Understanding Screw Sizes In Solidworks: A Guide (2024)

SolidWorks is a software application that allows users to design and model mechanical components. One of the most common uses of SolidWorks is to design fasteners, such as screws, bolts, nuts, and washers. When creating a screw in SolidWorks, it is important to first decide on the type of screw, such as a hex cap screw, and refer to the specifications, which are usually provided in inches. The size of a screw in SolidWorks is defined by its major diameter and threads per inch for ANSI inch threads, while metric threads are defined by the letter M followed by the nominal thread size in millimetres. Understanding screw sizes in SolidWorks is crucial for accurate modelling and ensuring compatibility with other mechanical components.

Creating a screw in SolidWorks

SolidWorks is a software application that can be used for creating 3D digital models. The software has a Design Library that includes common components used in mechanical design, such as screws, which users can easily add to their models. Here is a step-by-step guide on how to create a screw in SolidWorks:

Accessing the Design Library

The Design Library can be found in the task pane of the SolidWorks application. This library includes a range of standard parts, such as fasteners, which are commonly used in mechanical design and sold by suppliers. The Design Library is a useful feature for quickly adding pre-made components to your model, saving time and effort in the design process.

Using Smart Fasteners

SolidWorks introduced a tool called Smart Fasteners to streamline the process of specifying fasteners, including screws, in your model. While this tool may contain bugs, it can be useful when adding multiple fasteners to your design. Smart Fasteners can be accessed through the SolidWorks Toolbox, which is included with most versions of SolidWorks.

Adding a Screw to Your Model

To add a screw or other fastener to your model, simply drag and drop the desired fastener from the SolidWorks Toolbox or Design Library into your model. Automatic mates, or constraints, will be added if you select a compatible edge to drop the fastener onto. Once the fastener is in place, you can specify its type settings and add more fasteners of the same type if needed.

Customizing Your Screw

The Design Library primarily includes standard parts, but if you need a specialty screw or fastener, you can use models from supplier websites, such as McMaster-Carr. You can also add your own custom-designed standard parts to the Design Library. This allows you to create a library of commonly used screws or fasteners that are specific to your design needs.

By following these steps, you can efficiently create and customize screws in SolidWorks, utilizing the software's Design Library and Smart Fasteners tools to streamline your workflow and enhance your mechanical designs.

Screw size specifications

When it comes to SolidWorks, the Design Library is a commonly used feature, which contains many default standard parts used in mechanical design. It is particularly useful for fasteners such as screws, bolts, nuts, set screws, and washers.

The second number in the sequence denotes the number of threads per unit of distance between threads, also known as the "thread pitch". Unified screws provide the number of threads per inch. For example, 4-30 x .10 has 30 threads per inch. Metric threads display the number of millimetres per thread. So, M5-.4 x 15 indicates a thread every 0.4 millimetres.

The third number, generally following the "x", represents the length of the screw. With the exception of flathead screws, which are designed to sit flush with the surface, the length is measured to the bottom of the head. Unified screws express length in inches. For example, 1/8-10 x 4/6 has a length of four-sixths of an inch. Metric screws, on the other hand, measure length in millimetres. For instance, M5-.4 x 15 indicates a length of 15 millimetres.

It is important to note that the sequence of diameter, thread count/pitch, and length should always be maintained when specifying screw sizes.

Screw head design

Designing the head of a screw in SolidWorks requires careful attention to detail and a clear understanding of the desired screw type. In this case, we will be creating a hex cap screw, specifically a 1/4 20 hex cap screw.

To begin, we need to create a new part, ensuring that the specifications are set to inches as per the chosen screw type. We then move to the right plane and initiate a sketch using the polygon tool. The polygon tool allows us to create polygons with any number of sides, and for this screw head, we will select six sides. It is important to note that we can still rotate the polygon after placing it, so we must assign a vertical relationship to the origin to lock its position.

The next step involves adding dimensions to our sketch. Referencing the screw specifications, we set the "A" dimension, which represents the flat-to-flat distance on the hex, to 0.4280. With our sketch fully defined, we can proceed to extrude it. Before doing so, we ensure that the "Instant2D" command is disabled, allowing us to change the dimensional value to "A". This ensures that the dimension is displayed as "A" instead of a numerical value.

After extruding the sketch, we specify the distance as our "H" dimension, which in this case is 0.150. Similar to the previous step, we ensure that "Instant2D" is disabled, then double-click on the head to change the dimension to "H". This makes it more convenient for future modifications, such as creating different sizes or configurations.

With the basic shape of the screw head established, we can now round off the edges. To do this, we go to the front plane and start a new sketch. We create a center line down the center of the screw head and then draw a simple triangle with a 30-degree angle and a diameter equal to the "A" dimension. This triangle will serve as the profile for the rounding operation.

A useful trick in SolidWorks is to set the dimension of the triangle's diameter equal to the "A" dimension. By doing so, we ensure that the diameter of the cut circle always touches the flat-to-flat distance of the hex, creating a smooth and precise rounding effect. This trick allows for easy adjustments when designing different screw sizes, as changing the "A" dimension will automatically update the diameter of the cut.

In conclusion, designing a screw head in SolidWorks involves a series of careful steps, from creating the initial sketch to rounding off the edges. By following these instructions and paying attention to the specific dimensions and settings, users can create accurate and customizable screw heads in SolidWorks.

Screw size and 3D printing

When it comes to 3D printing, selecting the appropriate screw size is crucial for ensuring a secure and functional assembly. Here are some detailed guidelines and considerations for choosing the right screw size for your 3D printing projects:

Standard Screw Sizes for 3D Printing

M3 and M5 screws are the most commonly used sizes in 3D printing projects. These screws are typically used for attaching components or assembling printed parts. Having a variety of lengths for these screw sizes is recommended, as different applications will require screws of varying lengths.

Factors to Consider when Choosing Screw Size

When determining the appropriate screw size for your 3D printed project, there are several factors to keep in mind:

• Disassembly and Reassembly: If your project requires frequent disassembly and reassembly, consider using threaded inserts or self-tapping screws. These options provide a more secure and robust assembly, allowing for repeated installation and removal without degrading the plastic.
• Strength and Durability: For projects requiring higher strength or holding forces, metal screws with metal threads or inserts are recommended. Metal provides superior strength and wear resistance compared to plastic.
• Material Compatibility: Choose screws that are compatible with the material of your 3D printed parts. For example, self-tapping screws work well with ductile materials or those with high elongation, such as nylon powders or resins. However, they may cause cracking in brittle materials with low elongation.
• Thread Size: When designing custom threads, stick to larger thread sizes such as 1/4"–20 (imperial) or M6 (metric) or larger. Smaller screws may require customisation for better engagement and wear characteristics.
• Surface Finish: Consider the surface finish of your 3D printed parts. SLA and SLS 3D printing technologies provide a smoother surface finish, making them preferable for assemblies that will undergo multiple cycles of assembly and disassembly.
• Support Structures: Minimise support structures on threaded surfaces to ensure smooth assembly. Excess support material on threaded surfaces can hinder the assembly process and may require additional post-processing.
• Design Complexity: If your project involves complex assemblies or larger components, consider using threaded inserts or nuts incorporated into the design. These methods provide strong and secure fastening but require careful design and accessibility after printing.

Tools for Identifying Screw Sizes

To identify and work with screw sizes, there are some helpful tools and resources available:

• Screw Measuring Devices: Prusa Printers has created a 3D-printable screw measuring device that can help you sort and measure metric screws ranging from M2 to M5 and lengths from 4mm to 50mm.
• CAD Software: When designing custom screw threads or complex assemblies, consider using CAD software such as Fusion 360 or Blender. These tools allow for precise modelling and design of screw threads and mating structures.
• Hardware Stores and Online Retailers: Local hardware stores or online retailers like Amazon offer a wide range of screw sizes and types. You can take a sample screw to a hardware store to find a matching size, or purchase assorted screw sets specifically labelled for 3D printers.

Screw size and metrication

When it comes to SolidWorks, the Design Library is a commonly used feature, filled with components used in mechanical design, including fasteners such as screws, bolts, nuts, and washers. Understanding screw sizes is essential, and while it may seem daunting at first, it's actually quite straightforward.

Screw Sizes and Metrication:

Screw sizes can be measured using two systems: the imperial system and the metric system. It's important to know which system is used where you plan to purchase your screws. The metric system is based on millimetres (mm), while the imperial system uses inches.

Metric System:

Metric screw sizes are commonly seen on screw packages and are denoted by the letter "M" followed by three numbers. For example, "M6 x 1.00 x 25". Here's what each number means:

• The first number after the "M" denotes the screw diameter in mm.
• The second number represents the screw pitch, which is the distance between each thread on the screw, also in mm.
• The third number indicates the screw length, measured from the tip of the screw to where the screw head sits, in mm.

Metric machine screws are limited to four basic head shapes: countersunk, raised countersunk, panhead, and cheesehead. The head dimensions are directly related to the basic screw diameter.

Imperial System:

The imperial system, on the other hand, uses a combination of gauge numbers, fractions of an inch, and length measurements. Here's how to interpret screw sizes in this system:

• The first number represents the gauge, which corresponds to a certain fraction of an inch in diameter. For example, a #0 gauge screw has a diameter of 1/16 of an inch.
• The length of the screw is measured in inches, from the tip of the screw to where the screw head rests when fully embedded.
• The thread spacing, or pitch, is determined by counting the number of threads per inch.

It's worth noting that imperial screw sizes may sometimes only include two numbers: the gauge and the length. In such cases, the screw has a standard number of threads.

In conclusion, understanding screw sizes and metrication is crucial, especially when using tools like SolidWorks. By familiarising yourself with both the metric and imperial systems, you can ensure that you select the right screws for your projects, avoiding the frustration of ending up with the wrong size.

Frequently asked questions