More musings in response to questions about building a large-format 3D printer.
(Continued from yesterday)
make a direct clone of the M2. No thinking required.
The present-day M2 has survived four years of rather fierce Darwininan winnowing, so it’s a much better thought-out product than, ahem, you may think just by looking at it.
To build a one-off duplicate, you’ll spend as much money collecting the parts as you would to just buy another M2 and start printing.
Should you buy cheap parts to save money, without considering the requirements, you’ll get, say, the same Z-axis motor Makergear used on the original M2, the complete faceplant of Thing-O-Matic electronics, or crap from eBay described as being kinda-sorta what you want.
Sometimes crap from eBay can be educational, of course:
https://softsolder.com/2013/01/24/hall-effect-sensors-from-ebay-variations-on-a-specification/
I encourage thinking, particularly with numbers, because it leads to understanding, rather than being surprised by the results.
increase the rigidity of the X and Y axis
In round numbers, deflection varies as the fourth power of length: enlarge a frame member by 50% and it becomes five times bendier. If your design simply scales up the frame, it won’t hold the tolerances required to produce a good object.
https://en.wikipedia.org/wiki/Euler%E2%80%93Bernoulli_beam_theory
If you add more mass (“stiffening”) to the Y axis, then the Z axis motor (probably) can’t accelerate the new load upward with the original firmware settings and the Y axis motor may have trouble, too. Perhaps you should measure the as-built torque to support your design:
https://softsolder.com/2013/07/02/makergear-m2-better-z-axis-motor-calculations/
Reduce the acceleration and lower the print speed? Use bigger motors (if you can find a Z motor with the correct leadscrew) and lose vertical space? Make the frame taller and lose stiffness? Use two Z motors (like the RepRap Mendels) and get overconstrained vertical guides? Try building a kinematic slide and lose positioning accuracy? Your choice!
If your intent is to print more parts at once, buy more M2 printers, which will not only be cheaper, but also give you more throughput, lower the cost of inevitable failures, good redundancy, and generally produce better results. Some of the folks on the forum run a dozen M2s building production parts; they’re not looking for bigger print volumes to wreck more parts at once.
Conversely, if your intent is to learn how to build a printer, then, by all means, think about the design, run the numbers, collect the parts, then proceed. It sounds like a great project with plenty of opportunity for learning; don’t let me discourage you from proceeding!
However, I’ll be singularly unhelpful with specific advice, because I’m not the guy building the printer. You must think carefully about what you want to achieve, figure out how to get there, and make it happen.
To a large extent, searching my blog with appropriate keywords will tell you exactly what I think about 3D printing, generally with numbers to back up the conclusions. Get out your calculator, fire up your pencil, and get started!
(Continues tomorrow)
The Smell of Molten Projects in the Morning 
Just how big is the print volume you two are talking about? I agree it makes no sense to print large objects but a build footprint larger then 200mm square is sometimes useful, at least in one axis.
One thing you didn’t mention, heated beds get power hungry in a hurry. I’m currently rebuilding and modifying Leapfrg HS printer for a friend (200×300 build space but on a 360×420 piece of 10mm thick aluminum plate – original was glass). The bed alone can sink 600-800W and it would be much happier with 1000W or 1200W. That is one serious space heater especially in summer :)
btw. Thomas Sanladerer (of YouTube fame) recently featured a printer that hangs from strings around the room. Sure, realistic print volume is orders of magnitude smaller then the room, but I’m still amazed that thing works at all and prints aren’t even that ugly :)
My next printer will be Ultimaker based design with a dual extrusion via magnetic auto toolchanger. I’ll probably modify the original design with slightly longer Y axis to allow for stowing the unused extruder but I intend to keep the print volume down to standard 200mm cube. And of course the cantilevered design of the Z axis has got to go – though it’s much better in real life than on would think, the amount of flex it has too is annoying for my OCD personality:)
The link to the hanging printer video – it’s called Hangprinter :)
Boggle
He was going for maybe 50% over the M2 in all axes: three or four times the build volume. I like your notion of one longer axis to build beams and similar one-axis shapes, rather than embiggening everything; that’s roughly what the M2’s 200×250 platform offers.
A guy on the M2 forum observed that dual extruder really aren’t all that useful, except for the rare objects requiring either dissolvable supports or integrated flexible material. The drool problem seems intractable, although surrounding the object with shield walls apparently works well.
And, yeah, keeping the M2’s platform at 90 °C requires a bit more power than I’d like and a kilowatt seems … excessive! [grin]
As for 50% increase that sounds doable with proper linear rails supported on aluminum extrusion. It can be done on cartesian machines (this guy seems to be going in a right direction https://www.youtube.com/watch?v=E3vc4A_5x28), but that is really delta territory.
Both will suck in print times with anything under 0,4mm layers and accordingly large nozzles of course, and with that footprint PLA will likely be the only choice because of warping – luckily that means only 60°C bed so he could get away with 500W :)
Four colors, no waiting!
To me dual extruders are a must for supports, no other way to print interesting objects :)
Having the ability to print two colors at once is a perk but I’m not a designer so I rarely care for the color :)
Drool is a serious problem but once you park the inactive extruder away from the print it becomes managable – just make the nozzle swipe over a ribbed piece of high temp silicon on the way out of the parking zone and presto – no drool.
This is my take on the magnetic toolchanger design, excuse the shaky camera work https://youtu.be/l2VUBLtGJPo.
It just needs a bit more space so the parking zone doesn’t eat away at the build footprint. And when I really need to print something big I can remove the holders and revert to single extruder for extra space.
I like it! Looks like the head locates on two pyramids and re-positioning should be no problem. I’m mildly surprised the magnet provides enough grip to hold the hot end / fan against Y-axis acceleration, but supermagnets really are magic.
The Thing-O-Matic’s silicon wiper peeled hot gunk off the nozzle in one direction and neatly reattached it in the other direction: it was amazingly dependable! I’ve seen brass brushes clogged with bits of plastic, too, so a rotating brush / scraper may be the least-awful alternative.
The design I’m using has 4 chopped off cones – I think you once called them stabbing points, or some such name :)
You can print them and get pretty close but to really make them good I printed just holes on both surfaces. One side got turned brass cones glued in, then I added a temporary paper spacer, half-way filled the holes on the other part with glass spheres filled epoxy (any filler would work though). Finally I aligned and clamped both parts together with thin plastic foil in between so they don’t actually stick together. I ended up with perfect registration holes for my brass cones, and paper spacer made sure the parts bottom out on cones, not on the surface. Then magnets got glued in and I made sure to put the spacer in between them so they almost touch, but parts still bottom out on the cones.
Magnets are cheapies from China, marketed as N50 or N52 in 15x6x4 size. I used 12x6x3 before to good effect as well, two per part in both cases. Bowden tube never managed to pull it off and whole thing weighs very little so inertia is low. I also designed the parts so magnets are aligned to the center of mass as much as possible to reduce levers that act on it.
Added bonus is that in case of a bed crash head detaches before you destroy the heat break :)
Epoxy FTW! Well done!
I have a bunch of junked magnets around; thanks for the hint about the “commercial” equivalents.
The Wikipedia entry on neodymium magnet grades points out the low Curie temperature of some alloys. It doesn’t matter in your application (the plastic would melt first!), but every now and again somebody thinks of using them in a truly hot part of a printer. I expect the usual eBay sources have the lowest possible Curie point: the magnets don’t quite turn off in your hand. [grin]
(I added a link to the stabbing guides, just for reference)