Rat Rig V-Core

by ratrigprinters Jun 20, 2018
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There is a design decision that I do not fully understand. Maybe someone can enlighten me :-). The printed parts at the end of the X axis are not symmetric: one is screwed into the end of 20x20 extrusion of the X axis, but not fixed against rotation. The other one is press fit onto the extrusion without a screw, and secured from the side with a T plate. I assume that this is so that we have a little wiggle room both length-wise on one end and rotation-wise on the other, and the whole carriage does not bind if there is any slight misalignment in the frame, right?

Which STL do I need to print the extruder mount? I have the belt clamps and the probe mount. But I'm missing the file for the extruder mount as shown on page 23 from the new manual.

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I wonder how the actual print bed would be mounted here. Would I put it on top of the plate shown in the picture (the one that rides on the Z screws), and would it be offset on screws and springs for leveling? Or is there any other mechanism in place for leveling?

My personal experience with z axis drives on the V-Core is that it can happen quiet easy for the lead screws to move. Especially when the steppers are powered down. I will upgrade my V-Core to the 3 lead screw version but instead of 3 steppers I will use a GT3 belt to link all lead screws mechanically and use one bigger stepper to drive them all. Once they are adjusted to be parallel to the X extrusion there is not much that can move except for maybe some thermal expansion. These small things can easily be handled by mesh bed leveling. I have finally gotten my piezo z-probe working and the Duet 2 controller does a fine job with that.

Have FuN!
Jan P.

Tramming can be done either by auto bed leveling methods or by the firmware turning each of the individual Z axis motors to bring the bed trammed with the XY axis.

Thanks! Just for future reference, if anybody is reading this – the method using independent Z motors is described here for the Duet board: https://duet3d.dozuki.com/Wiki/Bed_levelling_using_multiple_independent_Z_motors

That is easy enough for 2 Z motors but if you have 3 of them (V-Core Upgrade Kit) you need a Duex extension board to have an additional driver for the 3rd motor.

check out the kit you sell because i really want this but the price :o i mean its a really nicely design and alot of work went in to it its just a bit out of budget :'( i know i could just source all the parts and build it that way but i would rather have all the parts come from the same seller oh well still a really nice build


I think it would help to clarify at the very beginning how wheels and pulleys are assembled correct, I went through step by step and only seen in way in to the build how the wheels and pulleys are put together right with washers and spacers. Sure could have read it all before starting, that was me being lazy ;-)

I was very impressed with the quality of the cuts, the extrusions are well cut to length and square at the cuts. There was no need to lay hands on them other than removing some shavings and wiping some lubricant.

Thanks !

Guys please check page 3 of the build guide https://drive.google.com/file/d/1Upd_vJQMKGXq_OxI3bd-cTxZgQqvf-wR/view it's missing the double T-Nuts for the Z-Motors... I'm at page 11 and now I need to build the whole frame again... or I get some drop in T-Nuts.

Love the build, and love the video, but there is something I can't quite wrap my brain around. I can see how you've set up your motors and belts, and I could see how they would move the carraige from left to right on the x-axis, but I can't see how it moves the whole gantry back and forth on the y-axis. I looked at the belt setup png, and i've seen this configuration before on a couple of different machines, but I just don't see how that works. Is there a better explanation, or a better video, or something to better illustrate how that axes work?

Maybe check this out:


A different approach to explaining the core-xy kinematics.

The bed plate is 329x329mm with 309mm screw hole spacing but.. what kind of hotbed can I mount?
Thank you

My hotbed is MK2b (12/24V) and is 310 x 310mm

Have you got a picture of your bed setup? I am thinking of buying one but can't quite wrap my head around the bed setup.

Hey guys, nice design. Frame looks rigid. Is it possible to buy four extra Z rail mounting plates? I can`t find it as a stand alone item, is it custom made?

Hi Tomaszs!
Thanks for your comment and interest. Yes the frame is designed to be very rigid using 24 x 4mm aluminium plates. For the Z rail mounting plates, currently we can't supply them individually because we produce the plates in "sets", so right not it is only available to order on its own. The files are available though if you want to get some cut.

Are you going to design mounts for IR- and BLTouch probes?
Awesome looking printer, I'm definitely going to build one in the future. Thanks for designing, sharing and making really good instructions how to put all of those nuts and bolt together! :)

Hi! Thank you for the kind words, we did put a lot of care into this design, we hope the community likes it.

We do intend to design mounts for BLTouch probes. We probably won't do this for IR probes as it is a very niche solution, but we'd be happy to link to a user design if someone were to make one!

Received my kit today and the first impressions are that everything looks as advertised and well made. Inquiring to see if any progress has been made on the BLTouch Mount? My Meshmixer skills aren't up to the task of modifying the current STL yet.

Hello, thanks for the great design!

I'm currently printing the parts to build the V-Core. But there ist no file called "belt clamp" as listet in the BOM under "printed parts". Or does it mean another file with a different name?

Hi! The correct part is "Sliding belt clamp" as is currently listed in the BOM on our Google Drive:

We suspect you were looking at a BOM that was downloaded a few days ago, before we corrected this typo. Thank you!

Thank you for this thing! Thumbs up to you!

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Hi! Why did you design it so that the dual z axis motors are offcenter? Doesn't that remove most of the benefit of having dual z axis in the first place?

It's called a "Cantilever Design". That's what single axed printers use. They also only have 2 linear rods. Dual-Z usually have 4 linear rods, rails, v-slots, etc.

Hi! Offsetting them should "preload" the tilt to only one side. If the pivot point is right in the middle, you could be more prone to having the bed frame seesaw around it.

But, then there is no point to having dual steppers anyway, since it does not combat the tilt introduced in any way? With your design there is no benefit at all to having both motors, in fact only making it worse due to human error. without dual motors, the tilt will self center the axis in one direction. with dual mototors it won't, and in fact would introduce a larger error due to the motors never being quite aligned.

With dual motors on opposite sides, you reduce vibrations and stop there being an increasing tilt which becomes a larger and larger problem the larger and more filled in model you print due to the plate getting heavier. Heck, with dual motors on opposite sides you can in fact still preload a tilt by having that motor be set slightly lower. (would recommend having measurement guides actually, having a sticker or marking on both sides of the build so you know where to level it on machine failure either way)

We opted for dual Z motors to provide an additional rigid mounting point and to prevent the bed from tilting in the left-right direction. Using dual motors and especially with dual drivers we can also decrease the load on an individual motor.

Wouldn't offsetting the motors to the front instead of the back of the sides make the same preload but in oposite direction and also give more stability to the front of the build plate?

That's an interesting idea and could be something to look at. The design itself does not limit the placement of the lead screws in Y direction so you are free to place them as you see fit.

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When is it available in your shop? I am waiting for it since months....

Hi! We understand and appreciate your impatience! We're eager to ship this beauty to the world as well. However, at Rat Rig, we never rush product launches because it's super important to us that you will be super happy with our product! With this said, we expect to have all parts in stock during the second half of July 2018 and launch shortly after we have them all.

Thanks foe sharing this fantastic project! Where i find the firmware? Possible in work video?
Thank you!

since we don't provide the electronics and the user is then free to choose whatever set up best suits their needs, it would also be hard to provide a full fledged configuration. However, you can get the basic settings from the product description, like build volume and from the motors and pulleys used. I'll also see if after the weekend I can push online the Marlin fork and configuration that is used on the prototype machine.

Is it possible to have a photo of your prototype? where do you plan to put all the electronic parts?


As we don't provide the electronics at this time it is up to the builder to decide where to place the electronics. On the test machines, the parts were placed at the bottom but so that the bed doesn't hit them. There's plenty of room.

We will have more photo and video content coming very soon.