Digitizing with Vector Cad-Cam

 

Parts can be reverse engineered from an image file by drawing points along the edges of the image.  The image file can be created with a camera or flat bed scanner, or may be an archival image document.  Typical image file formats are .bmp, .tif, .jpg, .gif, .png, etc.

 

Open the image file in a viewer program such as MS-Paint

 

Start-All Programs-Accessories-Paint

File-Open, and open the desired file  ( gasket300.zip )

Edit-Select All

Edit Copy

 

MS-Paint can be closed as it will not be needed again for this discussion, the copied image will remain in the Windows clipboard, even though MS-Paint is closed..

 

Start Vector Cad-Cam

Edit-Paste-Special, select Device Independent Bit map (DIB), OK

View-View All

 

 

This is a gasket from a Vickers hydraulic pump.  It was scanned on a flatbed scanner (under $100 plug and play device) at 300 dpi and in black and white mode.  The file was saved as a PNG format, which is a loss-less, but highly compressed image file format. The size of the file is approx 19 kb.

 

While the image is still selected (the red box around the perimeter indicates it is selected), select Change-Modify, and set the Z center to –1. OK

 

 

This will insure that any geometry drawn at Z=0 will be shown in “front” of the image file, and the geometry can also be selected using the box select method from the front view.

 

Unselect all (F2).

 

Set a line drawing color and width, which will give good contrast and visibility to the drawn contours.

 

With nothing selected, Change-Attributes:

 

 

Here magenta ( pink) is selected and a line width of .015 is specified.  Note that set defaults is automatically checked when no drawing entities are selected ( Unselect all above).  Any lines, points or arcs drawn after this is OK’d will be .015 wide and pink.

 

These construction techniques can be used to trace around many regular kinds of objects.

 

Creating arcs:  3 points along the circumference of an arc or circle define an Arc.  We will define arcs and circles by sketching 3 points along the edges of the contour and then using Draw-Arc-3 entities.

 

Use the zoom window button  to drag a box around the upper left corner of the image.  Click again at the bottom right of the area desired to be magnified.  Use the cursor arrow keys and the + and – keys on the keyboard to increase zoom and slide the image around to center it in the screen.

Draw-Point-Sketch

Move the cursor over the edge of an arc and left click to draw 3 points along the arc.  Be sure to sketch them in a logical order either clockwise or counter-clockwise.  Do NOT sketch them out of order.

Draw-Arc-3 Entities

F2 Unselect

The 3 points appear as small X’s and the arc is shown following the contour or edge of the gasket.  Note the jagged edges.  This is caused by the scanning mechanism.  We are trying to convert the outline to a series of regular contours consisting of lines and arcs, and possibly nurbs curves, so we will approximate the edge using these kinds of entities.

 

Creating Lines: 2 end points determine a line.  Sketch 2 points to create a line along a straight edge.

Zoom in to the next section of the image:

Draw Point Sketch along the bottom straight edge:

Select the first point at the end of the arc

 

Draw-Line Connect and Deselect All (F2)

 

 

Creating Lines: 1 end point tangent to an arc determines a line.  Sketch 1 points and an arc to create a line tangent to the arc.  With just the first point selected, select the arc pointing away from the selected point

 

 

Draw-Line Tangent

 

 

Creating Lines: 2 arcs can be connected with a tangent line. 

 

Sketch 3 points to define the arc on the left:

 

Draw-Arc-3 Entities

 

Next Select the left arc pointing towards the right and the second arc pointing away from the first ( this is called a logical sequence as the contour follows from one arc through the second)

 

.

 

Now complete the contour with Draw-Line-Tangent

 

 

Creating Circles, draw a partial arc using draw-arc-3 entities, and then modify the resulting partial arc to define a full circle.

 

Zoom in on one of the holes.  This scanned item was not perfectly flat when scanned and the holes appear a bit obround.  We know they are actually circles, so we will approximate their diameter and location from the scan.

 

 

Sketch 3 points along the circle where the scan seems to be the sharpest.

Draw-Point-Sketch

Draw-Arc-3 Entities

 

Double Click on the arc, or select just the arc and Change-Modify

 

Adjust the start and end angle to 0 and 360 to develop a full circle:

 

 

 

This is probably about the right size, but not quite the right location. 

 

To adjust the location of the circle:

 

1)      Special-Options-Snap Mode, Check No snap Points, OK

 

 

2)      Change to Modify Mode by clicking Change-Modify Mode, or  (F7)

3)      Hold down the shift Key and left drag on the 180-degree location of the arc to position it symmetrically around the scanned hole. Release the left mouse button after the arc is dragged to the desired location.

4)      You can use Ctrl-R to redraw the screen if there are artifacts left behind after the circle is moved.

5)      If the circle will not snap to the desired position: Special Options-Grid, Activate the grid with .001-inch increment and every 5th one showing.  Now you can drag the circle and it should snap within a .001-inch increment.  It may also help if you Zoom-Window and make the circle as large within the viewing area as possible.

     

 

You can also use Edit-Cut, Edit-Paste with X or Y displacement, to move the circle small incremental distances.

 

Adjusting a sketched line:

 

Leave the snaps turned off, and the grid turned on as in the circle adjusting routine.

Use Draw-Line-Free Sketch to approximate a straight section of the contour.

 

Note that the top of the line missed the edge of the gasket.

Change to Modify Mode ( F7)

Press and hold the CTRL key and left drag the top end of the line until it snaps onto a grid point that is along the edge of the gasket.

 

Creating complex curves:

 

When the outline of the gasket is not quite an arc or straight line, either a nurbs curve or cubic Spline can be created to approximate the contour.  The nurbs curve will appear as a single entity in the drawing.

 

Draw-Point Sketch a series of points along the edge.  Make sure they are in a logical order

3D-Curve-Interpolate points

 

 

Use Change-Trim-Extend and Draw-Line-Connect to join and trim the contours into a single closed chain, ready for creation of the desired cutter paths.

 

Scaling. 

 

When the bit map image file is first pasted into Vector, it is important that the image size be verified and adjusted if necessary, before tracing the outlines.

 

Record the measurements of the gasket using a scale or other more accurate measuring device.

 

Draw-Line-Free Sketch and draw a horizontal and Vertical line at the same measurement points in X and Y.

Double click on the sketched lines to determine the lengths of the drawn lines.

 

In this case the drawn X line (horizontal) is 16.1322, and the Y line is 18.6529.

The measurements with a scale were 5.125 and 5.950 as shown above.

 

This calculates to a scale of 5.125/16.1322 or .318.

 

If the adjustment is done immediately after initially pasting the image into the drawing, use Edit-Cut, then Edit-Paste, reset, Scale = .318, OK.

 

The resulting image is scaled to match the original part and can be traced with reliably scaled contours.