How to machine double lead acme threads on a CNC machine


The Accutron single-lead Acme style form thread profile is widely used in many engineering applications. Basically, it’s a type of right-hand lead screw with a pronounced thread crest and a flat root. It’s very similar to a standard Acme thread except that instead of having two different helix angles on each thread, it has only one helix angle for the entire length of the thread. This thread form is extremely popular with the aerospace industry and is specially designed for use in applications requiring lightweight, rigidity, and high torque requirements.

There are two ways to machine double lead acme threads on CNC.

The first method is to use a standard acme thread mill, which will produce the thread with a single pass.

The second method is to use a standard square end mill and machine the thread in two passes. This method will also work for single lead acme threads.

With either method you will need an angle setting block, or an angle measuring device, to set the compound angle of the spindle, and a rotary dial indicator on the table to measure X travel.

double lead acme threads

Create a tool with a negative rake angle (pointing towards the Z-direction).

In order to create a tool with a negative rake angle (pointing towards the Z-direction), go to the Tool Creation tab and follow these steps:

1. Click on the ‘Create’ button.

2. Choose one of three options: select ‘New tool’, ‘Copy from library’, or ‘Copy from workspace’.

3. If you choose to create a new tool, specify its parameters.

4. If you choose to copy it from the library or workspace, select either ‘Library’ or ‘Workspace’ in the drop-down menu. After that, select a tool in the list and click on the ‘Create’ button next to it.

Create the thread with a high feed and the helix direction of the flank.

The thread is created with a helix angle, which can be adjusted by the user. This is done using the directional shape of the thread (the shape of the section on any plane perpendicular to its axis). In other words, this helical shape is rotated around an axis to create a screw thread. For example, when you look at a screw under a microscope, you will see that it has a cross-section similar to that of a triangle or trapezoid. This section is called “thread form”.

Set the number of pitches you want in one revolution.

For a standard thread, the pitch is the reciprocal of the number of threads per inch. The same is true for metric threads, except the unit of measure is millimeters per thread. A thread’s pitch diameter can be measured with a micrometer or a caliper.

The pitch diameter of a thread is the diameter at which the width between the two threads and the width of each thread are equal to one-half of the pitch. It is also where the widths of the crests and roots of an external (male) thread and internal (female) thread are equal to one-half of the pitch.

Acme threads are measured by their nominal major diameter, or outside diameter (OD), and their number of starts, or threads per inch (TPI). The OD determines which size fastener will fit into an Acme threaded hole. The TPI determines the angle that each thread will make with respect to other nearby threads.

Make sure your toolpath is aligned to the start of the thread.

The first thing you need to do is make sure your toolpath is aligned to the start of the thread. In this case, I am using a 2mm end mill (a 1/8″ would work too) and the toolpath is aligned to the very edge of the end mill. If you are using a center drill or spotting drill instead of an end mill, then align your toolpath to the center of that tool.

In order to make a thread, we need to make a bunch of roughing passes across the width of the thread. For threads greater than 1/4″ diameter, I typically use a 3/16″ or 1/4″ ball end mill for roughing. The reason for this will be more clear later on when we look at finishing passes. If you are using an end mill for your roughing pass, then you need to create an offset for your toolpath by half the diameter of your end mill. This will ensure that our roughing pass cuts right down the middle of our part.

Check path and simulate to make sure everything is ready to go.

Open the part file and make sure there are no errors. Check the path and simulate to make sure everything is ready to go.

I will be using a 1/2″ diameter Acme thread milling cutter for this part. You can use a thread mill for any size thread but it is more economical to buy a thread mill for each size you will be making. This is because thread mills do not have cutting edges past the first cutting diameter. The rest of the body is just a placeholder to locate the tool when machining.

We will cover topics like how to create a double cut thread, how to machine a double lead thread, how to set up open cam software on your Mac, and how to use open cam software in conjunction with your CNC machining operation.

The first thing we need to do is decide how many threads per inch we want to create. Let’s say we want to make a 1/2″ x 13 thread. We need to determine how many revolutions it will take our machine to make one thread. If you divide the linear distance of your thread into the circumference of the piece you are machining, you will get the number of revolutions. So if my thread is 1″ long and I want a 1/2″ wide thread, then I will divide 2 pi by 1, which equals 6.283 revolutions.

The next step is to decide how many threads per inch you want to create. In this case, let’s say we want a double lead thread with 20 threads per inch. To get this number, multiply 6.283 by 2 (because it takes two turns for each thread), then multiply by 20 (because there are 20 threads per inch). The result is 250.1 turns or 100 turns for each end of the toolpath.

You can calculate the threading information for a double lead acme screw on your cnc machine by performing some simple math calculations.

Step 1: Find the pitch diameter of the thread.

Step 2: Find the major diameter of the thread.

Step 3: Find the minor diameter of the thread.

Step 4: Find the lead of the thread.

Step 5: Identify if the thread is right hand or left hand.

Step 6: Calculate RPM required to machine the thread at a specific rate (surface speed) (sfm).

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