The last few weeks have been busy, both on the academic front as well as the project front. I’ve done quite a bit of progress on Eta, primarily involving the mechanical aspect of Eta.
I ended my previous build log staring at a large pile of plywood cutouts. After sorting out the pile, I started assembling the bits according to my design. It started with the extruder, which is based off a collection of spring loaded direct drive extruders.
I also modified it by adding using a single hole to mount it onto a hinge, which was them bolted to some support plywood. This structure essentially allows the entire extruder to rotate along two axis as the bowden tube moves. In theory, this should keep the friction or constriction of the tube down, and prevent any dislodging of said tube. It isn’t fully balanced, but I’ll design a proper gimbal mount for it once I get the printer working.
Z Axis and Carriage
So Eta has a vertically mobile heatbed, and the extruder moves in the XY axises. 4 8mm support rods align the carriage, and 2 threaded rods on stepper motors hold it up. Originally, the plan was to have the stepper motors on the ground end of the axis, but space constraints made me place them on the upper side instead.
I drilled 15mm holes in the bed for the LM8UUs, and 13mm holes for the Z axis nuts. Since the nuts were hexagonal, I took the average distance between the tips & flats of the hexagons and drilled a hole in that diameter. I then broached the holes using the nuts themselves and a hammer, using two nuts in each hole to counter backlash.
Y Axises, Carriages & Stepper mounts
This took the most amount of work, I’ve assembled, adjusted and fixed the stepper motor mounts and motors, the idler pulleys, X carriage, Y carriage, and the X and Y axis rods.
The stepper motor mounts are straightforward, an L shaped plate with the stepper mounted in the middle, supported by small ribs. A limited amount of adjustment can be made using shims under the bolts. The idler pulley mounts are identical, except that they have an additional support structure which goes over the pulley. All four were assembled, leveled and bolted down.
Next I assembled the Y axis carriages. I’d made the upper parts of solid wood using a drill press to ensure accuracy, and added a support to fit the pulleys to below.
After testing however, I noticed several discrepancies between the Y carriage pulley placement and the X carriage. After extensive debugging, I discovered that the fault was the result of a miscalculation in my CAD design, and a machining error when I was making them. The errors meant that these Y blocks were a failure, and I’d have to make another pair. However, it takes an entire day at my college workshop to properly make these, and I am short on time, so I instead opted to modify the blocks.
I sliced apart the glue joints holding the plywood support frame onto the solid block, and measured the upper side of each block. I flipped both carriage blocks vertically, so their smooth sides pointed downwards. I drilled the holes at the correct distance, and cantilevered the pulleys on screws and washers. The threading in the wooden block is reinforced with superglue soaking into the wood.
The new blocks hold up to preliminary examinations, so I hope they’ll work well until I get proper blocks printed.
X carriage, and support rods
The hot end mount block is relatively straightforward. It consists of two symmetrical parts clamping onto a hot end and riding on a pair of LM8UUs. The rods themselves are fixed into the Y carriages.
Originally, I had planned for the X axis rods to measure 40cm, but due to the prior mentioned error with the Y carriage blocks, I mistakenly thought that I had miscalculated the length, and had another pair of rods cut. It was only when I was adjusting the setup that I realized my error and swapped out for the older rods.
To align the After a lot of careful measuring, modifications to the Y axis support biscuits, and tender, loving adjustments with a sledgehammer, I got the XY axis fully setup.
At this point, all 5 stepper motors are in ready, and all that’s left is to add on the belt, tubes, wiring and finer details. Stay tuned, as next week will feature testing out more electronics, and the possibility of having to use a decade old fire extinguisher in case the need for sudden fire drills arise!
Till then, Toodle pip, and thanks for following my development.