Motor shaft extension / camera Timelapse slider

https://drive.google.com/file/d/1xkvHfgUELyxdR4SBIGBQDutaWTCOMTbI/view?usp=drivesdkHi all,

im doing my first DIY/open builds project for this camera time lapse slider and everything is taking good shape, however, the motor I got has a shaft that is JUST too short for the rail and the belt rubs against it so I was wondering if there was a way of extending it.

The motor also has a small thread in the shaft, not sure if that helps, looks like 4 or 5mm.

The pulley is a 30-tooth from openbuilds.

Attached is a photo of what I’m describing, from the hole missing the set-screw you can see that the shaft doesn’t go all the way, and that the belt is making contact with the rail.

p