What would you do when designing a corexy ? Would you try to keep the carriage as light as possible and go with bowden only, or add more mass and stiffness so you could use direct extruder as well ? I know that by adding mass, I loose speed, but does it worth it ?
All depends on your needs and wants. I do this as a hobby not as a business so I can deal with a slower printer. Though the fusebox I am building, need to finish the darn thing, uses down and can get to pretty quick speeds from what I have been seeing.
I’ve built two Cartesian machines, one with Bowden and one without. Personally, I really enjoy my direct drive with the ease of just pushing down the lever to pull the filament out and it seems to have a better control over the filament as a whole.
If you don’t want to print over around 50mm/s go direct. If you think you’re gonna want to print at some serious speeds then Bowden is your way to go. It’s a tradeoff but you can print flexibles with a direct drive as well.
I would rather see a stationary heated bed, If you think about it, moving a bed causes vibrations, hot plastic can come unstuck, or the plastic itself can deform.
If you’re looking for speed, Bowden, otherwise direct drive. Bed-wise, I prefer the KISS (Keep it simple, stupid) approach and going Cantilever with a single lead screw. 10-12mm Rods are needed but you’re going to end up with a solid Z axis if done right.
I’ve built using leadscrew for movements, a rigid x,y,z axis and with no moving bed, with an mk10 nozzle, spits out nylon and other hightemp filaments with enclosure and a separate arduino env temp control, prints turns out smooth, no need to dry filaments (leave the temp control running 24/7 with filament inside) I try to keep the humdity level low inside the printer, still in trial though…
Thanks guys,
Just to clarify a little bit, I was talking mostly about the XY carriage on a CoreXY design, holding the Hotend/Extruder, not the entire printer itself.
I’m nearly done building a core xy printer, (still need to wire up the hotend and extruder). My initial choice is to go with direct extruder. I made the choice probably more based on my experience with the Prusa I3 design than anything else. But I may still ultimately go with something like this, http://mutley3d.com/Flex3Drive-1/
to remove the weight of the extruder.
Just go Bowden with a short tube. You should be perfectly fine with that unless you really want to print flexible filament
Bowden will let you do higher ACCELERATION, not higher FEEDRATE. The moving mass doesn’t matter when the printer is just coasting. I regularly print 80-120mm/s with 150mm/s travel with my direct drive CoreXY and it’s nothing special as far as linear hardware. 8mm rods on X and Y.
The difference between high acceleration and low acceleration is typically less than 20-30% in the final print times. It makes a noticeable difference but not a huge difference.
In comparison, Deltas arguably NEED Bowden drives because they can’t handle the size or weight of a direct drive extruder. But CoreXY gantries are identical to Cartesian gantries as far as extruder selection. Most Cartesian printers are DD and I would personally say most CoreXY printers should also be DD.
A lot of people worry about stall speed or missing steps, but ignore reverberations that happen with fast accelerations and jerk rates. A heavier carriage also increases these artifacts.
However, when deciding direct drive vs bowden, the choice depends entirely on your design goal. If you want to print flexible materials and have more control over the extruder, then direct drive is better, if you want high acceleration and cheaper construction then bowden. I’m designing mine with 10mm x rods, and 12mm y rods to compensate for the weight (which adds more weight to the moving mass, limiting acceleration). This will help control those reverberations, so long as the motors can withstand it.
You can even step up to nema 23 motors for more torque, but you shouldn’t need to.
If you design properly it should only take you 10 minutes to swap from bowden to direct, then you can adjust according to the requirements.