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Set screw (also known as Grub screw) is a special type of screw which is used to prevent relative moment of two parts. Unlike screw, a set screw is threaded over its entire length.
In many applications, a setscrew is used instead of key to prevent relative motion between the hub and the shaft.
The end of the grub screw is known as the point. The friction between the point and the part to be held, prevents relative motion between them.
Types of points in grub screws
As shown in the above image there are five types of points found in set screws. They are
- Cup point
- Conical point
- Oval point
- Dog point
- Flat point
Flat point: It is used when the lateral force applied randomly. It is also used at the places where the threaded part does not have sufficient thickness.
Dog point: It is used when the lateral force is large. It is also used at the places where the threaded part has sufficient thickness.
Conical point: It is used when the lateral force is small. It is also used at the places where the threaded part does not have sufficient thickness.
Oval point: It causes minimal surface damage to the held part. The minimal contact area helps in making slight adjustments without loosening the screw.
Cup point: It is used for fast permanent and semi-permanent assemblies. It is also used where some indentation by the screw point is acceptable.
Selection of set screw material
Following materials are generally used for manufacturing the set screws (or Grub screws)
- Nylon set screws: They are lightweight and water resistant
- Plastic set screws: They are inexpensive and corrosion resistant. They are generally used for light loads.
- Copper alloy set screws: They are wear resistant and have good load capacity.
- Aluminium set screws: They are thermally and electrically conductive. They are light and easy to manufacture.
- Bronze and Brass set screws: They are water resistant
- Stainless Steel set screws: They have good strength and are corrosion resistant
- Steel set screws: They have good strength
- Titanium set screws: They are strong, light and corrosion resistant
Apart from above material, sometimes finishing material is also applied to the set screws. Finishing material provides durability and corrosion resistance to the set screws. Here are some common finishing materials used for set screws.
- Zinc: Its coating acts as a sacrificial anode, protecting the underlying metal. It is applied as fine white dust.
- Chrome: Its coating gives a bright, reflective finish. It is decorative and very durable. It is applied by electroplating.
- Black oxide: Its coating is mostly used for aesthetic purpose. It does not enlarge the dimensions of the set screw. It is a processed black rust.
Applications of Set screw
Set Screw can be used in following conditions
- When the parts that are fastened, are thick enough to accommodate threaded hole.
- There is no place to accommodate the head.
- When the parts that are fastened, have sufficient strength to accommodate durable threads.
- These are used when the parts are seldom dismantled.
Featured image source:
By Allen Manufacturing Company Inc – Allen Manufacturing Company Inc (1913-01-01), “Allen Safety Set Screw advertisement”, in The Automobile Trade Directory[1], volume 11, issue 1, New York, New York, USA, page 325, Public Domain, https://commons.wikimedia.org/w/index.php?curid=30047592