How model worm (perpetual screw ) with variable pitch in SolidWorks?

I need to model worm with variable pitch (pitch came to zero !!) in SW 2012.
I can model worm with constant pitch.
I can model worm with variable pitch but:
when pitch is going under some value the operation is not succesful.....-
I add 4 pictures:
1. oryginal worm that i must to model
2. worm with constant pitch - operation OK
3. worm witch variable pitch - operation OK
4. error window when helix modified - pitch came to small values.

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3 Answers

Hello Michal
I have just about succeeded in modelling your worm in SolidWorks 2012. It is a very challenging assignment, mainly because SolidWorks doesn't want to create the body (or surface) because of self-intersecting geometries. I overcame this by splitting a swept circle into two half-circles - a simple procedure in theory but hard in reality because SolidWorks wouldn't accept the proper centerline. So I had to make two approximate bodies and enlarge them 1 pct to be able to join them into one and subtract them from a simple cylinder. Not perfect but useable. I won't mind writing in more detail, but it's late now, so take a look at the attached files and let me know if I should explain further.
Cheers
Steen

 
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Thanks for your answer. You got right. This method is ok.
There is other easier way eighter - By tomasz Niciński:

http://grabcad.com/questions/how-to-model-a-worm-perpetual-screw-with-variable-pitch-in-solidworks

Unfortunately when I ask my question something wrong hapened in Grab cad - so i ask the question 4 times............. and I do not know how to delete them.

 
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how to model worm(perpetual screw) with variable pitch in pro e cero element 5.0 plz part file

 
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