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Advice to choose a motion system (I’m a little skeptical about coreXY) - Strip and convert Anet A8 to a bigger printer

Posted by samuelcarreira 
Hi there,

I want to upgrade my trustfully Anet A8 to a bigger printer (and add a laser engraver as option accessory). That will be my first custom 3D printer, but I have experience on building other types of machines (I build my first lathe when I has 16) so apologies for my lack of knowledge on this area.

Here you can see the desired specs/functionalities of the printer:

I want a printer capable of print objects with a tolerance of 0.1-0.2 mm and I want good printed circles shapes.

fully enclosed:
Because I will print sometimes in ABS and I plan to add a laser engraver I need to fully enclosure the 3D printer

relation printer size/print volume:
Because I live in a small house, I need a high relationship between the printer volume and the print volume. I don’t mind to use an external box to store the power supply and the electronics if it saves some space when the printer is stored (I can store that box inside the printer chamber)

print volume:
I need at least a build volume of 440mm x 220 mm x 250 mm (XYZ) because I will use it as a laser engraver

build price:
I want to use the most components from my Anet A8 (stepper motors, mainboard, and extruder) and keep build lower than 150 € (I will buy the parts from Aliexpress)

print speed:
I prefer to print slow and have a good quality, so I am aiming to print at speeds of 40 mm/s

I don’t need a silent printer

print flexible materials:
I never printed flexible materials because of its cost, but it’s good to have this option for a future

print ABS:
I will print ABS sometimes (maybe 10% of my prints)

Some other details:
To reduce costs, I plan to build the frame on 2020 aluminum extrusions (with full metal brackets – I will not plan to fix the frame with 3D printed parts).

I am a fan of the direct-drive extruders, because I will not print flexible materials, I can choose a Bowden setup, but because of the size of the printer (longer Bowden tube) and to reduce costs I will like to use the MK8 extruder from my Anet A8 (no need to buy extruder parts). Also, because I will never want to print more than 40 mm/s I don’t mind about the extra weight if it’s feasible.

Now my doubts… I am looking here for advice about which motion system to choose:

Option 1: coreXY
I read a lot about the coreXY and other motion systems, but I am not convinced about that type of system. As you see I prefer printing accuracy over printing speed, and some people say that the coreXY can be problematic on the printer accuracy because it’s hard to tune the belt tensions. Also, I will use an 8bit board (running marlin) I am afraid of that hardware cannot handle the sync of the two stepper motors. And last but not least, I will need to calculate the costs of the 9mm wide high-quality belts (it’s not advisable to use cheaper belts).

Option 2: ultimaker style
I like the ultimaker style because it’s very compact and it uses shorter closed-loop belts. Because of the printer volume, I will need at least 10/12mm linear shaft rods for the movement and I will need to use bronze bushings instead of bearings (because of the rotational forces). I will save some costs on the linear rails of the coreXY option but the graphite/no oil bushings are more expensive. Another advantage is how easy it will be to isolate the stepper motors from the heated chamber.

Option 3: Creality ender 5 style
That’s my least favorite option. The main advantages is that it’s a mix between a coreXY machine and a Prusa style (with the X motor attached to X-axis) so I don’t need to mind about the two X and Y synced motors/driving belts. I will have to buy a dual shaft stepper motor for the Y-axis.

What do you think?

Thank you all
open | download - 3d printer radar.png (101.4 KB)
open | download - table compare.png (61.6 KB)
I keep seeing that nonsense about corexy being difficult because of "tuning belt tensions". There's is no mystery or difficulty. When you tension the belts, the tension on each belt affects the tension on the other. So when you tension the first belt, you leave it a little looser than you expect final tension to be. Tensioning the first belt will pull the X axis out of square with the Y axis. Then you tension the second belt (which will also tighten up the first belt) just enough to pull the X axis back into square with the Y axis. Done. There's nothing else to do. Squareness of the axes is your indicator of matched belt tensions (assuming the mechanism is square without the belts, as it should be). See: [drmrehorst.blogspot.com]

Ultra MegaMax Dominator 3D printer: [drmrehorst.blogspot.com]
To add, I have two CoreXY systems running on Ramps boards and have NEVER had an issue with them being too slow. You only run into problems when you start printing at very high speeds. With a Delta you run into problems much faster and even on a Delta you can easily print at 30~40mm's/second without issues of an 8-bit board being too weak smiling smiley

I think it's a mistake to write-off flexible filament. Flexible filament doesn't cost much more than PLA or ABS, unless you buy Ninjaflex. TPU is really great stuff- it's easy to print and there are a lot of uses for the tough, flexible parts you can make with it. I recently printed a pad for my car jack - yes it lifts my car on the printed pad! Prints come out very shiny and a little bit hairy, but easy to clean up with a heat gun or razor knife. Single-walled vases in TPU look great and can take whatever abuse you throw at them.

You can buy quality linear guides inexpensively via ebay if you know what to look for. Search for brands like NSK, IKO, and THK. Use the smart search feature and leave out part numbers containing MGN and MGH (that eliminates all the crappy Hi-Win knockoffs). Don't be afraid to buy used or NOS guides. Industrial machinery often gets replaced long before end of life, and a 3D printer is practically a no-load situation so the guides will last for years in a 3D printer. 12 and 15 mm seem to be the most common sizes. I've bought about 12 used guides in the last several years and have yet to get a bad one. The only specs you need to worry about are the length and number of bearing blocks. Guides can be shortened with a cut-off wheel on a grinder.

Ultra MegaMax Dominator 3D printer: [drmrehorst.blogspot.com]
I'm doing something very similar, with similar goals, and I would strongly advise you to reconsider either your goals or your price point.

I'm converting an Anet A6 to a 300x300x450 mm build size corexy printer using an extruded aluminum frame. My main goal is high speed and high accuracy for any type of filament.

While Anet makes cheap printers, they don't make good printers. You won't be able to get high accuracy using cheap parts, including parts from AliExpress. I'm working on a BOM and design for a conversion printer, a printer that starts off cheap and has low price upgrades along the way that gradually convert it over time into a completely different printer. I'd like to collaborate on this, so PM me your email and I'll send you the current BOM. I'm following a lot of Mark's advice as well, like using aluminum tubing for pulleys, etc.

It's fine if you don't want to collaborate, and I'll answer your question.
Corexy is great if you make it right, and Mark's blog has some really great resources for that.
I considered Ultimaker style for quite some time, but I found that linear rods are unreliable, especially for a large build volume like yours. There's a reason that the largest printer Ultimaker makes has a build volume of 330 x 240 x 300mm. Any larger than that and you are going to experience some serious flexing. Again, I would strongly suggest using linear guides, but if you want a cheaper solution then v-slot could do well for you.

A 3d printer costs 500 dollars. Any cheaper and you'll pay, any more and you'll earn.

For an aluminum extrusion frame, if you have an unsupported 400 mm gap you are going to run into problems using 2020. I would suggest using nothing less than 20-4040 for verticals and 20-2040 for horizontals, as well as supporting any horizontal span over 300 mm in the middle.

TL;DR Corexy with v-slot rollers is your best bet, but I would suggest giving yourself a larger budget. I'd like to collaborate, PM me your email if possible.
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