Large Printer Electronics Decision.

Hello, i have been wanting to build one of these printers for a while and i have a few questions for those who have more experience. Im looking to build a printer that has a printable area of 18x18x12. Ive decided to design the printer to raise and lower the print bed for the z axis. The extruder and hot end will move along the X and Y axis. It will likely have a gantry ( i believe that is the correct term for a beam or arm that travels along an axis) that moves front to rear along the Y axis. On that gantry there will be a moveable platform that the extruder and hot end is mounted to that travels side to side along the X axis.

For this design i will use two 20mm shafts to support the print bed using 4 linear bearings. The gantry that travels along the y axis will ride on two 16mm with 4 linear bearings. The platform the hotend and extruder are mounted on will also ride on two 16mm shafts and 4 linear bearings.

I will use acme lead screws( 1/2-10 ) to give it life from NEMA 17 stepper motors. The problem im having is the electronics. It would appear the best way to set up the motion would be to run a single stepper motor in the Z and X axis as the path they are traveling is relatively narrow compared to the distance. The Y axis would seem to benefit from the stability of being driven from both sides using two steppers and lead screws.

I also want to keep the option open to run two extruders and hot ends so i could use the PVA water soluble support material.

I would need a board that would allow for 6 stepper drivers, two of witch position the Y axis.

Is there way i could use RAMPS to do this? Or are the stepper drivers on the RAMPS already "assigned" the axis that they control? I would also need a board that can handle the current of a 18X18 heated bed, AND have three thermistor inputs and be able to control the 3 heaters for the heated bed and the two extruders.

I like the RAMBO board because it seems to be updated, but i also like the RAMPS because the stepper drivers can be easily replaced or upgraded is higher current drivers are needed.

What would be the best electronics to go with?

-Dan

Have you considered CoreXY mechanics for the XY plane, rathe than lead screws?

You can drive 2 stepper motors connected in series from a single stepper motor driver, although if you do this then you must either increase the power supply voltage or accept a lower top speed.

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Large delta printer [miscsolutions.wordpress.com], E3D tool changer, Robotdigg SCARA printer, Crane Quad and Ormerod

Disclosure: I design Duet electronics and work on RepRapFirmware, [duet3d.com].

There are a few issues you may need to address, I'm not an expert on large cartesians, however I do build deltas similar to this in size. While you are short of what I would consider large format printers, you are on the cusp of it, and things just aren't as easy as "I want bigger", in fact you will be surprised how quickly they spiral beyond what you expect. This list is by no means comprehensive either.

Your Z axis
Take a look at the CoreXZ printer by Nicholas Seward, it's similar to what you are describing.
I would change two things with your plan though, I would use aluminum extrusions (V-Slot!) for linear movement instead of heavy linear rails, and a bowden system for reduced mass/volume.


Electronics...
As mentioned, you are on the cusp of large format, which usually gravitate towards Nema 23's and large ($$$) stepper drivers. Efficiency is going to be paramount to wish to use Nema 17's, this means small pulleys for belts and slower speeds. You can run two steppers on one channel, however, your amperage is cut in half for each. The setup I mentioned above will handle common electronics much better. If it was me, I would be looking at either a Smoothieboard or Beagebone Black and a shield.



A few other things...
I don't know what nozzle size you plan to use, but if you plan on using a normal 0.35mm-0.5mm, you may wish to pick up a uninterrupted power supply, since prints this size can take a week! A power dip can wipe out a weeks worth of work and $100 worth of plastic. This is based on OUR printer, which will run absolute rings around what you are proposing. Your prints could take closer to a month.

Heated bed?
Think hard about what I just said about time frames, electricity and the smell of ABS being printed. That's going to run up your electric bill, especially if you vent to the outside, or need to run an air conditioner. If you do plan on a heated bed, this itself too will be problematic. You will need to source a heater (hint: China), and also a way to drive/control/power it. You will probably need 300-400 watts to power it, and this is beyond the amperage 3d printer controllers can handle. This means either a relay or external controller.

Depending on layer heights, you also will need a fairly modern computer to slice such objects. Our large delta (18in dia.x18in tall) has been known to crash most slicers while doing 0.18mm layers (much less 0.05!), and slicing at 0.1mm layer heights can take over an hour in Cura on an I7/16gigs ram/SSD equipped desktop. Slic3r, if it didn't crash, would take all day. Even after we helped find the bug in Cura related to this, we still crash it on occasion with large, not very complex prints. Even host software can be crashed trying to print large objects, a scaled up Tiki cup can bring down an older Intel Core based laptop running Repetier Host or Pronterface.


Lastly, what is your time frame/skill level/budget.
If you haven't built a Reprap based printer before, start now. Pick a design, build it, use it, learn it, THEN start on the big printer. Note that I don't mean go buy a Prusa kit to assemble, I mean buy printed parts and cobble it together yourself. It will pay for itself later. You will not only get a printer you can use to build your printer and better understanding of what's involved, but keep you from making some costly mistakes later. Not only that, but odds are, your printer will need a LOT of revisions before you get it working, much less happy with it, having a printer or machine shop is vital if you don't want to be driven to the poor house, as is experience.

If you have no experience other than using a printer, expect probably close to $2k by the time you are happy with it. If you have done a kit, but never done a Reprap from scratch, you might do it for 3/4 that. If you build a Reprap first, you could do it for probably $1000, maybe less. These are just guesstimate and could easily double or triple (especially if you are at the lower end of the skill chain).

If you have no printer experience other than reading, you could easily top $3k-$4k doing this project if you just dive right in, which unfortunately sounds like what you may be trying to do. Will you have a $4k printer? No. What tends to happen is you buy some hardware or electronics, then find it is just completely the wrong approach and then you have to go buy more/different parts and try another method. By the time you are done you spent $4k on a $1k printer. Whereas, had you built a $500 Reprap from plans, you could have two printers worth $1500 in parts and only having spent $1700. You will still make mistakes, but fewer of them, and less costly ones. This sounds extreme, but it will happen, your first printer you build/design always has cost over-runs. You try and cut corners where you shouldn't, use old/outdated ideas, use a product long deemed junk, break something, let the magic smoke out, etc. It happens.

Edited 1 time(s). Last edit at 11/22/2014 07:37PM by sheepdog43.

Dc42: I just briefly looked into the CoreXY. It seems complicated using all those cables. I feel that lead screws would be much simpler (and also slower) then that design. I'm not really looking for maximum speed. Id prefer quality to speed.

Sheepdog43: Excellent post! Much appreciated. This is my first printer I would be building. I totally understand the fact that what seems like only a bit bigger snowballs into a lottabit bigger/more complicated thing very quickly. I enjoy learning about this so much. I have been trying to read everything I can but sometimes it's hard because I'm not totally fimiliar with the terminology used so I don't know exactly what words to search for to find what I'm looking for.

I have a manual mill (G0704 that I plan to convert to CNC), MIG, TIG and plasma cutter. I also have very high experience building/fabricating things from scratch. I built a custom intake manifold out of modified lower intake manifold and sheet aluminum for the engine in my Supra. I feel that the physical building of this printer is going to be far easier then nailing down a solid design. The real area I lack is the knowledge of the electronics nessisary for something like this. My build platform of 18x18x12 is not something I would be filling up with a massive single part. My primary hobby is cars. So the reason I want a large X&Y is so I can print out larger sections of dash panels or engine under covers. These parts are only 1/8 inch or so thick so I don't see it being the most time consuming thing to grow/print. Also these printer parts would likely turn into molds to create carbon fiber parts so the lack of temperature stability of the PLA vs ABS is not an issue. I would also be putting this in my workshop shed where my mill is and would probrably stick to printing PLA so smell wouldn't be an issue.

I forgot to mention that I will be building the frame of the printer and build platform out of aluminum extrusion. Prolly a mix of 1"x1" and 1.5"x1.5". I looked into the linear bearings for the aluminum extrusion but I think using the hardened shafts would be easier to level and align. It would also give access to cheaper linear bearings. Seems that most people have very good luck with the cheaper Chinese linear bearings. And there so cheap extras can be bought to swap out with a faulty or bad unit.

I would think that using lead screws would lower the output torque required by the stepper motors due to the increase in mechanical advantage over using a belt or cable to more directly drive the axis. I'm going to come up with a rough diagram of what I'm looking to build any maybe you guys can critique my design.

The only thing more fun to me then actually printing things that I 3d model is designing the 3d printer itself! I'm going to look into the smoothie board and the beagbone black that you mentioned.

Thanks again,
Dan.

Every design has it's pros and cons, using two screws has disadvantages, mainly in leveling. You cannot lower or raise your bed by hand without destroying your calibration. They do however increase leverage, but watch the weight and "racking", where it gets knocked out of shape. I was never a fan of that system and after having used it, I was even less enthused.

Linear bearings work well, but you will need to lube the rails, this collects dust. This also something you will need to contend with. V-slot type systems are quieter, smoother running, and no oil/lube to deal with (V-slot uses cartridge bearings and delrin rollers). As a rule though, 3d printers DO NOT like dust. It will clog your nozzle, infest your pulleys, and contaminate your build surface. Despite some people building all-in-one printer/mills, it's not really even a good idea to even be in the same room as mills and cutting equipment.

On your parts, PLA will warp in a car on a hot day., While ABS will not warp in the car, it has severe warping issues once you exceed 4-5 inches in length, even with a heated bed. To go larger, you need a heated chamber. Using PLA for carbon is a good option, and there is also nylon. ABS is the devil.

Again, I HIGHLY recommend building a pre-designed printer first, at the very least a kit. It will save you time, money and a lot of headaches while filling in a lot of the blanks. Pick a design similar to what you ultimately want, this will let you see what is good and bad about the design. Some things on it are similar to CNC mills, but printers also present their own problems, like filament feed, temps, cooling and more. The frame and electronics are the easy part, the linear movement can be an issue, but really, extruders and hot ends are the bane of 3d printer users. They are where almost all your troubleshooting and learning will wind up Having no experience, and building from scratch, you will spend dozens of hours figuring out why it's doing ____. I cannot stress how much it will help you.

Quote
Chunks87
The only thing more fun to me then actually printing things that I 3d model is designing the 3d printer itself! I'm going to look into the smoothie board and the beagbone black that you mentioned.

You can contact me directly at wolf.arthur@gmail.com if you have any question about Smoothieboard.