PartDesign: Profilo ad evolvente
DisegnoPezzo IngranaggioEvolvente |
Posizione nel menu |
---|
DisegnoPezzo → Ingranaggio Evolvente... |
Ambiente |
DisegnoPezzo |
Avvio veloce |
Nessuno |
Introdotto nella versione |
- |
Vedere anche |
Nessuno |
Description
Descrizione
Questo strumento consente di creare un profilo 2D dell'evolvente di un ingranaggio. Questo profilo 2D è completamente parametrico, e può essere estruso con la funzione DisegnoPezzo Pad di PartDesign.
Per informazioni più dettagliate consultare le voci di Wikipedia per: Gear e Involute Gear
For more detailed information see Wikipedia's entries for: Gear and Involute Gear
Usage
Create the profile
Utilizzo
Create a spur gear
- Select the gear profile in the Tree view.
- Press the PartDesign Pad button.
- Set the pad's DatiLength to the desired face width of the gear.
- Click OK.
Create a helical gear
- Select the gear profile in the Tree view.
- Press the PartDesign AdditiveHelix button.
- Choose as Axis the normal of the gear profile, that is Normal sketch axis introduced in version 0.20. (In earlier versions the Base Z axis can be used as long as the profile's plane has not been altered.)
- Choose a Height-Turns mode.
- Set the DatiHeight to the desired face width of the gear.
- To set the desired helical angle an Expression for the DatiTurns is required.
- Click the blue icon at the right of the input field.
- Enter the following formula:
Height * tan(25°) / (InvoluteGear.NumberOfTeeth * InvoluteGear.Modules * pi)
, where25°
is an example for the desired helical angle (also known as beta-value) andInvoluteGear
is the DatiName of the profile. - Click OK to close the formula editor.
- Click OK to close the task panel.
Hint: To make the helical angle an accessible parameter, use a dynamic property:
- Select the profile.
- In the Property editor activate the Show all option in the context menu.
- Again in the context menu, select Add Property. Note: this entry is only available when Show all is active.
- In the Add Property dialog:
- Choose
App::PropertyAngle
as Type. - Set
Gear
as Group. - Set
HelicalAngle
as Name (without a space). - Click OK.
- Choose
- Now a new property DatiHelical Angle (space added automatically), with an initial value of
0.0°
, becomes available. - Assign the desired helical angle to the new property.
- In the formula of the DatiTurns property of the AdditiveHelix, you can now reference
InvoluteGear.HelicalAngle
instead of the hard coded value of e.g.25°
; again assumingInvoluteGear
is the DatiName of the profile.
Cut a hub for an involute splined shaft
- Activate the correct body.
- Create an internal involute gear profile with the required number of grooves and adapt the values of pressure angle, addendum-, dedendum- and root fillet coefficient. See also the table in Notes below for feasible values. For example:
- DatiExternal Gear: False
- DatiNumber Of Teeth: 12
- DatiPressure Angle: 37.5°
- DatiAddendum Coefficient: 0.45
- DatiDedendum Coefficient: 0.7
- DatiRoot Fillet Coefficient: 0.3
- Select the gear profile in the Tree view.
- Press the Pocket button.
- Set the pocket's DatiType to Through All.
- Check the pocket's DatiSymmetric To Plane option.
- Click OK.
Properties
- DatiAddendum Coefficient: The height of the tooth from the pitch circle up to its tip, normalized by the module. Default is 1.0 for the standard full-depth system. introduced in version 0.21
- DatiDedendum Coefficient: The height of the tooth from the pitch circle down to its root, normalized by the module. Default is 1.25 for the standard full-depth system. introduced in version 0.21
- External gear: True o false
- Alta precisione: True o False
- Modulo: Diametro diviso per il numero di denti.
- Numero di denti: Impostare il numero di denti.
- Angolo di pressione: Angolo acuto tra la retta di pressione e la normale alla congiungente i centri degli ingranaggi. Di default è 20 gradi. (Altre info)
- DatiProfile Shift Coefficient: The distance by which the reference profile is shifted outwards, normalized by the module. Default is zero. Profile shift may be positive or negative. introduced in version 0.21
- DatiRoot Fillet Coefficient: The radius of the fillet at the root of the tooth, normalized by the module. Default is 0.38 as defined by the ISO rack. introduced in version 0.21
Notes
- In order for two gears to mesh they need to share the same module and pressure angle. Expressions may help to ensure consistency. Their center distance needs to be
(NumberOfTeeth + OtherGear.NumberOfTeeth) * Modules / 2
(that is in case of the sum profile shift being zero). Subtract the number of teeth in case of an internal gear.
- Profile shifting can be used to prevent undercut on gears with a small number of teeth. Another application is to adjust the center distance of two gears with a given number of teeth and module.
- When visually checking for proper meshing or interferences a much lower value for VistaDeviation is helpful, e.g. 0.05 instead of the default 0.5. Otherwise the representation in the 3D view may be too coarse.
- For standard gears the most common pressure angle is 20 °, followed by 14,5 °. Other applications, notably splines, use higher angles.
- The standard full-depth system uses an addendum coefficient of 1.0 and a dedendum coefficient of 1.25, resulting in a clearance of 0.25 (the difference between the addendum of the one gear and the dedendum of the other). The actual tooth length is the sum of both coefficients, multiplied by the module.
- Tooth length reduction may be required to prevent undercut or to strengthen the teeth (see stub teeth). For internal gears the addendum (here pointing inwards) may need shortening to avoid certain interferences or non-involute flanks; when indicated in combination with longer teeth of the pinion.
- For splined shafts and hubs ISO 4156 defines the following parameters:
Pressure Angle 30 ° (flat root) 30 ° (fillet root) 37,5 ° 45 ° Addendum Coefficient 0.5 0.5 0.45 0.4 Dedendum Coefficient 0.75 0.9 0.7 0.6 Root Fillet Coefficient 0.2 0.4 0.3 0.25
Limitations
- It is currently not possible to adjust the tooth thickness. Tooth and tooth space are distributed equally on the pitch circle. Thus the only way to control backlash is to adjust the center distance in a gear paring.
- There is currently no undercut in the generated gear profile. That means gears with a low number of teeth can interfere with the teeth of the mating gear. The lower limit depends on the DatiPressure Angle and is around 17 teeth for 20° and 32 for 14.5°. Most practical applications tolerate a missing undercut for gears a little smaller than this theoretical limit though.
Tutorials
Video: How to make gears in FreeCAD
Correlazioni
PartDesign
- Structure tools: Part, Group
- Helper tools: Create body, Create sketch, Attach sketch, Edit sketch, Validate sketch, Check geometry, Create a sub-object(s) shape binder, Create a clone, Create a datum plane, Create a datum line, Create a datum point, Create a local coordinate system
- Modeling tools:
- Additive tools: Pad, Revolution, Additive loft, Additive pipe, Additive helix, Additive box, Additive cylinder, Additive sphere, Additive cone, Additive ellipsoid, Additive torus, Additive prism, Additive wedge
- Subtractive tools: Pocket, Hole, Groove, Subtractive loft, Subtractive pipe, Subtractive helix, Subtractive box, Subtractive cylinder, Subtractive sphere, Subtractive cone, Subtractive ellipsoid, Subtractive torus, Subtractive prism, Subtractive wedge
- Boolean: Boolean operation
- Dress-up tools: Fillet, Chamfer, Draft, Thickness
- Transformation tools: Mirrored, Linear Pattern, Polar Pattern, Create MultiTransform, Scaled
- Extras: Migrate, Sprocket, Involute gear, Shaft design wizard
- Context menu: Set tip, Move object to other body, Move object after other object, Appearance, Color per face
- Preferences: Preferences, Fine tuning
User documentation
- Getting started
- Installation: Download, Windows, Linux, Mac, Additional components, Docker, AppImage, Ubuntu Snap
- Basics: About FreeCAD, Interface, Mouse navigation, Selection methods, Object name, Preferences, Workbenches, Document structure, Properties, Help FreeCAD, Donate
- Help: Tutorials, Video tutorials
- Workbenches: Std Base, Assembly, BIM, CAM, Draft, FEM, Inspection, Mesh, OpenSCAD, Part, PartDesign, Points, Reverse Engineering, Robot, Sketcher, Spreadsheet, Surface, TechDraw, Test Framework
- Hubs: User hub, Power users hub, Developer hub