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Changing the Express Dual Grinding Wheel – Important Care Points by Carl Nurse, R&D Manager.

Posted on October 14, 2014 at 12:00 PM

Once you have been shown how to change the grinding wheel (stone) on an Express Dual and have done it a couple of times it becomes a simple, second-natured process. However, with familiarity comes the possibility for even the best to miss a tiny detail that can result in a problem when grinding…

A call into Technical Support from time to time may be about a feed problem with the Express Dual. During grinding, we are told, the grindstone seems to increase contact with the cylinder or even ‘jump into’ the cylinder and this on a machine that has no automatic infeed! The hand wheels do not rotate and gravity pulls the weight of the grinding wheel stone carrier and shaft away from the cylinder, so what is happening? The first question we will ask is ‘Have you recently changed the grinding wheel? This may seem odd to ask but it is probably the route of the problem.

To remove the stone carrier (sleeve and nut) and change the grinding wheel the main shaft bearing is removed from the left hand end of the main shaft. The problem occurs upon reassembly. If the bearing is not put back in the same position on the shaft, the side arm to which the bearing is bolted may bind up in the slot of the feed column. The side arm will rub against the inside of the feed column and act like a brake. When the hand wheel is turned in use any display will show that the feedscrew position has changed, but all effort goes into compressing the spring within the feed column rather than moving the side arm and raising the shaft and grinding wheel. During grinding the movement from the impact grind overcomes the friction between the side arm and feed column and spring tension pushes the grinding wheel into the cylinder without any apparent operator input.

This problem might also be seen as an initial turn of the hand wheel failing to apply feed but further hand wheel rotation then resulting in the grinding wheel ‘jumping’ into the cylinder. The severity of the problem depending upon how much the side arm is binding.

This may seem an easy problem to create but it is just as easy to avoid:

  • Take careful note of where the bearing sits on the main shaft.
  • When the bearing is off, note if there are any raised ‘bruises’ on the shaft where the bearing grub screws were tightened. If the grub screw catches the edge of such a bruise when the bearing is replaced it might just move the bearing sideways a little. Carefully remove the raised ‘bruise’ with a file or abrasive cloth.
  • Once all is back together, lean or bounce on the top of the hand wheel or side arm to see that the side arm moves freely in the slot of the feed column and that the spring action is present.
  • Keep an eye on the inside faces of the slot in the feed columns - if rubbing is evident - check for free movement as above.

 

For additional information contact: support@bernhard.co.uk