unable to sweep along a helix path to create thread

[office6PUWT]

Could someone suggest why autocad is unable to sweep my 1mm square along a helix path I've drawn to create an internal thread inside a 3d exercise shape entitled 'eccentric cam'. Perhaps there is a better way to create this thread? see attaced file and instructions

[leeminardi · Accepted solution]

As a start  review this recent thread.  For your task subtract the swept shape from the hollow cylindrical hole.

[office6PUWT]

Very helpful info, should I use a triangle instead of a 45 degree rotated square as my object when creating threads? and what is the best way to to ensure that the depth of my thread is 0.5mm given that I can only specify the side dimensions of my object and it needs to be a closed poly line?

Luke

[leeminardi]

Make the radius of the helix equal to the radius of the hole plus the thread depth.  The angle of the triangular swept shape is a function of the thread pitch.  You can make a sketch in AutoCAD to determine the shape. Create a rectangle with width = thread depth and height = pitch.  Draw lines from midpoint of pitch side to opposing corners.  Scale the shape up afterwards to ensure full penetration.  

I'm not on my AutoCAD PC right now or I would draw a picture.

[office6PUWT]

Ok, thanks to your advice and this thread I have sweep. but the angle of my triangle is moving by 45 degree as a result of the process? Baffling. Am I doing something with my UCS perhaps? see before and after pics.

[leeminardi]

I experienced strange behavior with sweep for your thread task.

I swept a triangle alone a helix and for only the first few turns the triangular shape was incorrectly rotated as seen here. After the first 4 turn the orientation seems ok!

BEFORE SWEEP

AFTER SWEEP

I then made the helix longer so that the "bad" threads would be outside the solid from which it will be subtracted.

Note, the triangle for the swept thread cannot be too large that when it is swept along the helix is will self-intersect.  If it does then a solid cannot be made with sweep. A smaller triangle is used that does not fully cut the wall surface of the cylindrical hole To compensate I subtracted a cylinder (red) from the hole first.

The next step was to subtract the helix swept triangle (cyan) from the inside of the cylindrical hole.

This calculation proved to be too much for AutoCAD.

The helical thread solid has a lot of faces and in practice the geometry for the threads would not be modeled but more likely handled as a note that specified the thread size to be tapped after the basic geometry were machined or 3D printed.