RatRig v-core 3 extrusionless x-gantry mod

This is an upgrade to my previous mod to eliminate the aluminium extrusion from the x-gantry. You can run with just a single rail or with 2 rails screwed together by aluminium blocks. 

A single rail can save a lot of weight, while also eliminating thermal effects on z-offset. However, when using only a single rail, keep the following things in mind:

• A rail without the extrusion is not straight. The rails are only straight if you screw them to something that is straight. They usually have some bowing when not screwed against something else. Select your straightest rail, the z-rails are the same size.
  With the dual-rail option, they keep each other straight.
• A single rail without extrusion isn't as stiff. I wouldn't do this on larger variants of the v-core.

The main reason for making this mod is to resolve inconsistent z-offset caused by the x-gantry warping if its temperature changes.

I kept having to adjust my z-offset and my first layer was unpredictable. I resorted to preheating the printer for a long time before starting a print, but still had problems prints that filled more of the bed. The first 2 objects would be fine, the next would be too close to the bed.

With this mod, all of those issues are gone. Perfect first layer every time, without having to preheat the printer.

Discord user yolo-dubstep did some more testing of the deflection in an enclosed printer and plotted these results:

My results

I did a bed mesh before and after the mod, with a cold printer and with a printer that was preheated for 15 minutes with the bed at 80C. The results speak for themselves. After the mod, the bed mesh is still flat when the printer is hot. The bed mesh doesn't change anymore in the x-direction. The z-offset will not change during the print. Finally I can rely on it.

Why does this mod resolve the issues with z-offset changing? The stock v-core 3 has a stainless steel linear rail on top of a black aluminum extrusion. That extrusion is really good at absorbing heat from the bed. The aluminum and steel expand at different rates and the bimetallic effect warps the gantry.

With this mod, the top and bottom of the gantry are identical. The aluminum blocks in between are separate and cannot cause any warp. As an added benefit, I have attached the carriage of the bottom rail to the bottom of the EVA for extra rigidity. My y-resonances are almost nothing after this mod. This does not save weight. It adds about 100g, because rails are heavy. But my printer runs smoother than ever.

Parts to buy

This mod only uses off-the-shelve parts. You will need:

Both single and dual rail:

• 4 screws M5 x 20mm, DIN 912 (xy-joiners to metal plate)
• 4 nuts M5 (regular not locking)
• 4 screws M3 x 20mm, DIN 912 (rail to xy-joiners)
• 6 threaded inserts, M3, same as EVA3. For the x endstop block and to optionally attach the insert more rigidly to the xy joiner.

Dual rail:

• 1 extra linear rail, same dimensions as your x-rail. The z-rails are the same size, so you can swap with them if your new rail isn't straight.
• 16 aluminium blocks, 10x10x10mm, threaded. You can buy those from various sellers on aliexpress. I used these: https://www.aliexpress.com/item/4000377602362.html?spm=a2g0o.order_list.0.0.21ef1802WpRkWN. I recommend buying some extra, so you can check their dimensions with callipers and pick 16 that are exactly the same height.
• 32 screws M3 x 8mm, DIN 912 (rail to blocks)
• 4 M3 nuts that you file the edges off to fit in inside the rail counterbore.

Printed parts

I split the xy-joiners into 2 pieces to make it easier to print. Print joiners with text up, opening down. Print the rail part with the long bit pointing up.

• Left and right xy-joiners. They attach to the bottom plate with 2 screws in the middle that you can tighten well. These are modified to not need the spacers, just the bearing stacks. The holes for the M3 screws have to be drilled through. They are not all the way through to not break the bridging to make it easier to print.
• 2x XY joiner insert.
• Modified EVA bottoms. These ducts are modified to screw to the cart on the bottom rail for extra rigidity.

EVA2 / V-core 3.0

On popular request, I have added a version that should be compatible with EVA2 (a modified version of MFBS's gaping maw duct) and xy-joiners for v-core 3.0, which uses toothed and smooth idlers instead of bearing stacks. I have not tested these myself, please post a make and confirm if they work, or tell me what should be changed.

Updates:
2022-07-15: Added CHC volcano duct, which is 1.5mm lower than the regular volcano duct. This gives it about 1.5mm clearance to the bed.

2022-08-03: Fixed 3.0 joiner insert holes to have a thicker sacrificial layer so the slicer doesn't remove it.
 

2023-04-26: Added files for 12mm tube between 2 rails as a stiffer alternative. I am not sure the thermal properties are as good as the alu blocks, but I needed it to provide stiffness to lighter, hollowed-out rails.