O-ring canal design

[mynetself]

Hi guys, I have a couple of questions which I wasn't able to find answers to elsewhere. One thing before the questions, I am a TOTAL noob. Never done any CAD, FreeCAD or other, never done any design, though I did do a technical drawing course at Uni (a long time ago! lol) so do understand technical drawings. Other than that, tabula rasa!

But I have determination and patience. And I've always tinkered around with small DIY stuff, and so I decided I wanted to build a properly modded PC. I have a design in my mid, and quickly realised it won't work without a proper design, especially since I'll need to have custom parts built/cut/engraved for me!

So I found some tutorials online and I've already started working on my part design... the first piece of the entire design is a GPU water-block. Or rather, a water block bridge - Essentially a connector for inlet and outlet flows from two or three graphics cards. Basically I want to run the cooling loop in parallel and need to split the inlet/outlet flows into two or three. But it has to look cool


The questions:

1) How can I design an O-ring canal? I can't see how to do this as a pocket since an O-ring canal is more like a "donut pocket" rather than a circle one. Also, I need it to have a semi-circular section, and of an arbitrary shape so not a circle or a similar shape. I am failing to see how to do this using pockets, if it can be done at all.

2) How can I constrain the center of a circle to lie on the 45deg diagonal of a square piece without constraining the distance from the edges? (The distance will eventually be specified at a later stage.)


Last thing, the setup. I'm at work now, so don't have the full details of my PC config available but I'm using FreeCAD 0.16 on Win10. It's a 64bit machine, an older AMD processor on a Lenovo ThinkPad T420s, if it matters. (Have external monitors, not getting blind over a design )


Any help is appreciated!

[DeepSOIC]

But it has to look cool

Then you ought to try FC v0.17 pre! Because it has b-spline tool in sketcher!

It should also answer your question about the o-ring groove. In FC v0.16, you either have to use a technique of helper pad (see "Hole on pipe wall" classic), or use Part workbench. In v0.17, sketch attachment is much more versatile. The main thing is, forget that you need to map sketches to faces...

Actually, I thought that a proper groove for o-ring should have a rectangular cross-section, with the total area more-or-less equal to cross-section area of the actual o-ring. But I'm no expert in this question.

[bejant]

DeepSIOC posted in the meantime but here is my reply anyway:

Hi mynetself and welcome!

1) How can I design an O-ring canal? I can't see how to do this as a pocket since an O-ring canal is more like a "donut pocket" rather than a circle one

You can model the o-ring, then subtract it to create the canal.

Also, I need it to have a semi-circular section, and of an arbitrary shape so not a circle or a similar shape. I am failing to see how to do this using pockets, if it can be done at all.

Sketcher the cross section, then use Part Design > Revolve.

2) How can I constrain the center of a circle to lie on the 45deg diagonal of a square piece without constraining the distance from the edges?

One way:

20170411a.png (5.15 KiB) Viewed 3564 times

Don't hesitate to post back if I missed something or if you have more questions.

[mynetself]

Thanks for the replies guys! Will try and tinker with FreeCAD tonight...

2) How can I constrain the center of a circle to lie on the 45deg diagonal of a square piece without constraining the distance from the edges?

One way:

OK, should have been a bit more precise. Your suggestion is clear to me, my problem comes in when I want to constrain a pocket on an extruded piece . So, step 1, extrude part. Step 2, build circular pocket which I want to constrain to the diagonal of the (rectangular) piece.

I can sketch another square/corner, but then if I pocket the whole thing, I probably won't get what I want, the circular pocket only?

[sgrogan]

Hello mynetself! Welcome to FreeCAD and the forum
I can sketch another square/corner, but then if I pocket the whole thing, I probably won't get what I want, the circular pocket only?

See Sketcher_External you will also want to do a forum search on "topological naming" to understand the short comings of this approach. You may also use Expressions

Actually, I thought that a proper groove for o-ring should have a rectangular cross-section, with the total area more-or-less equal to cross-section area of the actual o-ring. But I'm no expert in this question.

Never less Typical fill factor is 75% @ 15% deflection. An excellent reference for all things gaskets: https://www.parker.com/literature/ORD%2 ... ndbook.pdf Section 4 details groove design.

[mynetself]

See Sketcher_External you will also want to do a forum search on "topological naming" to understand the short comings of this approach. You may also use Expressions

Actually, I thought that a proper groove for o-ring should have a rectangular cross-section, with the total area more-or-less equal to cross-section area of the actual o-ring. But I'm no expert in this question.

Never less Typical fill factor is 75% @ 15% deflection. An excellent reference for all things gaskets: https://www.parker.com/literature/ORD%2 ... ndbook.pdf Section 4 details groove design.

Thanks for all the help, will most certainly be digging around for all the suggestions... I can forsee a long design/FreeCAD long Easter weekend!

[mynetself]

Hi again, finally did manage to get to a satisfactory point... thanks for helping out!

I generated the o-ring canals with a square section instead of cirle, and I used the boolean subtract tool. This worked fine, but I also learned it slows everything down by a lot (I'm on a 2012 ThinkPad ). Since my section is square, for the next attempt I'll probably just first create the o-rings by a pocket + internal pad, and then go about my design, seems much faster.

Anyway... the final (lower part) of the water block connection:

Water_Block_Connection_PoC.PNG (41.34 KiB) Viewed 3308 times

This is very much proof-of-concept, first I want to try it out and see if it's watertight and all. But I'm still pretty happy for the design itself, my first ever CAD design!



So the next question I have is how do I go about building this? Because it involves canal etching, I'll need a CNC router... Can I export my design to a format a CNC router will understand natively? (Guess that's a pretty basic question, but I've never played with a CNC router before, nor had any work commissioned.)





The info I wasn't able to paste last time last time
OS: Windows 10
Word size of OS: 64-bit
Word size of FreeCAD: 64-bit
Version: 0.16.6706 (Git)
Build type: Release
Branch: releases/FreeCAD-0-16
Hash: f86a4e411ff7848dea98d7242f43b7774bee8fa0
Python version: 2.7.8
Qt version: 4.8.7
Coin version: 4.0.0a
OCC version: 6.8.0.oce-0.17

[chrisb]

To get rounded O-ring canals you can try fillets. Make sure the radius is less then half of the canal's width.

For CNC path generation you can try the Path Workbench in 0.17. There are predecessors in 0.16 as well, but there has been really very much development in 0.17. The structure is clearer, better user interface, better handling. You can develop in 0.16 and finally use 0.17 for the path generation; both versions can be installed in parallel.

If you want to get it machined I think that the STEP format is a common exchange format. Ask your CNC provider what he needs, FreeCAD can export many different formats.