TRIMMING BLOCKS WITH LKB (LEICA) 1 MICROTOME

• Turn on power and diffuse light with toggle switches on control unit.
• Make sure Mode of Operation knob is in manual position.
• Place specimen block in chuck and tighten chuck with hex key.
• Place chuck in holder and tighten screw on bottom of holder.
• Adjust angle of chuck in holder if desired by loosening screw on side of holder.
• Place holder in slot on specimen arm and lock into position with lever on top of specimen arm.
• Place glass knife in knife holder and secure with top screw on right side of holder.
• Adjust knife to appropriate angle by loosening screw on left side of knife holder and moving holder toward or away from you until angle scale on right side of knife holder is set desired angle (usually 2-5° ).
• Rotate knife holder until knife is parallel to arm.
• Release arm by moving lever on left side on microtome from locked to free position (toward back of microtome).
• Adjust binoculars and light.
• Binoculars should be set at the lowest magnification and focused on block when block is level with knife edge.
• Light should be pulled toward front of microtome until it is shining on the block face when block is level with knife edge.

Block Trimming

• To trim face of block:
  • Holding block at level of knife, move knife toward block by turning the macro feed knob (back knob, right side of microtome) clockwise toward back of microtome.
  • Move specimen past knife by pushing down on specimen arm and then returning arm to upper position above knife.
  • Advance knife by turning the macro feed knob clockwise a short distance.
  • Continue until excess plastic has been removed from block face and area of the specimen to be sectioned has been exposed.
• To trim left and right sides of block:
  • Move knife away from specimen by turning macro feed counter-clockwise.
  • Rotate knife holder so that the knife approaches block at an angle.
  • Tilt upper edge of block toward knife by unlocking and rotating chuck holder toward knife.
  • Adjust knife position with lower screw on knife holder until edge of block is roughly at center of knife.
  • Trim block edge by moving specimen past knife and advancing knife toward block with macro feed until block face is reduced by desired amount.
  • Move knife to opposite side of block an equal distance past horizontal and rotate upper edge of block toward knife.
  • Repeat procedure to trim other edge of block.
• To trim top and bottom sides of block:
  • Move knife away from specimen by turning macro feed counter-clockwise.
  • Rotate head so that block is positioned at 90o angle to original position.
  • Rotate knife to one side of block as above, but do not rotate block toward knife.
  • Move knife toward block and adjust knife position with lower screw on knife holder until edge of block is roughly at center of knife.
  • Trim one edge of block as above.
  • Move knife away from specimen by turning macro feed counter-clockwise.
  • Rotate knife to other side of block and adjust knife position and distance from block . Do not rotate block toward knife.
  • Trim remaining edge of block. Turn block 90° to initial position.
  • The top and bottom edges of the block should be parallel to each other and to knife edge.
  • Rotate knife holder to horizontal position so that knife is parallel to block face.
  • Remove knife from holder.
  • Using brush or canned air, dust plastic shavings from microtome.

   

• Notes on trimming:
  • Amount of trimming depends on size of section desired.
  • In general, the smaller the block, the easier it will be to section.
  • The most desirable block face does not exceed 0.5 mm.
  • The above procedure yields a block in the shape of a trapezoid.
  • The top and bottom edges of the block must be parallel.
  • The left and right sides of the block are angled so that the top edge is shorter than the bottom edge.
  • It will be necessary to use several glass knives during the trimming process.
  • Change knives when they develop deep nicks or become dull so that it is difficult to force the knife through the block.