MetaEtch Help

MetaEtch is for hobby cnc milling of printed circuit board patterns from simple bitmap source graphics. MetaEtch can generate regular outlines for simple trace isolation. MetaEtch can optionally produce pocket milling of blank interior space, which can minimize inter-conductor coupling associated with regular outlines. And MetaEtch can even generate drilling tracks. MetaEtch was created just to make it easier to produce hobby level electronic circuits using hobby level cnc equipment and basic graphics software.

The sample graphic (below left) is an actual circuit pattern for a simple optoisolated thyristor motor control circuit. All help descriptions will be in reference to this sample image, but any image that meets the described criteria can be used. To the right of the bitmap sample is a SVG scalable vector image representing the actual result of the process. If you do not see two images below then you need to install the Adobe SVG viewer browser plugin in order to view the vector graphics and preview images that MetaEtch generates.

Users must have basic fundamental knowledge of bitmap graphics and hobby cnc eccentric technology. MetaEtch Help does not cover or teach or explain either topic. There are many sources of pertaining information and users are encouraged to master both skills for their own benefit irrespective of it being required to use this program. Basic graphics skills go a long way toward accomplishing many hobby related endeavors in many ways. If you don't understand the following discussion, then you really should study up on the underlying principles which are really very, very basic.

MetaEtch is really just a simple one page low level front end image processor that calls on a series of high level back end programs which actually perform the conversions from raster to vector to dxf to gcode. Other front ends for other applications can also call on the same back end programs to do more than just circuit milling. Look for other exciting vector geometry hobby cnc applications based on the same technology.

Consequently, each subsequent processing stage is a distinct program which opens in a new window. You must allow pop-up windows from to proceed. We do not use any pop-up ads here anyway. The use of new windows greatly enhances the feasibility and efficacy of the entire process.

Minimal javascript is employed which should be compatible with most modern browsers. The applications are designed for MSIE and tested with Netscape and Firefox browsers. No other browsers will be supported due to their low market share. Any known incompatibilities with supported browsers will be noted below.

Firefox, on some installations, displays a warning that the SVG format is incorrect, then displays the SVG source code rather than the image. This should be easy to correct soon.

Scale Bitmap Graphics
In order to get predictable accurate results the bitmap source graphics must meet the following criteria,

#1 the bitmap must be to scale at 333 dpi. If the input is not drawn at 333 dpi then the output will be scaled as if the input was 333 dpi. At 333 dpi each pixel represents approximately .003". This value was chosen specifically for certain technical reasons to facilitate both efficiency and accuracy.

#2 the circuit pattern must be depicted in black and white with white representing the area that will be milled out. Grey pixels get converted to either black or white based on a non-specific threshold value. Grey pixels should be avoided because the result will be less predictable, the process will be less efficient, and the tool path will not be as smooth.

Colored pixels in the overall circuit pattern must be avoided because colors have extended meaning. In this case, color is used to depict drilling operations. Therefore any unintended non-grey pixels may cause signifigantly erroneous results. See Drilling Holes.

White pixels should not extend to the edge of the image. The entire image should be (or will be) surrounded with black to define a specific workspace area. White pixels near the edges mean the tool will approach those edges which requires cosideration and setup to avoid collisions with clamping fixtures and such.

Milling Parameters
The only option is to select a pocket milling tool size or not. If no pocket tool is selected, the result will be a plain outline (on layer 0). If a pocket tool is selected, then pocket milling paths (on layer 1) will preceed outlines with a full stop (for tool changes) in between.

The outline tools is assumed to be a v-point engraving bit. MetaEtch is particularly well suited for a specific micro engraving bit that I sell on Ebay which typically cuts from .009" to .015" wide, depending on the depth of cut and hobby cnc machine characteristics. MetaEtch assumes a theoretical actual outline tool diameter of .012". Machine and milling variations can of course affect the actual width of cut so this is a relative spec. Final edge tolerance is related to actual machine settings and performance.

With a theoretical outline tool diameter of .012" and a designated bitmap resolution of .003" per pixel, MetaEtch can only cut features that are at least 4 pixels wide. More narrow features simply won't get cut because the prescribed area would be narrower than the tool. If you are cutting circuits for .026" pitch pin spaced components, you should not expect MetaEtch to establish the cuts between pins. It works much better to use a more optimized single pass machining technique to obtain the kind of accuracy required at that level of detail. Pads for .031" pitch pin spaced devices are less troublesome and should be easily obtainable.

The selectable pocket tool diameters are multiples of .003". Just select one close to the actual intended tool diameter. All generated pocket mill tool path overlap will be more than .003" so the actual tool size is not that critical. Only the outline tool cutting diameter will affect actual output tolerance. The pocket tool never cuts beyond where the outline tool will cut.

Final milling options, paths and parameters such as feed rate, depths, etc are finalized in upstream conversion processes. MetaEtch basically just lets you pre-select some options related to printed circuit board projects. See help in the upstream applications for details of their operation.

Drilling Holes
A novel mehod of specifying holes is used to allow color to be used to designate hole location without interfering with black and white pattern composition.

3 primary colors Red Green Blue each can specify one of up to three drilling sequences to perform in that order. Each color, therefore each drilling sequence is separated from all other machine sequences with a full machine stop for tool changing. Thus metaetch produces drill procedures for 3 different drill tools, or 3 different size drills with red first and blue last in order.

A primary color is defined as any non-grey pixel with one RGB component greater than the two other equal RGB components. So it can be any shade of a primary color, but it should not be a nondecisive mixture of color, the behavior of which is not defined, and for which results will be unpredictable. It's best to use solid red green or blue to avoid all confusion.

A single colored pixel does not constitute a valid drill location. A valid drill location is defined as the middle pixel of any horizontal group of pixels. So if you just draw a crosshair, as in the sample above, then the center pixel will be recognized as the intended target. The crosshair lines should only be one pixel wide. The horizontal bar should be an odd length so that one exact center pixel will exist at the center of the crosshair.

Any horizontally consecutive colored pixel group can qualify as a drill hole so the presence of color should be tightly controlled to avoid unintended consequences. For this reason, JPEG source images should not be used at all because the compression algorithm produces arbitrary noise that could produce unintended drill locations all over the place.

Color drill location marks are further required to be fully contained within a black (unmilled) area. Drill marks on white areas are undefined and not predictable.

Vector Conversion
As mentioned, MetaEtch is a low level front end to multiple higher level upstream processes which actually complete the process. MetaEtch simply does some modest image processing and data collection in preparation for further processing.

When you hit VECTORIZE, the processed image will be turned over to another application in a new window. The application will do a raster to vector conversion and output smooth bezier curves in SVG format. From there the SVG can be converted to DXF, which can be converted to gcode with many features.