Problem visualizing curve of thin parabolic reflector

Post here for help on using FreeCAD's graphical user interface (GUI).
Forum rules
and Helpful information
IMPORTANT: Please click here and read this first, before asking for help

Also, be nice to others! Read the FreeCAD code of conduct!
PaulUK
Posts: 15
Joined: Fri Jan 19, 2018 8:43 am

Problem visualizing curve of thin parabolic reflector

Postby PaulUK » Thu May 06, 2021 11:16 am

Dear All,

I constructed a reflector that is 2.5mm thick and the edge is curved. However, over part of the reflector edge there is a strange effect. Please can someone tell me what it is or if there's a way to prevent it, or if its just some strange of bug?

My system is:
OS: Windows 10 Version 2009
Word size of OS: 64-bit
Word size of FreeCAD: 64-bit
Version: 0.19.24276 (Git)
Build type: Release
Branch: releases/FreeCAD-0-19
Hash: a88db11e0a908f6e38f92bfc5187b13ebe470438
Python version: 3.8.6+
Qt version: 5.15.1
Coin version: 4.0.1
OCC version: 7.5.0
Locale: English/United Kingdom (en_GB)

I hope that I have provided enough information to help. Note that this happens on the same version of FreeCAD on a much older computer with Windows 7. Thank you.
Image 1
Image 1
reflector_1.PNG (69.08 KiB) Viewed 146 times
Image 2
Image 2
reflector_2.PNG (91.77 KiB) Viewed 146 times
Image 3
Image 3
reflector_3.PNG (164.63 KiB) Viewed 146 times
Attachments
Reflector_Template.FCStd
File for reflector example
(18.05 KiB) Downloaded 8 times
Bance
Posts: 1959
Joined: Wed Feb 11, 2015 3:00 pm
Location: London

Re: Problem visualizing curve of thin parabolic reflector

Postby Bance » Thu May 06, 2021 11:42 am

PaulUK wrote: Thu May 06, 2021 11:16 am that is 2.5mm thick
It is not, it is of variable thickness.

Were you aiming for constant thickness?
PaulUK
Posts: 15
Joined: Fri Jan 19, 2018 8:43 am

Re: Problem visualizing curve of thin parabolic reflector

Postby PaulUK » Thu May 06, 2021 12:14 pm

Bance wrote: Thu May 06, 2021 11:42 am
PaulUK wrote: Thu May 06, 2021 11:16 am that is 2.5mm thick
It is not, it is of variable thickness.

Were you aiming for constant thickness?
Initially yes, but with moving things around I'm not surprised that it is not but had not noticed. I would correct this later. This model was intended to try rounding the edge and not final. That is when I noticed this strange visual effect.

I will be wanting constant thickness. Thank you.
Bance
Posts: 1959
Joined: Wed Feb 11, 2015 3:00 pm
Location: London

Re: Problem visualizing curve of thin parabolic reflector

Postby Bance » Thu May 06, 2021 12:40 pm

I have changed some of the constraints on the sketch, most particularly the semi-circle that forms the edge should be tangent to the curves that form the dish. I have added a construction line to maintain constant thickness.
reflector.png
reflector.png (35.06 KiB) Viewed 105 times
Attachments
Reflector_Template-1Bance.FCStd
(12.33 KiB) Downloaded 12 times
PaulUK
Posts: 15
Joined: Fri Jan 19, 2018 8:43 am

Re: Problem visualizing curve of thin parabolic reflector

Postby PaulUK » Thu May 06, 2021 12:54 pm

Bance wrote: Thu May 06, 2021 12:40 pm I have changed some of the constraints on the sketch, most particularly the semi-circle that forms the edge should be tangent to the curves that form the dish. I have added a construction line to maintain constant thickness.

reflector.png
Ah I see. Thank you very much. This is what I was hoping to do. I shall check the sketch to see how it should be done. Much appreciated.