Large Format CoreXY?
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@ov_darkness said in Large Format CoreXY?:
Furthermore - ball screws are out of the question,
Why that? Just out off curiosity...
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@deckingman said in Large Format CoreXY?:
I started out with printed mounts but despite the fact that they were thick and printed in PET-G, the combination of heat from the motors and belt tension would cause them to distort after big multi hour prints.
I concur and am able to add further evidence...
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@o_lampe ball screws are not self-braking. So when you have a substantial weight (10mm slab of aluminum 800x800mm in size weighs ~17kg and 800x800x4mm Robax sheet weighs about 6,5kg) on it, they will drop when motors are not energized. Therefore, you'd need trapezoidal screws (they hold large weights much better), motors with brakes, more than three motors (over constraining your bed), or you'd need to move XY gantry in Z axis instead of your bed (so you're basically building a Voron).
in my opinion, using trapezoidal screws is the simplest, most efficient way to solve this problem.
This comes from a person that's operating, servicing, and training people to use 600x600mm bed printers. -
Or use a motor with a worm gear to drive the ball screws, or to drive belts to lift the bed. Either way, the bed won't move when you power down. It's cheaper, simpler, and more reliable than motors with brakes or other add-on gizmos, looks a lot better and takes up less space than counterweights.
https://www.ebay.com/itm/191714031261?epid=711126295&hash=item2ca30bf69d:g:A7UAAOSwPhdVB2f0
I used this gearbox in my corexy machine to lift the bed with belts. It doesn't require any special configuration, or any extra connections to the controller to operate a brake. Just connect it as a Z axis motor and you're done. With 3D printer loads, the 30:1 drive can't be back driven. The NEMA-23 motor provides plenty of torque to lift a heavy bed assembly.
In that picture I was using steel core belts, but have since switched to glass core. Belt stretch is negligible.
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@mrehorstdmd
I'd give you two ThumbsUp for mentioning wormgear and counterweight.@ov_darkness
Cudos for taking bad design to improve something by misusing trapezoidials and an overcontrained bedframe.
But in the end you'd pay for it with needing several huge stepper motors to overcome the extra friction, adding wear to the leadscrews and the bed gantry. -
@mrehorstdmd said in Large Format CoreXY?:
With 3D printer loads, the 30:1 drive can't be back driven.
This interesting gear will probably have no backlash even without load, because the
is probably the antibacklash mechanism of
This is high quality and worth its high price IMO.
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Interesting, yeah its a 1m stick of 40x20, but I oriented the 40x20 long side up to help reduce sag from gravity. Sounds like I could benefit from it being oriented the other way to help reduce flex under belt tension. I'm going to stick with V-slot just for ease of use. At the end of the day its running a 1mm nozzle or larger, so I'm not looking for ultra precision.
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@joergs5 The adjustment on the Rino slightly repositions the disc gear with respect to the worm gear to minimize backlash in the gears. This is the catalog page on the gearbox without the motor. It's the low backlash version which specs at <=8 msec of arc. In this application, backlash shouldn't matter as the load of the printbed mass will always keep the gears engaged on the same side of the teeth regardless of direction of motion. I think you mostly have to worry about backlash if the vertical load is very low mass or in a horizontal motion application where gravity isn't going to help prevent it.
The new price on that gearbox is about $700 without the motor. The ebay part is a real bargain at $108 including the motor, ready to drop in. That's about what it would cost to buy a NEMA-23 motor with a brake.
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I build alot of large corexy's.
To go big and keep relative "good" speeds - Going to recommend a few things:
Bigger belts - 9 or 12mm, allows for higher tension and allows for greater accelerations with a heavier mass, since they are stiffer due to size.
Metal - Frankly, metal is an important change. A plastic mount that was ok on a smaller machine may be insufficient on a larger one, particularily with higher tension from bigger belts.
Dual shear - Cantilevered Idlers allow for way too much flex. if your design uses them, don't. I support my motor shafts with an additional bearing and this allows me to tension belts well, and print fast.
Don't be afraid to upscale your Z rods or go with belted Z. Eventually it doesn't make sense to lift a thick bed (and they need to be thicker to not bend under their own mass) so there's a sane point where you park the bed.
But honestly, might just be time to change to dual Y motors with 9-12mm belts and then an X motor that travels along with it.
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@mrehorstdmd said in Large Format CoreXY?:
gearbox is about $700 without the motor.
There's a saying in german "wer billig kauft, kauft zweimal", which means when one buys cheap, you have to rebuy a second time. I tend to buy high quality parts since some time, if I can afford it.
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@joergs5
I've purchased numerous used industrial items on ebay. Often you can get the expensive item at a cheap price... But sure, sometimes they operate at cheap performance.But at that savings, you can get two or three and have a backup... And still be under half price. As long as the eBay item isn't removed due to wear, and it's the same part number.
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@joergs5 said in Large Format CoreXY?:
There's a saying in german "wer billig kauft, kauft zweimal",
There's a saying in english "perfect is the enemy of good" and the low cost Liberty ship are a prime example.
Must be a cultural difference.
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@zapta said in Large Format CoreXY?:
low cost Liberty ship
Thanks for this, I didn't know this history detail yet.
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@joergs5 said in Large Format CoreXY?:
There's a saying in german "wer billig kauft, kauft zweimal", which means when one buys cheap, you have to rebuy a second time.
In english we have a slightly more quipey version: "Buy once, Cry once."
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@joergs5 said in Large Format CoreXY?:
@zapta said in Large Format CoreXY?:
low cost Liberty ship
Thanks for this, I didn't know this history detail yet.
Liberty ships were a British concept adopted by the USA during to the second world war. They were lightly armed merchant ships of a simply design which could be mass produced and some 3000 were built during those war years. Some 200 or so were sunk during the hostilities but only 2 remain today.
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@deckingman thank you Ian, yesterday my brain extension (read: wikipedia) already helped me to update my short time memory
It is always interesting to learn from history! -
seeing as I have a bunch of large machine builders here, any recommendations for grounding/shielding/random shorts to the board and resetting it?
See some of my other posts, but I'm struggling with some sort of an electrical issue that is causing the board to reset. I've tried grounding steppers and the hotends, but even with a brand new duet 3 board I'm still seeing the same issue.
My next thought is to try shielded cables for the steppers and all wires running out the machine. The cables are maybe a meter long. Any ideas?
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This post is deleted! -
@michaelr123 Hi my point of view of "big" printers:
The limit for voron or other printers design is the 2020 extrusion toooooo weak.
Use a fu**king big and heavy frame is mandatory (even for small printers) use 4040 extrusion filled with resin+concrete and a lot of them.
In my presious builds I added a lot of extrusions to increase the rigidity of my frames and it was far better and the price stay low.
More extrusion could help to make and keep the frame square (with precise extrusion cuttings) and avoid twisting when you move it.
More weight -> less vibrations.
For example I modified the JUBILEE design to fit 2040 extrusion filled with steel and silicone to gain a lot of weight and reducing vibrations: https://www.lesimprimantes3d.fr/forum/topic/43356-mon-imprimante-3d-jubilee-toolchanger-protocreation/?_fromLogin=1#replyForm
With big frame you can more easily use big motors/belts/gantry/rails with less problem. -
I haven't even posted any pictures of my machine to this thread!
its a 400x800 print space system built around the biggest sheet of glass I could get at lowes
It's been a pet project for years now as I slowly redesign and spend money improving it. I think the gantry system is is ok shape, the electronics are now top notch with the Duet 3
the Z-axis definitely needs to be redone at some point. I reused an old v-rail setup I had on a leadscrew printer that I built a long time ago. The point of this system is to be able to print 30" or so parts for fiber glass molds, furniture, and just big parts in general out of mostly PETG and PLA, nothing crazy on the materials front, yet...
Link of it running a dual part cooling fan setup to really crank up the speed on small parts!
https://imgur.com/a/YCJaCZ9I ordered some flexible, shielded cable from zyltech, so I'm going to move everything to that style cable inside the drag chain. I'm not a huge fan of how I'm handling the traveling YY motors. I know the right way to do it is to use drag chains on both sides, but it seems a little unnecessary at this point.
I'm excited to work on input shaping and pressure advance with this system. I think pressure advance will especially help out the super volcano nozzle. Getting the seems to form properly with a 1mm nozzle is really tough with just making it extrude extra material.
My next dream is a scara arm that travels up a rail mounted to the wall with a 2' working area to build really tall parts. I think I want to get this machine nailed down before moving on to the next one though!
