On Thu, 31 Jan 2013 09:20:28 -0800, wrote:

I am working on a 5th axis for the mill. I think it will need a brake.
I'm not sure if the servo motor will be able to hold position for some
operations. I have looked at magnetic particle brakes and they ain't
cheap. So I'm thinking about making one. Or some type of
electromagnetic brake. The brake, when actuated, must not cause any
motion of the axis, and I'm just not sure what would work best.
Eric

I've had several occasions to put brakes on servos, and a couple where
it was important not to disturb the position. It's not as easy as it
sounds, depending on what "any" in "must not cause any
motion of the axis" means. The fussiest one I did involved locking a
table on a direct drive servo on a machine to dril tiny radial holes
in a part. It took a couple tries to get the disturbance under a few
tenths. The final design was a disc brake with the pads mounted on
flexures (flexure = zero free play) and actuated by an air cylinder.

--
Ned Simmons