How to effectively use the saw to open deposit boxes and doors?

The tips I can give you is to bring 2 bags of ammo along with you aswell for the bank job. Also don't place an ammo bag to soon because with the low effectiveness of the saw you are surely going to need it the 2 ammo bags to get through all the lockboxes. Edit: Taking ammo from the ammo bag also refills your blades.

Just set them up and keep on sawing, the saw system is also abit lacking in that you have to aim it correctly to actually open the boxes. You need to aim at the right hand side of the boxes and use the saw like you would use an automatic gun, you need to burst fire. Because any additional hits against anything (in the air you don't lose your 'ammo') will take away the 'ammo' for the saw.

Just gently tap fire 2 times on deposit boxes and exteriors of ATMs, 5 times on metal doors. Don't waste blades on wooden doors, just shoot the doorknob in, and carry as much ammo as you can, including both the ace of the original skill (allows for one extra blade).

Use the skill above granting 20 percent harder blades (I don't know if the 25 percent extra ammo skill affects saw blades, however). It's really only useful in the bank, personally I reskilled myself in technician. Shaped charges are better for getting through doors and you can carry a gun that actually kills enemies at distance.

Click, do not hold. If you hold you could accidentally use the blade once. Two clicks for deposits, about five for doors, and two to open ATMs.