Three men who bought machetes and built practice bombs ahead of a planned Christmas Day slaughter at Federation Square have been jailed for decades over the foiled plot.

Ahmed Mohamed, Abdullah Chaarani and Hamza Abbas are three of four men convicted over the plan to behead people and set off bombs in 2016.

Hamza Abbas, Ahmed Mohamed and Abdullah Chaarani arriving to the Supreme Court on Friday. Credit:AAP

The fourth is Hamza Abbas' older brother Ibrahim Abbas, who is serving up to 24 years after pleading guilty to the plot last year.

The group had bought machetes and built practice bombs ahead of their arrest, just three days before Christmas.