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Saturday, January 17, 2009

Modeling screw threads (2 of 2)


Learn how to model screw threads using helical curves and booleans in Rhino. The threads shown are the type you would see on the end of a light bulb. Changes to the cross section profile and path will provide you with ways of making alternate styles of threads as well.

Video: 2 of 2

18 comments:

Nick Carter said...

The tip on orienting the thread form to the helix was great, but why didn't you model an industry standard vee thread? The only place I've seen round threads like that is on lightbulbs. It would be nice to cover modelling an actual thread form (root and crest are particularly important) with proper clearances for a particular thread fit tolerance.
But the principles and demonstration were excellent, and I thank you.

Brian James said...

Hi Nick,
The idea for this video tutorial did come out of a light bulb model I made recently. So you are exactly right... they are definitely that type of thread. I think I could re-post this with a introductory explanation that might set the proper expectations. Thanks for the feedback!

Nick Carter said...

I thought it looked lightbulb-ey. Don't let my comments detract from the excellence of the video, it helped me tremendously.

Tom said...

Excellent, as a new user I was excited to see this tutorial as I had been wondering how to model screw threads for a project I am working on. Some times all we ned is the concept. After making several light bulb threads I started experimenting with other tread profiles and was pleased to see how easy it was to make threads of various types.

Thank you very much for this one. One thing I have not figured out is how to do this on a tapered thread such as an NPT fitting would be. Hope you can expand on this subject as I'm sure others would also like to do this.

Brian James said...

Hi Tom,
You can use the same techniques to make the NPT threads as well. These two wiki pages are very useful if you don't have a machinery handbook. http://en.wikipedia.org/wiki/Screw_thread and http://en.wikipedia.org/wiki/National_pipe_thread
The key difference is to use an equilateral triangle as the cross section and then sweep it along the helix from the mid point of it's base. Also make sure to use the correct number of turns per inch in your helical curve for a given thread size. Hope this helps and thanks for the comments.

Tom said...

Hi Brian,

I probable did a poor job of explaining my problem with the NPT threads. How do I get the Helix coil to follow the contour of lets say a Truncated Cone. Were the the bottom of the cone is a smaller diameter than the top of the cone. Thanks for the web sites they are very useful. Cheers.

Brian James said...

Tom,
Try the "Pull" command to pull the helical curve to the surface of your truncated cone. Does this do what you'd like?

Brian James said...

Tom, I just had another thought... you could also use the "Spiral" command which would maintain the desired pitch better then a projected helix.

Tom said...

Hi Brian,

Your second thought is a keeper, brilliant.

All the lights are on, thanks so much. Cheers.

Anonymous said...

This is a great instructional video for a very common application. I only wish I had this knowledge about a month ago.

Thank you.

Jason

Sam Iqab said...

Every time I sweep 1. the cross section isn't consistent with the helix, i.e., the the helix is just out of whack. I am orienting the curve perpendicular, and aim sweeping 1, and its Roadlike top. but still, I get a really funky sweep. HELP ME!

Brian James said...

Hi Sam,
I think that you will get an even sweep if you change the style from roadlike top to roadlike right. The orientation of the helix and the active cplane/viewport when picking it play a part in the result. In the video, the axis of the helix is aligned with the Z axis. If you have the helix aligned with the X axis and pick it in the perspective veiwport, then you'll get a funky sweep with roadlike top. Let me know if that doesn't work for you.

Anonymous said...
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Anonymous said...

Hi, when I sweep the curve along the helix, the curve kind of turns around itself to the end.
The flat side of the curve turns more and more to the top, no matter what option I chose in the sweep dialogue. It seems to have sth to do with the orientation of the helix. I'm working on a Mac Beta, so that might be a problem?
Anyway, really great videos to get started with the rhino!

Brian James said...

Thanks for the report... it sounds like the Sweep1 options might not be completely hooked up in the Mac wip yet.

Brian James said...

I checked the most recent Mac wip and the "roadlike top" option is working correctly in Sweep1.

Email your file if you like and I'll take a look.
brian(dot)james(at)mcneel(dot)com

Ondine said...

I just have to say, this tutorial was orgasmic!

Brian James said...

Thanks Ondine! I'm glad it was helpful.