creating a variable pitch thread

[xj4life]

I'm tring to create a variable pitch thread/screw on the inside of a hollow cyclinder with the rough dimensions shown in the following link. Notice the total rotation is 160 deg because the same pattern is repeated again with 20 deg between them.

http://img.photobucket.com/albums/v356/xj4life/catia questions/catia_ramp.jpg

I do not normally design stuff like this. Mostly just basic solid intersections. Here's what I've tried:

1) Creating a surface by sweeping a line, anchored at one end at the cyclinder axis and the opposite end following the profile i want projected onto the cyclinder surface. This works great but I'm not sure how to use it to split a solid because it is not a continuous surface (20deg space between them). I know how to split solids but this is not a "complete" surface.

2) Intersecting two solids like I'm used to. One solid is extruded axially (160deg piece of cyclinder) and the other is extruded from the side and has the profile I want. This does not work because it creates undercuts that are undesirable for the tooling that forms this part.


Any suggestions are helpful. Thanks a lot

 

[solid7]

Having created many of the types of threads that you are speaking of, here is my recommendation: Use a boolean operation to remove the threads from the part.

First, define your part profile in a sketch, minus threads, of course. Next, define your thread profile in a separate sketch.

In the Part Body, using the part profile, make a solid of whatever the part looks like, minus the threads.

Create a new Part Body, and make it your active work object. Using the thread profile, select the "helix" option. You have all the basic information, but go to the bottom of the dialog, and under "radius variation", select "profile". This is where you select the profile of the part to define where you will subtract the threads from. After getting the helix as you want, rotate the thread profile about it. You may have to move the sketch about to get it just right.

After you have the threads as you like, use the Boolean -> Remove function, and subtract the Part Body with threads from the Part Body.

Before removing, you may also want to do some manual splitting of the solid, to accurately model the last thread.

Hope that helps.




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