Calling all gurus -  What is the best practice?

On Tool changers -

 Is it better to release the drawbar once when you drop the loaded tool, and only close it once the selected tool has been loaded?  or
 Is it better to clamp the drawbar once the current tool has been dropped, and releasing the drawbar again just before pickup of the selected tool?

I'm not sure how the commercial machines do it, but the way I programmed mine, the drawbar does not close between "put tool" and "get tool" commands. (your first scenario.)

My drawbar is pneumatic, so I have a pressure switch installed as an extra layer of safety (between the valve and the drawbar) in the event of an issue with the pneumatics.  For example, when the drawbar is activated, the SW checks that the pressure has actually gone up before moving the gantry.  I also have an indicator light on the panel to show the drawbar status.

Thanx for the reply - I currently have it the same. Was just wondering if there is a negative impact on the simple with more clamp and release, or is it better the actuate the drawbar less.  Pressure vs Wear And tear I guess

Drawbars stay open ready for a new tool during a tool change.
I don't know of any Machine Tools that come OEM with the drawbar closing once it releases a tool and awaits the next tool.