Lost External Geom Mapping

[ShadowedR]

I'm losing my mind here with lost external geometry mapping.

I'm trying to create a sleeve for a 3D Printing project of mine, where I can quickly go and update the inner diameter to fit.
Something like this:


I start by creating a spreadsheet and creating two variables - diameter and 3d printing offset.


I draw my base shape and revolve it by 20 degrees:



Next I make a new sketch and map to the external geom of my base shape and I start drawing cutouts, mapping externals as I go along.
as an example:


Until I end up with my final shape:


Here is just and overview of the steps:


so, now I go back to my spreadsheet and change to diameter I want from 50 to 30 and everything updates perfectly.


Now I go and update the diameter to 100 and my references start breaking:




*Note, while typing the post I played around to get the relevant screenshots. The problem seems to occur when you increase the diameter by a large amount. If you go 70, 80, 90, 99, 101, etc it doesn't break. But by moving from say 30 dia to 101, it'll break.

I must be doing something wrong here?

Attached is the test project

test.FCStd

(180.6 KiB) Downloaded 26 times

and I am using:
OS: Windows 7
Word size of OS: 64-bit
Word size of FreeCAD: 64-bit
Version: 0.17.13522 (Git)
Build type: Release
Branch: releases/FreeCAD-0-17
Hash: 3bb5ff4e70c0c526f2d9dd69b1004155b2f527f2
Python version: 2.7.14
Qt version: 4.8.7
Coin version: 4.0.0a
OCC version: 7.2.0
Locale: English/SouthAfrica (en_ZA)

Thanks in advance.

[chrisb]

Welcome to the forum.

I must be doing something wrong here?

You are not really doing something wrong, but you can do better. The reason of this behaviour is well known, you may search the forum for "topological naming". Improvements are on their way but we don't know how, if , and when they will occur in a stable FreeCAD version.

You can vastly improve your design, if you reference sketches instead of faces. Normand has given some hints in the documentation: https://www.freecadweb.org/wiki/PartDes ... ble_modelsFeature_editing#Advice_for_creating_stable_models.

[ShadowedR]

Thanks for the info Chrisb,

I started off by referencing the sketch itself to create my first circular groove.
Next, "Sketch002" is mapped to "Sketch" and Groove001 is applied.
finally, I apply a polar pattern to Groove001 to cutout the other side of my base shape.

So up until this point, everything is mapped to a sketch, not a face.
I just redid it on my project and it still breaks.

[chrisb]

So up until this point, everything is mapped to a sketch, not a face.
I just redid it on my project and it still breaks.

Please upload the new file.

[ShadowedR]

Here you go, although it must be said the first file was also mapped to sketch and not the face.
Just redid it to be sure.

test.FCStd

(183.47 KiB) Downloaded 23 times

[chrisb]

Here you go, although it must be said the first file was also mapped to sketch and not the face.
Just redid it to be sure.

That's wrong in both cases. Sketch001 is mapped to the selected face of the revolution.

Besides: You cannot map a sketch to sketch, you only can use the sketches for external geometry references.

[ShadowedR]

You must excuse my liberal use of terminology here, I'm rather new to parametric cad and a hobbyist in general designs and CAD.

OK, so let me walk you through my design process, one step at a time and you can show me what I am doing wrong

1. Draw my basic shape, fully constrained


2. Revolve


3. Select face and make a new sketc



4. Hide Revolution and show Sketch


5. External Geom from sketch directly.


I am beginning to understand that step 3 is where the new sketch is then mapped to the face of the revolution, OK.
So I should rather then just make a new sketch mapped to a plane, and reference the external geom from there?

[NormandC]

So I should rather then just make a new sketch mapped to a plane, and reference the external geom from there?

Exactly. You can create a datum plane attached to the XZ or YZ plane and angle it using the Attachment Offset fields (pitch yaw roll - I never remember which is which ). Then you attach your sketch to it. Or you can do the same with the sketch directly without going through the datum plane process.

I have a few more suggestions but I'm out of time...

[ShadowedR]

I have a few more suggestions but I'm out of time...

Whenever you have more time, I am willing to listen.

[freedman]

I made a quick file. I would have modeled it this way.