How to create a dome on a solid, with decent control

ol_loo

Hello, i am trying to add a "doming" on a flat solid, and so far i have not found a satisfactory way. Leet me describe how i usually do that, i first create a wider version of the outline on the same place, then i may offset it down on the Y axis, then i create a point along the center which will be the meeting point of the two spline, finally i create two splines joining corners, on perpendicular planes, finally i use a loft tool, using the solid as object to modify, the splines as guide and the point as summit, with the splines controle points i can adjust exactly the shape of any transition. Unfortunately i have not been able to achieve this in onshape, the best i could do is to select the point as summit which makes a dome but with the wrong shape and very little control over anything.


here i moved the sumit point to 15mm to make the problem more obvious, but here is the result, normally the cutout should be circular, and the overall shape should be smooth, contrary to what we can see here. So i use one face, the point as summit, and perpendicular start condition with intensity to 1. But no matter what start and end option / intensity the result is always wrong, mostly because i cannot select another shape on a draft as the starting point which would solve half the problems, and secondly because i could not use spliens as guide, for some unclear reason. 



If anyone knows how to achieve what i mean, please advise.
Thanks

GregBrown

Can you share the model?

steve_shubin

@ol_loo

https://cad.onshape.com/documents/9a086d060d68f71cd0318d62/w/20c8c5ea4b9c4a08c1de0f58/e/2b433cd0c6d6be5f976dbb4a

Is this shape roughly along the lines of what you were looking for ?

In this model, the entire rim at the top of the circular hole is on plane

You can adjust transitions by altering magnitude within the loft

And there’s also adjustment by changing amounts within Sketch 2

steve_shubin

@ol_loo

Sketch 1 in both part studios is now fully constrained

Evidently, my eyes (or brain) weren’t working all that well earlier this morning

Sorry for not catching this earlier. 

Evan_Reese

There are a number of ways depending on what you're going for, but here's a go-to for me. This wouldn't guarantee a perfect planar circle when cut. For that you'd probably need the circle to be part of your loft profile, or add an arc as a guide to the method I've shown. Keep in mind that curve quality is important for smoothness, so I've taken the time to make a nice clean spline for the corner instead of just an arc fillet.