I would think that DC braking parameters on a mill would not be as critical to set up as they are on a lathe. The mass of the load should be pretty constant - just a few different bits - end mill, face mill, fly cutter. But I do understand the theory of "it works for me so I'm leaving it alone!" I am an electrical engineer for the last 49 years. I was doing analog and logic design back before the microprocessor era. I would not need any luck to complete the circuit board - just motivation! 
Once I understood how the braking parameters changed in relation to the load, I was satisfied that I had it set up as best I could do. Although I have the components here in a drawer, I realize that there is no room inside the unit to add another circuit board with a heat sink on it. An external setup would look pretty bad so the cost/benefit was not overwhelming. An alternative braking setup would be to use the "coast to stop" setting along with a relay to put the resistor across two of the 3 phases to the motor. I would bet that it would stop the motor in about 2 or 3 revolutions. While pursuing that idea, I though about the screw on chuck on my southbend. Stopping that quickly with a screw on chuck could be a real adventure.
An engineer buddy of mine that is a woodworker uses dynamic braking on all of his "spinning" stuff - Saw, sander, planer, etc. His saw stops in about a quarter second. The motor really groans when he shuts it off. He uses water heater elements as resistors. He gets them at the dump! My little 300 watt resistor pales in comparison to his multiple kilowatt ones! He also gets his heavy duty braking relays at the dump from old AC units. He proudly claims that the "life cycle cost" of his braking system is "0". Although it seems like a bit of overkill to stop so quickly, his claim is that most bad things happen when the blades are spinning down. I have tossed a few pieces of wood with my table saw when I got too anxious and tried to move the piece before the blade had stopped.
My mill is a Grizzly G0695. It has a built in VFD. The rpm is limited to 2250. I have some small end mills that I would like to run faster than that. I have the vfd manual but have not changed anything as yet. One of these days I will make the changes to the unit and probably destroy the bearings in the motor
Once I understood how the braking parameters changed in relation to the load, I was satisfied that I had it set up as best I could do. Although I have the components here in a drawer, I realize that there is no room inside the unit to add another circuit board with a heat sink on it. An external setup would look pretty bad so the cost/benefit was not overwhelming. An alternative braking setup would be to use the "coast to stop" setting along with a relay to put the resistor across two of the 3 phases to the motor. I would bet that it would stop the motor in about 2 or 3 revolutions. While pursuing that idea, I though about the screw on chuck on my southbend. Stopping that quickly with a screw on chuck could be a real adventure.An engineer buddy of mine that is a woodworker uses dynamic braking on all of his "spinning" stuff - Saw, sander, planer, etc. His saw stops in about a quarter second. The motor really groans when he shuts it off. He uses water heater elements as resistors. He gets them at the dump! My little 300 watt resistor pales in comparison to his multiple kilowatt ones!
He also gets his heavy duty braking relays at the dump from old AC units. He proudly claims that the "life cycle cost" of his braking system is "0". Although it seems like a bit of overkill to stop so quickly, his claim is that most bad things happen when the blades are spinning down. I have tossed a few pieces of wood with my table saw when I got too anxious and tried to move the piece before the blade had stopped. My mill is a Grizzly G0695. It has a built in VFD. The rpm is limited to 2250. I have some small end mills that I would like to run faster than that. I have the vfd manual but have not changed anything as yet. One of these days I will make the changes to the unit and probably destroy the bearings in the motor
