Tapered Thread Modeling

[cbrf23]

Hi,
I've had problems with modeling screws that follow a tapered profile in the past. Usually I can work around this in a variety of ways, but this time, I'm really not sure how to proceed.

If I make my profile sketch big enough to cut away at the tapered portion, it becomes self intersecting, and will not complete.

I've attached a model showing the problem. Any ideas how to make this work? I am really struggling here and I'm not sure how to make this work.

 

[Cockroach]

Taper threads such as API EUE, NUE, LTC,STC, Buttress, Line Pipe all follow the same methodology. You simply mimick those motions the machinist would perform during turning operations and then cut the thread as your last operation.

I prefer to have the classical run-out to the vanishing point on Box and Pin forms, this gives the piece a more professional appearance than simply pulling straight out of the thread. I do this by having Path A follow the thread in full form, then splicing Path B to it at the start of the vanishing point. My method standardizes three revolutions with a pull-out along a 45 degree angle during this operation. In other words, I spiral out at the same pitch rate of the threads while increasing my radius along that helical path. Works very well.

Big problem, tremendous size for the file. If you're into the art, you can try this method. But for practical engineering purposes, a cosmetic thread gets the point across.

Good luck with it, it can be tricky.

Regards,
Cockroach

 

[cbrf23]

Hi cockroach. I understand what you are saying, and usually I try to follow a similar methodology in creating models. In the example I attached, the issue I'm having is that I cannot do this, as solideorks does not see the cutting path as a single point operation, but rather sees the cut path as a solid body that for whatever reason cannot intersect itself.

Anyone have any ideas on this particular file?

 

[cbrf23]

I tried breaking it up into sections by doing a convert entities on the helix using a 3d sketch, and then splitting the sketch to only do 180 degree increments all around the tapered section. I had issues with this as well.

Still looking for a way to build this.

Thanks!

 

[Cockroach]

I think you have your thread wrong.

The profile doesn't look right, you may have picked up the wrong location to the vanishing plane.

What is that thread designation?

Regards,
Cockroach

 

[cbrf23]

Hi Cockroach. It is not a standard thread. The thread profile is correct. If you look at the sketch labeled "Sketch: Profile and Tool Path" you can see my blank profile and the tool path (essentialy the path of the minor diameter). My Helix is built to follow that toolpath. The thread profile needs to sweep along the helix and cut the part, but solidworks wont let it because the cutting path intersects itself when made big enough to do the job correctly.

 

[Eltron]

Try doing the inverse. Inste4ad of cutting into the body, see if you can do a swept extrude to add the thread profile to the base body.

Dan

http://www.eltronresearch.com

Dan's Blog

 

[cbrf23]

Eltron, thats a good idea. I will try that tomorrow.

 

[Cockroach]

Yeah, if the cutting path is self intersecting then the Sweep-Cut will failing.

You may need to two the cut in two passes. First cut the left hand side, then use another identical path to cut the right.

Good luck with it!

Regards,
Cockroach