Hi, all!
I’m getting cracking with the redesign of my third 3D printer, and I thought I’d make a little progress log here in case anyone’s interested.
Some background on the project:
When this printer was originally conceived of, I was jobless and had a bunch of spare parts from previous printer builds and unfinished/shelved attempts at such. Hence the challenge became to design a printer that used as many of the spare parts as possible, and to use as few fresh, new, extra bought-in parts - hence coining the printer “SPish” for “Spare Parts -ish”. Taking this spare-parts scrappiness approach into the CAD, I ended up with a very messy, very slow CAD document that was very hard to work on, especially when modifications were required as a few upgrades were made.
Here are some views of the current iteration of the printer:
Issues with this iteration:
- 3D printed bed carrier is not rigid or repeatable enough
- PSU mounted at the rear of the unit pushes the mainboard forward into the frame, not allowing enough space for adequate cooling, hence-
- Drivers overheat
- Z leadscrew setup takes up a lot of space
- 3D printed XY motor mounts deform and deflect with motor heat and belt tension
- Belt tension puts unwanted torque on the XY linear carriages, made worse by the leverage the belt has by being secured so high up relative to the carriages
- Frame is not perfectly square or perfectly flush in construction due to manual processes used
- XY rails mounted on said frame are very cheap and low quality (bearings have a kind of skipping, catching quality), and they also don’t sit perfectly in the V-channels of the aluminium extrusion, leading to high potential for error in the fixing of the rails to the extrusions
- Inaccuracies in construction and fabrication result in inconsistency of the sensorless homing, such that at times it “homed” mid-axis and subsequently crashed on the next move
- Some compliance of unknown origin in the Y axis prevented the acquisition of clean usable data for input shaping
- Bed and hotend heaters aren’t powerful enough
- Weight of the motors on the flying cross gantries combined with their placement on said gantries resulted in poor printing performance and strong moments on the assembly under high acceleration
- The bed plate itself is badly out of flat
What am I going to do about it?
- The XY linear motion setup will be mounted on a single, rigid stainless steel plate affixed to adapters at the top of the frame, establishing a better linear reference than the frame itself, and allowing me to reuse the current frame
- XY motors will be mounted such that they will not be part of the moving mass, and will move to two motors per axis, instead of one
- Belt tensioning will be designed in a way so as not to have adverse effects on the mechanical system under high tension (ideally, regardless of tension applied so long as it is sufficient)
- Heaters will be upgraded
- Mainboard cooling will be upgraded and its mounting changed to avoid incursion into the volume of the box frame
- To enable this, the PSU will no longer be attached to the printer, and will be VHB-ed to the underside of the desk on which the printer is currently affixed
- The Z axis will move to a belted solution, and will have a sheet metal bed carrier, supporting a cast-and-machined tooling plate as the bed, to achieve higher flatness
- Higher quality linear guideways will be bought for XY
- The new XY assembly will make extensive use of CNC-milled and/or SLM metal parts to avoid the deformation issues that plastics have under such extreme conditions, yet still be engineered such that a gross excess of extra moving mass is avoided
Additional comments, upgrades, and criteria:
- Target acceleration is 50ms^-2, ~5G
- Target top speed is 1ms^-1
- Whole layer cooling is to be implemented, but it’s more of a “want” than a “need”
- A toolboard may or may not be implemented in some form, as I was displeased with the size and weight of the wiring harness to the toolhead in the current/previous iteration
- Will upgrade from TMC2209 drivers to TMC2240 drivers for some extra robustness and performance headroom
- You’ll notice me scarcely mention the toolhead in this post, and most likely for the foreseeable future, as I consider the toolhead from the current iteration to already be pretty close to ideal/optimal - I do not expect it to need work:
Where are we today?
So far, the printer has been disassembled down to the box frame (and the Z rails too, while they are still of the cheap-and-cheerful kind, they are acceptable in this use case), though still retaining some of the original design’s reinforcements, which may yet be removed:
You will be able to notice evidence of filing, done in order to mount the X-axis linear rails in the original iteration. Don’t mind all the cables, and the other custom 3D printer to the left.
I have largely started the CAD document afresh, giving it a proper structure and only importing the most relevant parts from the previous iteration. This is going to allow me to operate a lot more efficiently and smoothly, and will give less room for dependency-related errata to occur.
From this point, I have reassembled the box frame in CAD, and have already redone the mainboard mounting and cooling (now using two 4028s instead of a single 4010):
(I haven’t bought the 4028s yet, and the USB-B connector is missing, as I have replaced it with the pigtail that you can see on my left hand, which leads into an external USB-C breakout, which works better for me)
What’s next?
Next, I’ll be working on the XY stage, which is going to be the bulk of the hard work, and which I expect to take weeks, if not months. I’ve been making some rough concept sketches in my notebook, and generally getting my thoughts in order, ahead of launching into prototyping/iteration:
The plan at this point is to have an adapter block at each upper corner of the box frame, that a motor mount and tensioner can then bolt to, with tapped holes at the upper extent, to which the XY reference plate will be attached, with the linear guideways subsequently attached to that.
I’ll be updating this topic as the design process progresses. See you then!
