I am a newbie to 3D printing, but been involved with machining, including CNC, since 1985.
I am looking for owners of Monoprice Maker Ultimate 3D Printers, and their thoughts on them. My main concern is accuracy and repeatability, I am not thrilled with belt drive, rather have ballscrews. These are CNC, after all.
Belts stretches, ball screws do not.
There’s not much force involved with 3d printing. The extruder doesn’t really touch the object. The extruder assembly doesn’t really wiegh very much. And it’s going kinda slow when it is actively printing.
We all agree (I think) that ballscrews are superior in almost very way. Except two… price and weight. But belts usually work just fine.
At @Mobile_Makerspace1 we have a makerbot that uses belts. We haven’t had any serious problems with them.
The belts have an initial stretch, then they’re pretty stable. If the machine is designed properly then they will be at a decent tension.
They are cnc, but are not mills. The load is very light and you don’t need to worry about all of the stresses that a mill takes. The biggest stress I’ve found is from belt tension.
Belts are fast and cheap. If you’re worried then you can use gt3 belts instead of the standard gt2. But that will require some major design changes, you might as well design your own printer.
We can not attain the speeds we get with belt drive systems from a screw drive system yet. There is a closed loop motor control system project that might change that. Most closed loop systems are too expensive.
The belt drive seems to work for our needs. We are not cutting so there is no real resistance else than inertia. Too much resistance might lead to skipped steps, since we use stepper motors instead of closed loop systems.
Belt drives are perfectly suited to X and Y motion in 3D printers. You get really great drivetrain parameters (gear ratio etc) for the desired force/speed profile. Design for 3D printers is very different from designs for mills. One reason for this is the fact that most 3D printer controllers allow “jerks” (velocity jumps) where the tool runs through sharp corners without slowing to a stop. The compliance of the stepper-and-belt drivetrain is necessary to keep the resultant impulse forces down to an acceptable level.
You CAN build a 3D printer with ballscrews, but you end up needing much, much bigger and more expensive motors and motor controllers, for an imperceptible difference in print quality.
If you do want to see a screw driven 3D printer, check out https://plus.google.com/+ShaukiB/posts/986FF4jkU2y
His printer is a delta style printer that is not as fast as most and makes an annoying whining noise. It is by @shauki .
I use a large CNC mill and have quite a few printers. While similar they are not the same and do not see the same stresses and forces.
My printers have lead screws for the Z (those don’t move fast) and belts for X and Y which do move very fast. The operation is almost silent. I get very precise and repeatable prints off my printers. Typically I’m within .004" of the intended result. Your biggest variation will be the filament used and not in the mechanical set up of a good printer. Filament calibration is key to precise repeatable prints. I find little difference between parts off my mill and parts off my printers when it comes to repeatability and accuracy. In most cases I can use the same manufactured parts interchangeably regardless of the method used to manufacture them.
I do not know much about the printer you are investigating other than I’m not a fan of cantilevered beds but I would expect to pay upwards of $800 for a really good printer. On the other hand paying 4K does not mean that it will work much better than a $1,200 printer.
I would not worry about the use of belts in 3D printers.
@Jeff_Parish thanks, you answered the most important questions I have regarding 3D printers, repeatability.
Back in the 90s, I had worked on projects that had tolerances of +.0005 -.0000, true it wasn't TIR, but tight enough.
When printing things like sprockets, especially miniature sprockets, tolerances are tight. When printing 6 or 8 at a time, I
want them to be exactly the same. 3D printers have a Machine Home and a Part Home positions in their code, do they not ?
If need be, I can work with G-Code, as I used to edit and write some G-Codes back in the 80s and 90s. Some of the NC machines
ran off of mylar tapes.@Wayde_Gutman When printing multiple parts you will have small variances between them depending on where they are on the bed and if a feature falls on a full step or between micro steps. Most good printers can hold a tolerance of 0.1mm so that has to be planned for in your designs. You will also need to use a nozzle that is suitable for the feature size you are printing. I’ve gone as small as 0.2mm but typically use a 0.3 or 0.4mm nozzle. How small a part or detail are you planning on working with?
I have quite a bit of experience printing tight tolerance multi-part assemblies from multiple printers each using different filaments. When you get to the point of calibrating filaments I can share my calibration techniques with you if you would like.
Printers have a machine home for the entire build plate but I’ve not seen individual part home positions. I have used the pause/home feature on my printers many times to swap filaments mid print or check things and then start up again with no discernible issue on alignment. There is a feature in some slicers where you can print parts in sequence instead of all at once which might make it easier to pull out an individual part home position from the g-code. Printing parts in sequence could seriously limit your print space.