# Torque capacity of D-shaft (shaft with a milled flat)

• cumfy
In summary, the discussion revolves around finding the torque capacity equation for a D-shaped shaft with a D-shaped hub and without a set screw. While there is no direct reference for this, a past forum post referenced Roark's Handbook which provides an equation for a similar application. This equation takes into account the radius of the shaft and the flat side of the shaft.
cumfy
There are numerous references to the basic equation for the torque capacity of a keyed shaft, but I can find absolutely nothing for a simple D-shaped shaft (ie a plain shaft with a single, plain, parallel flat milled on it) with a D-shaped hub. No set screw.

It seems so simple but there's nothing, the nearest reference I could find was on this forum 5 years back https://www.physicsforums.com/showthread.php?t=293700, in which no one could give a solution.

Anyone know of a definitive treatment/reference ?

I believe there was a solution in the forum 5 years back where a user referenced Roark's Handbook. I've used the following equation from Roark's on a past project for what appears to be similar to your application. At the time, I didn't have access to FEA software to check against.

Tau_max = Torque/(B*r^3) where B = 0.6366+1.7598*h/r - 5.4897*(h/r)^2 +14.062*(h/r)^3 - 14.510*(h/r)^4 + 6.434*(h/r)^5 where h = the radius of the shaft minus the radius of the flat side of shaft (assuming you draw a circle tangent to the flat side line).

## 1. What is a D-shaft?

A D-shaft is a type of shaft that has a flat, D-shaped cross-section. This shape allows for a more secure connection with a corresponding part, such as a gear or pulley, compared to a round shaft.

## 2. How is torque capacity determined for a D-shaft?

The torque capacity of a D-shaft is determined by its diameter, material strength, and the depth and width of the flat surface. The wider and deeper the flat surface, the higher the torque capacity.

## 3. What is the maximum torque that a D-shaft can handle?

The maximum torque capacity of a D-shaft can vary depending on its size and material. However, on average, a D-shaft can handle torque ranging from 10-25% higher than a round shaft of the same diameter.

## 4. Can a D-shaft handle both clockwise and counterclockwise torque?

Yes, a D-shaft can handle both clockwise and counterclockwise torque. The flat surface allows for a secure connection in either direction.

## 5. Are there any limitations to the torque capacity of a D-shaft?

Yes, there are limitations to the torque capacity of a D-shaft. If the torque exceeds the maximum capacity, the shaft may experience bending or shearing, leading to failure. It is important to consider the specific application and choose a D-shaft with an appropriate torque capacity.

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