Thank you again - I thought it was something I was doing wrong. That’s reassuring.
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So, it’s not just me…
Parallel viewing of the basic helices helps show the distortion that unfailingly occurs when attempting to splice two “strands” together.
As seen here, the junction seems shifted slightly to the left, breaking the usually straight line one would have expected.
A longitudinal view of the same shows the cut-off point as an off-center circle,
whereas a successful intersection with a plane always features an indentation, with its attendant and opposed protrusion being hard to see…
What I see in your side view of the threads indicates that angles on the top and bottom of the thread are different.
When I model threads the angles are the same and there’s no problem stacking sections to make a longer screw.
Here’s an example of that with perfect alignment of two sections.
So how do I avoid the problem?
In other words, what should I do differently? The method I use is as follows: Form a helix and a cylinder of the same dimensions, alt-rotate the helix and scale it down in the x and y axes. That a distortion occurs at both ends of the result is unexpected and puzzling to many people, as this string attests.
Don’t use Scale. Use a properly drawn profile to sweep round a helical path. I’ve shown this before. John posted a link to it in the first post in this thread.
The method you are using is OK for approximating threads but it’s not accurate
Read the post before my OP, and again after your latest. Still don’t see the link you’re referring to, or at least fail to recognize it as such…
Really? You don’t see the video tutorial in my post there?
I do now…
Thanks.
You could do that. Now you’ve got reversed faces in that area and the threads are still only a rough approximation or screw thread. If threads like that are acceptable for your modeling. It probably doesn’t make any difference if they line up properly so you might as well save yourself the trouble and let them be.
A little something I found on the internet and unabashedly stole the content and paraphrased a bit:
So you want to print 3d fasteners.pdf (56.5 KB)
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I use CAD files from McMaster-Carr quite frequently although for use in SketchUp the 3-D Step files can be pretty huge. If nothing else they are excellent as guides.
Those faces were reversed only for illustration purposes. Of course, they’d be right-side out if I intended to use that shape in a model.
Although my attempt at using it was a failure, your proposed solution is obviously the way to go, I’m only trying to understand the odd outcomes of some operations, such as the valentine-shaped intersection that’s a constant result of this way of creating workable threads.
