How to add Sketch Elements without disturbing my Extrusions

k_w214

Hello

I have a part that I want to edit

I wish to add some sketch elements (shapes) to an existing sketch and then add new extrusions from them
However, when I add new elements, Onshape does its own " Guesswork " about the new element and screws up all the original extrusions. 

For example, i might add a circle to an existing sketch, and onshape automatically makes a hole through the part

How can I add new sketch elements without onshape automatically altering extrusions from the sketch

Best Regards

NeilCooke

Short answer is no. If modifying the original sketch changes the design intent then you should create another sketch for other features, referencing the first sketch. 

john_mcclary

@k_w214

The extrude is not guessing. It is a logical calculation based on some boolean logic.

Any enclosed shape will either be an extruded body or an ignored area.
All "construction" lines will be ignored by this logic.

All shapes below are fully enclosed:
if the shape has an edge that touches "white space" than it will be filled
if the shape is fully within another enclosed space, than it will be cut

this gets more confusing when you start "nesting" shapes within each other.

Best way to practice this is to draw some shapes, extrude them, then exit the sketch, click "Final" and move things around. Until you understand what is happening intuitively. 

NeilCooke

Edit the extrude and select the hole that is created to add it to the extrude definition. 

k_w214

Yes, that would be what I am doing right now, 

- Edit sketch
- Go through all my extrusions to fix Onshape's automatic changes

Wondering if there is a way to disable the automatic changes?
It gets really bad if i divide up a square into two parts, then Onshape will only extrude one random part. 

NeilCooke

Short answer is no. If modifying the original sketch changes the design intent then you should create another sketch for other features, referencing the first sketch. 

john_mcclary

@k_w214

The extrude is not guessing. It is a logical calculation based on some boolean logic.

Any enclosed shape will either be an extruded body or an ignored area.
All "construction" lines will be ignored by this logic.

All shapes below are fully enclosed:
if the shape has an edge that touches "white space" than it will be filled
if the shape is fully within another enclosed space, than it will be cut

this gets more confusing when you start "nesting" shapes within each other.

Best way to practice this is to draw some shapes, extrude them, then exit the sketch, click "Final" and move things around. Until you understand what is happening intuitively. 

k_w214

Thanks for the answers everyone. 

I will keep Onshape's boolean logic in mind as it flips between filled and cut areas

Generally, adding new sketches seems to be a cleaner way to editing a complex part