance to moments are required, the VGFR series with a toothed guide should be considered.
For example, for a round bar with a diameter of 50-70 mm, when the finger opening range must be at least 48-72 mm and the one-sided stroke must be at least 12 mm, the VGFR72-192 or VGTR73-194-L models can be considered as preliminary options. This is not a ready-made calculation for every case, but a guideline for the selection logic.
When a three-finger centering pneumatic gripper is needed
A three-finger centering pneumatic gripper is selected when it is important not only to hold a round part, but also to align it relative to the axis. This design is especially effective when feeding a workpiece into a chuck, collet, measuring device, jig, or technological fixture.
The three fingers move radially toward the center and distribute the gripping force across several contact points. This helps achieve a stable position of the round part before the next operation.
A three-finger gripper is a rational choice for:
- bushings;
- flanges;
- rings;
- cylindrical housings;
- shafts when gripped from the end face;
- parts that need to be centered before installation.
The VGTZ series uses T-shaped guides and is suitable for standard centering tasks. The VGFZ series is equipped with a toothed guide and is designed for more demanding conditions where load capacity, stable movement, and operation with increased moments are important.
For compact round parts, VGFZ34-68 can be considered. This model has three fingers, a stroke of 6 mm per jaw, and a maximum allowable distance between fingers of 70 mm. However, the final choice depends not only on the part diameter, but also on the design of the custom fingers, surface material, weight, and cycle conditions.
External gripping or centering: the key difference
External gripping answers the question: how to hold the part reliably during movement.
A centering gripper answers another question: how to hold the part and position it along the axis at the same time.
A two-finger parallel model should be selected when:
- the part is moved horizontally;
- there are two opposite gripping areas;
- centering around the entire circumference is not required;
- a wide choice of sizes and stroke versions is important;
- the fingers need to be adapted to the specific part geometry.
A three-finger centering gripper is needed when:
- the part has a round cross-section;
- symmetrical fixation is required;
- the risk of misalignment before installation must be reduced;
- centering by the outer diameter is important;
- the workpiece is fed into a machine, collet, or fixture with limited tolerance.
Friction-based and form-fit gripping
With friction-based gripping, the part is held by friction between the custom fingers and its surface. This option is possible, but it requires a sufficient force reserve. The result is affected by oil, coolant, dust, surface roughness, coating, and robot acceleration.
For smooth or oily parts, friction-based gripping may not be sufficient. In such cases, it is better to use fingers with a form-fit stop: they rest against a shoulder, groove, protrusion, slot, or another feature of the part.
Form-fit gripping is especially useful when:
- the part is heavy;
- the surface is covered with coolant or oil;
- the workpiece has an offset center of gravity;
- the operation includes acceleration, rotation, or sudden stopping;
- high repeatability of machine feeding is required.
Why custom finger length matters more than it seems
Gripping force is specified for a particular force application point. The farther the working surface of the finger is from the jaw, the lower the actual force in the contact area with the part and the higher the moment load on the gripper.
Excessively long or heavy fingers can lead to the following problems:
- reduced holding force;
- vibrations during opening and closing;
- increased load on the guides;
- lower repeatability;
- accelerated wear;
- housing deformation if the allowable overhang is exceeded.
If the required finger overhang exceeds the allowable range for the selected model, it is usually better to choose a larger gripper size rather than try to compensate by increasing the pressure. According to our recommendations, the fingers should be as short and lightweight as possible within the limits of the technological task.
How to account for part weight and center of gravity
The maximum workpiece weight specified in the model card should not be treated as a universal limit. It depends on the gripping method, finger shape, coefficient of friction, direction of movement, and cycle dynamics.
During selection, the total weight of the assembly is calculated:
- the pneumatic gripper itself;
- custom fingers;
- adapter plate;
- sensors;
- the part;
- a rotary unit or compensation module, if required.
The position of the center of gravity is especially important. A long round workpiece can create a high load on the gripper and robot wrist even with a relatively low weight. The farther the center of gravity is from the mounting point, the higher the moment on the jaws, gripper housing, and robot flange.
How to choose between VGTR, VGFR, VGTZ, and VGFZ
VGTR are two-finger parallel grippers with T-shaped guides. They are suitable for standard automation tasks, moving round parts, loading and unloading machines, and transferring workpieces between operations.
VGFR are two-finger parallel grippers with a toothed guide. They should be considered for higher loads, increased finger length, higher stability requirements, and minimal backlash.
VGTZ are three-finger centering grippers with T-shaped guides. They are suitable for round workpieces when centering by the outer diameter is required.
VGFZ are three-finger centering grippers with a toothed guide. This series is used in more demanding applications where load capacity, stable positioning, and service life when working with round parts are important.
What to check before ordering
Before selecting a pneumatic gripper for round parts, prepare the following:
- a drawing or 3D model of the workpiece;
- outer diameter and tolerance;
- part length;
- weight and material;
- surface condition: dry, oily, with coolant, rough;
- gripping area;
- gripping method;
- center of gravity position;
- required orientation during feeding;
- cycle time;
- data on the robot, gantry, or automatic line;
- need for sensors, a rotary unit, or self-locking.
Clean compressed air is required for stable gripper operation. Moisture, dust, and oil in the pneumatic line can lead to wear, jamming, and unstable movement of the moving components.
Selecting a pneumatic gripper for a round part
A pneumatic gripper for round parts should be selected together with the custom fingers and the installation method in the cell. For horizontal transfer of bar stock or a cylindrical part, a parallel gripper is more often used. For precise feeding of a bushing, flange, or ring into a machine, a three-finger centering model is usually the more rational choice.
Send us a drawing, 3D model, or workpiece parameters. KIPVALVE specialists will help select a pneumatic gripper for round parts, custom fingers, position sensors, and compatible components for your technological process.
Frequently Asked Questions
Can a two-finger gripper be used for round bar stock?
Yes, if the part is moved horizontally and the custom fingers provide reliable external gripping. For round bar stock, KIPVALVE documentation specifies the use of the VGTR and VGFR parallel series.
When is it better to choose a three-finger gripper?
When a round part needs to be centered before installation into a chuck, collet, fixture, or measuring unit. Three fingers provide symmetrical holding by the outer diameter.
Why can a part slip even when the gripping force is sufficient?
The cause may be oil or coolant on the surface, long fingers, an offset center of gravity, robot acceleration, or the use of friction-based gripping where a form-fit stop is required.
Can gripping force be increased by raising the pressure?
Only within the limits specified for the particular model. Pressure above the allowable range does not replace the correct choice of gripper size, finger shape, and gripping method.
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