5 Replies Latest reply on Jul 22, 2016 7:38 AM by John Stoltzfus

    Holes not recognised in rolled sheet when flattened?

    Tom Durrance

      Hi

      I have a cylinder with a series of fittings in it.

      I want a flat plate with all the holes already in the cylinder, so it can be sent for rolling and when finished all the holes are in the correct place.

      I made a sheet metal cylinder/ barrel drawn with centre point arc, and made into sheet metal as base flange

      I then place the barrel in position with mates on the current assembly and then edited it in the assembly.

      The editing I did was to sketch a hole over the fitting, dimension it and the cut extrude, up to next.

      Once completed I open up the part with all the holes extruded through, and it flattens ok with all the holes.

      But when it becomes a drawing the holes will not dimension

      and when I convert to a DWG again the holes are not recognised as circles

      Would be grateful if someone could help

        • Re: Holes not recognised in rolled sheet when flattened?
          Jim Moses

          Hi,

           

          Just going by what you have wrote, I am guessing the holes are coming up as splines in your 2d AutoCAD, Reason being is that the hole will only be a true circle in one penetration of the plate, as if the hole is drilled/punched prior to the roll it will make the hole elliptical and if the hole was to be cut while in a cylindrical shape when flattened it would be elliptical in the flattened state.

           

          I would think about how you are actually manufacturing it and what the holes are doing and then design and detail it accordingly, if the hole shape in the cylindrical or rolled state does not effect the design then place and cut the hole in the flattened state, which would be much easier to manufacture as drilling or punching holes on a cylinder can get complicated and require special fixtures

           

          Regards,

          • Re: Holes not recognised in rolled sheet when flattened?
            John Stoltzfus

            The reason is you cut the holes while the pc was in the "Rolled" position which is a true representation with the hole being a perfect circle when rolled, however in the flat they are an ellipse. 

            If you would un-fold the sheet metal and then add your holes you would end up with the hole shape being an ellipse when rolled.

            Anytime you add holes in a rolled sheet metal pc there are two things that make life a little more challenging, if you do it the way you show it is easier to mate additional parts, but the flat pattern is distorted and doing it the other way makes it easier to dimension the holes but more difficult to mate parts to.

            • Re: Holes not recognised in rolled sheet when flattened?
              Dennis Bacon

              Tom,,, The only thing I can think of requires a bit of work. Probably about a half hour for this part but it looks like you have put some time in this. You do realize that when you put the holes in the formed cylinder that when it is flattened the holes will become elliptical. This is do to the stretching of the outside surface and compression of the inside surface when it is rolled. If you had a stack of papers and rolled it the ends would no longer be square. Sheet metal doesn't work like that.

              If you put the holes in between an unfold and a fold (while the part is flat) then your drawing would indicate round holes and be measurable. But when you roll it this size will change. Slightly in this case. You have to be careful that your fittings will still fit. You may want to make the holes slightly oversized...

              What I did is > unfold the part > used the reference point with center of face option > started a sketch and shift selected the points > converted those points to sketch points > use the circle tool and attached circles to each point > made the circles tangent to each corresponding cut and removed the tangent relations > dimensioned the circles > did a boss extrude (offset on each cut) to make your holes smaller > then did a cut extrude (normal). Now you have good round holes in the flat. Then did a fold. I only did this on a few holes but you get the idea. Notice the holes with the center marks and dims.

              I see you are using 2012 so my file won't help.