Hi,

I'm trying to model a thread like in the attached photo. Is there a built-in command in MoI to taper the end of the thread? Right now, I've copied the thread profile and then offset it on the rail spline so it goes inside the solid object. After that, I want to add a fillet to the hard edges (as seen in the screenshots), but for some reason I can't get it to work.

Can someone please take a look at my attached 3DM file and see if they can figure out why it's not working?

BTW, is my method of creating the tapered end legit?

Many thanks,
Frederik

your thread is a little outside the neck bottle at the ends. It needs to come in a bit.
I would go to the curve cut the place where you have section tapering in then blend that section I would then rebuild the curve to make it one curve. . At that point you can sweep it with your profile and boolean the thread and neck together. once that is done you can fillet it.

Hi Frederick,

re:
> BTW, is my method of creating the tapered end legit?

The general concept of creating the tapering by submerging a surface is legit, you just need to do it a bit more.

Currently your thread surfaces are just barely skimming along the outer surface of the cylinder.

That type of "barely skimming" shaping is difficult to boolean.

Instead of that you want both the tapered end and also the non tapered area to push down into the cylinder's surface with some margin instead of trying to make it barely skimming along the cylinder's surface.





Making those areas push down through the cylinder a little ways will make it easier to boolean.

- Michael

Hi Val,

Many thanks for helping me with the technique. I followed your tips, and I believe I've got kind of the same result on the first object. However, on the second object, I can't get the Fillet to work on the selected edges again. I've performed a Boolean Union on the threads and the cylinder object, and it says "solid"... but nothing happens when I try to apply a Fillet.

I noticed there seem to be some overlapping edges in a section of the thread, but I'm not sure how to get rid of those. Maybe this is what's causing the Fillet not to work? I've tried using the "Merge" command on some broken edges, but I can't make them merge together.

Please, if anyone can take a look at my 3DM file again — the screenshot is from the same view as the 3DM is saved. I would really appreciate it. I'm currently trying to learn how to create threads for 3D printing.

Thanks,
Frederik

Hi Michael,

Thank you! If I've performed a Boolean operation (union) with success, so that my thread and cylinder becomes a "solid object".. Does the "barely skimming" thread, before the boolean, still cause problem when I want to add the Fillet later?

Hi Frederick,

re:
> Does the "barely skimming" thread, before the boolean, still cause problem when I want to add the Fillet later?

Yes it can, in your case here there is kind of a little shelf where you want to fillet:







- Michael

Hi Frederick, here's a filleted version. I used FlowExtendSrf (http://moi3d.com/forum/index.php?webtag=MOI&msg=9747.7) to extend the thread surfaces so they pushed through the cylinder with a little margin and then boolean union and filleted with radius = 0.35mm .

- Michael

Thanks again Michael, much appreciated!

Did you need to re-model the thread from scratch for this to work, or can I somehow use FlowExtend on my existing thread? I downloaded FlowExtend now, but I don't understand what it does.. It added a lot of flat planes to my model when I tried to use it on my edges (see screenshot)?
____

BTW, is there a way to add a shortcut for "Reset Current view"? I only found a script to "ResetAll views".

Hi Frederick,

re:
> Did you need to re-model the thread from scratch for this to work, or can I somehow use FlowExtend on my existing thread?

I used it on your existing thread but basically resetting it using Edit > Separate to break it into individual surfaces, then selecting all edges and hitting Delete to do an "untrim" and recover the full underlying surfaces.

Then I used FlowExtendSrf on each individual thread surface.


> I downloaded FlowExtend now, but I don't understand what it does.. It added a lot of flat planes to my
> model when I tried to use it on my edges (see screenshot)?

You're getting a bunch of pieces extended there including the cylinders and cylinder end caps which don't need it. If you break it into surfaces using Edit > Separate you can be more selective for which pieces to extend.


> BTW, is there a way to add a shortcut for "Reset Current view"? I only found a script to "ResetAll views".

Try this one:

script: /* Reset current view */ var vp = moi.ui.getActiveViewport(); if ( vp ) { vp.reset(); }


- Michael

I'm not sure what I'm not understanding...
I'm a "polygon modeler", so I'm not used to all the difficulties with Fillets and Chamfers, and the "broken edges" that I experience when learning modeling in MoI. There must be something fundamental that I'm missing because I really struggle so often when trying to add Chamfers or Fillets to my objects.

In the attached examples (3DM file included), I start with the thin joined surfaces. They look clean to me… I offset this using the "Shell" command, and now this is a "solid". When I select the highlighted edges, I can perform a partial Fillet on the edge (but it's limited to only half the thickness of the shell). And the Chamfer doesn't work at all?

What is it that I'm missing? Also, is there some kind of "optimize" command that cleans my model from corrupt edges and welds edges within a certain distance?

I wouldn't shell the separate parts. If you look at the profile of the curved interior area the shell pushes that portion out. I would revolve the whole top part, shell that then cut the curve interior away. that guarantees a clean profile. At that point you can chamfer/fillet the edge.
On a side note, shell has a similar effect in poly modelers as well.

Hi Frederick, sorry you're having difficulty.

Yes, CAD modeling tends to be more finicky than poly modeling. That's generally because CAD modeling is trying to generate geometry that accurately represents shapes and not just making a "looks like it" approximation.

There are some tips here for people coming from a poly modeling background:
https://moi3d.com/forum/index.php?webtag=MOI&msg=4865.2

The main concept is in CAD modeling you want to build a simplified extended shape and then cut that up using booleans.

For your case here that means the initial target that you want to get to is this:



You can use Shell to get this:



Then the largest fillets:



Boolean difference with a cutting line to cut it in half:



2nd largest fillets:





So note that once you have formed the initial solid it's good to try and keep working on it as a solid if possible because you can then use booleans to cut pieces.

- Michael