Van Norman Flywheel Grinder Uneven Grinding Force Problem

An occasional complaint about both the FG5000 and FG10000 Model Flywheel Grinders is that while grinding, the motor will "drop" or feed-in aggressively all by itself.  There are four possible reasons for this behavior...

1) Backlash at the Handwheel (rare) - this 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 Loc-tite added to help it retain the adjustment.

2) Feed Nut out of Adjustment (most common) - perform the split brass feed nut adjustment procedure.  Make sure that the feed screw threads are lubricated with the correct lubricant.


a) Power Column Procedure - Lower Column to the lowest point. While raising the column, tighten the hex-key screw in the top of the leadscrew 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 leadscrew 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 tightens 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.

3) Burrs or Scores in the Guide Rods (rare) - 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.

4) Worn Feed Screw  - the feed screw threads may be worn.  Check the condition of the threads and replace if needed.  If you replace the feed screw, the best practice is to replace the nut and the key also. 

Understanding how it works

When being moved down the lead screw nut is in a fixed vertical position and the lead screw is rotating in the nut to force the lead screw (and column) downward.  The nut is pulling the column down.  The column wants to travel down due to the sheer weight of the grinding head. But during grinding the stone and flywheel cause resistance to this downward movement. The lead screw applies added downforce by pulling up on the nut.  When the lead screw slips the threads in the nut it happens quite slowly and is almost unnoticeable because of the desire for the column to move in the down direction (it's heavy), but a few seconds after the threads slip, they once again grip the screw well and this then drives the head downward with what seems like additional force.  And then they start the slow process of stretching and slipping over again.  

The reality is that during the moment of what sounded like a dropped head it was actually grinding with the desired downward force and then began the process of slipping again.  When you hear it your brain thinks the opposite is happening, that the head is falling into the flywheel, but really it's the auto-grind motor finally getting purchase on the leadscrew nut and forcing the head down on the flywheel like it should have been doing all along.

As always, if this information does not solve your problem you can call 800-553-5953 for assistance from Irontite during normal business hours.