Mirroring of an extrusion problem?

[Anonymous]

Hello, all,

I am trying to design a very simple testle table, nothing fancy at all, all done in a single part file to get me used to multi body parts.

I have set up a new plane to be the angle of the legs, I create a leg on a new sketch on that plane, mirror it around the XY plane to get a leg on the other side. It all looks ok, however if I measure the angle between the outer face on the original part and the mirrored part the two faces are not quite parallel (angle of angle 177.19 between them), this is a complete mystery to me as all the individual angles appear to be setup correctly.

On further inspection it would appear that if I create rectangle on the leg plane, extrude then mirror, the two faces are parallel. If however I go back and modify a point by removing one of the perpendicular constraints, to make a rhombus the faces are not parallel any more.

I have included an example file with a rectangle and a rombus on the same sketch, both extruded as one piece, then mirrored, the two rhombus faces are not parallel, as shown in image (attached), yet the two rectangles are!

Am I missing something or is this a bug?

Thanks in advance

Nick

[CCarreiras]

There's nothing odd... your extrude is slightly distorced...

If you distorce the upper square, you will have similar behavior...

[SBix26]

As Carlos said, this is not a bug.  This is basic geometry.  You've created planes at compound angles.  If you measure the angle of each of those faces to the YZ plane, they are exactly the same.  

You can also see this by measuring between the two, as you showed in your first post, but rotate your view to the Front view-- you can see that the angle measurement itself is on an angle, and you can see that the faces are not perpendicular to the front view (to the XY plane).

Try this mental exercise: imagine that Work Plane7 is perfectly parallel to the XY plane, making the two surfaces co-planar; now imagine Work Plane7 rolled 90° so it's parallel to the XZ plane, making those two surfaces at whatever angle your rhombus corner is.  So you see that in between those two extremes, the angle will be somewhere in between also.

Hope that sheds a little light.

Sam B

[Anonymous]

Thanks for all the information, I did keep thinking it was me being daft but then I thought about it again and I was making sense!

What you have said does make sense to me now

Many thanks

nick