HOW TO CREATE A 3D MODEL OF PARALLEL THREADS IN 3D CAD SOFTWARE

In this article, we discuss the method for creating a 3D model of a parallel thread. In common, there are five steps for creating a 3D model of a parallel thread:

• Step 1: Search for the thread specifications.
• Step 2: Create a shaft whose diameter is equal to the major diameter of the thread.
• Step 3: Create the thread profile that uses the shaft's axis as the thread axis.
• Step 4: Create the helix, which has the same pitch as the thread.
• Step 5: Use the "Swept Cut" function to cut the material of the shaft to create the 3D model of the thread.

Let's continue with the example of an external metric screw thread M6x1 6g.

Step 1: Search for the thread specifications

First, we need the dimensions of the external metric screw thread, M6x1 6g. Read this article, "How to Create a Parallel Thread Profile with CAD Software", to know how to search for thread dimensions using this website. We got the information for the external metric screw thread, M6x1 6g, as below:

Now go to step 2.

Step 2: Create a shaft whose diameter is equal to the major diameter of the thread

We make a shaft with a diameter equal to the thread's major diameter, that is: 5.884mm. We also add a chamfer to the shaft end that we want to be the start of the thread; this chamfer is used to remove the burr at the start of the thread. The size of the chamfer can be calculated using this formula: C = (major diameter - minor diameter)/2 + tolerance. Let's say the tolerance is 0.1mm; the chamfer value will be C = (5.884 - 4.835)/2 + 0.1 = 0.6245 mm.

Step 3: Create the thread profile that uses the shaft's axis as the thread axis

Follow the instructions in this article, "How to Create a Parallel Thread Profile with CAD Software", to create a thread profile for the external metric screw thread M6x1 6g. Use the axis of the shaft as the axis of the thread. We can choose the end of the shaft as the standard plane for the thread profile.

For the external thread, the basic form of the thread is the top of the thread (male shape), so we will use the bottom of the thread or valley form of the thread (female shape) to create the basic valley profile for the "Swept Cut" function. Just choose a valley outside the shaft, trim unnecessary lines from the thread profile, and we have the basic valley profile.

Step 4: Create the helix, which has the same pitch as the thread

Create a plane such that the normal vector is the axis of the shaft and goes through the tip of the basic valley profile. Use this plane to create the helix curve. The basic diameter of the helix equals the minor diameter of the thread, and the pitch of the helix is the pitch of the thread. The length of the helix is determined by the effective length of the thread; the length of the helix should be one pitch longer than the effective length of the thread. And the direction of the helix is determined by the right- or left-hand thread.

Step 5: Use the "Swept Cut" function to cut the material of the shaft to create the 3D model of the thread

After we have the basic valley profile and the helix as the path, use the "Swept Cut" function to remove material from the shaft to create the 3D model of the external metric screw thread M6x1 6g. Some 3D CAD software doesn't have the "Swept Cut" function; at that time, we will create a "Swept" function to create the shape of the valley, then use "Boolean Subtract" to subtract the shape of the shaft from the shape of the valley, and we will have the 3D model of the thread.

The way to create the 3D model for internal parallel threads is the same as with external threads. For internal threads, the basic profile of the thread will be the valley profile or bottom profile of the thread (female shape); use it as the basic valley profile.

Here is an example of creating a 3D model for the internal metric screw thread M6x1 6H. We search for the specifications listed below:

The tolerance for the major diameter is not specified, so we use the same tolerance as the pitch diameter.

First, create a hole such that the diameter is equal to the minor diameter of the thread, which is 5.035 mm. We also add a chamfer to the hole; the size of the chamfer is C = (6.075-5.035)/2 + 0.1 = 0.62 mm. Next, create the thread profile and the helix. Finally, use "swept cut" function to create the thread shape.