On Tue, 09 Aug 2011 14:13:28 -0500, Karl Townsend
wrote:

My "fill in" project for the summer has been a ball screw and air
cylinders for my knee on the Excello CNC mill. Still got several parts
to fabricate but I was close enough to fit it all together today to
check for problems.

I found a good one. Drop the air and power to servo and the table
drops like a rock. I knew it would go down, but the speed was totally
unexpected. I'm going to need to add some sort of "dead man" brake to
the servo. That is, drop power and the brake closes.

Any good suggestions for what to use? Keep in mind I'm a cheap skate.

Karl

I've used this type of brake sandwiched between a servo and an
overhauling load in a situation similar to yours. Warner Electric and
Electroid make similar brakes, but they're much (like 2 or 3X) more
expensive. You do have to consider how to coordinate application of
the brake with both intentional and unintentional loss of motor
torque.
http://www.ogura-clutch.com/products...y=2&product=61

--
Ned Simmons