What is really happening is not a drop, but rather a slip in the lead screw that controls the column. While grinding, the machine is actually pulling down on the grinding head, and when the leadscrew nut is out of adjustment or worn it will slip past threads while grinding. As it slips the downward force gets less and less and then once getting past the slip point it grabs fully for a short time and this is the aggressive-sounding grind action noticed by the operator. It's the machine doing catch-up after slipping the threads.
But there are other possible things that can cause this kind of behavior so let's just go through them all.
This backlash at the handwheel is caused by a worn key or keyway at the handwheel. Either the key or the part with the area where the key fits into (keyway) will require replacement. Also, the bear hug nut that is a Ny-loc thread used on the power column units only sometimes backs off its adjustment. It will need to be readjusted and Loctite added to help it retain the adjustment.
Perform the split brass feed nut adjustment procedure. Make sure that the feed screw threads are lubricated with the correct lubricant.
USE CAUTION TO AVOID PINCHED FINGERS OR CLOTHING BEING CAUGHT IN MOVING PARTS WHILE PERFORMING THESE STEPS
a) Power Column Procedure
Lower Column to the lowest point. While raising the column, tighten the hex-key screw in the top of the lead screw nut. Listen to the power column motor while tightening the leadscrew nut until you hear the motor begin to strain. Stop raising the column and back off the hex-key screw one-quarter turn. Your lead screw nut is now properly adjusted.
b) Manual Column Procedure
For Manual Column Machines, lower the column to the lowest point. While raising the column using the handwheel also tighten the leadscrew nut as described above for the power column. When the leadscrew nut has been adjusted to the point that significant drag occurs, back the leadscrew nut hex-key screw one-quarter turn.
Note: Do not attempt to reposition the hex-key wrench while the power column is moving. Instead, lower the column again then reposition the hex-key wrench and begin raising and tightening again. After installing a new leadscrew nut you may need to repeat this process several times until the nut is properly adjusted.
the head of the adjustment bolt may be gouging or digging into the guide rod which causes the column to hang up at the burr and then abruptly "drop". The burr should be removed and if severe, the rod or rods will require replacement.
the feed screw threads may be worn. Check the condition of the threads and replace them if needed. If you replace the feed screw, the best practice is to replace the nut and the key also.
As always, if this information does not solve your problem you can call 800-553-5953 for assistance from Irontite during normal business hours.
Making the best Valve Refacer for over 100 years.
Made in the U.S.A. and built to last generations.
Irontite Products Inc. professional diesel engine repair tooling for casting repairs, injector sleeve replacement, and cooling system additives.
When you need it to be IronTite!
Need to order supplies or OEM replacement parts?