Acme Screw Torque Calculator
Calculate Acme power screw torque from thread angle, mean diameter, lead, axial load, nut friction, collar friction, collar diameter, and screw speed.
⚙Named Acme presets
Load a common Acme or trapezoidal screw setup, then adjust the load, friction, collar, and speed for your application.
📏Thread, load, friction, and collar inputs
Use the maximum lifting, clamping, or translating force on the screw.
Use pitch or mean diameter, not the outside diameter.
Lead equals pitch for a single-start screw.
Standard Acme is 29°; ISO trapezoidal is commonly 30°.
This is the screw thread friction coefficient before flank-angle correction.
Changing the nut material updates this field; you can override it.
Mean rubbing diameter of thrust collar, washer, or bearing face.
Equivalent sliding friction used for collar torque.
Used for travel speed and input power estimate.
Acme screw torque result
🔧Friction and geometry grid
📚Reference tables
| Nominal screw | Mean diameter estimate | Common lead | Typical use |
|---|---|---|---|
| 1/2-10 Acme | 0.450 in | 0.100 in/rev | Bench vise, small clamp, or hand slide. |
| 3/4-6 Acme | 0.667 in | 0.167 in/rev | Router lift, light table lift, or fixture screw. |
| 1-5 Acme | 0.900 in | 0.200 in/rev | Machine jack, press screw, or adjustable support. |
| 1-1/2-4 Acme | 1.375 in | 0.250 in/rev | Heavy clamp, platen press, or lifting screw. |
| Tr20x5 metric | 18.2 mm | 5.0 mm/rev | Linear actuator or machine axis with bronze nut. |
| Nut pair | Planning friction | Torque effect | Self-lock note |
|---|---|---|---|
| PTFE lined nut, lubricated | 0.04 to 0.06 | Low raising torque | May backdrive at higher lead angles. |
| Delrin or acetal nut | 0.07 to 0.10 | Low to moderate torque | Good for light, quiet motion. |
| Bronze nut, lubricated | 0.08 to 0.12 | Common power screw value | Usually self-locking at modest leads. |
| Cast iron nut, oiled | 0.12 to 0.16 | More input torque | Higher hold margin, more heat. |
| Steel on steel or dirty service | 0.18 to 0.25 | High torque and wear risk | Check lubrication and galling. |
| Collar support | Equivalent friction | Best fit | Watch item |
|---|---|---|---|
| Ball thrust bearing | 0.01 to 0.03 | Powered actuators and frequent lifting. | Bearing load rating and contamination. |
| Needle thrust bearing | 0.03 to 0.05 | Compact thrust support under high load. | Washer hardness and lubrication. |
| Lubricated steel collar | 0.06 to 0.10 | Simple hand jack or clamp collar. | Rubbing diameter and heat. |
| Bronze thrust washer | 0.08 to 0.14 | Shop fixtures and sliding thrust faces. | Wear-in changes torque. |
| Dry or dirty collar | 0.18 to 0.30 | Only for conservative rough checks. | Can exceed thread torque. |
| Check | Formula basis | Good screen | Meaning |
|---|---|---|---|
| Lead angle | atan(lead / pi x mean diameter) | Small for jacks | Steeper lead raises efficiency and backdrive risk. |
| Acme friction | mu x sec(half thread angle) | Use actual lubrication | Thread angle increases normal force. |
| Thread torque | F x d/2 x tangent friction term | Positive and stable | Torque at screw thread before collar losses. |
| Collar torque | F x mu collar x collar diameter / 2 | Lower with bearings | Often a major part of handwheel torque. |
| Efficiency | F x lead / (2 x pi x torque) | Higher with lubrication | Overall value includes collar loss. |
💡Torque tips and safety
Acme screws is utilized in applications where a load must move slow, and Acme screws are often used to lift a platform or clamp a workpiece to a machines. The torque required to turn an Acme screw is dependent upon the load on the Acme screw, the geometry of the thread, and the friction between the Acme screw, the nut, and the thrust surface. These values needs to be estimated in order to determine the size of the motor that is required to turn the Acme screw, or the effort that is required to turn the handwheel.
A change in either the thread angle or the lubrication of the Acme screw can impact whether the load easily lift or stalls when attempting to turn the Acme screw. The Acme screw torque calculator require that the user enters the load, mean diameter, lead, and friction coefficients for the thread and collar. Each of these values has an impact upon the resulting value of the required torque.
How to Calculate Acme Screw Torque
The mean diameter of the Acme screw is the value that is located between the major and minor diameter measurement of the screw. The lead of the Acme screw is the distance that the load advance during one complete turn of the Acme screw. The lead angle for Acme screws is typically 29 degrees which provides higher friction against the movement of the load than a screw with a flat thread surface.
In addition to the friction between the Acme screw and the nut, there is also friction between the load and the collar that holds the Acme screw. The friction between these components can be very high. For instance, if the load is steel, the dry friction between the steel component can be more than the friction between the threads of the Acme screw.
Because the calculator has separate fields for the collar diameter and friction coefficient, these two separate friction coefficients can be accounted for separate. For instance, if the plain collar is replaced with a ball thrust bearing, the required torque will decrease. Such a decrease in the calculated torque will be reflected in the holding torque result of the calculator.
Another important parameter related to the behavior of the Acme screw with the load is the self-locking behavior of the screw. With a lead angle and friction coefficient that is typical for both Acme screws and loads, it is unlikely that the load will attempt to move on its own; this behavior is referred to as self-locking. An increase in the lead or the friction coefficient can impact the ability of the Acme screw to hold the load.
The lowering torque result will indicate whether or not the load will remain in place without the need for an external brake to the moving load. In reality, the conditions of the Acme screw system can be different than those that is described within the calculation. For instance, dirt or grit can increase the friction coefficients between the screw and the nut.
The load may be unevenly distributed, the temperature of the components may change, or the components may wear over time. Each of these issues will increase the friction between the Acme screw and the nut. As a result, the service factor is applied to the load that is entered in the calculator to determine the resulting torque that must be applied to the screw.
The efficiency of the system is another parameter that is related to the calculation of the torque that is required to turn the Acme screw. The efficiency of the system is a function of the lead angle of the Acme screw, the friction coefficients for the thread and the collar, and the service factor. As with efficiency alone, the efficiency of the system will be lower than the efficiency of the thread alone due to the friction between the collar and the load.
Low efficiency is not always a bad thing, especially for applications where the load with be very heavy or the load will not be moved very frequent. The speed of the Acme screw is related to the rotation of the Acme screw. If the rotation speed of the Acme screw (RPM) is increased, the linear speed at which the load moves is also increased.
However, higher RPM will also increase the heat generated by the system due to friction between the components, which may shorten the life of the lubrication for the screw. The power calculations is performed in order to determine whether the motor that is to be used will be able to handle the load. Determining the power of the system allows for an understanding of whether a small motor can handle the job, or whether a larger motor or even a cooling system is required for the motor.
Some of the most common mistake for those who are calculating the torque for an Acme screw is using the wrong diameter for the screw, or ignoring the friction between the collar and the load. One of the most common mistakes is using the major diameter of the screw as the mean diameter for the screw. This will lead to underestimations of the torque that is required to turn the Acme screw.
Another of the most common mistakes is to ignore the friction between the load and the collar. If the friction between these two components is ignored, the effort that is required to turn the handwheel will be greater than the value that was calculated by the thread-only friction calculation. Another consideration for the design of the Acme screw system is the friction between the components.
The friction between the nut and the Acme screw may change over time due to wear of the nut, for instance. If the torque required to raise the load increases over time, it may be necessary to check the collar of the system to ensure that it isnt the reason for the increase in the required torque for raising the load. One of the factors in the calculation of friction coefficients is the material of the nut.
One of the most common materials for nuts is bronze. Bronze can handle heavy loads, and bronze readily accepts lubrication. Another potential problem with bronze is that bronze can gall against stainless steel Acme screws if the fit of the screw and nut is too tight.
Another material for nuts is plastic. Plastic nuts require little maintenance, and they are quiet when the load move. However, plastic nuts may soften with high temperature, or may deform under high pressures.
If the lowering torque result is a negative number, it indicates that the load will move on its own. In other words, it will be possible for the load to create enough force to rotate the Acme screw to move the load. In such cases, it may be necessary to incorporate either a brake, locknut, or a motor with holding torque.
By calculating each of the parameters listed above, the designer is able to understand how the various components of the Acme screw will interact with one another. For instance, using a larger lead will increase the rate at which the load moves, but will decrease the holding torque of the system. Using a thrust bearing in place of a plain collar will reduce the required torque to turn the Acme screw, but will increase the cost of the system.
Using lubricated service instead of dry service will reduce the required torque by thirty percent or more. These types of trade-offs in the system are easily understood once each of the parameters is entered into the torque calculator. An Acme screw is essentially an inclined plane that is rotated around a cylinder.
The torque calculator estimates the force that is required at the rim of a handwheel or at the shaft of a motor. Such a calculation takes into account the angles of the thread of the Acme screw and the friction that exists between the screw components that rub against each other. Once each of the parameters are understood in relation to the torque that is required to turn the Acme screw, it is possible to make design decisions regarding the diameter of the Acme screw, the lead of the screw, the lubrication of the system, and the type of collar that is to be used in the system.
