From scratch:

Diy brushless motor drill:

https://www.youtube.com/watch?v=zGdYtokAhIU

Repair a drill:

https://www.youtube.com/watch?v=IC70Ovn454Y

Diy sanding machine:

https://www.youtube.com/watch?v=hNMKMTpjoYQ

Electric air compressor/pump:

https://www.youtube.com/watch?v=xejZW-2ogQs

https://www.youtube.com/watch?v=fB0rBl5wlU0

AAA powerbank/backup supply:

https://www.youtube.com/watch?v=Ghs5kxjrhig

PVC mini drill/dremel:

https://www.youtube.com/watch?v=Pblh_A4mZfw

DIY miter saw:

https://www.youtube.com/watch?v=nnwndTDjeP4

Polishers:

https://www.youtube.com/watch?v=DRArvTsKDXw

Water Pumps:

https://www.youtube.com/watch?v=SDZ5hVuoXmY

Diy jigsaw:

https://www.youtube.com/watch?v=4TyCK_hLe18

Using other tools:

Drill powered circular saw:

https://www.youtube.com/watch?v=YJBuH6lVrEw

Miter saw from hand saw:

https://www.youtube.com/watch?v=EbVcWgUdKAk