Scripted Parts: Ball Bearing - Part 2/it

Tutorial
Argomento
Parti con script - Cuscinetto a sfere - #2
Livello di difficoltà
Base
Tempo di esecuzione
30 min
Autori
r-frank
Versione di FreeCAD
0.16.6706
Files di esempio
Vedere anche
Nessuno

Introduzione

Questo tutorial si propone di introdurre i principianti alla creazione di parti con script python all'interno di FreeCAD.
Questo tutorial descrive come costruire un cuscinetto a sfere con un flusso di lavoro che consiste nel creare degli schizzi e rivoluzionarli.
Il codice produrrà un nuovo documento di FreeCAD con 12 forme (anello interno, anello esterno e 10 sfere).
Esso sarà simile a questo:

Workflow

The workflow is more or less identical how you would create the part in part design workbench.
Just some small differences.

• Create a new empty document and make it the active document
• Draw the basic shape of the outer ring consisting of four straight lines and four arcs

• Connect the lines and arcs and upgrade them to one single wire
• Upgrade the wire to a face
• Revolve the face to get a shape
• Draw a circle
• Upgrade circle to wire
• Upgrade wire to face
• Revolve face and apply boolean cut to obtain groove in outer ring
• Draw the basic shape of the inner ring consisting of four straight lines and four arcs
• Connect the lines and arcs and upgrade them to one single wire
• Upgrade the wire to a face
• Revolve the face to get a shape
• Draw a circle
• Upgrade circle to wire
• Upgrade wire to face
• Revolve face and apply boolean cut to obtain groove in inner ring
• Insert balls with same workflow as in part 1 (because of effectiveness)
• Set view to axometric
• Zoom to fit all

Making the groove

Drawing an arc needs either three points or a start angle and an end angle.
In the sketcher we would use constraints to define the start point and the end point of the arc.
Since we can't do this in scripting, we draw a rounded rectangle and revolve it to get a basic "ring shape".
Then we draw a circle and revolve it to get the geometry of the groove.
Then we apply a boolean cut to the two revolved shapes and we have the complete shape of the inner/outer ring.
Side note: Since we can't use coincident constraints on the end points of the lines/arcs we have to convert our
geometry to a wire, upgrade it to a face and then we are able to revolve the face to get a shape.

Inserting the balls

The correct sketcher-based workflow of inserting the balls would be:

• Draw an arc (semi-circle) with center being identical with the origin and draw a line closing the "open" side of the arc
• Convert the two elements to a wire, upgrade to a face, revolve around z-axis to get a ball shape
• Use "translate" command to move the ball into correct position
• Repeat the above steps nine times involving math function to create and position the other balls
• This repeat-operation could be programmed with a loop

Now this is not effective, inserting primitives and positioning them is easier and faster in this case.
So we use the same method as in "Scripted Parts: Ball Bearing - Part 1".

Link

Script di oggetti: La pagina wiki che spiega i principi fondamentali di scripting
Script di dati topologici: Un tutorial per fornire le basi di scripting
Parti con script: Cuscinetto a sfere - Parte 1: Costruirlo con primitive di Parte
Bearings from scripted sketches: Base per questo tutorial, grazie a JMG ...

Code

## Ball-bearing script
## 11.08.2016 by r-frank (BPLRFE/LearnFreeCAD on Youtube)
## based on ball bearing script by JMG
## (http://linuxforanengineer.blogspot.de/2013/12/bearings-from-scripted-sketches.html)
#
#needed for doing boolean operations
import Part
#needed for calculating the positions of the balls
import math
#needed for translation and rotation of objects
from FreeCAD import Base
#
#VALUES#
#(radius of shaft/inner radius of inner ring)
R1=15.0
#(outer radius of inner ring)
R2=25.0
#(inner radius of outer ring)
R3=30.0
#(outer radius of outer ring)
R4=40.0
#(thickness of bearing)
TH=15.0
#(number of balls)
NBall=10
#(radius of ball)
RBall=5.0
#(rounding radius for fillets)
RR=1
#first coordinate of center of ball
CBall=((R3-R2)/2)+R2
#second coordinate of center of ball
PBall=TH/2
#
#Create new document
App.newDocument("Unnamed")
App.setActiveDocument("Unnamed")
App.ActiveDocument=App.getDocument("Unnamed")
Gui.ActiveDocument=Gui.getDocument("Unnamed")
#
#Lines for basic shape of outer ring
L1o=Part.makeLine((R4,0,TH-RR),(R4,0,RR))
L2o=Part.makeLine((R4-RR,0,0),(R3+RR,0,0))
L3o=Part.makeLine((R3,0,RR),(R3,0,TH-RR))
L4o=Part.makeLine((R3+RR,0,TH),(R4-RR,0,TH))
#Corner rounding for basic shape of outer ring
A1o=Part.makeCircle(RR,Base.Vector(R4-RR,0,RR),Base.Vector(0,1,0),0,90)
A2o=Part.makeCircle(RR,Base.Vector(R3+RR,0,RR),Base.Vector(0,1,0),90,180)
A3o=Part.makeCircle(RR,Base.Vector(R3+RR,0,TH-RR),Base.Vector(0,1,0),180,270)
A4o=Part.makeCircle(RR,Base.Vector(R4-RR,0,TH-RR),Base.Vector(0,1,0),270,360)
#Connect Lines and arcs to make wire and upgrade to face, revolve and apply cut to obtain groove
OR=Part.Wire([L1o,A1o,L2o,A2o,L3o,A3o,L4o,A4o])
OR=Part.Face(OR)
OR=OR.revolve(Base.Vector(0,0,1),Base.Vector(0,0,360))
C1=Part.makeCircle(RBall,Base.Vector(R2+(R3-R2)/2,0,TH/2),Base.Vector(0,1,0),0,360)
GRo=Part.Wire([C1])
GRo=Part.Face(GRo)
GRo=GRo.revolve(Base.Vector(0,0,1),Base.Vector(0,0,360))
OR=OR.cut(GRo)
Part.show(OR)
#
#Lines for basic shape of inner ring
L1i=Part.makeLine((R2,0,TH-RR),(R2,0,RR))
L2i=Part.makeLine((R2-RR,0,0),(R1+RR,0,0))
L3i=Part.makeLine((R1,0,RR),(R1,0,TH-RR))
L4i=Part.makeLine((R1+RR,0,TH),(R2-RR,0,TH))
#Corner rounding for basic shape of inner ring
A1i=Part.makeCircle(RR,Base.Vector(R2-RR,0,RR),Base.Vector(0,1,0),0,90)
A2i=Part.makeCircle(RR,Base.Vector(R1+RR,0,RR),Base.Vector(0,1,0),90,180)
A3i=Part.makeCircle(RR,Base.Vector(R1+RR,0,TH-RR),Base.Vector(0,1,0),180,270)
A4i=Part.makeCircle(RR,Base.Vector(R2-RR,0,TH-RR),Base.Vector(0,1,0),270,360)
#Connect Lines and arcs to make wire and upgrade to face, revolve and apply cut to obtain groove
IR=Part.Wire([L1i,A1i,L2i,A2i,L3i,A3i,L4i,A4i])
IR=Part.Face(IR)
IR=IR.revolve(Base.Vector(0,0,1),Base.Vector(0,0,360))
C2=Part.makeCircle(RBall,Base.Vector(R2+(R3-R2)/2,0,TH/2),Base.Vector(0,1,0),0,360)
GRi=Part.Wire([C2])
GRi=Part.Face(GRi)
GRi=GRi.revolve(Base.Vector(0,0,1),Base.Vector(0,0,360))
IR=IR.cut(GRi)
Part.show(IR)
#
#Balls#
for i in range(NBall):
  Ball=Part.makeSphere(RBall)
  Alpha=(i*2*math.pi)/NBall
  BV=(CBall*math.cos(Alpha),CBall*math.sin(Alpha),TH/2)
  Ball.translate(BV)
  Part.show(Ball)
#
#Make it pretty#
App.activeDocument().recompute()
Gui.activeDocument().activeView().viewAxometric()
Gui.SendMsgToActiveView("ViewFit")