Presenting the NFAN CoreXY 3D printer (no replies)

I started out about 3 years ago with a Prusa i3 clone with a laser cut wooden frame. It was a great machine to learn about 3D printing. Just about everything was wrong with the machine so I started upgrading things and it improved a lot but I hit a certain level where it was just taking too much time and too little return of investment. The mechanics were so weak just looking at it would make it bounce and wobble. It was a lot of fun to tinker and hack with it though.

A year ago I built a diy cnc router, the Openbuilds OX. I used all Chinese parts and after a steep learning curve I was confident enough to mill out parts for a new 3D printer.

My goals were:

• Create an all metal 3D printer using my cnc router
• Make it really sturdy and stiff
• Easy to maintain and upgrade
• After setting it up it shouldn't need much more adjusting, I based the name on this goal: NFAN, No Further Adjustments Necessary. It's not how it is yet but it's a goal I'm striving for.
• Use the nema23 stepper motors I got with the CNC kit, for which I got three stepper motors with more torque so I had a few spare.

I've based my design on the CoreXY mechanics, inspired by the_digital_dentist, tech2c and many others and picked the things that spoke most to me. I had a lot of fun designing it in a 3D package.

here's a picture of the design:
http://www.makercentral.net/media/nfan/wip004v93.png

I machined the plates on the router. I used 3 and 6mm plates for stiffness. I accidentally ordered aluminium that was a bit too soft (1050 I think) to be machined but it plowed through after some adjustments liberal application of wd-40.

After most of the parts (pulleys, idlers, belts, v-slot wheels, etc) arrived I started building it and it came together without too much problems (to my surprise!). Some parts are on their way, and in the mean time used my old prusa i3 parts. The duet ethernet is yet to arrive so I used the arduino/ramps1.4 board for now with marlin 1.1.9. It has worked quite well so far, though the 12V stepper motor drives means the motors run relatively slowly at 80mm/s max. Hopefully the duet with 24V will double the speed.

The plan is to use an all metal hot end holder, but for now I used my old one which seems to work fine. I also used the old extruder for now.

Here's a short video showing the build print with test fitted steel reinforced belts. They're too stiff as the_digital_dentist said, I can confirm he's right :)
[youtu.be]

The very first print that came out was a lot better than what I've ever been able to print with the old Prusa i3 clone. The layers are very consistent, very little compliance/backlash and can print at 80mm/s without any ringing and resonances visible in the print. I used the same slic3r profiles I used with the prusa i3, so I didn't need to do any tuning.

Here's a macro shot of a 20x20x20mm hollow, single walled box:
http://www.makercentral.net/media/nfan/_MG_2230.jpg

Here's the corner view:
http://www.makercentral.net/media/nfan/_MG_2234.jpg

The layer height is 0.25 or 0.24, I can't remember. I realized at some point that the z steps are 0.04mm (lead screws with 8mm thread per turn, 200 steps per rev. 8/200 = 0.04, I use full step because the nema23 don't seem to run smoothly with 16x micro step) per step so 0.25 isn't possible to print exactly and may result in repeating z layer patterns.

Here's a space shuttle launch thing from thingiverse, reduced in size by a factor of 0.6. It stands about 30mm tall and 0.24 layer height, printed at 60mm/s (or as fast as the short layer times allowed, slowing down to 15mm/s at the top layers. I used an off print head 120mm 1000rpm cooling fan which may not have been enough cooling for those top layers.
http://www.makercentral.net/media/nfan/_MG_2254.jpg

http://www.makercentral.net/media/nfan/_MG_2223.jpg

(td) There are a few things that didn't work based on my design:

• The z axis lead screws were designed to be fixed with a bearing on both ends but it was over constrained and couldn't adjust it so it would be moving freely. I ended up removing the top one. The v-slot wheels are great at constraining any lateral movement so it has no impact on print quality. It's very smooth now. It actually drops on its own weight if the stepper motor isn't connected.
• The z plates needed slots instead of holes. Something went wrong during the machining stage of one of the z plates and it was off by 2-3mm. It's also a good thing to have slots to have better adjustment options to align the print bed extrusions with the xy gantry. I used a bubble level to get into the ball park, then used 2040 extrusions and let the top of the frame rest on the bed, then tighten the screws. It worked pretty well.
• I've leveled the aluminium heated bed with shims. I used four raiser plates of 5mm high to screw in the v-slot extrusion, and on the other end threaded holes for the heated bed to be mounted. This worked well except because of thermal expansion the bed would raise or drop by about 0.5mm making it hard to get the z offset adjusted correctly. I scraped the varnish off the glass plate numerous times until I loosen 3 screws on the raiser plates for the thermal expansion. The v-slots allow some room for expansion yet constrain the heated bed in the z direction. Simple yet effective so far.
• The aluminium heated bed (mk3) wasn't perfectly level. I made a mounting plate with an adapter for a dial indicator. With this I could measure the levelness (or lack thereof) of the heated bed. On one edge the offset was about 0.3mm. I used a glue clamp and another 2040 extrusion to bend it a bit more level. Overall the bed is now within 0.15mm level. It's hardly ideal but it'll have to do for now. If you have any tips where I can source an aluminium tooling plate and fitting silicone heating I'd greatly appreciate it! I like the setup of digital_dentist a lot, I think that's the way to go. I might have a look into the kinetic mounting method.
• The lion clamps are constantly in the way. This is in part due to the x carriage being a bit close to the print surface. It easily knocks them off. I may redesign the mounting so that the hot end sticks out more so it clears the clamps. I designed it like that as anything sticking out too much and moves around quickly will work like a spring so the closer the hot end is to the x carriage plate it will be stiffer.
• The nema23 stepper motors are high torque. This means if a step is done it will jump more than a nema17 stepper motor at low speeds. which leads to visible though very small ridges you can feel more than you can see. Hopefully the Trinamic 256x interpolation will smooth things out. I like the extra power though, high accelerations are possible. It's a bit noisy though.

(tu) What worked very well in my design:

• The v-slot wheels with the eccentric nuts, this is really easy to design and build. It allows for some alignment errors to be adjusted away.
• the v-slot extrusions allows for endless upgrades and it's easy to enlarge the build volume. With v-slot nuts you can insert even if the ends are inaccessible is very convenient. You have the 'twist' time inserts but also wider, more robust ones with a little spring ball at the back. These stay put where ever you put them and have a longer thread, and won't damage the slot if you want to tighten it down.
• machining my own plates has worked so much better than I expected. Machining 1050 aluminium isn't easy but with shallow depth of cuts and lots of wd-40 it's amazing how such a non rigid cnc router can still deliver usable machined parts.
• the openbuilds delrin lead screw nuts are great! They are self lubricating and there are versions with anti backlash adjustment, though no backlash is to be found yet. Maybe if the nuts get worn more I may need to put the grub screws in and tighten it down. The advantage of these nuts is you don't need any lubrication, which only attract dust and may grind to a hold at some point.
• All the idlers are supported at both ends with 6mm thick plate aluminium instead of springy printed plastic parts. I think this has really helped make stuff stiff, despite the aluminium rods for the idlers.
• The z axis end stop. I just use a regular micro switch without any adjustment. I put it somewhere along the z extrusion so it's in the ballpark. When homing, x and y must be homed first. The frame is large enough that the nozzle isn't over the heated bed so the z axis can raise up higher. It hits the end stop, then I use an eeprom settable variable with M206 Z-5.3 or something to shift the z axis back in position. This way I don't need an end stop adjustment screw, I can just use software to adjust the z height. It's the same idea as using a servo lowered z probe I used on the old prusa i3. It used an offset too. Hopefully this will work the same with the duet.

All in all I'm really pleased how it turned out.

There are still some improvements I want to make:

• Replace the hotend holder with all metal machined aluminium, or reprint it with single hotend holder.
• Design and machine a new extruder/cold end drive
• Replace the 5mm aluminium smooth rods for the idlers. It doesn't seem to have much impact on print quality at 80mm/s though but some hardened steel smooth rods are ordered.
• Replace the 6mm glass reinforced belts with 10mm. All the pulleys and idlers are 10mm so it should be an easy fix. Even so, hardly any compliance or backlash is visible, even at 80mm/s but I may see it if I push beyond that speed.
• replace the ramps1.4 board with a duet ethernet so I can put it somewhere more convenient and with trinamic stepper motors with 256 interpolation mode should make it much quieter and smoother and hopefully faster at 24V.
• The design shows the back 2020 vertical supports but in my actual build printer it's located at the front. I will add 2040 support on the back as well later for extra stiffness. The frame may be slightly over build that way, still there's a bit of flex I want to get rid of.
• once all parts have arrived I'll clean up the wiring and put the electronics in a metal case.
• I need to sort out the psu. I want to use a single 24V psu with a 12V buk converter eventually. Still, I can hear the stepper motors whine, and when the heater cartridge in the hot end is at its set point, you can hear the motor whine pitch shift in the rhythm of the pid frequency. I'm not sure if this translates into the print. I'll have to think of a way to test this. Led PSU's aren't the best for changing inductive and resistive loads.
• I've ordered 10 pin connectors with screw terminals for the x carriage to be able to easily switch tool heads. I'm planning to add a dremel/light spindle for pcb milling and a laser module. I like the tool changer E3D has designed. I may give it a shot when they've released the design files and maybe sell parts for it.
• The disadvantage of the z end stop at the moment is that some space is wasted, so a larger heated bed covering the entire area of the build volume isn't possible. I use a 200x200mm mk3 heated bed for now. I'll have to come up with a different solution if I use a 300x300mm bed. I may look into the piezo devices. I've got a diy prototype based on DjDemonD precision piezo z-probe ideas. If you look closely, the design has a pad with a circle in it, which is the piezo disk. The idea is to have a fixed location on the z axis extrusion. Use the nozzle or gantry to hit the plate and trigger the z end stop.
• To be able to properly print ABS, the printer needs an enclosure. I'm playing with the idea of using acrylic plates with neodynium magnets to keep them in place. I'm not sure if it'll rattle badly or if it's alright. It's easy to remove panels with magnets.
• add led strip lighting.
• print or buy some dragchains to make wiring a bit neater.

If anyone is interested in the design files I'd be happy to share them, at least once I've ironed out the quirks.

Please let me know what you think! Any suggestions are welcome!