# Power-off safety braking



## Dale_Mahalko (Mar 26, 2016)

For people with epilepsy and other consciousness control disabilities such as narcolepsy, it is dangerous to have a seizure or loss of control when you're next to a running high-torque machine.

A deadman's switch that must be squeezed or pressed to keep it running is a good idea to stop the machine, but it may still take several seconds for heavy rotors and spinning loads to coast to a stop.

There is a safety device called a power-off brake, which is electromagnetic. When powered, the brake is disengaged and the device operates normally.

When power is cut, springs engage the brake to rapidly stop the equipment. Depending on how strong the brake is, this can provide up to nearly instantaneous stopping of the load, to render it safe as quickly as possible.

There are also combination clutch-brakes, so that the load disengages from the power source, reducing the amount of mass to be halted by the brake.

I have no idea on the costs, but it seems worth researching as an add-on machine tool safety measure.

One example Google search result for this:
http://www.warnerelectric.com/power-off-brake-products.asp


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## Nick Hulme (Mar 30, 2016)

If you are running a machine with a 3 phase motor and a decent inverter you have DC-injection braking and external resistor braking options, they can be stopped really quickly, don't forget that a chuck or a blade held by a thread which tightens up under load can spin off under heavy braking and can end up anywhere, or everywhere at once in your shop ;-) 

 - Nick


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## Wizard69 (Apr 1, 2016)

Brakes can enhance safety but as alluded to above they can cause things to come loose. In fact on my 9x20 I've had the chuck come loose under a normal power down.  This is why I've suggested to people new to machining to look for a lathe without a screw on chuck.   It is just safer and arguably  more versatile to have a bolted on chuck, cam lock or something similar.  

In industry we use lots of clutch brake assemblies, usually for faster cycle times, but those are mostly air operated.   They certainly have their good points.


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