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Now is the time to try about the completely different approach, making the gears look like old schematics, old writing on old paper, where we will work on the strokes.  This will get you something like this, with overlapping contours, we will have to get rid of.     But it has a large number of nodes, it will take quite a while to edit them manually for the desired rough look, so, here is an automatic simplify operation (shown at an increased zoom level).  A multi-stop gradient is needed for ink also (not shown), and it has to have fitting colors but good contrast with the paper (like browns for old paper and light blue for blueprints). Apply the gradients. draw a random blob with the freehand tool, will it in a color similar with the background (but slightly darker or lighter), unset the stroke, simplify if needed and blur a lot:  Select all the gears, duplicate, make the duplicate darker (black), apply some blur and decrease the opacity:
Give the gears an aged look. Go back to the black and white drawing. 'Set the stroke color and unset the fill color. So select the gear (gears if we have more) suffering due to this unwanted overlap and convert the stroke to path. Then go to another gear which covers it, duplicate, select the duplicate and the former stroke and do a difference operation. Repeat with all the gears covering it until we get to something like this. Then convert all the remaining strokes to paths. Now make the drawing look rough. Repeat for all your gears. Now define a multi-stop gradient for the paper - light brown/yellow for old paper or dark blues if we want to go with a blueprint (I have not decided yet about the way to go). Then add some texture to the paper: Add some more until you are happy with the texture. Soften the focus.