Plotter blades: Offset Compensation?

GIS Premium Blades

Offset compensation for drag blade plotters

Offset compensation ?

 Offset is set too big Offset is set too small


Plotter blade offset correction

Plotter blade offset too big

Plotter blade offset too small
  The offset value set on the plotter is greater than the actual offset value on the blade. The plotter travels further beyond the corner than would be necessary for exact compensation. Artificial tips are created. The offset value set on the plotter is smaller than the one actually present on the blade. The correction made by the plotter is not large enough. The corners of the contour are rounded.
With drag knife plotters, the tip of the drag blade is displaced from the center by the offset dimension "O". This causes the blade to be aligned in the cutting direction. The tip therefore follows the axis of the plotter by this distance "O", what usually has to be compensated. This is done automatically by the control of "real" cutting plotters. With modified drawing plotters or CNC milling machines with drag blades, the contour can be corrected by the CAM program or by means of a special program (e.g. "Skalp") before the file is plotted.

IMPORTANT is with all drag blade plotters that the offset value that is set actually corresponds to that of the blade. If necessary, make a test cut with a square and change the offset setting on the plotter until the corners are exactly right-angled.

Initial problem: Where is the tip of the drag blade?
Plotter blade offset compensation A special problem of the drag knife plotter is that at the beginning of a figure to be cut it is random at first where the tip of the blade is, because the blade is freely rotatable in the blade holder. Only one thing is certain: the tip is somewhere on a circle around the axis of the blade holder with the radius corresponding to the true offset value.

Only after a plotted path of slightly more than 1 x offset the tip is definitely "behind" the axis. The result is that at the beginning of the figure it has a random contour over a short distance.

Usually the plotters are controlled in such a way that this unsafe initial part is plotted again after closing the contour to ensure that the contour is really closed and can be safely weeded.

Conclusion: For very fine objects, you should select offset values that are as small as possible in order to keep these unavoidable initial errors small.

Hint: For particularly filigree work, you can plot a short line (in later waste) before plotting the actual contour, the alignment of which corresponds to the start of the following contour (if you know where your software sets the starting point). Then the knife is already aligned in the corresponding direction.
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