Thanks! Glad it’s of interest!

First off, there is a “Show” checkbox for the background image — clear that and it’s at least hidden.

Okay, picking up where we left off — since Carbide Create won’t cooperate, we have to work out some way to get an even grid which is about the dimensions we need, so…

7" ÷ 0.0625 == 112 squares

4.375 ÷ 0.0625 == 70 squares

112 × 0.063 == 7.056

70 × 0.063 == 4.41 — since we’d liefer 4.32623792, we’ll instead use 69 which equals 4.347

So, change the stock size to 7.06 W × 4.35 H and set the grid spacing to 0.063.

Select the rectangle tool, click somewhere in the center of the drawing and then at an edge to get two rectangles which can be easily selected, then select each in turn and change their position (starting from the bottom left corner) and dimensions to:

X 0.063

Y 0.000

Width 6.930 (110 × 0.063)

Height 4.347 (the full height)

and

X 0.000

Y 0.063

Width 7.056 (the full width)

Height 4.221 (67 × 0.063)

Note that since Carbide Create seems to work from the center of a selected object even when a corner is set as the origin it will be best to set the size first, then click Apply, then set the values for the origin, then click Apply a second time.

After all this, you should have a screen something like to:

Then, select the circle tool and draw a circle at each corner, snapping it to the square intersection left or right or above or below (not to the diagonal) — each circle should have a radius of 0.063 inches:

Then select two of the circles and the two rectangles and perform a Boolean Union:

and

Repeat with the resultant shape and the two remaining circles, then draw in the geometry for the lid.

(In retrospect, it would’ve been easier to’ve rounded 3.175mm up to 3.5 or even 4 or 5mm and used metric)

To save everyone else the math, the number are:

X 0.189

Y 0.126

Width 6.678

Height 4.095

X 0.126

Y 0.189

Width 6.804

Height 3.969

Draw in circles and union as before to arrive at:

(Arguably the outer rectangle should have a slightly greater radius)

Save the file, and duplicate it in the filesystem, (or open it and do File | Save using a new name) — there will need to be two files, one for the box itself, and the other for the lid.

Open each file, set the stock thickness to match the desired stock, and do CAM operations for each element.