How to Flatten a Hollow Cylinder [VIDEO]

Article by Jim Peltier, CSWE updated December 15, 2014


When dealing with Sheet Metal parts, a best practice is to define it as a sheet metal part sooner rather than later. This often means making your first feature a Base Flange, but it can also make use of the Convert to Sheet Metal command if your part is imported into SolidWorks or if the shape is easier to model as solid (no need to use the shell command, but more about that in another tech tip).

However, in this particular case, we have a hollow cylinder which we need to get a flat pattern from. Obviously, this needs to be a sheet metal part in order to flatten. What many users find is that Convert to Sheet Metal does not work quite the same way on a part that does not have a large flat face.

The most common cause of complications to the above process is when a user does not create that angled cut but instead makes a rectangular cut as shown in the screenshot below:

Exaggerated for emphasis

Don’t try this at home (exaggerated for emphasis)

In looking at the magnified sketch, the resulting cut will have both an acute and an obtuse angle (as indicated by the light blue). Sheet metal parts in SolidWorks require edges to be perpendicular to the flattened face. A cut like this will not allow the perpendicular edge, it creates a slight knife edge. Therefore, use the angled sketch as demonstrated in the video and pictured below:

This method maintains perpendicularity

This method maintains perpendicularity to the outside face

It may have been difficult to see in the video, but if you are dead set on using the Convert to Sheet Metal command, you need to have a planar (flat) face. No, the edge of your sheet metal part doesn’t count. This is why you will often find that people will create a very small flat section using a boss-extrude to create a flat section at the end. This is time consuming and unnecessary (it can also cause rebuild errors if you make changes) unless you use the Insert Bends command instead, which allows the selection of a linear edge.

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Jim Peltier, CSWE

Jim has been using SolidWorks since 2001, and has spent most of that time working in the design of industrial automated manufacturing equipment. He has been working as an Applications Expert at Javelin Technologies in Oakville, Ontario since July 2012 and is a Certified SolidWorks Expert (CSWE).