After building the first side, I just repeated the operations for the second side. I had cut all the plywood at once in the beginning to make sure the dimensions were identical, using the same saw setup. Next step was to drill and tap all the holes in the aluminum bar stock for the long X rail mounts. I followed the same process as detailed earlier to make sure the rails were straight and aligned properly.
I made plywood stepper motor mounts and bearing support mounts, all from the same birch plywood stock that I’ve been using for everything on the machine. Here you can see the left and right sides of the frame, along with the rails placed on top. The ball screw assemblies are in the center, but they will be mounted to the outer portion of the frame sides.
Here is a picture of the completely assembled Z axis attached to the Y axis. The only parts missing are the linear bearings that will be mounted to the bottom of the gantry.
It’s looking like a CNC machine!
The next bit of progress on the machine was back to working on completing the Z and Y axis components. I spent some time in Fusion 360 learning to create drawings from the components in my model. This allowed me to print out a scale drawing to use as a template for quickly and accurately placing all of the holes in the following part. An 8.5″ x 11″ sheet of paper just fit all the holes for this piece.
In order to get the ball nut coupler to be flush with the Y carriage, I used a router table and a hand chisel to lower the plywood carriage slightly:
The final task on this part was to make the Z stepper mount out of plywood. I glued it together and clamped it to dry overnight.
Although I left enough space for the epoxy to form a meniscus at the edges, I decided I wanted to get the rails right up to the edges, per the original design. I used a shoulder plane while the epoxy was only partially hardened and it planed down beautifully to remove the meniscus along the outer edges. After the leveling epoxy was completely cured I bonded the aluminum rail mounts (with rails still installed) into place on the gantry, using an adhesive epoxy. I think I forgot to mention earlier during the Z Axis buildup, that all the aluminum bar stock was chemically etched prior to epoxying them to the plywood, in order to get the best bond. On one set of rails, I sanded the bonding surface with 120 grit prior to etching; another recommended method for better bonds. I’ll see how each method holds up and perhaps do some more formal testing of different bonding methods in the future.
To help align the rails, I placed identical length aluminum bar stock in between the rails at each end, where the ball screw supports will be mounted. Then I built part of the Y carriage and installed it on the rails, to hold them in alignment at the center.
Once the epoxy cured I put a dial indicator on one set of guide bearings and measured the error all along the length of the opposite rail. I loosened one to three rail mount screws at a time and made fine adjustments to the rail until I had no more than +/- 0.0005” error throughout the full length.
With the epoxy leveling complete on the gantry face, it was time to prepare the Y Axis profile rails and their aluminum bar stock mounts.
When I had mounted the Z Axis rails, I clamped the rails against a straight edge and then used an automatic center punch to mark all the hole positions on the aluminum bar stock. Then I removed the rail and drilled all the holes on the drill press. That turned out to be less than ideal since the center punch was smaller in diameter than the rail mount holes and I wasn’t perfectly centered with each hole. Luckily there was enough play around the M4 screws to correct these minor errors, but I needed a better method for the Y Axis.
Again, I clamped a straight edge against the registration surface on the side of the profile rail, then aligned that with the aluminum bar stock and clamped the bar stock together with the rail. Rather than using the small diameter spring-loaded center punch to mark each hole, I found a drill bit that exactly matched the diameter of the holes in the profile rail. I inserted this bit in each hole and gave it a good tap with a hammer, leaving a mark at the center of each hole. This allowed me to drill all the holes more accurately at the drill press. I still ended up with some slight errors from my less than perfect alignment of the drill bit with the marks on the bar stock. For the second Y axis rail I tried yet another method…third time is a charm!
Leaving the rail/bar assembly clamped together, I brought the whole assembly to the drill press. I aligned the first hole on one end with the drill bit and could easily see when it was centered. I drilled the first hole, then tapped it and put a screw in. Next I drilled and tapped the hole on the opposite end and put a screw in. Followed up with one in the center, gradually removing clamps as I went. Now I could drill all the holes without having to mark anything. This method was much faster and more accurate as well. With the holes drilled and the rail still attached, the rail acted as a guide for the tap to ensure it was vertical. The tapping operation went much faster this way as well.
I didn’t take a lot of pictures of this whole process, but here are a few shots of the work and progress:
Rails laid in place on the gantry for fit check: