Path must not be a null shape

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oliverspozi
Posts: 24
Joined: Wed Mar 29, 2023 1:18 pm

Path must not be a null shape

Post by oliverspozi »

Hi,

I am trying to create a subtractive helix, however I keep running into the error mentioned above.

I have two versions of the project, one trying to subtractive and the other merely trying to sweep across the helix to later on perform a cut with said shape. However both result in the same error and i don't know how to correct it without having to restart the entire project over again. There are other components to this, however I have chosen to just include the part I need to thread.

Sweep and cut version:

https://easyupload.io/gzcrff

Subtractive sweep parts WB:

https://easyupload.io/cc2bxs

Any advice would be greatly appreciated. I am still relatively new to freecad for the time being
chrisb
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Re: Path must not be a null shape

Post by chrisb »

There are several flaws in your model:
- you have a leftover XY_Plane003 on top level
- you need a ShapeBinder of the helix inside of the body (or you use PartDesign Helx right away)
- CopyHelix has beyond its nice name no connection to the helix and can thus not serve as a path
- the height of the section might be too big. There is the danger of self intersections
- you want probably set the Frenet option for the helix
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smktec
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Joined: Thu Mar 05, 2020 5:37 pm

Re: Path must not be a null shape

Post by smktec »

you should use sub shape binder to import the path into the body. Then simply edit additive pipe and replace "object" by Binder and it works.
Attachments
Proj2_Subtractive A.FCStd
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Proj A.FCStd
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chrisb
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Re: Path must not be a null shape

Post by chrisb »

smktec wrote: Sun Apr 02, 2023 8:30 am you should use sub shape binder to import the path into the body. Then simply edit additive pipe and replace "object" by Binder and it works.
Can you please run CheckGeomtry with BOPCheck on the Helix? Here I had fixed the existing ShapeBinder and CheckGeometry runs endless.
A Sketcher Lecture with in-depth information is available in English, auf Deutsch, en français, en español.
oliverspozi
Posts: 24
Joined: Wed Mar 29, 2023 1:18 pm

Re: Path must not be a null shape

Post by oliverspozi »

@chrisb

If the height of the section is too big, how would I go about addressing this then?

The dimensions required for the helix are as follows:

Pitch: 0.04545
Height: 0.73
Radius: 0.875248
oliverspozi
Posts: 24
Joined: Wed Mar 29, 2023 1:18 pm

Re: Path must not be a null shape

Post by oliverspozi »

@smktec

Thank you very much for that. Any advice where I could learn about your process of doing that? Obviously I can reverse engineer it but just for future purposes?

Thanks
chrisb
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Re: Path must not be a null shape

Post by chrisb »

oliverspozi wrote: Sun Apr 02, 2023 9:00 am If the height of the section is too big, how would I go about addressing this then?
You can either use an expression where you subtract e.g. 1/100mm (don't know how this would be in imperial miles) or you use an external reference.
I see also that the section has a peculiar angle with respect to the helix. I would rather place it at the origin or attach it properly to the ShapeBinder, which as an additional benefit would simplify the sketch.
Ask back if you need more information or the model.
Attachments
SnipScreenshot-b7fad1.png
SnipScreenshot-b7fad1.png (50.27 KiB) Viewed 899 times
A Sketcher Lecture with in-depth information is available in English, auf Deutsch, en français, en español.
oliverspozi
Posts: 24
Joined: Wed Mar 29, 2023 1:18 pm

Re: Path must not be a null shape

Post by oliverspozi »

@chrisb

I actually see what you are talking about with regards to the angle. Thanks for pointing that out.

I am going to redo the helix instead and see what happens. Do you know how the other gentlemen linked the Shape Binder bits? I have absolutely no idea on how to do that.

I ended up just doing your version of the helix with the respective radius and it worked out a lot better than what I was doing tbh
oliverspozi
Posts: 24
Joined: Wed Mar 29, 2023 1:18 pm

Re: Path must not be a null shape

Post by oliverspozi »

@chrisb

Some advice, so I am uncertain which radius to use for my sketch to get the correct helix radius. The dimensions are:

Major DIA: 1.78
Pitch DIA: 1.7505
Minor DIA: 1.7242

I feel it should be the Major DIA / 2 but just want to confirm.

The sketch is below incase you need further clarification

https://easyupload.io/5vmjfz
chrisb
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Re: Path must not be a null shape

Post by chrisb »

oliverspozi wrote: Sun Apr 02, 2023 9:38 am Some advice, so I am uncertain which radius to use for my sketch to get the correct helix radius.
I can't tell, because I don't know what you want. Is the outer diameter or the inner given? What is it for? It is often helpful so see more of the big picture.
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