Difference between revisions of "Framing and Pen Centering"

Revision as of 10:10, 22 December 2010

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Introduction

Before discussing centering and framing, let us first orient ourselves. When our Inkscape drawing is displayed on our computer screen, the drawing page has a well defined top and bottom as well as a left and right. To help visualize the edges of the page, we can display the page's boundaries via the "Document Properties" item of the "File" menu. The top of the Inkscape drawing plots near the headstock end of the egg so we'll refer to that end as the egg's top or top pole. (The headstock is the end of the Eggbot with the egg motor -- the motor which turns the egg.) The bottom of the Inkscape drawing plots near the tailstock end of the egg making that end the bottom or bottom pole of the egg. The Eggbot moves to the left or right in our drawing by rotating the egg. It moves or down in our drawing by moving the pen arm.

Centering

Warning: This discussion assumes that you are using v2.1.0 or later of the Eggbot Control extension. You can check which version you are running by selecting the "*" tab of the Eggbot Control extension.

1. The first step in centering your drawing on your egg is to center your drawing relative to the top and bottom edges of your drawing page. You can either do this manually or by using Inkscape's alignment tools. In either case, begin by selecting everything in your drawing with the "Select All in All Layers" item of the "Edit" menu. To then manually center, select the "Selection" tool from the left edge of the Inkscape window. That's the tool whose icon is a pointer; it should be the top most tool in the vertical stack of tools along the left edge. With that tool selected, then click in your drawing page and then while holding the mouse button down, drag the selection to center it. To instead center using the alignment tools, choose the "Align and Distribute" item of the "Object" menu. An alignment window will appear along the right edge of the Inkscape window. In the "Relative to" field of that window, select "Page". Next, check the "Treat selection as group" checkbox. Finally, click on the vertical centering icon: that's the third from the left icon in the second row of icons.

2. In the Eggbot Control extension, go to the "Options" tab. Ensure that the "Start with pen centered" checkbox is checked. If it is not checked, then check it and then click the "Apply" button. The "Start with pen centered" option tells the Eggbot that where the pen is positioned when you begin your plot is the point in the center of your Inkscape drawing page. Specifically, if your Inkscape drawing page has the dimensions width × height then the pen is positioned at the (x, y) point (width / 2, height / 2).

3. After you have loaded your egg or other object into the Eggbot, center the pen at a point half way between the egg's poles. You are here telling the Eggbot that you've positioned the pen at the midpoint of the egg's height.

4. From the "Plot" or "Layers" tab, click the "Apply" button to begin a new plot. Your drawing should be well centered on your egg.

Framing

Are you instead having problems with your drawing extending too far to either end of your egg? If so, then here's some framing tips.

First, keep in mind that the recommended template size of 3200 × 800 pixels is just a guideline. It's a good first approximation for laying out drawings for the Eggbot. The actual top and bottom plotting limits will vary with a variety of factors including the shape, diameter, and position in your Eggbot frame of the egg or other object you plan to plot on. Even the shape, diameter, and holding position of the drawing pen can influence the top and bottom limits. The upshot of all of this is that some experimentation is needed in order to determine reasonable top and bottom plotting limits: given all the variables there's no one template that will always work perfectly. And, there is not even any obvious automatic electronic means of centering the pen or determining the plot range that accounts for all of this variability.

There is, nonetheless, a straightforward and reliable procedure to get the plot centered correctly every time. By following this procedure, you can reliably fill the available plotting region to the extent possible.

1. In your Inkscape drawing, draw two short horizontal lines, one near the top of the Inkscape drawing page, one near the bottom. Consider putting them in a separate layer labelled something like "1-test".

2. Plot this layer alone. If the two endpoints are where you want them -- very close to but not hitting the physical limits --then you are good to go. Otherwise, adjust their positions and try plotting them again. Repeat this process until you achieve satisfaction.

3. Once these two limits are determined, position your drawing within the drawing page such that it extends from one line to the other: nicely centered and now filling up the available drawing region.

4. Delete the parallel "test" lines. Or, you can put your actual drawing on another layer, and just plot that layer.