need help to improve an extrusion

tom_lahey

Please review the attached link.
This part is the top half of a urethane rubber horn bulb for an antique car.
You will see when zooming in that the  script edge  in the rubber horn bulb is at 90 degrees to the bulb surface when near the top of the bulb... near the "north pole"
But as the script comes down the curve of the bulb, nearer towards the equator, the script, as it projects vertically, creates an angle that traps air bubbles when casting.
Is there a way to fillet or fill  so the edge of the script is always at 90 degrees to the bulb surface?... to eliminate the bubble traps, such as in corners when casting from urethane rubber.
Ideally would like to stop the extrusion at the face of the hemisphere, and restart it such that it wraps the hemisphere  and extrudes at 90 deg to the hemishpere.
I only extrude.050 past the surface, so I don't need much draft 
I cannot even seem to get the fillet command to work, it always turns red, and I gave up.
I dont mind  just email me at laheyth@gmail.com., then I dont have to come search the forum.

https://cad.onshape.com/documents/9d5ce8067ad5872c1318052c/w/d800b006406b291722b36511/e/15ea07578056a1ad02b0084d

matthew_stacy

@tom_lahey, rather that extruding the text defined in Sketch 2, consider using that sketch to "split" the surface of the bulb.  Then "thicken" the split surface.  Model.

"Extrude" propagates uniformly normal to the sketch, whereas "thicken" works normal to the surface, which can vary locally.

This approach is not perfect, as there is distortion associated with projecting the sketched text (flat) onto the curved surface of the bulb ... but it may be an acceptable method to address your manufacturing concerns.  Cartographers have struggled with this same distortion issue for centuries (projecting a curved surface onto a flat sketch, or visa versa).

Does this help at all?

tom_lahey

I see your commands, is there a way to see the file, so I can learn what to do with the split command and thicken?

robert_scott_jr_

Tom. I tried the Fillet tool also and it took a very small fillet (.1mm) up to a point and turned red probably because of the sharp corners it was trying to resolve. - Scotty

tom_lahey

makes sense, I donts see fillet as a good solution, I need to keep the script sharp and crisp

matthew_stacy

tom_lahey said:

I see your commands, is there a way to see the file, so I can learn what to do with the split command and thicken?

@tom_lahey, there is a link to a shared Onshape document in my September 24th response.  Click on the blue hyperlink that says, "Model".  Copy that document to a new workspace.

Use the rollback bar to step through the feature history line by line.  Double click on the split and thicken features so you can see what settings to use.  

Regards.