[solved] Cross Section

[Watertreatment]

Hello, I am a self taught QCAD, BASIC user and LOVE the program. I have to pay someone to do my 3d stuff though. Oh well.
Can someone tell me how to get a cross-section on an angular cut of round pipe? I cut round pipe at various angles in my projects but
am tired of manually trying to approximate curves and area and it is wasteful in my time and prototyping.

In my drawing, you can see a simple piece of tubing, one end cut square (90deg) and the other end, cut at 60 degrees. I want to see how that
60 degree cross section would look please.
Thank you.


Paul M
Yuma, AZ

Windows 10 64bit
QCAD Pro, 3.27.6

[CVH]

Paul,

Well, the side view of the 60 degree cut is just the same as the 90 degree.
(I know there is a difference at which side this is placed depending the drawing standard but here it doesn't matter)

The view in the plane of the cut is an Ellipse.
The semi-minor axis is the radius, the semi-major axis is equal to radius/sin(60).
Or the minor axis is the diameter and the major axis is equal to diameter/sin(60) or 1.154700538... times the diameter.

Luckily, most input fields can do math in QCAD, you can simple enter '.../sin(60)'

This all isn't really hard in plain 2D, it is a bit more complicated with an isometric projection for example.
QCAD is equipped with several projection tools, see Modify .. Projections (near the bottom).
Also see:
https://www.ribbonsoft.com/en/blog/135-qcad-3-2-1
https://www.ribbonsoft.com/en/blog/125- ... for-qcad-3
https://www.qcad.org/doc/qcad/latest/re ... ct_en.html
https://www.qcad.org/doc/qcad/latest/re ... al_en.html

Regards,
CVH

[Husky]

Hello Watertreatment - welcome to the QCAD forum.

In my drawing, you can see a simple piece of tubing, one end cut square (90deg) and the other end, cut at 60 degrees. I want to see how that
60 degree cross section would look please.

You can tackle that from different angle. Fair question would be how precisely has the result to be? To archive a high precision you could go ahead and do a projection based on 12, 24 or even 48 construction lines. That is laborious but I've the feeling that isn't necessary in this case. I'm correct?

Assuming an average solution will do it brings us to the expected shape of that cross cut section - an ellipse. Good thing is that QCAD offers tools for the ellipse and thanks to your drawing all measurements are already in plain sight to be used. No math necessary. Ye-haw!

I guess you still know the measurements but if not just put dimension to the relevant entity's and it will look like this:

Husky-2022.09.05-02.png (31.02 KiB) Viewed 2461 times

Then launch the tool for Ellipse (Ellipse with Diameters[ED]), use the values of the 4 dims to create two ellipses ........ piece of cake.

Husky-2022.09.05-03.png (13.7 KiB) Viewed 2461 times

A bit more advanced to create the same ellipses would be to skip the step of creating dims and get the needed values for X/Y by picking them directly in the drawing with the "Distances Point to Point" tool.

Pipe cross section.gif (3.61 MiB) Viewed 2461 times

[Watertreatment]

CVH and Husky, thanks SO much. Yes, this is not high precision stuff but it DOES help to be close as I transfer these cuts to flat plates to then be cut on my waterjet. I appreciate the help so much!! I now have a new tool in the toolbox thanks to you!

Paul

[CVH]

Yes, this is not high precision stuff but it DOES help to be close as I transfer these cuts to flat plates to then be cut on my waterjet.

Paul, make no mistake, every cross section of a cylinder is exactly an ellipse.

It is certainly not an 'average solution', 'close' or low in precision, it couldn't be more accurate.

DIMs or Length Property values are rounded numbers.
When it is drawn near the origin, the last proposal of Husky will be equally exact in floating point as the radius divided by the sine of the angle.

For R=100...110 that is up to 12 decimal digits. The waterjet will only use 3 or 4.
On top, it will use arc or line segments to approximate the ellipse.

The difference is that the notation 'R/sin(angle)' itself is infinite exact.

Regards,
CVH