Controlling direction of move face?

laird_broadfield

Or, more precisely, see below:



I'm moving the curved underside face (and its symmetrical companion.)  I've chosen the highlighted top surface plane as my direction, so what I thought I'd get was a move purely in the -Z direction (as indicated by the pull arrow.)  Where is the extension in the -X direction coming from, and how can I not have it?  Translate is behaving more like Offset; the effect I want is pure -Z translate

bradley_sauln

Could you please share the document? It looks to be just a visual effect as the slider at the bottom of the move face menu is towards the middle. If you move the slider all the way to the right you will see the final result fully and if I am correct you will see the end result you are expecting

laird_broadfield

I broke it into a separate doc, here you go:
https://cad.onshape.com/documents/344d36f7688300fc25eb4871/w/710a3eb624112b54300ad2b5/e/a65b7c9fb6828f30e2ab5d45

Before the move face, the long edge of the top face is 19.25.  After Move Face 1, the long edge is 20.376.

laird_broadfield

NeilCooke

It's because the natural extension of the surface will make the top edge longer. If there was a very small flat at the sharp edge it would behave as you are expecting because it would be able to extend the flat face. 

laird_broadfield

NeilCooke said:

It's because the natural extension of the surface will make the top edge longer. If there was a very small flat at the sharp edge it would behave as you are expecting because it would be able to extend the flat face. 

Only if the movement of the original face is "outward".  What I want (and thought I specified via choosing translate) is "downward".

Let me ask it differently -- how would I achieve what I want?

NeilCooke

If you move the face downwards what would happen to the edge that joins with the top flat surface? It would have to move to the right. if you make a small cut along that edge to create a small vertical surface then there is something to extend downwards. The only other option is to move the top face downwards at the same time. Whatever your do you will end up with a vertical face where the edge once was. 

laird_broadfield

I get what you're saying, but I'm not clear why the edge of the top flat surface wouldn't stay where it is, and the edge of the undercurved surface would translate directly downward, resulting in said new vertical face.  As a practical matter, yes, I could make that cut as some micromillipico-sized face that's below a functional size and doesn't mess up my model -- but fudging the shape so as to hint the engine feels very work-around.

NeilCooke

It's just impossible for the modeling kernel to guess what you want - basically you can't get it to create new edges or faces. Best bet would be to move the top flat face downwards at the same time, then add material back on at the top.