Rotation Query - Rotation cause twisting of Object

[Michael Siggers]

Hi

 

Attached is a model I am working on but am having trouble rotating an object.

 

The object in question is an extrude, currently on the 'None' Class. This object is effectively a piece of 40 x 40mm timber which is to be on the inside corner of a sloped 6mm MDF form. The slope of the 6mm MDF is 15 degrees.

 

As can be seen from the Model, I have rotated the 40 x 40mm object in one direction to fit in the corner, which can be seen in one of the orthographic views, noting how it sits directly on the inside of the 6mm object.

 

So................. when I rotate it in the other direction, it becomes twisted for some reason and does not 'sit' in the corner properly. This happen whether I set up a Working Plane or use Auto plane for the surface of the object.

 

I can not get my head round why it is twisting. It should fit snuggly in the corner of the 6mm MDF. I have made it longer than required as I was planning on using the Trim tool to cut it to length, with horizontal cuts, at the required points.

 

Any thoughts would be appreciated.

 

Kind regards

 

Mike

Cooker Hood.vwx

[Michael Siggers]

So, a quick update.

 

I think it is a result of the compound slopes with the 6mm Hood, as even though on plane view it os 90 degrees at the corners, when an angled section is taken, it is slightly over 90.

 

Still can not quite get my head around it, but essentially, it appears to be because of the geometry.

 

Kind regards

 

Mike

[Pat Stanford]

I am not seeing any distortion in VW2025.

 

You have already rotated it in the front view. If I then go the the Left view and rotate it from there it appears correct to me with slope in both planes.

 

[Michael Siggers]

HI @Pat Stanford

 

This may help make it clearer. Attached is a file with the one object.

 

1. Created a Rectangle,
2. Extruded Rectangle
3. Changed to Front View
4. Rotated 15 degrees
5. Changed to Left View
6. Rotated 15 degrees

Now, look at the front and left views, and it is twisted.

 

I double checked the working planes when rotating.

 

Kind regards

 

Mike

Rotation Query.vwx

[Michael Siggers]

...... and some screenshots;

 

1. Front View
2. Left View
3. Top Plan View

 

It can be seen in the front view and Top Plan view that the object is now twisted slightly.

 

Mike

Edited September 19, 2024 by Michael Siggers
Added Text

[Michael Siggers]

Here is a revised model where I have rotated it 20 degrees.

 

The twist is more obvious when looking at the elevations.

 

Mike

Rotation Query 2.vwx

[EAlexander]

This doesn't look twisted to me, it just looks like the Orthogonal view making a bit of an optical illusion.  The Top/Plan view shows all the lines parallel.  

 

Try switching to normal perspective mode and take a look there.  It takes a while to get used to working with orthogonal views on angled stuff as they mess with the perspective.

 

e.

[Michael Siggers]

Hi @EAlexander

 

I have to disagree as you can clearly see the rear corner in the elevation view, orthogonal, which should not be visible.

 

I posted another file where I've rotated it more to emphasise the issue.

 

Also attached is the Top/Plan view, (pressing 0 on the number pad), and it can be seen the object is twisted.

 

Mike

 

 

Edited September 19, 2024 by Michael Siggers
Added text.

[rDesign]

7 hours ago, Michael Siggers said:

HI @Pat Stanford

 

This may help make it clearer. Attached is a file with the one object.

 

1. Created a Rectangle,
2. Extruded Rectangle
3. Changed to Front View
4. Rotated 15 degrees
5. Changed to Left View
6. Rotated 15 degrees

Now, look at the front and left views, and it is twisted.

 

I double checked the working planes when rotating.

 

Kind regards

 

Mike

 

I followed your steps in this post, rotating the object with the Rotate Tool, snapping to the same point for each Front & Left rotations, and I do not see any kind of 'twist' that you are talking about. Everything looks correct -- and no different from the other files you've posted. 

 

Top / plan View

 

1 hour ago, Michael Siggers said:

I have to disagree as you can clearly see the rear corner in the elevation view, orthogonal, which should not be visible.

 

Why are you expecting it not to be visible? It is a wireframe view, not a hidden line. So you're seeing through the timber.

rotation test.vwx

Edited September 20, 2024 by rDesign

[Tom W.]

I agree with Mike. I would have expected these two lines in plan to align with each other:

 

 

This is the twist he's referring to.

 

If I instead place a Working Plane diagonally through the Extrude + rotate it once on that plane I get the desired results:

 

 

I don't really understand why the same results aren't achieved by rotating it twice in orthogonal views.

[Michael Siggers]

6 hours ago, rDesign said:

Why are you expecting it not to be visible? It is a wireframe view, not a hidden line. So you're seeing through the timber.

Hi

 

I was referring to the rear line being visible in the orthogonal elevation view in shaded mode.

 

Mike

[Michael Siggers]

1 hour ago, Tom W. said:

 

If I instead place a Working Plane diagonally through the Extrude + rotate it once on that plane I get the desired results:

Hi @Tom W.

 

This is what I ended up doing on the model I was working on.

 

For curiosity, going to try the same thing in Sketchup later and see if the result is the same.

 

Mike

[Benson Shaw]

Hi, all

 

Two items

1.  I would use different words.  The 40x40 is not twisted (eg twist to wring out a washcloth). Yes, it is rotated, which explains view displaying edges with some separation. Also, it will never fit flat against both sides of the hood.

2. The planes of the hood, tilting from 2 directions, do not meet at a right angle,  They intersect the layer plane at 90°, but plane to plane angle is greater than 90.  Think about a really flat pyramid. Adjacent planes rise a bit from a square base, but the apex is almost on same plane as the base. Now flatten it all the way - angle between the planes is 180° (they are co planar). An infinitely tall pyramid will have adjacent planes approaching 90°.  Face/face angle for other rises is between 90° and 180°.

 

A pyramid face to face angle is 93.84° if both sides tilt 15°. 

Resaw or machine the 40x40 to fit against both "faces".

Eg slice 1.92° from 2 adjacent faces of the 40x40.

 

hth

 

-B

[Michael Siggers]

3 hours ago, Tom W. said:

 

If I instead place a Working Plane diagonally through the Extrude + rotate it once on that plane I get the desired results:

Hi @Tom W.

 

This is what I ended up doing on the model I was working on.

 

For curiosity, going to try the same thing in Sketchup later and see if the result is the same.

 

Mike

[Michael Siggers]

Thank you @Benson Shaw

 

Yeah, after much racking of my brain, (getting old 😃), I figured the angle between the two angled surfaces was not 90 degrees.

 

Ignoring those and looking at the other file with just the 40 x 40mm object, just confused as to why it becomes slightly rotated when rotating the object the way I have.

 

Mike

Edited September 20, 2024 by Michael Siggers
Spelling mistake

[Benson Shaw]

[Michael Siggers]

Thank you @Benson Shaw

 

Much appreciated.

 

Do you have any thoughts on the other file and why the object becomes rotated when rotating it in two separate operation on two different planes?

 

Mike

[Michael Siggers]

Hi

 

I can confirm it does exactly the same in Sketchup, and for some reason creates an additional rotation of the object.

 

So, the best way is as @Tom W. suggested and creating a Working Plane across the diagonal and then rotating.

 

Mike