Summary

You can find the official BI V2.5 Belt Conversion Kit here. My kit was designed before Boots Industries decided to offer a belt upgrade.

This is a conversion from string (fishline) to belt for the BI V2.5 from Boots Industries.

https://www.youtube.com/watch?v=FteUXxGRRuA
https://www.youtube.com/watch?v=MjtJLVtaFhU

Instructions

BOM

(for one tower)
1 x 16 Teeth GT2 Pulley
2 x M3 4mm Grub Screw
1 x 212cm GT2 Belt
4 x F605ZZ bearing
2 x M5 25mm
2 x M5 Nyloc Nut (or self locking)
5 x M3 10mm

PRINTING

All parts are printed in ABS, 0.2mm height, 3 perimeters thick, 100% infill (except the carriage addon, I've printed it down to 20%, strong enough, faster).

Carriage addon

This was using a 0.35mm nozzle. The belt tensioner is a little tricky to print, the ratchet teeth and belt grooves are so small, have to slow down the print to 10mm/s for their layers. This part put my little Prusa i3 to its limit.

Belt tensioner

TOP PULLEY IDLER

I originally used the existing printed bearing spacers (in red in the photo below), but I discovered that they interfere with the bearing, making it harder to spin, so I included my own spacer, more accurate.

The actual pulley is just press fit.

Top pulley idler

You'll need to cut the original bolt flush to the nut. There are seats for the nut and the round head bolt.

Top pulley idler nut cutted

Before inserting the top pulley assembly on top, be sure to clear the endstop's cable, so it'll not touch moving part, or interferes.

Endstop cable

BOTTOM PULLEY

The motor needs to be unmounted to add the flanged bearings holder. See instructione here for removing the original pulley.

Use the M3 10mm screws for fastening the bearing holder in place, and M5 25mm with Nyloc nuts for the bearings.

Bottom pulley

Just align the 16 Teeth GT2 Pulley with the flanged bearings.

Bottom pulley alignment

CARRIAGE ADDON

You'll need to remove the original flag first, it was glued in my case, so I had to break it.

Removing the flag

You can reuse the flag if it's still in one piece, or use the one provided here.

Reuse Flag

Just clean the parts where the surfaces come in contact. Use the existing screws (the ones for tightening the strings) to anchor it to the original carriage, the 10mm M3 on the bottom end, the 20mm on top.

Assembling the ratchet and belt anchor is straightforward. Once the belt is attached to the carriage side, pass it through the lower and upper pulleys, then use the ratchet to fix it in its final position.

Ratchet

You can use small clamps to help mounting the belt.

Clamp

FIRMWARE

Since the new pulley doesn't have the same diameter, the steps/mm needs to be readjusted. There is various ways to update the value: in the source code for recompilation, from the LCD menu or in the host EEPROM feature. I'll cover only the firmware code update, as you should already know how to do it in LCD or host.

Belt vs cable pulley

The 16 Teeth GT2 Pulley gives me exactly 100 steps/mm.

Marlin
Open the Marlin.ino file with the Arduino IDE, locate the defines below in Configuration.h and change accordingly:

#define DEFAULT_AXIS_STEPS_PER_UNIT   {100,100,100,291}

The first 3 values in the array define the X, Y and Z motor steps per mm respectively. The last value is for the extruder.

Repetier

Open the Repetier.ino file with the Arduino IDE, locate the defines below in Configuration.h and change accordingly:

#define XAXIS_STEPS_PER_MM 100.00  #define YAXIS_STEPS_PER_MM 100.00  #define ZAXIS_STEPS_PER_MM 100.00

Enjoy your new belt driven printer!

BI v2.5 String to Belt Conversion