Welcome Aboard The Struggle Bus
Designing this 3D printer has been a struggle thus far. I’m battling perfectionism every step of the way. Note that perfectionism here is not a good thing as it gets in the way of progress. This is not about attention to detail or being organized; those things can exist without perfectionism. The perfectionism I’m writing about is setting high expectations as the bare minimum of what must be accomplished. It’s procrastinating or making excuses for why I can’t get things done because I”m afraid I can’t actually do something to a certain standard. It’s overthinking things and struggling to make decisions, even in the preliminary stages of doing something I care about because everything has to be correct, even from the beginning. If, for example, you’ve ever hesitated a while before drawing on a pristine, blank sheet of paper, then you have some idea of what I mean. For some reason, that first line on the paper is a big freaking deal.
I know this 3D printer will not be perfect but I admit I have high expectations for myself and every aspect of this project. Not only do I want this machine to function well and meet all the requirements I previously outlined, but I also want the CAD work to be great, the manufacturing process to be logical and awesome in every way, and all the supporting documentation to be clear, concise, thorough, and interesting. That’s a lot of stuff to try to get right all at once. I know it’s not reasonable for me to get all that right from the beginning, but I’m trying anyway. Trying is okay, but being stressed, disappointed, even discouraged when I think I’m missing the mark, is problematic. I need to find some way to be happy with my work when it's not awesome, so I can stay sane enough to keep moving forward and improve the next time. I’ve been listening to an audiobook called, “How to be an Imperfectionist” by Stephen Guise. Stephen makes an excellent point about the difference between a perfectionist and an imperfectionist in terms of goals and accomplishments.
“Your floor and ceiling are important considerations in life. Your floor in this case is the absolute minimum you need to be satisfied in life. Your ceiling is your upper potential and wildest dreams. If you’re living in between your floor and your ceiling, you’re happy, because you have the minimum of what you need to be happy. And it goes without saying that you won’t surpass your ceiling (or else it isn’t a ceiling). Perfectionism is a problem because it makes “perfection” your floor. When this is the case, you don’t have a ceiling. The floor is also the ceiling because perfection can’t be surpassed! This setup seems cramped even to me, and I live in a 150-square-foot “micro studio” apartment!”
- Stephen Guise
Cross Gantry Design
Late April - early May I started out working on the Cross gantry design and just got a bit overwhelmed with it. I didn’t know where to start. I needed to figure out where things needed to be placed in relation to each other. How is any of the gantry going to be mounted? Are the shafts I have going to work in this application? The whole gantry may be too heavy to support itself. I tried to plow ahead anyway, despite feeling overwhelmed and lost. I just threw a bunch of stuff in the assembly for the cross gantry somewhat haphazardly hoping to be able to make progress after seeing parts together. I spent some time shuffling the parts around in the assembly hoping that would help me figure out what to do. Eventually, I made a subassembly of the drive components and another subassembly of the idling components that would be driven by the stepper motor. I still haven’t figured out the details of how/where the drive assemblies are going to interface the linear guides.
Cross Gantry Hot Mess
Cross Gantry Belt retainer
Still puzzled, I went on to design a belt retainer since that was the only part that wasn’t entirely contingent on the placement of the other gantry components. One end of a belt will be held in the groove on the bottom of this retainer. The groove that passes through the top will allow the belt to pass through freely. There will be another very similar looking belt retainer on the back end of this one, retaining the other end of the same belt. This belt retainer concept is explained more in my notes about the CoreXY head later in this post.
After taking a stab at this belt retainer I stopped working on the cross gantry and went back to working on the coreXY gantry. I intend to do a stress simulation test of both gantries once I get them modeled anyway, so they both still need to be completed enough for that test.
I had already designed the coreXY printer head before I had even considered the cross gantry printer. This coreXY head design features the same serviceability as the cross gantry head in that the hotend is assembled and then mounted onto a part that can be easily removed from the rest of the tool head without disturbing the gantry.
CoreXY Head Subassembly
CoreXY Hotend Mount Subassembly
CoreXY Print Head Assembly
I hadn’t read Ryan Carlyle’s book on 3D printer engineering before I started designing this print head. He describes some best practices for linear guide size and spacing, linear bearing count, and linear bearing spacing that I haven’t followed in this design, so I’ll be making several design improvements in the very near future. When I started designing the head, I was just trying to put the shafts and belt retainers as close together as possible to keep the head from getting too enormous.
The head currently has 4 linear bearings inside it, but I will likely remove one because it is probably over constrained with all 4 bearings and will be more likely to bind. The 10mm shafts are too close together (40mm apart currently), so I’ll make them somewhere between 50 - 100mm apart per Ryan’s advice in Volume 1 of his 3D Printer Engineering book. The bearings are also probably too close together on each shaft too so I’ll have to re-read what Ryan wrote about how bearings should be spaced. Igus, a linear hardware manufacturer also provides recommendations on bearing spacing on their website, which I will also reference. It is very possible that the 10mm diameter shafts are not beefy enough for this gantry size, so again I’ll revisit that 3D printer engineering book and find the section on calculating proper thickness over unsupported spans.
CoreXY Belt retainer
I started with a different belt retainer design as well. I had success with the belt holding concept like the orange one pictured so I went with that same concept of having teeth in the retainer that match the belt’s teeth to keep the belt in place. The belt is tensioned by tightening a long screw which pulls 2 belt retainers closer together.
CoreXY Sliding Belt Retainer Rev01
CoreXY Stationary Belt Retainer Rev01
Soon after I designed the blue belt retainers, I read a blog post by Mark Rehorst about his issues with belt clamps. He describes a belt retaining concept which I believe is similar to my own, however instead of having teeth modeled directly into the clamp, he used another scrap of the same belt and sandwiched the belts together between printed parts. Over time, in the areas of the belt nearest to his clamps, the outer material of his belts would tear and pull away from the metal inner core. I figured mine could do that too since my retainers have the same concept, just a different execution. So I redesigned my retainers to loop the belt inside them like Mark’s follow-up solution, hopefully relieving some of the stress concentrated on one area of the belt. I still tension the belts at the print head in the same manner as I had originally. Tightening the long screws on the right side of the tool head to pull two belt clamps closer together, or loosening the screws to allow the belt clamps to move further apart.
Pending Build Challenges
Currently, there are several tapped screw holes on this head, instead of pockets where I can put nuts. I would like to avoid tapping small, fine threads in plastic as much as possible, so I’ll need to come up with alternative solutions for those tapped holes if possible. Perhaps I can get more nut pockets in, or I may figure out how I could use metal threaded inserts. I may even need to reconsider how some of these parts will be made, resulting in redesigning the tool head.
The way this print head is designed, the base head may result in a complicated, 4-part mold for casting. If I make a simple 2-part mold with the parting-line running vertically around the middle of the head, the recess for the hotend mount will be an undercut, making the casted part difficult to de-mold. Perhaps the undercut from the hotend mount recess won’t be too problematic, depending on how flexible and resilient the silicone mold is. Though if I do manage to put nut pockets in the head, they will likely be undercuts in a 2-part mold as well.
CoreXY Gantry Design
On a 3D printing google group I frequently lurk on, I posed my question about potential problems with belt-positioning on the printhead of a coreXY. To recap, I wanted to align the belts on the head on the same vertically oriented plane, but I haven’t seen that done on many coreXY 3D printers that weren’t considered poorly designed printers.
My Intent - Belt terminations Vertically aligned on Tool Head
Recommended - Belt Terminations Offset on Tool Head
Top View of a Core XY Gantry
Wouldn’t you know it, Ryan Carlyle himself, (The guy who wrote the 3D printer engineering book I mentioned a million times) responded to my post! Okay, he does frequently post in that particular forum/google group, but I was really excited and grateful that he took the time to read my post and respond to my question. Anyway, aligning the belts on the same vertical plane the way I intend is not an inherently bad design, as long as I keep the belts parallel to the linear guides and perpendicular to themselves in all the right places.
CoreXY Belt Path Sketch
The belt path I had in mind still follows all the parallel/perpendicular rules I previously found described on a couple of websites and blogs. I sketched out my intent for a core XY belt path when I was designing the head months ago. I used different pen colors for clarity but it's likely only clear to myself. The green pulleys (1 smooth, the rest are 16-tooth) interface the blue belt on the same horizontal plane. The red pulleys (again 1 smooth, the rest are 16-toothed) interface the purple belt on a different plane. I modeled more of the gantry in Fusion 360 so it probably makes more sense when looking at the model.
Top View of CoreXY Gantry with Belts as of 5-22-2020
CoreXY Gantry with Belts as of 5-22-2020
The next thing I’m going to do is figure out the recommended shaft diameter for the 600mm length I need. I may even need to look at other ball bearing-less options for the linear guides, like fully supported shafts instead of the end-supported shafts I have. I can use the 10mm hardened steel shafts I currently have on the Z-axis of a smaller machine in the future. Out of curiosity, I’m going to try running a stress simulation on the CoreXY gantry I have now to see how severely the current shafts will bow. Then perhaps I’ll be able to see what a difference a different diameter shaft or fully supported shafts would make in different simulations. Once the linear guides are finalized, I’ll refine the belt retainers, the printer head, and update the rest of the gantry.
Has perfectionism ever been a problem for you? Have you taken a road trip on the struggle bus lately? Let me know your thoughts in the comments section at the bottom of this page.
Guise, Stephen. How to Be an Imperfectionist: The New Way to Self-Acceptance, Fearless Living, and Freedom from Perfectionism
. Selective Entertainment, 2015.
Find this book at www.amazon.com
Another Interesting 3D printer Failure- How NOT to Design a Belt Clamp
Carlyle, Ryan. 3D Printer Engineering Volume 1: Motion Platform Design.
Groton: Sublime Publications, 2019. Print.
Find this 3D Printer Engineering book at www.sublimepublications.com
Draft Written: May 14, 2020
Last Updated: May 29, 2020