How can I dimension hole locations on a flattened cylinder?

jeremy_lee540

I have a cylindrical extruded sheet metal part with various thru holes that I am trying to dimension. Unfortunately, once the part is laid flat the round openings aren't round anymore and the dimension tool will not snap to any of the mid points. I expected that I would have to call out the diameters with a just an arrow and note, which is fine, but I can't figure out how to call out their locations. Any ideas?

The first part in questions is T18 cryoshield 2 in the linked document.

https://cad.onshape.com/documents/c07e7911ee53c8bd2452944e/w/8dfc7a3cbf5c5afa3fa06679/e/7ccb9aec77a90eb7c306b748

NeilCooke

Hi @jeremy_lee540 - this is a tricky one because, of course, if you want the hole to be circular in the rolled state it must be deformed in the flattened state.

First of all, there is no need to "finish" your sheet metal part unless you are going to add some post-rolled features to it (which then won't show up in the flat).

• Delete the finish sheet metal feature (or roll back before it) otherwise the next steps won't work
• Create a sketch on the flat face in the flyout tab on the right and add either centerlines or arcs/circles to represent the hole center and diameter (although in reality, it is not a circle, so you should only probably dim the center) - sketch points will not work so centerlines must be used to locate the center
• In your drawing, right-click the view, select show/hide sketches and choose the sketch
• Now you can dim to the sketch entities

Hope that is sufficient for what you need.

jeremy_lee540

Thanks Neil, I tried finishing the model as a last resort when I couldn't figure it out All set now.

NeilCooke

Hi @jeremy_lee540 - this is a tricky one because, of course, if you want the hole to be circular in the rolled state it must be deformed in the flattened state.

First of all, there is no need to "finish" your sheet metal part unless you are going to add some post-rolled features to it (which then won't show up in the flat).

• Delete the finish sheet metal feature (or roll back before it) otherwise the next steps won't work
• Create a sketch on the flat face in the flyout tab on the right and add either centerlines or arcs/circles to represent the hole center and diameter (although in reality, it is not a circle, so you should only probably dim the center) - sketch points will not work so centerlines must be used to locate the center
• In your drawing, right-click the view, select show/hide sketches and choose the sketch
• Now you can dim to the sketch entities

Hope that is sufficient for what you need.

jeremy_lee540

Thanks Neil, I tried finishing the model as a last resort when I couldn't figure it out All set now.