Making glass knives with the LKB 7800,
Introduction,
Glass knives are used to make ultra-thin sections for electron microscopy but also semi-thin sections for light microscopy. Glass knives are made of specially selected glass and it is advisable to use only this type of glass. Usually available with a length of 400 mm, width of 25 or 38 mm and a thickness of 6.4 , 8 or 10 mm.
After cleaning the glass strip with e.g. Teepol, the strip is stretched in the LKB 7800 and glass squares are broken by zips with a cutting wheel. Then these squares are zipped diagonally and two knives are broken. A knife has a sharp side of high quality and a blunt side (foot).
Semi-thin sections (0.5 µm - 2 µm) that can be used for light microscopy can be cut with glass knives on an ultramicrotome e.g. Reichert-Jung Ultracut E, but also on a rotational microtome e.g. LKB 2218 Historange microtome.
This image report shows the manufacture of glass knives. A LKB 7800 'Knifemaker' and glass strips made by LKB are used. The formerly large Swedish brand LKB has been taken over by the company Leica. Leica still has the glass strips in her program as well as spare parts such as a set of cutting wheels, for the LKB 7800. The original LKB glass strips are still sold by, for example, science services in Germany. Link: https://www.scienceservices.eu/lkb-glass-knife-strips-ultramicrotomy-grade-various-thicknesses.html
All images can be enlarged by clicking on them.
A = Release button
B = Clamping lever
C = Bearing block
D = Clamping head
E = Zipper track selector
F = Guide plate
G = Support for glass strips
H = Marking point 200 mm
J = Break button
K = Zipper bar
L = Front glass holder
M = Front adjustment disc
N = 2 Glass breaking pins
O = Limit for 25 mm wide glass strips
P = Limit for 38 mm wide glass strips
Original box with glass strips from LKB. These strips are 400 mm long, 25 mm wide and 6.4 mm thick.
Glass strip 400 mm long, 25 mm wide and 6.4 mm thick.
Carefully rub the glass strip with cheap soap (soap without all kinds of additives) and wash and rinse thoroughly. Pay special attention to the sides of the strip because that is where the knife edges will be. Rinse with AD and dry with tissue. From that moment on, wear gloves to prevent the glass from becoming greasy again.
The yellow oval marks the 200 mm point.
Take a good look at the strip and see where the glass is broken (read glass).
Place the glass strip on the device with the breaking side facing down. Check that there are no glass splinters under the glass strip or support plate (G).
Press the glass strip against the guide plate (F) and lift the strip over the spring-loaded limiters (O and P) until the right side of the glass strip is at the 200 mm point.
Lower the clamping head (D) using the clamping lever (B) until it touches the glass strip (still holding the glass strip).
Lower the clamping head (D) using the clamping lever (B) until it touches the glass strip (still holding the glass strip).
Release the glass strip and tighten the clamping lever (B) until the strip clamps securely. Do not use force.
Set the zip track selector to #.
Pull out the zip-rod (K) with a smooth movement. The glass will now be zipped in with a small diamond wheel.
Pull out the zip-rod (K) with a smooth movement. The glass will now be zipped in with a small diamond wheel.
Slowly turn the break knob (J) clockwise until the glass breaks. Experts say that: "the slower the knob is moved, the sharper the fracture surface will become." Then turn the breaker back again.
See how this teacher explains 'slow breaking' at 9min 12sec. Video from Youtube: Link or click on the image.
Support the zipper bar (K) with your right hand and at the same time move the clamping lever (B) to the output position. This support serves to prevent the clamping head (D) from damaging the glass strip.
Support the zipper bar (K) with your right hand and at the same time move the clamping lever (B) to the starting position. This support serves to prevent the clamping head (D) from damaging the glass strip.
Push the zip-bar back into the starting position.
Remove both glass sections.
Creating squares: Lay a glass strip on the device with the breaking side facing down. Check that there are no glass splinters under the glass strip or support plate (G). Press the glass strip against the guide plate (F) and press the strip against the limiter (O) (see yellow arrow).
Lower the clamping head (D) using the clamping lever (B) until it touches the glass strip (press the glass strip against the guide strip (F)). Release the glass strip and tighten the clamping lever (B) until the strip clamps securely. Do not use force.
Leave the zip track selector (E) at #.
Pull out the zip-rod (K) with a smooth movement.
Pull out the zip-rod (K) with a smooth movement.
De ‘vork’ onder het einde van de glasstrip plaatsen.
Place the 'fork' under the end of the glass strip.
Slowly turn the break knob (J) clockwise until the glass breaks. Then turn the break knob back again.
Support the zipper bar (K) with your right hand and at the same time move the clamping lever (B) to the starting position. This support serves to prevent the clamping head (D) from damaging the glass strip.
Push the zip-bar back into the starting position.
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