Negative scale: command vs. gumball

Hi All - what do you think about an idea to let command scale (1d, 2d,3d) behave as Gumball scale and mirror object(s) if negative. At least as a switch in command options (AllowMirror=Yes/No). Is there any reason why these two are different? I’d like to be able to mirror with negative command scale.


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Hah… Didn’t even realize inputting negative numbers in Scale would mirror, good trick! Not sure I’d ever use anything other than -1 to just mirror without scaling, but it’s a cool feature nonetheless… I see that BoxEdit also works this way. Definitely +1 (or should I say -1?) on this for the Scale command.

Hi @pascal,
Is there any reason why Gumball and BoxEdit allow negative scale as mirror and regular Rhino commands don’t ?


Hi Jarek - no reason that I know of other than that Gumball came later and Scale has not caught up, I bet no one thought of it - to the functionality it introduced…


Ha, thanks Pascal. I’m glad I was the first one that did ; )

But the catch seems to be that you need to know the exact size of the object in the axis you are (negative) scaling. If you use a number smaller than the dimension it just shrinks the object, if the number is larger then you get a stretched mirror.

Yeah, I forgot Gumby has changed in V6 - using + or - and a numnber expands or shrinks by that amount in model units now; add units to override model units. (or 2x if the gumball is centered - that is, it shrinks that much from handle to the gumball center)


Hi @nick, @pascal,
Looks like now the command version of Scale (2D and 1D too) mode does take the absolute value of what I type to use either as a scale factor or the distance. So I don’t see a problem with reading ’ - ’ as a mirror and then scale by the given factor.

No need to change Gumby, but I actually thought at some point it was discussed to use double – or ++ to decrease/increase the size in given direction, no? Now I see that single ‘-’ is taken as a dimension reduction, not a negative value for scale; still just dragging the scale handles allows mirroring in Gumball…


right now + and ++ in the scale value do the exact same thing here. If I have a cube that is 20mm on X, when I input “+2” in the X gumball scale (gumball centered on object) the resulting length is 24mm (+2 from center on each side). If I input “++2” I also get 24mm. Is this the intended behaviour?

Also, is there a way to make that 20mm dimension to become a explicit width, like 25.6mm, instead or usind scale factors or additions? Like I would type a new value in the Boxedit numeric field?