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RailCore II

by kraegar, published

RailCore II by kraegar Jun 27, 2017
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Fusion 360


RailCore II by kraegar is licensed under the Creative Commons - Attribution license.

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RailcoreII is a Core-XY based Reprap 3d printer designed by J. Steve White & Tony Akens. The initial idea to collaborate on a printer started in the #RepRap IRC channel, and centered on some common goals we both had in mind for a new printer design.

Core-XY motion.
All Linear rails for movement
Space & Cost Efficient, enclosable frame
Key components being printable, or able to be milled
Flexibility and Scalability in the design
A professional looking printer
Self Sourced and Easily customizable

Steve had previously built the “railcore”, the “alpha” version of this printer. We took what he’d learned from it, and began the design on the new printer. All design work was done in Fusion360.

As we progressed, we decided to “publish” this printer in an open, documented format for others to build as well.

The frame is designed to be 1515 aluminum extrusion. This was a space efficient choice, and it makes building the printer easy, as standard M3 hardware works like a T-Nut, fitting into the extrusion nicely. To add rigidity, we use melamine sides to stiffen the frame. (These can be cut out of any material you prefer, including plywood, acrylic, aluminum, etc). The total cost for the actual frame components (Extrusion, corner cubes, and sides) is roughly $100.

From there, some key design decisions were to make the build volume a 250mm cube. This kept the total printer size to what we considered reasonable. The design is easily expandable to 300mm cubed, and a new version at these dimesnions is forthcoming. Some notable aspects of the design: dual leadscrew Z-Axis with a belt drive between them, Stacked idlers duo-planar belt path, and lots of flexibility. The electronics in the design are the Duet (Wifi or Ethernet), 24v PSU, 0.9 degree steppers. We used an E3D v6 for the design, as it’s the most common hotend at this time. Support for other hotends will be forthcoming (needing only a different Y carriage). Semi-Direct drive or full bowden is supported.

A special thanks to Filastruder, Duet3d, E3D, SeeMeCNC, and 713Maker for supporting the project.

Link to the Bill of Materials For the 250^3 & 250^3 with Z-leveling versions:

Full CAD assembly in Fusion 360 for the 250^3 version: http://a360.co/2z30VXH

Link to the Assembly Guide for the 250^3 version:

There's an optional "ZL" build, to add 3 point automatic bed leveling: https://www.thingiverse.com/thing:2765693

Link tot he assembly guide for the 250^3 version with Z-Leveling:

Link to the Fusion 360 model of the 250^3 version with Z-Leveling:

BOM For the 300 & 300ZL Version: https://docs.google.com/spreadsheets/d/1ePSq-bL4-4rGUdbzkxtMmNftXPYwv5IH47edacloU4E/edit?usp=sharing

Fusion 360 model for the 300^3 Version: http://a360.co/2BZLzTA
Assembly guide for the 300^3 version:

Fusion 360 model for the 300ZL Version: http://a360.co/2D5OryV
Assembly guide for the 300^3 version with Z-Leveling:

Gallery of sample prints: https://imgur.com/a/QNLli

Facebook discussion group for RailCoreII builders & owners: https://www.facebook.com/groups/RailCore/

Forum for RailCore discussion FAQ, and build logs: http://forum.seemecnc.com/viewforum.php?f=116

10/23/17 Update: Almost all the files renamed to match the BOM and documentation better. Orientation of all models fixed to show how to best print them.

2/11/18 Update: Front & Back X carriages updated, Front and Back Stationary Idler Carriers updated.

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This looks like a really interesting design, and I'll be looking in depth at it over the next day or so, but those diagonal belts have me really curious. There's no issues with that? No drawbacks or worries about friction against the edges of the pulleys?

The belts are completely planar in Z. They're only at an angle in x/y. So if you line up your idler stacks carefully and have them solid enough the bolts don't tilt, there's no rubbing.

(In other words there's a "top" belt and a "bottom" belt - they never cross paths top to bottom.

Comments deleted.

Could you explain some pro's (and con's ;-) ) of the Railcore II if battled against a Hypercube Evo? They look pretty similar. Hypercubes uses 3030 extrusions though, and that sounds like it is better, but I understand your comments earlier here about the sidepanels giving a lot of sturdiness instead.

Your design is pretty easy for enclosing the sides, but are there any thought about enclosing the top? I think if used to print ABS that would be a big +

Enclosing the top will happen for sure. The only real change is the idlers need moved out of the print volume, to minimize the # of holes needed in the top (just 4 for the belts, and a way to feed in the filament). It just hasn't moved up on the priority scale yet.

The hypercube looks fine, as does the Voron2 and the DBot. All different implementations of the CoreXY motion. We don't really try to compete, we just do our own thing. That said, the reason the RailCore exists is because we both felt that linear rails were the best way to handle the motion & constraint. The entire design revolves around that one premise.

One extra note, the railcore is also extremely adaptable. You can quite easily use whatever hotend, extruder, bed, print surface, Z probe, etc you want. (The titan aero being one that while possible, would cost you a chunk of X/Y or Z volume)

We also have an edge (I think) with working with 713maker for making some components out of aluminum. They're already doing idler mounts, stepper mounts, and the bed/carrier for us. I recently sent them a design for the e3dv6 mount, and a titan mount. As time goes on, more of the critical printed parts will be available milled from them.

The major cost components in the BOM that push the price up for the RailCore are a premium controller (the duet is the best there is currently) and the linear rails.

Thanks for your reply Kraegar. I am not trying to play you out with an opponent. I am just trying to find what's best suited to fit my wishes. I like however the way the steppermotors are mounted within the frame of the hypercube. But your design is very interesting because of the linear rail indeed, and having 713maker in your team is a pro for sure

Putting the steppers external was intentional. It kept the frame far more space efficient, so the printer is far smaller in footprint, and also keeps them external for when we put a top on it and fully enclose it, so they won't be in the hot internal area.

I really like this design. Thanks for sharing your project!

I will make this 3d printer. At first I was thinking to wait for the 300x300 version but at the end I have decided to go for 250x250 as I have already a 300x300 printer.

Almost all the items are already on the road! Hope to start the assembly within 1 month, when I will have most of the items! I think I'll enjoy the work and hope to reach your great results! Anyway, thanks again for putting all here.

Excellent - as you order, be sure to look at the item name / description to make sure the parts match up. (We had an instance of a link in the BOM switching from the 5mm ID idlers)

I'm curious what you'll be doing for side panels? I will be able to cut HDPE side panels soon, as sourcing the melamine has been difficult.

Also, you may want to join our facebook group for comments and help during your build.

You'll love the RailCoreII!

Yeap, the BOM has been checked many times to confirm that all components are the correct ones, specially for me as I had to buy all from other shops that allows shipping to Italy.

About the side panels, I was thinking to use some transparent plexiglas panels, width 5mm. I have found them at 21 euro each and they seems nice. Or 3mm width at about half of the price. Anyway, that's one of the last things that I'll buy as I will take them from a local store.

I'm already on the facebook group, and of course will post some pictures when I'll start the work on RailCore 2!

The only changes I have done were the heater and the heat bed.
I am using a 230v silicon heater (with a SSR) so that I can use a smaller and fanless PSU (and also improve the energy efficiency).
About the heat bed, I have edited the project to use a plain surface on the back, and use the temperature sensor already included in the silicon heater.

Sounds like you've thought it out well! I'd recommend HDPE if you can find it over plexiglass. It can be cut on a CNC or lasercut, and won't crack like plexiglass can. Though plexiglass should be fine. If you can't get approximately 1/4" (6.35mm) then the printed stepper & idler mounts may need modified to suit. I can assist with that if needed.

Sounds like you've got it well thought out - if I can help, hit me up here or on Facebook!

(If you're going with a 713maker bed & carrier, I do know they'll ship to Italy, if not, I'll be interested to see what you come up with for the bed!)

Thanks for your advices!
I think I'll go with the plexiglas to keep the price reasonable low.

About bed & carrier, I have asked some quotation and ended with two possibility: get the bed & carrier of the Ultimaker 2 (260 x 230) or make produce your bed & carrier from China (production prices in Europe were too high, and shipping from the US were also too high). I have choised the China way. In that way I can try the 3 points bed calibration, and I think I'll like it!

I'd have concerns about cracking with plexiglass on the sides, but if that happens it's always easily replaced! Would love to see your progress.

Is the one Y-axis rail rigid enough to carry a direct extruder?

Yes - we use a very short bit of PTFE between the extruder and the hotend, but it's essentially direct drive. All of the weight is on the Y rail.

Any chance you could please upload full build's 3D model here?

It's available at this fusion 360 link: http://a360.co/2z30VXH

That way what you're downloading is always up to date, rather than me trying to keep every file on thingiverse updated all the time.


As a note, the BOM is going through some final revisions, and the assembly guide is going through final edits now. Should wrap up in the next week or so.

Great work! and I love the detail that you put into the manual.

Thanks! We have a couple guys building them now, and they're shaking out a few bugs here and there, but it should be all tidied up soon.

I'll me building the gantry for my modified Duplicator 5S.

I’m looking at building my first printer. I already have a Maker Select v2.1, but wanted something bigger and quicker.
This printer looks almost exactly like what I want except for one thing. I would like a 300x300 print bed. How hard would it be to scale it up to allow a bigger bed?

We're looking into redesigning at a 300mm^3 volume, it's definitely the most common question we get. For the most part, things will scale just fine. Scale up the extrusions, the linear rails, bed, heater, and sides, and you're mostly good to go. Where the trouble is most likely to come in is spanning the Y axis unsupported over that distance as it is (just a linear rail holding the Y carriage). We have various ideas around that, but nothing solid planned due to time constraints. Possibly simply bolting on a 1515 to the back of the rail, modified X carriages, and a change in how the layer cooling is done would solve it, we just haven't laid it out yet. The Z axis may need slightly bigger lead screws, but we're working on some other interesting ideas there as well.

So, it'll be coming at some point, we just don't have an ETA yet.

(Currently we're working with a vendor who's going to be able to supply milled aluminum motor & idler mounts. While not required, they'll look great, and provide some good stiffness to the belt path)

For some sample prints off of the current design, you can see my gallery here: https://imgur.com/a/QNLli

Kraegar these are freakin' nice photo's! What kind of multicolor technique did you use on the multicolor part? And how is the 300x300 coming along?

Thanks! For the multi-color parts, I just did a pause and filament swap, them resume. The RepRapFirmware macros for swapping filament made that easy.

The design for the 300 will be done in the next day or two. The ZL version of it will take a couple days longer. There's a slight bit of work needed on the BOM for it, and some minor updates to the assembly guide for the 250 to make it work for the 300.

Thanks for the quick reply. I'll keep an eye out for a bigger version. I'll keep looking for something completed in the size I'm looking for and maybe once you have something released, I can build another one.

I posted the BOM & CAD model for the 300^3. The assembly guide will be coming along soon.

Most impressive, sir! Looking forward to working on this one.

Thanks! Come join us on FB or the forum for more updates and such!

I probably should, but sadly, at this point I do not book face....
However, I am following on the duet forum and the seemecnc forum!

I love the design, though I have a few questions, firstly, why did you not use double synchronized Z instead of the current solution? And secondly, why not 3030 extrusion instead of 2020?

Using a single stepper with belt drive for the Z axis means we don't have to worry about the two steppers getting out of sync on power down, etc. A single stepper has plenty of power to drive both leadscrews, so using two was completely unnecessary. However, we are looking into a new duet feature of using three independent steppers for Z, to due true bed levelling. We'll likely use three nema 14's for that.

For the extrusion, we actually use 1515, not 2020. The side panels are bolted directly to the 1515 extrusions, acting as giant braces reinforcing the entire side of the printer, tying all of the extrusions on a side together at once. By having 5 of these panels on, the printer is drastically more rigid than most built with larger extrusions with an open frame. Using 1515 was space & cost efficient, and also let us use m3 hardware in place of T-Nuts, so putting it together was cheaper and easier as well.

Interesting. Another small question have you considered creating variants of the 3d printed parts for 3030 extrusion that seems to be more commonly available and used (thus basically provide an upgrade path for people having Hypercube or some other printer based on 3030 extrusions)?

We haven't - the 1515 is pretty integral to the design... and the total cost for Misumi pre-cut 1515 for the printer is only $32. That's for the entire frame, including the Z Axis. We're working on a scaled up version of the design, but it will continue to use 1515.

Though I'd drop in a sample pic printed with RailCore II:


Nice design, could you share more pictures ? Include one of the Z bed mount ;-) thanks

Thanks! More pictures are coming! I took hundreds during my build, which is mostly complete now. Just a little tidying up to do on the wires, and some other small details. I'll try and get some pictures up ASAP.