I am between projects at the moment so I figured I would make a few upgrades to the AutoGraph end effector. 

I changed from a 3D printed design to a laser cut design. Two reasons -> 1) laser cutting is at least 10X faster so allows for faster iterations, 2) I was never able to print the 3D printed parts to a tight enough tolerance on my 3D printer.

Instead of two cylindrical guide rails and four linear bearings, I am now using just one rectangular guide rail and two carriages. Using two guide rails added too many constraints on a design that can not hold a tight tolerance. The result was the pencil cart and push plates would bind up during travel and ultimately prevent the ability to make very light pencil makings. Travel is very smooth with the single rectangular guide rail. After making adjustments to the carriages and lubricating, the carriages would slide down the rail just by gravity. 

The last significant change was selecting a new spring. The spring selection between the push cart and pencil cart is critical for achieving a wide range of pencil markings from light to dark. I played around with spring options for about two hours last Saturday before arriving at one that allows a very light pencil marking at the low side and doesn't push the pencil lead back into the pencil at the high side.

All of the upgrades came together during initial testing tonight. The new end effector successfully made "light" and "dark" pencil makings with promising contrast between the two. After more than two years since I started on AutoGraph, it's looking like I may actually finish this project. 

Now on to getting the 2 axis plotter wired up and working with GRBL.