Correct setting of Bedknife Zero Reference by the Scratch Method

Posted on June 11, 2014 at 3:45 PM

Carl Nurse, Technical & Development Manager at Bernhard has been with the company for for almost two decades, so there isn't much he doesn't know about our product range. In this short series of technical guides Carl looks at a number of tips and tricks that even the most seasoned Bernhard user may not be aware of.

Most of our Anglemaster users are completely familiar and comfortable with the principle and use of our ‘scratch’ method to establish the zero reference from which to grind bedknife (bottom blade) angles. On occasion however we get a call from a user with concerns over the angles being ground and it becomes apparent that the method is not being applied correctly…

When the scratch is taken across the top face of the bedknife by the face of the grindstone, is should be across the WORN part of the blade, that area close to where the cut occurs, where grass and debris has passed or, dare I say, contact may have occurred. This may only be a narrow band but it is this area that establishes the zero angle passage of the reel (cylinder) blades. Where problems appear the scratch is often taken incorrectly, across what remains of the previous grind or original angle ground of the top face of the bedknife. If this is set as the zero datum the angles ground relative to this will be incorrect with various possible results:

  • Quality of cut may be affected.
  • Grinding may take longer as more/too much material may be removed.
  • Bedknives may not last as long.
  • Subsequent grinds will mean the top face angle gets steeper and steeper until the digital setting procedure on those Anglemasters to which it is fitted will not allow a zero datum to be set (This is the point where a call to tech support may suggest that the applied setting practice has been incorrect).

A simple explanation usually can re-establish correct practice and rectify a problem. Where a user is really struggling to see the wear pattern they may find it easier to use the approach as applied to the first grind of a new blade:

  • Take the scratch across the remaining/original ground face.
  • Press the datum/zero set button and hold it pressed then use the +/- keys to change the value from 0° to that angle required/originally created by the manufacturer before releasing the zero reset button. Where a protractor drum is used , rather than set the drum at zero to the pointer, set at the angle required/originally created by the manufacturer.
  • Grind the top face from this position after which the correct front face angle will be ground at the angle as displayed by the electronic display/protractor drum after mounting bar rotation.