Prusa Mk3 Y-axis belt tensioner V2 - GT2 20T w/ 5mm bore

Description

This is a Y-axis belt tensioner designed for standard gt2 20T or toothless idlers with 5mm bores.

The 3mm bore idlers that Prusa uses are difficult to find, so I created a remix of this model which supports 5mm bore idlers. Additionally, the 5mm bore idlers have dual bearings which results in a slightly better alignment of the belt and the idler.

Printers Supported:

- Prusa MK3 - Prusa MK3s - Prusa MK3s+

Fasteners:

- 2x M3x10 screw → frame mount - 2x M3 hex nut → frame mount - 2x M3 Nyloc hex nuts → tension adjustment - 2x M3x16 screws → tension adjustment - NOTE: the original design calls for 16mm, but I found 18mm worked better for me - 1x 5x22 mm cylindrical pin (ISO 8734 / DIN 6325) or 5mm screw - Pin is highly recommended (I used these rods and cut the 5mm to length with a dremel: https://amzn.com/gp/product/B08N4TSNPW) - You may instead substitute a M5 screw (22-25 mm) cut to length. Please note, this should work, but I have not tested the remix with a cut screw.

Print instructions:

- Material: PETG - Perimeters: 3 - Infill: 20-25% - Infill pattern: Rectilinear - Layer height: 0,15 mm - Supports: Supports from build plate only

Assembling:

Align the two dots printed on the exterior of the tensioner. Install the tensioner onto the frame with the dots facing down .

If the blue part is upside down the belt path will be wrong .

Tighten both screws equally as you tension the belt.

Setting belt tension:

I've found through trial and error as well as online research that the best method for tensioning the belt is to use a tuner app (e.g. pano tuner on iOS). You will use this app to tension the belt according to it's resonant frequency, similar to tuning a guitar. To properly set the belt tension, follow these steps:

- Ensure the room is quiet - Open the tuner app on your phone - Slide bed to the front and then push to the rear of the printer to reset the belt tension - Place the microphone near the center of the belt - Pluck the top belt like a guitar string - Note the frequency from the tuner app → target frequency: 90 - 110hz - Tighten/loosen the tensioner equally on both sides - Repeat starting at step 3 until the app shows 90 - 110hz as the frequency NOTE: 90hz is typically recommended as the target frequency, but I found this was too loose and causing some ringing on my printer. However, be aware that tight belts place more load on the stepper motors.