Fixed/Mobile choice in X,Y,Z axis and in Extruder configuration? December 11, 2014 06:04PM |
Registered: 11 years ago Posts: 20 |
Re: Fixed/Mobile choice in X,Y,Z axis and in Extruder configuration? December 11, 2014 07:49PM |
Registered: 10 years ago Posts: 869 |
I think you mostly got them when speaking in general terms. There may be some variances between exact implementation. A few corrections would be to not say zero backlash for gravity-held z-axis, but rather minimal backlash. Printer 4, what you call a polar 3d printer, isn't a polar 3d printer. That's typically called a delta printer. This is a polar printer. There are also other non-traditional designs. Look up Nicholas Seward work at Concept Forge for some unique takes on various designs thinking sorta outside the box. Also all your designs primarily focus on FDM 3D printing. There are other types of additive 3d printing than just FDM, such as SLA, SLS, MJM, etc ...Quote
erosnicolau
1. Am I seeing correctly the pros-cons of these designs? I mean, this is where you'd point out any pros/cons I've missed out or miss-hit
Yes. Look at commercial printers by Stratsys et al. Those are the printers where quality and speed are most important and price isn't. What do they use? There's various implementations, but I don't think any are delta or polar style printers. A lot of quality and print speed can depend on quality of components. Many designs trade saving money for sacrificing speed or quality. For instance, generic commercial threaded rod and nuts instead of acme thread and ball screws. Cheaper NEMA 17 steppers instead of larger, faster, more powerful NEMA 23 (or other). I don't think anyone can say absolutely that one design is "the best", they just have their preferences.Quote
2. What, in your opinion, is the best approach for best print accuracy? And what is for best speed?
I'm not sure what you're referring to as the split extruder. If you mean a setup where the filament is fed through a tube by a remote extruder motor and only the hot end is moving, that's referred to as a bowden tube configuration. It's not present as it's actually complicating the process and you're not gaining anything. Your total machine height is the same as you have the height each of the 3 supports of the delta configuration would need to be to reach each limit of the print bed, but you'd also have whatever your maximum height is to lower the bed as you print. You could just extend each support of the the same height and eliminate the complexities of a moving bed, additional stepper, threaded/acme rod, etc. In most cases, expanding the height of the delta is just an incremental cost with slightly more extrusion/slides, longer belts, and a bit more wire for any top mounted electronics (if any).Quote
3. Why haven't I seen, yet, a printer of the type 3 above (bed moving in Z downwards, extruder moving in X and Y, fixed to the top) but with the kind of split extruder you see on the Polar-3d type? This combo, to me, should bring the most pros ant the least cons.
Cost. Can you find me a meter long ball screw for less than $1.80? I use lead screws for my x-axis as they are quieter than my cheap threaded rods, but I got them free from Misumi as part of a promo so cost wasn't a factor.Quote
4. Why is everybody only using direct timing belts on these babies - why not ball screws or at least a dual pulley 1:5 reduction combo - for slower but more accurate prints?
Re: Fixed/Mobile choice in X,Y,Z axis and in Extruder configuration? December 11, 2014 11:01PM |
Registered: 14 years ago Posts: 128 |
Re: Fixed/Mobile choice in X,Y,Z axis and in Extruder configuration? December 11, 2014 11:33PM |
Registered: 11 years ago Posts: 5,780 |
Quote
erosnicolau
Hi, there,
I've been researching different 3d printer configurations lately and I saw pretty different approaches in how to choose what's fixed and what's moving in a 3d printer. Basically, 2 rules apply generally:
- the lighter the moving parts, the speedier the print can be
- the lighter the moving parts, the less inertia, resulting in the more precise printing.
...
Thanks for your infinite patience on this one...
Eros
Re: Fixed/Mobile choice in X,Y,Z axis and in Extruder configuration? December 12, 2014 04:26AM |
Registered: 11 years ago Posts: 20 |
Re: Fixed/Mobile choice in X,Y,Z axis and in Extruder configuration? December 12, 2014 09:12AM |
Registered: 10 years ago Posts: 869 |
You're making assumptions that movement is always in the up direction. At some point, you'll have to go down to start a print. So initially, there could be a bit of backlash. A growing trend is auto leveling with a z-probe. With such an implementation, the z-axis is making very small adjustments as each layer is printed, introducing the possibility of a bit of backlash. Also, gravity pulls things down, the extruder squirting out plastic wants to push it up. Now all the forces above are pretty minimal so backlash is pretty minimal, but you can't say it's eliminated. Some people also use their printer for more than just FDM. Light milling, cutting, or drawing may have different amounts of forces involved.Quote
erosnicolau
- Where is backlash possible in that config, given that the movement is always in one direction (up) and always preloaded (by gravity)?
There are many ways that you can speed up a print, but they can dramatically increase cost or complexity. Why stop at 2 nozzle...get a Kracken and have 4. Or two independent dual nozzles. There are more and more designs that are coming out that implement multiple hot ends, mixing of filament, multi-color, multi-material, etc. I wouldn't say that area is in it's infancy, but it's also not fully mature and prime time yet, at least at a Reprap-affordable-for-mortals price point. But it's getting there.Quote
- Your argument about the importance of speed takes my mind to two things:
- the dual nozzle approach (a .3mm for details and a 0.8mm for filling) of RoboX 3D
- a (continous?) variable speed gearing. the gear change could be made either with a solenoid (for a binary kind of gearing) or with an extra stepper motor (for a CVT like a dual cone, belt-driven one). food for thought...
I kinda jumped thoughts and I wasn't very clear leading to the conclusion. I was describing what a bowden tube was, but then was saying that the type of setup you described as " (bed moving in Z downwards, extruder moving in X and Y, fixed to the top) but with the kind of split extruder you see on the Polar-3d type" wouldn't gain you anything. If I'm understanding you correctly, you're asking why you don't see a delta-style printer that has a z-bed that moves downward as the build progresses, right? If that is, then what I say still stands. It makes the process more complicated unnecessarily with more hardware requirements. You may lower the weight of the hot end assembly, but there are other ways to do that without complicating the design unnecessarily.Quote
- You say the Bowden tube config complicates things without achieving anything. By this you mean it yields poorer quality prints? To me, reducing the mass of the moving oozer is an achievement in itself. Please detail your statement a bit, so I can better figure what you're thinking on this one
Speed, quality, price. Chose two.Quote
- Yes, speed and quality don't mix well. Unless you find ways to make a "2 in 1" machine (dual extruders, gearboxes...)
Have you built a printer of your own yet? If not, I'd suggest building a simple one to get your feet wet. It doesn't have to be a primitive one or low resolution, but dual nozzles and dual speeds adds a lot of sources of frustration.Quote
My quest for now remains for the lowest inertia moving configuration, and so far, from your responses and my suggestions, I get as keepers:
- good quality parts
- stronger motors
- CoreXY
- (Bowden tube extruder?)
- dual nozzle (thin and thick) extruder
- maybe a dual speed gearing
Re: Fixed/Mobile choice in X,Y,Z axis and in Extruder configuration? December 19, 2014 03:32PM |
Registered: 11 years ago Posts: 20 |
Re: Fixed/Mobile choice in X,Y,Z axis and in Extruder configuration? December 19, 2014 04:43PM |
Registered: 10 years ago Posts: 869 |
Honestly, when considering everything else with the printer the z-axis backlash is probably towards the end of the list of things to worry about. If it was CNC milling or a lathe and you had some serious forces at play then it would be more of a concern. But I think most just don't think about it or care and rather have the convenience of the auto leveling.Quote
erosnicolau
- I was even wondering how in the world do all these "auto-leveling" printers take all that Z-axis fidgeting into account, lash-wise...
I believe what you are describing is this.Quote
- something I've yet to see on a 3d-printer: a throttle cable linking the remote motor to a gears-only hot-end. A throttle cable has high torsional rigidity - at least in one direction. This means that, mounted correctly, it is capable of driving very precisely the gearset of the extruder when extruding. For suckinng, you measure and take into account the lash involved by the slight torsional elasticity in the opposite rotational direction. Yes, you still have elasticity variables, like in the case of the Bowden tube approach, but at least all the variables are in a single component (the throttle cable) which has been designed for running at high speeds and a long life, not in the varying properties of each filament roll. I'm gonna get me some spare cables to test how they fare.
Re: Fixed/Mobile choice in X,Y,Z axis and in Extruder configuration? December 19, 2014 04:46PM |
Registered: 11 years ago Posts: 20 |
Re: Fixed/Mobile choice in X,Y,Z axis and in Extruder configuration? December 20, 2014 09:58AM |
Registered: 11 years ago Posts: 5,780 |
Re: Fixed/Mobile choice in X,Y,Z axis and in Extruder configuration? December 20, 2014 01:38PM |
Registered: 11 years ago Posts: 1,049 |