On Tue, 09 Aug 2011 16:28:42 -0700, Larry Jaques
wrote:

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.

Got an extra air cylinder? Fab up some brake shoes with discarded
disc brake pads and spring-load them to clamp on the ball screw by
default. When air is applied to the servo, it's applied to the spare
cylinder which opens the brake. Kill the air and the brake
auto-engages. A 1/2" stroke cylinder would do it.


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

Aye, iffen it's cheap you'll be wantin', laddy, just keep a pair of
vise grips handy.

I may just use a variation of the vise grip. Tighten gibs as soon as
move complete, Just put an extra limit switch on this. But, it makes
machine a one man show, nobody else could run it.

Karl