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Press Fit Calculator

Calculates elastic cylindrical co-axial pressure connections for compact or hollow shafts in either hot or cold state. The program calculates geometric parameters of the joint, minimal fit, standard or actual fit, and pressed-on parts material selection.

The calculation is only valid for press fits in which permanent deformations will not occur after the connection. The deformations do not include trueing of peaks and ridges on the surface texture.

This calculation is only valid for connections that are not loaded by outside pressure or are made from tubular parts with unlimited length. The parts are made from materials that behave according to Hooke's law.

The calculation does not consider the influence of centrifugal forces, ribs, or other reinforcement parts or in parts where the temperature is distributed unevenly.

A press fit joint with unlimited length is a joint with the length that equals the diameter or greater. If it is shorter, the real contact pressure is greater than calculated. This calculation provides more safety against the press fit loosing.

General information

Minimal interference is determined when securing the least required loading capacity of the press fits, together with other factors.

The maximum interference is determined without existing plastic deformation, according to the HMH plasticity condition (Huber, Misses, Hencky) together with other factors.

Pressing speed must be slow (about 3 mm/s ~ 0.12 in/s) while making the press fit. High speed reduces load capacity of the fit.

Calculated temperatures must be considered as minimum, because they do not consider temperature averaging during the pressing process, nor the hub cooling time after pulling it from the furnace, for example.

TipSee the Engineer's Handbook for formulas, materials, and other instructions used for designing elastic press fits.

Procedures

Design a press fit

 On the ribbon, click Design tabPower Transmission panelPress Fit Calculator.On the Calculation tab, set the desired values, criteria, and materials.Click Calculate. Click OK to insert press fit calculation to the Autodesk Inventor Assembly.

Calculation in Metric Units

This procedure creates an example using the sample specifications.

Sample Data:

• Clamping Factor (pressing) n1 = 0.055
• Hub Material = Steel
• Shaft Material = Steel
 On the ribbon, click Design tabPower Transmission panelPress Fit Calculator.On the Calculation tab:In the Required Load box, select Required Torque and enter Torque = 500 and Safety Factor = 1.In the Dimensions box, enter Outer Diameter = 100 and Connection Length = 78.In the Advanced box, check the Surface Smoothness box and enter Clamping Factor = 0.09 and Clamping Factor (pressing) = 0.055.In the Temperature box, select Limitation of Shaft Cooling.In the Hub Material box, check the box to open Material Database. Select Steel and click OK.In the Shaft Material box, check the box to open Material Database. Select Steel and click OK.Click Calculate. The optimum H8/u8 fit is designed and the ambient temperature is calculated as 20° C, on the condition is that the shaft is not cooled.Click OK to insert press fit calculation to the Autodesk Inventor Assembly.

Calculation in English Units

This procedure creates an example using the sample specifications.

Sample Data:

• Torque Mp = 370 lbforce ft
• Safety Factor k = 1
• Outer Diameter D2 = 4 in
• Shaft Diameter D1 = 3 in
• Connection Length L = 3 in
• Clamping Factor n = 0.9
• Clamping Factor (pressing) n1 = 0.055
• Hub Material = Steel
• Shaft Material = Steel
 On the ribbon, click Design tabPower Transmission panelPress Fit Calculator.On the Calculation tab:In the Required Load box, select Required Torque and enter Torque = 370 and Safety Factor = 1.In the Dimensions box, enter Outer Diameter = 4 and Connection Length = 3.In the Advanced box, check the Surface Smoothness box and enter Clamping Factor = 0.09 and Clamping Factor (pressing) = 0.055.In the Temperature box, select Limitation of Shaft Cooling.In the Hub Material box, check the box to open Material Database. Select Steel and click OK.In the Shaft Material box, check the box to open Material Database. Select Steel and click OK.Click Calculate. The optimum H8/u8 fit is designed and the ambient temperature is calculated as 68° F, on the condition is that the shaft is not cooled.Click OK to insert press fit calculation to the Autodesk Inventor Assembly.

References

Press Fit Calculator

Sets parameters for calculation of a press fit.

 Access: Ribbon: Design tabPower Transmission panelPress Fit Calculator

 Enter values for required transferred loading. Required Torque Performs a calculation according to required torque. Required Force Performs a calculation according to required force. Torque Maximum torque required to transfer between shaft and hub. Force Axial force required to transfer between shaft and hub. Safety Factor Enter the value of safety factor. This value is multiplied with force or torque and in fact describes size of over design. Use higher number than 1.0 specially if non-static load is applied.

Dimensions

 Enter dimensions for press fit. If you enter values that do not correspond with other dimensions, the values are displayed in red. Outer Diameter Enter outer diameter of the hub. Shaft Diameter External shaft diameter in place of contact. Inner Diameter Internal shaft diameter of hollow shaft. If solid shaft is considered use 0.0. Connection Length Enter length of pressure connection.

Limits and Fits

 This part of the panel is used to find standard fit for shaft and hub. Fit Symbol Standard hub and shaft fit that is calculated based on ISO or ANSI standard. Change... Opens the Limits and Fits Mechanical Calculator - Interference Fit dialog box. You can adjust the maximum and minimum interference. Click OK to return to the Calculation tab. Fundamental Deviations If the corresponding standard fit for the calculated maximum possible and minimum possible interference cannot be found, the limit deviations are calculated and numerically expressed. In the tolerance field, you can adapt the limit deviations. You cannot exceed maximum possible or minimum possible interference. If so, the calculated interferences are shown in red and display an error message. To adapt limit deviations, clear the check box for the Specify manually option in the Fundamental Deviations box. Note: When you click Calculate, Design Accelerator presents a new solution or calculates new limit deviations. Your changes are not saved. When you edit the fields, partial results are calculated. It is not necessary to start the calculation again.

 Assembly Clearance Assembly clearance is an important dimension for the shaft cooling temperature calculation and hub warming. You can specify the dimension only when the Assembly Clearance check box is selected. Surface Smoothness Surface quality affects the size of the trueing at contact surfaces and the size of efficient interference. Trueing is not applied to perfectly smooth surfaces. For smooth surfaces, the efficient interference equals the minimum interference and the maximum loading capacity. The Surface Smoothness fields for editing surface quality are only available when you select the Surface Smoothness check box. If you clear the check box, you can specify the value of trueing. The surface quality value is not used in the calculation. Clamping Factor The calculation contains a table of minimum values for the steel parts clamping coefficient. Click the arrow on the Clamping Factor box to open the Clamping Factor table. Clamping Factor (pressing) Applies this factor for connections manufactured (connected) in the cold state. Pressing force affects the assembly shaft and hub.

Hub Material

 Opens the Material Database where you select a material. Edit the properties of the material, if needed. Material can be selected form predefined values. All properties that are used in calculation are displayed and can be modified if "user" material is selected.

Shaft Material

 Opens the Material Database where you select a material. Edit the properties of the material, if needed. Material can be selected form predefined values. All properties that are used in calculation are displayed and can be modified if "user" material is selected.

Temperature

 Limitation of Hub Warming Up Sets limitations for hub warming up. Limitation of Shaft Cooling Sets limitations for shaft cooling. Hub Warming Up Specifies the minimum warming up temperature for the hub if the connection is assembled in the hot state. Base Temperature Specifies the base temperature of the surroundings environment. Shaft Cooling Specifies the minimum cooling temperature of the shaft if the connection is assembled in the hot state.

Results

Displays the results of strength proportion calculation. Also, the hub warming temperature is shown, which can be reduced by using shaft cooling.

Summary of Messages

Displays the reports about calculations. To open the Summary of Messages area at the bottom of the tab, double-click the double line at the bottom of tabs or click the chevron.

Toolbar Commands