Today’s Machining World Archive: January 2007, Vol.3, Issue 01
Dear Shop Doc,
We usually run our Brown & Sharpe machines at cycles less than 30 seconds. I was setting a stainless steel job at 120 seconds and my turret would double index at times. One of my co-workers said to grind some height off the trip dogs. The shop foreman saw me grinding on the trip dogs and hit the ceiling! He said to adjust the backshaft clutches instead. When I asked him what to do, he just said “adjust the screw.” Which screw, what direction, how much? Help!
Your foreman is absolutely correct about not grinding on trip dogs. Never do that. All trip dogs should be at the same height.
When your backshaft clutch pocket and eccentric are in good shape and adjusted properly, the machine will not double index no matter what cycle time you are running.
The first thing to check is your eccentric screw (properly called the operating screw). If the edges are rounded or worn or the bottom of the screw is no longer flat, then replace it. They are cheap when compared to replacing the clutch. A worn screw will damage a good clutch pocket eventually.
Examine this first. Unfortunately, changing the operating screw will not solve your problem if your clutch pocket is overly worn. Look for wear in detent end. Test this by manually activating the clutch. If the pin drops back into the pocket, the clutch is worn and should be replaced. Again, keeping a good operating screw and proper adjustment will prevent premature clutch failure.
Adjusting the eccentric pin end of the operating screw attains the proper clutch tooth spacing. Do not adjust the spacing by adjusting the abutment screw. This is a common mistake.
Adjusting the trip lever stop screw sets the proper depth of the operating screw. This adjustment prevents the operating screw from contacting the bottom surface of the clutch pocket when in the “disengaged” position. Confused yet? It’s not that complicated. For complete instruction with diagrams on how to properly adjust your backshaft clutches go to www.servocam.com/helpdesk/. There you will find instructions for proper settings for both mechanical and air-actuated systems.
You will find the instructions on how to properly set your clutches to work with mechanical activation or air activation. The difference in the setting is noted in the instructions.
If you keep your operating screw in good condition and properly adjust your clutch assembly you will get years of continuous service from your machine without fighting index problems every time you change between a fast and slow cycle.
Vice President, AMT Machine Systems