[Histonet] cutting angle

[Alan Bright]

Dorothy,

I will try. I am saying when the angle indicator on the knife holder is at 0º on the specimen side of  a standard 'c' profile knife, the knife is at 0º. As most knives are sharpened with a 5º to 7 1/2º facet angle would then say on a 5º facet angle that you could section with a clearance angle of 3º with the knife set at 8º using the angle indicator  on the knife holder. If the knife has been stropped which  would increase the knife facet angle then this would have to be allowed for by increasing the angle indicator on the knife holder by another 2-3º. Disposable blade holders are manufactured with an offset angle built in and will section with the angle indicator on the knife holder set at 3º to 7 1/2º. This is the main point, it would be very beneficial if all manufacturers used the same angle indicator on their knife holders, as inexperience users having an issue with knife angle settings would be able to indicate when asking for assistance what true angles they are using. Disposable blades could have a fixed angle set as there is no variation between blades purchased from a single source, but experienced users would argue that being able to adjust the angle for different types of specimens and perfection is desirable and I tend to agree. The main results to look for is if the angle is to steep then you will get no sections for awhile and then a very thick section as the specimen is hitting the base of the facet and compressing the specimen to a point where eventually the specimens compression is so great it will spring forward and be forced into cutting a thick section or forcing the specimen from the object holder.  If the angle it to wide you will get chatter on the specimen face as the knife edge is just scrapping the specimen face. Taking into account that the knife or blade is sharp.

A cold mirror could be used to view the specimen/knife interface in a cryostat.

Orientation of the specimen face is very important but not an issue I wish to cover in this email.

The last part of your email is the hardest to answer, as I would have thought by now you should have had no problems setting up knife angles, but hopefully what I have written above may help. 


Best Regards

Alan Bright

Bright Instrument Co.Ltd.
St Margaret's Way
Huntingdon
Cambridgeshire
PE29 6EU
England

Tel No:+44 (0)1480 454528
Fax No:+44 (0)1480 456031
Email: abright <@t> brightinstruments.com
Web Site: www.brightinstruments.com
 
-----Original Message-----
From: Traczyk7 <@t> aol.com [mailto:Traczyk7 <@t> aol.com] 
Sent: 04 May 2005 22:07
To: Alan Bright
Cc: HACKERLAB <@t> aol.com; histonet <@t> lists.utsouthwestern.edu
Subject: Re: [Histonet] cutting angle


Hi Alan,
Help me out here, are you saying that the knife gauge angle and clearance angle are the same?  If not, then does it really matter that the gauge markings are accurate?   Setting a 1 to 3 degree clearance angle is still a problem.  Can't very well stick my head in the cryostat chamber to view the block/knife interface from the end.  And of course there is then the problem of the bevel angle of the blade varying between manufacturers.  Also, you mentioned "flat" specimen face but wouldn't having the block parallel to the knife edge be important also?
I have successfully set up many cryostats, in this life and in my past lives as both a rep and a tech.  I have never been able to determine a universal method for adjusting knife angle but welcome any advice that will make me look brilliant to my customers. Thanks, Dorothy