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Big Blue Saw Blog

Tips for Fixing Problems with CAD Files

We are often asked to diagnose problems with CAD files that don't work with our online quoting system. There are a couple basic rules for formatting CAD files: enter only the outline of the design you want us to cut, and make sure that the endpoints of all segments meet.

But some problems with CAD files can be tough to diagnose.  Let's take a look at a few common problems and their solutions.

Hidden overlapping lines

The CAD file shown below seems simple enough: a rectangle with two round holes.

But when we upload the design to the online quoting system, the system shows the circles as positive space. The rectangle is nowhere to be seen!

 

 

To diagnose this problem, we'll need to take a look at the diagnostic view. On designs with unclosed lines or other problems, there will be a link to the diagnostic view.

 

The diagnostic view shows something unusual: an endpoint on the upper segment of the rectangle. This indicates that we may have an extra segment in the outline.

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To find the extra segment, we will open the design in our CAD program, QCad. We'll  use a selection box to select the entire corner area.

 


 

QCad highlights any selected segments by showing blue squares as its endpoints.  You can see in the image below an extra segment that overlaps the line at the top. We'll delete this and try the online quoting system again.

 

Success! The online quoting system now shows the correct outline of our file.

 Selection 248

 

Endpoints not meeting correctly

  Occasionally, you will see a message like the one below.

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This message can be due to a variety of problems, but typically this is due to the outline not being complete. Let's take a closer look using the diagnostic view as mentioned above.

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The green circles indicate endpoints of segments. Where a green circle appears, the quoting system was unable to match the endpoints of two segments together. So it makes sense to zoom in to check each of these areas for problems.

Opening the file in QCad and zooming in on the area in the upper center shows a section that doesn't look like a smooth outline. We can correct this by deleting any extra segments, and making sure that segments meet at their endpoints.

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After deleting the unnecessary lines and making sure the remaining segments meet at their endpoints, the online quoting system can now correctly deterimine the shape of the piece to be cut.

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Self-crossing contours in thin areas

Let's take a look at another kind of problem: self-crossing enclosures. These show up as orange areas in the online quoting system. The image below is typical of a certain kind of design we see from customers.

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From experience, I know that the long thin cutouts at the bottom can be a problem. Remember that the kerf width of the waterjet is about 0.04 inches (1 mm) in diameter. So the narrowest areas in the cutouts likely won't be able to be cut. So I would guess that the these areas have not been reviewed correctly by the original designer.

Opening the file in QCad and zooming in shows that this is indeed the case. You can see in the image below that rather than meeting at a point, the lines making up the edges of the slots are crossing over each other.

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 With some use of the "Trim" tool in QCad, the design can be cleaned up as shown below.

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And now the design is ready for the online quoting system, as seen here.

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Now that you've seen how to fix some of the more common problems, why not try uploading your design to our online quoting system?

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