I need help with threads tapering off to be tangent.

[RBobroski]

I am trying to make a Left handed thread that allows a device to screw onto a 3/4" threaded vacuum hose. I can get the threads themselves in, but I can not figure out the best way to have them taper. T2.jpg is the original way I had it with the straight profile, and that gives me a huge ledge at the culmination of the trajectory. When I tried to wrap the trajectory out a bit in T2.jpg it still left me with a little something. Ideally I want the thread to slowly blend to almost a single point tangent to the surface as you can see with what I was trying to do with that sketch but I don't know how to remove material using a boundary blend. This thread is strange too as the start of it seems to be a protrusion, but then the second to last wrap actually decreases the diameter while the final wrap cuts through that decreased diameter; it's like a half cut half protrusion so I was starting with a smaller ID and doing it all as a cut. These threaded hose profiles have always given me trouble; any advice? Also you can see in T1.jpg that the thread starts weirdly...do I have to increase my trajectory way above and then cut it off to prevent this?

Thanks for all the help in advance.

 

[Enginerd9]

Trajpar!

I assume first that you're making threads by cutting a cylinder. If so, cool. You can cut the threads using a helical swept cut, and you'll need to define some parameters in order to do that sucessfully.

So, you'll need a sketch which does the cutting, a trajectory to serve as your cut path, and some kind of parameter to dictate the thread density. That's easily done if you understand the helical sweep cut...

So, if you create a datum trajectory that tapers either straight or curved (tangent at the terminal end?), you should be able to select that as the trajectory for the helix. I did a practice run with it on a cone, and it followed the datum sketch I made which was driven by the cone surface. It seemed to work pretty well.

For some reason I really like to say TRAJPAR! though. It's fun.

If guns kill people, cars drive drunk.

 

[PheasantPlucker]

Try playing around with the swept profile sketch to include something similar to the attached pics. Run your path out the top of the cylinder to achieve a clean exit there.

 

[PheasantPlucker]

missed one pic

 

[Enginerd9]

Yeah! That's what I was trying to desribe! Nice!

If guns kill people, cars drive drunk.

 

[RBobroski]

Thanks for the help with the trajectory! That is exactly what I was looking for.