Hi ! Yesterday, I finished all the assembly of aluminium brackets, I am happy of the rigidity of the chassis. However after installing the new Z Nut Support on the lead screw, I understood that I totally failed the design of this part, and I saw a few other parts where there is not any margin for adjustment.
Failure is part of the process, but most people do not talk about the why, which matters.
I took already a lesson when I had to adjust and 3d print a few times the hotend support that links together the rod on X and Y. This is a very tricky part to adjust because the 8 mm rods are long (600mm) and any small offset (of few tenth of mm) generates enough force that deflects a little the rod and the result is a bushing that binds when you move it. I am using only brass bushings, those do not tolerate any deflection on the rod, you learn quickly the hard way that it is not aligned and squared properly.
Let's have a look to the problem
The Z Support is not having the proper length, it is a few tenth of mm too long or short, what happens is that my Z axis rods are all well aligned and the associated bushing to not bind, but the stepper motors push and there is a small oscillating movement. The leadscrews are fine, straight and the stepper and top bearing are perfectly aligned with no wobble. What happens is simply that due to the incorrect length it pushes and it bends the lead screw, the nut is having small tolerance but it is enough to make it move a bit side ways and follow the helix path generating oscillations moving up/down alternatively each side of the extrusion profile, and of course the brass bushings are not happy and bind alternatively. It is not good for the nut, the lead screw and the bushings. Also due to the long length this small oscillation is slightly amplified.
What I miss on the support is to attach not on the side but to attach it on the top or the bottom of the extrusion profile and to have slots to provide adjustment in order to avoid any deflection on the long lead screw. During the assembly screws are put in loose way on the extrusion, you move the bed on Z to adjust until there is a smooth move and it should be ok. There are a lot of components in this chassis and having the ability to adjust is more pragmatic than trying to have the "good" length.
It will change the usable Z height I need to check further what is the best combination, an offset can be introduced on the Z but I want to minimize it.
I found a similar minor issue on the belt path, I designed the belt supports with no adjustment. I already have a lot of adjustment on the pulley due to the choice of the external longer than needed rods to provide it. But I put a not needed constraint at this level, so I am going to redesign them to have a larger belt width and easier access for maintenance.
Forthcoming Parts
Re designed Z Nut Support and testing, re designed X/Y Belt Bearing Supports, 400mm heatbed with 250V AC SSR, waiting for my TB66xx external stepper drivers.
Previous Parts
- https://steemit.com/technology/@boucaron/why-building-yet-another-3d-printer-part-1
- https://steemit.com/technology/@boucaron/why-building-yet-another-3d-printer-part-2
- https://steemit.com/technology/@boucaron/why-building-yet-another-3d-printer-part-3
- https://steemit.com/technology/@boucaron/why-building-yet-another-3d-printer-part-4
- https://steemit.com/technology/@boucaron/the-hotend-head-3dprinter-part-5
- https://steemit.com/technology/@boucaron/xy-stepper-motor-supports-3dprinter-part-6
- https://steemit.com/technology/@boucaron/z-stepper-motor-supports-3dprinter-part-7
- https://steemit.com/technology/@boucaron/test-assembly-3d-printer-part-8
- https://steemit.com/technology/@boucaron/lcd-support-3d-printer-part-9
- https://steemit.com/technology/@boucaron/x-y-optical-end-stops-3d-printer-part-10
- https://steemit.com/technology/@boucaron/small-heat-bed-assembly-3d-printer-part-11
- https://steemit.com/technology/@boucaron/power-supply-unit-holder-3d-printer-part-12
- https://steemit.com/technology/@boucaron/cable-management-for-the-hot-end-head-3d-printer-part-13
- https://steemit.com/technology/@boucaron/firmware-first-heat-first-moves-xy-gantry-alignment-3d-printer-part-14
- https://steemit.com/printing3d/@boucaron/induction-probe-on-the-z-axis-aluminium-brackets-3d-printer-part-15
Intresting project
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