Choices of boat styles and knife angles for fullest range of capabilities
Consider new boat styles that are now available since the last time
you might have ordered a knife!
SPI Supplies offers three different types of diamond knives (life science,
materials science, light microscopy/histology) and six different boat
styles. For most ultramicrotomy applications the standard life science
diamond knife in the standard boat (Style S) is the preferred combination.
For those cutting hard materials, be they hard because they are hard
materials science samples, or hard because they are hard tissue materials
such as bone, teeth, or cartilage, the SPI Supplies materials science
knives should be selected. Or for work at the LM level, the "light
microscopy" knife should be selected. And for some very specific
applications, such as cryo sectioning, one might want to select a diamond
knife and boat designed specifically for that application.
There are two angles important in selecting and using diamond knives, the
included angle and the clearance angle.
The included angle is measured between the two facets that form the
knife edge. The standard included angle in SPI Supplies diamond knives is
45° which is what is used for routine sectioning. Optional angles are
35° and 55°. Or just about any other angle desired can be special
ordered with no additional cost. Just tell us your needs and we can usually
produce just about anything needed.
A 35° included angle is the angel of choice when any kind of deformation
(e.g. compression effects) must be kept to a minimum. A good example would
be those researchers needing the very highest quality of a result. However,
like with everything else in life, with diamond knives, there are also
trade-offs. The lower angle, in addition to making the edge far more
fragile, also results in a noticeably faster wear rate, meaning that the
knife will have to be resharpened more quickly. The larger angle 55°
is recommended when one is sectioning the very hardest of materials and
they want to have longer knife longevities. However, as the angle becomes
more and more "blunt"one also experiences more distortion and compression
effects, often times even leading to an over all inability to cut
samples with 55° edges that could be easily cut with 45° edges.
One final comment and that is that at times, certain hard materials that
can not be cut with a 45° included angle can be cut with a
35° knife. However, again it is a matter of trading off since the
35° will surely wear out very quickly. However, for some really
important and high priority samples, that price might not be too high
to pay in order to get any results at all, especially if one is
contemplating the use, to study the sections, on a $500,000 to $1,000,000
instruments!
The clearance angle is the angle between the back diamond facet
and the block face in the ultramicrotome. SPI Supplies diamond knives,
as a consequence of the use of the new laser alignment technology,
exhibit perfect alignment with the back plane of the boat. The actual
clearance angle during sectioning, therefore, is the angle actually
called for on the ultramicrotome angle setting. The suggested clearance
angle, for optimum results, is usually 4° or 6°, and is indicated
on the name plate on the knife and also on the quality certificate. One
can use clearance angles outside of this stated range, in order to realize a
broader range of sectioning conditions, however, for angles larger than
10° we would urge caution since such an angle could result in
excessive stress on the edge, thereby damaging it beyond repair. Angles
less than 2° would similarly be not advised because of
the danger of the knife rubbing against the block face resulting in
uncontrollable knife "chatter".
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Monday December 01, 2008
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