SHEAR tool BUG or geometrically incompetent user?

Rhino
,
1

hey there,
i am having trouble to use the shear function. when i transform a new object i can shear it along the x axis. when i add a new object select both and want to apply the same transformation again (shearing along the x axis) i cant figure what is happening. the objects are not only shearing but also starts to rotate. why is that?
also if i simply want to shear the object back into its original shape its imppossible. searching this forum a lot of people also had this problem or simply didnt understand the tool. is this a bug or intended? how to use this?
maybe it would help to add a function (or a step) to the shear tool that allows users to define the shear axis first?

2

Hi Cl.c,

What Rhino version are you working in?

The dynamic help is really helpful in getting started in unfamiliar commands.

Everything here works as expected. We will need steps to repeat if you are seeing an issue.

image
image1660×659 79.5 KB

3

The shear direction is perpendicular to a line from the shear origin to the reference point.

If you have a rectangle and you want to shear the top sideways you naturally will choose a bottom corner as the origin and the adjacent top corner as the reference. You choose an angle and get a trapezoid. All good.

You then want to adjust the shear so you select the bottom corner as the origin again and instinctively you choose the same top corner as the reference point. But instinct is wrong! By doing that you are choosing to shear perpendicular to the side of the trapezoid; you set an angle and the point shoots off diagonally, which gives the impression of rotation alongside a horizontal component of the shear.

You need to set the reference point directly above the shear origin and then the trapezoid will shear in the horizontal direction you wish.

HTH
Jeremy

4

thanks a lot for the quick response.
as jeremy explained to me the shear direction is always perpendicular to a line between the origin to the reference point.
while i assumed intuitively that i could define the shear direction by chosing a third point, while in reality this third point just defines the shear amount.
as in my case the first transformation on a rectangle matched this assumption i was confused when it behaved differently in the second step. so no bug. jeremy perfectly explained the thinking that led to the result in the next post, and i woult take a guess that it already happened to other users as well.
anyways, i think adding the option to adjust the shear direction in a second step could be an upgrade to the shear tool, it would feel more direct and controlable and would decrease the number of steps (like drawing additional guide lines) before hand in my opinion.
just picture the scenario of a trapezoid that you want to shear back to a rectangle:
i could pick two corners of the trapezoid and then use smart track to move the second corner back in a perpendicular position. doing this now is quite a challenge.
just a proposal to make the UI a bit more intuitive maybe.

5

thanks a lot jeremy, that explains it!