CoreXY Belt Tension Comparator – "The Equalizer" (Voron 2.4/Trident)

🔄 UPDATE [Feb 18 2026]:-The Equalizer V2.0 

Belt tension measurement tool for Voron 2.4. Designed for SPI digital indicators (or compatible).

What it does:

• Compares Belt A vs Belt B deflection to match tension

• Profiles tension along entire belt length to detect wear or misalignment

• Rotate 180° to switch between belts - same contact geometry for both

Bill of Materials:

Indicator:

• 1× SPI dial indicator model 20-700-1

Bearings & Hardware:

• 4× 604ZZ bearings (stacked: 2 for Belt A, 2 for Belt B)

• 3× M4 washers 0.8mm (between bearings)

• 1× M4×30mm screw (self-taps into plastic)

Spring:

• 1× Spring from Amazon Assortment - select appropriate stiffness (~2-5N)

Hardware:

• 1× M3×12mm BHCS

• 1× M3×10mm BHCS or SHCS

• 3× M3 nuts

Files:

STEP files included for remixing (different indicators, bearing spacing, etc.)

Status: Prototype. Files "as-is" for community testing.

I have confirmed that the Mitutoyo Absolute (ID-U1025E) can be used with the same Indicator Chassis as the SPI version, but the Plunger Carriage requires a slight modification:

• Current Fix: The mounting hole for the Mitutoyo plunger is slightly too small and needs to be carefully enlarged with a drill bit for a proper fit.

• Coming Soon: I am currently designing an improved version of the carrier to allow for a firmer grip.

• Design Goal: This update aims to better maintain strict perpendicularity between the belts and the bearing axes, ensuring the highest possible accuracy.

• Release: I will publish these updated files on Printables as soon as I finish the final precision tests.

🔄 UPDATE [Feb 7, 2026]: 3-Bearing Version Available

Added a new body and plunger variant that uses 3 bearings per post instead of 2:

• 1x F604ZZ (flanged) + 2x 604ZZ (plain) per post — 9 bearings total

• Taller roller surface, easier to handle and position on the belt

• M4 screws thread directly into the plastic body — no M4 nuts needed

• No piston sanding required — slides freely as printed

• The longer plunger channel compresses the spring less, resulting in a softer feel

New files:

• Body_8mm_Stem_3xBearings.stl

• Body_9_5mm_Stem_3xBearings.stl

• Tension_Plunger_3xBearings.stl

All other parts (M3 knob) are shared between both versions. No preload plug needed for the 3-bearing version — trim coils for a softer spring, or add washers/spacers inside the plunger tube for a stiffer one.

A good starting point is an assortment kit like this Mardatt 240pcs spring kit on Amazon (15 sizes, OD 4–6mm, wire 0.3–0.5mm, lengths 10–50mm) — plenty of options to experiment with.

This is still experimental — I'd appreciate feedback from experienced Voron users on whether the 3-bearing version works better in practice, and on what spring works best for belt tension comparison.

🔄 UPDATE [Feb 5, 2026]: V2 Tension Plunger Available

Added Tension Plunger V2 for use with standard compression springs (inspired by Diyshift's GT2 Belt Tension Meter).

V2 Simplifications:

• ✅ Works with Amazon spring kit (credit: Diyshift)

• ✅ No preload plug needed

• ✅ Self-adjusting tension (optional: add washers inside plunger tube if more tension needed)

• ✅ Rear screw (under dial indicator) now acts as spring guide only - use M3x20-22mm BHCS wrapped in heat shrink to prevent spring catching on threads

Spring Specifications for V2: Compression Spring, 304 Stainless Steel, 6mm OD, 0.6mm Wire, 50mm

Which version:

• V2 Plunger → Standard compression springs. Rear screw = spring guide (wrap with heat shrink)

• V1 Plunger + Preload Plug → Pen springs or custom springs. Rear screw = tension adjustment

New file: Tension_Plunger_V2.stl

🚧 Development Status: Fresh Release

Full Disclosure: This is my take on a belt tension comparator. The photos and video illustrate the working prototype. You might notice in the footage that I was missing the proper flanged bearings (F604ZZ) and used a temporary improvised spring.

Rest assured: The STLs provided here are the Final Version (v1.0) with all necessary corrections for the flanged bearings and tolerances. I will update the gallery with "clean" photos of the final assembly as soon as my hardware arrives.

📹 [Watch it in action]

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## Overview

This tool is a Belt Tension Comparator designed for Voron printers (2.4, Trident) or any CoreXY system using 6mm or 9mm belts.

Unlike standard gauges that rely on the variable tension of a printed spring, this tool is designed to transfer a known tension reference (gravity) to your printer belts. It utilizes a stacked bearing design to minimize friction.

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## Design Features

- Stacked bearings (F604ZZ + 604ZZ) create a ~7-8mm tall roller surface

- 6mm belts run entirely on bearings with no plastic contact

- 9mm belts are fully supported across their width (minimal edge overhang)

- Minimizes friction and prevents belt edge deformation

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## Method of Operation (Calibration)

Since internal spring constants vary, this tool must be calibrated against a known weight before use:

1. Reference: Hang a known weight (e.g., 1.5kg or a 1.5L water bottle) on a vertical spare belt

2. Zero: Attach the tool to this belt and rotate the dial bezel to read "0"

3. Transfer: Move the tool to your printer's belts. Adjust the printer tensioners until the dial reads "0"

This method uses gravity as a constant reference, eliminating errors caused by spring tolerances.

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## Bill of Materials (BOM)

### Bearings & Main Components

1x Dial Indicator

- Model Used: Designed for SPI 20-700-1 (or similar Imperial standards)

- Stem Diameter: 9.5mm (3/8 inch)

- ⚠ IMPORTANT: This design uses a 9.5mm mounting hole

- Note for Metric Users: If you have a standard 8mm dial indicator, you will need to print a small adapter sleeve (bushing) or wrap a layer of tape around the stem to fit the 9.5mm hole snugly

Bearings:

- 3x F604ZZ Flanged Bearings (Bottom of stack)

- 3x 604ZZ Plain Bearings (Top of stack)

Spring:

- 1x Spring (Standard ballpoint pen type)

### Hardware (Screws & Nuts)

M4 System (Bearings):

- 2x M4 x 18mm BHCS (For the two stationary posts)

- 1x M4 x 12mm (Preferred) OR 14mm BHCS (For the center moving piston)

- 1x M4 Washer

- ⚠ CRITICAL: If you use the 14mm screw for the center piston, you MUST use the washer under the screw head. Without it, the screw will go too deep and drag against the main body

- 3x M4 Nuts (Captive)

M3 System (Mechanism):

- 1x M3 x 22mm BHCS (For the Tension Knob/Plunger)

- 1x M3 x 18mm BHCS or SHCS (For the Dial Indicator Clamp)

- 1x M3 x [10mm - 20mm] SHCS (For Preload Plug - length depends on desired spring compression)

- 3x M3 Nuts

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## Print Settings

- Material: ABS or ASA

- Perimeters: 4 (Recommended for rigidity)

- Infill: 40% (Grid or Cubic)

- Orientation: Print flat on the bed. No supports required

- Brim: Recommended ONLY for the M3 Knob (due to small contact area)

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## Assembly Tip

The movement of the central piston is critical. Even perfect prints can have tiny layer inconsistencies.

Recommended Step: Before assembly, lightly sand (lap) the flat sides of the Piston part.

- How: Place a sheet of fine sandpaper (400+ grit) or use a flat sharpening stone on a table

- Action: Rub the piston sides gently against it a few times to smooth out any layer lines or "elephant foot"

- The Goal: The piston should slide inside the Gauge Body channel freely, with absolutely no resistance or binding

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## Files

- STL: Includes the main body, lever, preload plug, and the M3 knob

- STEP: Assembly file included for remixing or modification

(The included knob is part of the "PlasticLamp" collection. If you require a different shape or size, other M3 variants are compatible)