×
INTELLIGENT WORK FORUMS
FOR ENGINEERING PROFESSIONALS

Log In

Come Join Us!

Are you an
Engineering professional?
Join Eng-Tips Forums!
  • Talk With Other Members
  • Be Notified Of Responses
    To Your Posts
  • Keyword Search
  • One-Click Access To Your
    Favorite Forums
  • Automated Signatures
    On Your Posts
  • Best Of All, It's Free!
  • Students Click Here

*Eng-Tips's functionality depends on members receiving e-mail. By joining you are opting in to receive e-mail.

Posting Guidelines

Promoting, selling, recruiting, coursework and thesis posting is forbidden.

Students Click Here

Jobs

How to create involute gear

How to create involute gear

How to create involute gear

(OP)
Hello everyone.

I have faced problem with create involute gear in NX. First of all in Cartesian coordinates the involute of a circle has the parametric equation:

CODE

x=r*(cosΘ+ΘsinΘ)
y=r*(sinΘ-ΘcosΘ) 
In NX there is law curve -> law by equation but when I put this two equation I get line. What I do wrong?

I also found this manual:

Link

but when I create gear with small numbers of teeth the shape of teeth doesn't match shape of co-working gear. In attachment I put my gear with imported geometry from Hasco to show problem. Anyone have forced similar problem and can help me?

With best regards
Michael

RE: How to create involute gear

I did it few years ago..
Link

RE: How to create involute gear

You must add variable t=0

xt=function(t)

RE: How to create involute gear

(OP)
I have this values:

CODE

t=0
xt=r*sin(t*360)-2*pi()*r*(t*360)/360*cos(t*360)
yt=r*cos(t*360)+2*pi()*r*(t*360)/360*sin(t*360) 
I also tried

CODE

xt=r*sin(t)-r*t*cos(t)
yt=r*cos(t)+r*t*sin(t) 

but I get line. Please look at the attached pictures.
Link
Link
The main problem is, when I create gear with small no of tooth for example z=20, there are some differences between my model and imported geometry from hasco. There are also collisions with co-working gear. Do You remember which function You used to create law curve?


With best regards
Michael

RE: How to create involute gear

Attached is a zip containing several different GRIP and User Function programs that will create gears. Perhaps you might be able to use one of them for your task. After downloading the file, edit the file extension from .zipper to .zip before attempting to extract the files.

John R. Baker, P.E.
Product 'Evangelist'
Product Engineering Software
Siemens PLM Software Inc.
Digital Factory
Cypress, CA
Siemens PLM:
UG/NX Museum:

To an Engineer, the glass is twice as big as it needs to be.

RE: How to create involute gear

(OP)
Yes Cowski You have right but:

Quote:


On 14-1/2°PA gears undercutting occurs where a number of teeth is less than 32 and for 20° PA less than 18. Since this condition becomes more severe as tooth numbers decrease, it is recommended that the minimum number of teeth be 16 for 14-1/2° PA and 13 for 20° PA.
I had taught that

CODE

Zlimit=2*y/sin2alpha.
so for normal tooth y=1 
and for alpha=20° 
Zlim=17 
So to prevent undercut I choose Z=20 to small gear. I think the main problem if in involute function or in angle.

With best regards
Michael

RE: How to create involute gear

(OP)
Thanks John I will try your solution. Do you have any manuals about law curve by equation, because in documentation there is only one example.

With best regards
Michael

RE: How to create involute gear

(OP)
Thanks everyone for help. Tomorrow I will try Yours examples.

With best regards
Michael

RE: How to create involute gear

Look in your NX installation, in the folder \Program Files\Siemens\NX 10.0\UGOPEN\SNAP\Examples\More Examples\Gear. There you will find a VB program that creates involute gears. It uses SNAP functions, but, if you don't have SNAP, it should be easy to adapt to use NX/Opejn functions, instead.

Part of that program is a function that calculates a point on an involute curve, as follows:

CODE --> VB

' Calculates positions on a segment of an involute curve   
   Private Shared Function InvoluteFunction(data As Object, u As Double) As Position

      ' Note that the involute curve here is parameterised by radial distance from the origin (r).
      ' The more common approach is to parameterise by angle (theta) but this causes a
      ' singularity at the start point (derivative vector has zero length), which leads 
      ' to a nasty Bezier curve whose first and second poles coincide.

      Dim params  As Double() = CType(data, Double())

      Dim a   = params(0)         ' Radius of base circle of involute
      Dim r0  = params(1)         ' Radial parameter value at start point of involute segment
      Dim r1  = params(2)         ' Radial parameter value at end   point of involute segment
      Dim r = r0 + u * (r1 - r0)

      Dim theta As Double = System.Math.Sqrt(r*r - a*a)/a
      Dim x As Double = a * ( System.Math.Cos(theta) + theta * System.Math.Sin(theta) )
      Dim y As Double = a * ( System.Math.Sin(theta) - theta * System.Math.Cos(theta) )

      return new Position(x, y, 0)

   End Function 
Note the comment about the singularity at the start of the curve. It's possible that this is causing a problem in the Law Curve function.

In some cases, the involute curve is extended with a straight line. This might be related to the "undercut" idea mentioned in cowski's answer

Red Flag This Post

Please let us know here why this post is inappropriate. Reasons such as off-topic, duplicates, flames, illegal, vulgar, or students posting their homework.

Red Flag Submitted

Thank you for helping keep Eng-Tips Forums free from inappropriate posts.
The Eng-Tips staff will check this out and take appropriate action.

Reply To This Thread

Posting in the Eng-Tips forums is a member-only feature.

Click Here to join Eng-Tips and talk with other members!


Resources