I've done what you are talking about many times.
I've used a milling machine with a 3-axis digital readout and used a CNC machine with digitizing software.
The digitizers are expensive and take time to order, install and learn, so I'll tell you how I did the other.
Whether using a digital readout or a CNC machine, you need a method of consistently taking readings. If you use a dial indicator with a sharp point, then the coordinates you get will be the true surface. The sharp point will tend to pierce the soft material, so hold a piece of .001" feeler stock between the point and the surface.
Take your readings with one axis (X or Y) held in position. Label a sheet of paper with that axis reading, then write down the other axis (X or Y) and the Z for each point.
Always stroke the Z axis to get the same zero reading on the dial indicator, then record the Z reading from the display.
If you're holding the Y axis still, then move the x axis in increments that will adequately define the surface, taking a reading at each increment. If a surface is curving wildly, then the points you record must be very close together. If the surface is smooth and regular, with little change, then the points can be fairly far apart.
Take a guess at the increment (guess large) and record a stripe. input the points into smartcam as a "Create, Curves, Spline". Then "Edit, Explode" the spline into a polyline using the tolerance you choose (.0002"?). Make a line that crosses the polyline halfway between two of the input points. Group the polyline. Use "GeoEdit, Group Trim" and choose "Split". Select the line as the "Element in Trim Profile" and Go. Use "Utility, Measure" to snap the end of the polyline where you just split it. Now go back to the machine and position the machine to these coordinates and see how close the reading is. If it is acceptable, then the increment you chose will be OK. If not, you'll have to use a smaller increment.
Try to take readings as close as possible to breaks in the surface, such as the split line, without crossing over the breaks. The spline that you are going to fit in SmartCam can't handle sharp angles.
It's better to take too many points than too few. It's better to record a larger area than required.
If you use a ball point indicator or a round probe. then the polylines that you end up making in SmartCam will actually be representing the curve through the end of the ball. To make these useful, you must "Transform, Move" them up in Z 1/2 of the diameter of the ball. Now they represent the center of the ball. Next you must create a Lofted Mesh with an offset of 1/2 the diameter of the ball. Watch the arrows to make sure you are offsetting in the right direction. The mesh will then be a representation of the surface. You can make a surface from the offset mesh if you are using FreeForm.
Good Luck
Gene Bowen
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