Shredder
Shredders are spinning blades in Portal 2 that destroy objects and players dropped into them. They function just like pits and slime, but are factory themed.
Creating Shredders
1. Create a long, thin brush. Tie it to a func_rotating entity with the following settings:
Property Name Value Name shredder1_left_axle Blocking Damage 500
2. Create another long, thin brush. Tie it to a func_rotating entity with the following settings:
Property Name Value Name shredder1_right_axle Blocking Damage 500
3. Create a prop_dynamic_override entity with the following settings:
Property Name Value Name shredder1_left Parent shredder1_left_axle World Model models/props_gameplay/shredder_left_b.mdl
4. Create a prop_dynamic_override entity with the following settings:
Property Name Value Name shredder1_right Parent shredder1_right_axle World Model models/props_gameplay/shredder_right_b.mdl
5. Position the props so that the teeth interlock and the brush entities are in the center of their respective props.
6. Create a 256x1024x128 brush where things would fall into it. Tie the brush to a trigger_hurt entity with the following settings:
Property Name Value Name shredder1_trigger_hurt Damage 500 Damage Cap 500 Damage Type CRUSH
7. Create a brush in front of that brush and tie it to a trigger_multiple entity with the following settings:
Property Name Value Name shredder1_dissolver Delay Before Reset 5
and the following outputs:
My Output Target Entity Target Input Parameter Delay Only Once 
OnTrigger !activator Dissolves 0.00 No
8. Create another brush in front of that brush and tie it to a trigger_multiple entity with the following settings:
Property Name Value Name shredder1_destructor Delay Before Reset 5
and the following outputs:
My Output Target Entity Target Input Parameter Delay Only Once OnTrigger !activator SelfDestructImmediately 0.00 No
9. Create a logic_relay with the following settings:
Property Name Value Name shredder1_relay_on
and the following outputs:
My Output Target Entity Target Input Parameter Delay Only Once OnTrigger shredder1_trigger_hurt Enable 0.00 No OnTrigger shredder1_dissolver Enable 0.00 No OnTrigger shredder1_destructor Enable 0.00 No OnTrigger shredder1_axle_left StartForward 0.00 No OnTrigger shredder1_axle_right StartForward 0.25 No
10. Create a logic_relay with the following settings:
Property Name Value Name shredder1_relay_off
and the following outputs:
My Output Target Entity Target Input Parameter Delay Only Once OnTrigger shredder1_trigger_hurt Disable 0.25 No OnTrigger shredder1_dissolver Disable 0.00 No OnTrigger shredder1_destructor Disable 0.00 No OnTrigger shredder1_axle_left Stop 0.00 No OnTrigger shredder1_axle_right Stop 0.25 No
11. Create a func_instance_io_proxy with the following settings:
Property Name Value Name shredder1_proxy
and the following outputs:
My Output Target Entity Target Input Parameter Delay Only Once OnProxyRelay1 shredder1_relay_on Trigger 0.00 No OnProxyRelay2 shredder1_relay_off Trigger 0.00 No
12. Trigger OnProxyRelay1 on shredder1_proxy to turn the shredder on and OnProxyRelay2 to turn the shredder off.