ZeroG Mercury One.1 modified Front Idlers

Warning!

If you use these parts, you will need the rest of the mods that go with it, you will change the geometry of your printer motion system and you will need to make sure that the edges of the bed, the end stops, the belt tension, and everything else is double checked. I am not responsible for any damages to your printer, or any of the parts. If you don't know how to do this, this mod may not be for you!

Using this mod, and all the mods that go with it will also flip the X axis so the linear rail will now be forward, instead of on top. This is also in line with the Voron line of printers, for instance, but different from the original ZeroG Mercury One design. So you will need to select another toolhead and X carriage mount for that toolhead. There will be recommendations further in these instructions.

Introduction

My very first 'serious' (-ish) printer was a Sovol SV05 which soon after I purchased it, was upgraded to a ZeroG Mercury One. Absolute mad props to the ZeroG team, it was a huge improvement over the original. Then I enclosed it using my own design. At that time the ZeroG Nebula enclosure was rumoured, but not yet made public, so I simply designed what I thought made sense. Funny enough, my enclosure and the Nebula are similar, but NOT the same. Keep this in mind if you have a Nebula enclosure and want to use my mods. Later I added ZeroG Hydra as well.

As I used this quite heavily modded printer regularly I started to have some wishes, and ran into some issues:

• I wanted to use a similar toolhead as I had on my Vorons, ideally the same (the one I use is the Dragonburner). This assumes the linear rail is at the front though.

• I wanted to use a Cartographer sensor. That also puts demands on the carriage, which are easily addressed with commonly available carriages for the Dragon Burner. The one I use both on my Voron 2.4 and on the Merc now can be found at chirpy2605's 'alternative voron mounts' github.

• My belts had a habit of riding up and down the bearing stacks of the stepper mounts. This caused excessive wear. This was partly due to 'builder fault' (ie: me being a dunce), but even when I was 100% sure things were assembled perfectly, they kept moving all over the place.

• I suspected the front idler mounts were bending towards the rear of the printer due to belt tension and the torque of the steppers. In the original design, the front idler mounts are only attached with a single M5 bolt.

• I suspected the stepper mounts, in turn, were being bent forward, because they are only attached to the frame with 2 M5 bolts, nearly in a straight line left-to-right, so with very little resistance to any force perpendicular to that.

• I wanted to have a bit more travel for the front idlers to tension the belts. Though you shouldn't need all that much if you do your belts right, I am a bit lazy, so... more is better ;)

Looking at the Voron 2.4 that sits right next to my Mercury I quickly realized that it did not suffer from the issues, and already had the attributes I was looking for. So, I basically wanted to 'Voron-ize' my Mercury One! The models here only cover the idlers. You will need the other parts in the set too for a fully functioning set.

Suitability and fit

This mod assumes there is a frame outside of the original 'Ender 5' style frame, and that the extrusion that sat in the front, left to right, at the top, is removed. As you can see in the photo, besides being fastened to the Y extrusion, it is also screwed into the 2040 extrusion (vertically) and into the frame to the side, horizontally.

Also note that the cover and the adjustment screws stick out in front of the original 'Ender 5' style frame. If you have doors that close immediately against that frame, this mod will not fit as-is.

Inspiration

These idlers were heavily inspired by the Chunky Alpaca idlers for the Voron 2.4 by TheVoronModder. See here for the original. The bearing carrier is nearly identical (but not actually copied), the idler 'frame' obviously is not.

Disclaimer

Another one?! Yes, another one. The solution I came up with for modifying the 'running gear' is by using the Voron layout of bearing stacks: washer-bearing-bearing-washer. With the right bearings, this means that there is a 6mm track between the flanges of the bearings that the GT2 belt sits in. The manufacturer of the GT2 belts, Gates, says that should be 7mm. The Voron team went with 6. The ZeroG team decided to go with the manufacturers recommendation. I would generally agree with the ZeroG team and the manufacturer, they should know best. But I also know there are thousands of Vorons out there with that same bearing stack layout, functioning just fine. So.... YMMV. If you don't feel comfortable with this..... This is not the mod for you!

Also, if you adopt one of the components of my mods, you will either need to use all of them, or design or find the other parts to complete the whole set, to suit the same belt spacing.

Bill of materials

• Dowel, ø5x18mm, 2x

• Washer, M5x1x10, 4x (outer diameter can actually be between 7 and 12mm or so)

• F965 bearing, 4x

• SHCS M5x60, 2x

• SHCS M3x8, 6x

• SHCS M3x40, 4x

• SHCS M6x20, 2x (dependent on extrusions used, can also be M5)

• M3 Slide in, hammer nut, or anything similar, 2x

• M5 Slide in, hammer nut, or anything similar, 2x

• Heatinsert M3x4x5 ('voron style') x8

Printing

You will need all to print all parts, and you need to print the 'Front Idler - Bearing Stack Carrier' twice. The mounts and covers are different, the carrier is the same on both sides. Use the default print settings recommended by the ZeroG team. Use decent quality ABS or ASA. It is not recommended to use filaments with any kinds of fillers (glass or carbon fiber) since the layer adhesion is usually much worse than without, and may cause the parts to fail. White filament is also often (but probably not always) weaker. YMMV, blah, the usual caveats. PETG and PLA are not heat resistant enough and will fail.

Print the bearing stack carriers 'on their back'. The covers can be printed flat on the bed. The housing parts should be printed as an 'M', with large opening that the carrier will slide into towards the bed. You will probably need to add some supports for bridging the top (as printed, or side when mounted).

Assembly

Print as directed above, remove supports (if any).

Press heat inserts into the carrier. They need to be inserted into what will be the back of the carrier so they get pulled into the part, rather than out of the part. Check the photo and image to see how the carrier will be sitting once mounted. Press heat inserts into the front of the housing, top and bottom holes.

Assemble the bearing stacks by sliding a washer, 2x F965 bearing (with the narrow sides towards each other), followed by a washer onto the ø5mm dowel. Check the drawing of the bearing stack for the order and orientation. Make sure the whole stack sits nicely in the middle of the dowel. Click the dowel into the front of the carrier (see photo for orientation). Be careful to make sure the dowel sits entirely in it's recess. I had one sit a bit crooked which caused the belt to creep a bit and cause wear on the belt. I pressed it in further and now it seems OK. I may have to widen the dowel slot, please let me know if you run into trouble with this!

Slide the slide in nuts into the extrusions, screw the housing into position (see photo for orientation) using the M5 bolt (towards the rear, top to bottom), M3x8 into the extrusion to the side (horizontally) and M6x20 into the upright extrusion. Don't tighten fully until it's properly in position. Slide the carrier into the recess in the housing, you can't get it wrong with regards to clockwise/anticlockwise rotation, but you CAN get it wrong front to back. The bearing needs to face to the front, the body of the carrier to the rear.

Insert the M3x40 screws into the middle two holes of the front plate, and the M3x8 screws into the outer ones. Screw into the front and carrier. The middle two screws will be what you will use to adjust belt tensioning.

To guide the belt through, you can remove the front plate temporarily, it's not needed for stability at that point, but you obviously need the front plate screwed in place as soon as you will tension the belts.

The other parts you need

You will also need:

• My modified XY carriages for ZeroG Mercury One.1 with Voron belt spacing.

• My modified stepper mounts for ZeroG Mercury One.1 with Voron belt spacing.

Version history:

• 2026-09-30: No change to the models (yet), but added remark about making sure the dowel sits properly in it's slot to avoid belt wear if it is crooked.