2 x 2 inch aluminum 80/20 extrusion was used as the support structure for the Z axis stage. This was a more cost effective option than getting a custom support structure machined as well as offering more flexibility for future use. Standard joining plates and right angle brackets were used to secure the structure and ensure its rigidity. The four main vertical pieces bolt directly into the aluminum table base, while the two horizontal cross struts can be positioned at any height depending on the tool head being used.
Z Axis 80/20 pieces intailly mounted to table base.
Cross Struts set 6" below maximum height
As pictured in the above images, during the initial assembly of the machine, the cross struts were positioned at about half the build height for testing purposes. Currently on the machine, the cross struts are positioned at the maximum build height (not pictured).
Z Beam mounted
Once all the 80/20 pieces were positioned and secured, the Z beam was temporarily mounted in order to test its positioning. It can be variably positioned in the X plane so tool heads of different sizes can be set so that they are centered over the build base. In the above image it is set so that the nozzle tip of the plastic extruder will be perfectly centered over the build base, in order to maximize the build area. Using my CAD model, I made some jigs by laser cutting some scrap pieces of acrylic to the exact length required for positioning the cross struts and Z beam to the correct position, instead of measuring with calipers.
Once the X axis had been assembled and tested, it was straightforward to get the Y axis completed.
Assembled X and Y axes with Buld Plate
The End Stop flags were adjusted on each axis to give enough clearance so that nothing will crash into each other in the event of a software error. The Orange Cat5e cabling in the above picture is simply used to connect the end stops to the stepper motor drivers. The Build Plate fastens directly into the Y axis carrier block. During test runs of both axes, the build plate was checked to make sure there was no excessive vibrations due to its size and the fact that it only is secured in the center.
X and Y axes Electronics Set-Up with the RepRap Electronics
The RepRap 3rd Generation electronics made it fairly simple to get the axes moving once ReplicatorG was configured for my machine. This basically consisted of calculating the travel of an axis in mm per step of the stepper motor. I used Skeinforge to slice a simple test part and then ran this code with ReplicatorG to test the movement of the axes under simulated print conditions. In the above image you can see the micro controller and two stepper motor drivers, all powered by the standard computer power supply.
Close-up of Optical Endstop Flags and X axis ACME Leadscrew
Above you can see the ACME lead screw with the anti-backlash nut. The thread size initially was 3/8″-12, 1-start on all axes (as pictured here) but was later changed to 3/8″-8, 2-start. This increased the speed of the X and Y axes three fold. It is attached to the NEMA 23 stepper motor via a shaft coupling. This shaft coupling has one side threaded in order to better secure the acme screw. You can see in the the below image that that on the other end of the acme screw there is a shaft collar which is pressed right up against the bearing in the bearing mount block. There is also another shaft collar pressed up to the other side of the bearing. What this does, is it takes a majority of the load off the smaller internal bearing in the stepper motor and puts it on that big 3/8″ bearing, thus reducing wear on the motor.
Testing the X axis
Testing of the X axis with the 3rd generation RepRap electronics was successful. As you can see in the pictures there are optical end stops at each end of the Y axis. The end stops for the X axis are actually mounted on the underside of the Y axis. The flags for the end stops are the adjustable black plastic parts that were actually printed on a commercial 3D printer. I could have printed them on the machine itself once I got it running, but I did not want to take the risk of having no end stop protection until then.
