# Self Reversing Screw Design

• George Zucas
The answer to your question is in the kinematics of the rolling contact. Tangential speed on the rolling cam varies with the radius and the cam follower contacts the wall of the groove over a range of radii. Ideally, it should roll on the groove wall without slipping, and this requires that the radius of the follower must vary as well. If a cylindrical follower is used, there must necessarily be slipping, and slipping means additional wear.

#### George Zucas

Hello everyone,

I am trying to design a self reversing screw. What I am doing is, I am sketching a rectangle and using extruded cut option in Solidworks, cut it along a helical curve. One more and this time in the opposite direction. It comes out nicely. Now what I don't know is, should I use a rectangle or a trapezoid for the profile? I examined a self reversing screw and I am sure it was a rectangle. Though I've found a video on youtube and the guy there uses a trapezoid. Does anyone know this? Trapezoidal thread seems more logical but then I wonder why the one I've seen is rectangle. I'd like to get as much information as possible about self reversing screws, especially the relationships between the screw dimensions and the small part that is going around (sorry I don't know its name). Google doesn't help much. Here is the video:

(Skip to sixth minute)

Thank you.

Last edited:
The answer to your question is in the kinematics of the rolling contact. Tangential speed on the rolling cam varies with the radius and the cam follower contacts the wall of the groove over a range of radii. Ideally, it should roll on the groove wall without slipping, and this requires that the radius of the follower must vary as well. If a cylindrical follower is used, there must necessarily be slipping, and slipping means additional wear.

Dr.D said:
The answer to your question is in the kinematics of the rolling contact. Tangential speed on the rolling cam varies with the radius and the cam follower contacts the wall of the groove over a range of radii. Ideally, it should roll on the groove wall without slipping, and this requires that the radius of the follower must vary as well. If a cylindrical follower is used, there must necessarily be slipping, and slipping means additional wear.

Yeah after some more investigating I got it. It is logical but the screw I've seen confused me a bit. Thanks.

Last edited:
Thanks Felmon. I've found that in one of the previous projects company manufactured such a screw. They told me to make one similar to that so I copied it. It was a trapezoidal section and the angle between the side lines were 60 degrees. It has been in use for 15 years so I think the wear is not a problem (or it is not by much even if it isn't the best design possible). I made the follower similar to this:

http://www.abssac.co.uk/uploads/site/products/p_ogw2f/img_selfreversing.jpg

## 1. What is a self-reversing screw design?

A self-reversing screw design is a type of screw mechanism that allows for the screw to rotate in both clockwise and counterclockwise directions without needing to turn the screwdriver around. This is achieved through a specific thread pattern on the screw and a corresponding design on the screwdriver.

## 2. What are the benefits of using a self-reversing screw design?

The main benefit of using a self-reversing screw design is the convenience and time-saving aspect. With a regular screw, the screwdriver needs to be removed and repositioned when it reaches the end of the screw. With a self-reversing screw, this step is eliminated, making the process quicker and more efficient. It is also useful in tight spaces where there is limited room for the screwdriver to rotate.

## 3. How does a self-reversing screw design work?

A self-reversing screw design works by using a specially designed screw that has a thread pattern that allows for clockwise and counterclockwise rotation. The screwdriver also has a corresponding design that allows it to engage with the screw and rotate in both directions without needing to be repositioned. This is achieved through a combination of different thread angles and depths on the screw and screwdriver.

## 4. What applications are self-reversing screw designs commonly used in?

Self-reversing screw designs are commonly used in applications where there is a need for quick and efficient screwing, such as assembly lines, construction, and manufacturing industries. They are also useful for tasks that require repetitive screwing, as it reduces strain on the user's hand and wrist.

## 5. Are there any drawbacks to using a self-reversing screw design?

One potential drawback of using a self-reversing screw design is the cost. These types of screws and screwdrivers are more complex to manufacture, which can result in a higher price compared to regular screws. Additionally, the unique thread pattern may make it difficult to find replacement screws or screwdrivers if one is lost or damaged.