Felt the need for further comment about blade angle with older AO 820
microtome. 

You wrote:  "It is correct that the blade holder is permanent and the only
way to adjust the angle is with the block holder".  

You do not adjust the blade angle i.e the cutting angle at the block holder
- block holder adjustment (the x/y axis adjusment) only provides is
orientation of block face to the blade which is set at its cutting angle.
Once block is trimmed and ready for sectioning,  you are locked into using
the cutting angle - determined by blade holder and bevel angle ON
disposable blade.  With today's tissue cassettes, block face adjustment has
become blessedly minimal - we only readjust block face for some block
recuts but we do change holder adjustments to accomodate the blade being
used. 

We found using old AO 820 blade holder that some brands of knives are
slightly different due to how they were manufacturered/treated.  Some
blades just work better than others in this holder, and you may have have
to try various brands.  Ask for samples if you experience too much
difficulty with any one disposable. blade. 

A significant reason why blade holders are now totally adjustable is
probably because the old holder WAS a permanent angle.  Microtomists still
need to refine cutting angles for any given blade use. There have been long
discussions about this on Histonet, check out archives.  One can use the
820 standard knife holder (for C profile steel knives), buy a disposable
blade insert to achieve fine tweaking of cutting angle. This may be
important IF one really dislikes or cannot work with old 820 holder. 

Have a good weekend after this long (whew!) lecture



Gayle Callis
MT,HT,HTL(ASCP)
Research Histopathology Supervisor
Veterinary Molecular Biology 
Montana State University - Bozeman
PO Box 173610
Bozeman MT 59717-3610
406 994-6367 (lab with voice mail)
406 994-4303 (FAX)



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