What Should The Blade Angle Be On My Microtome?

What should the blade angle be on my microtome? When I set the blade angle at one place on the marks of the blade holder, it works for company X’s blades. But I got some trial blades from company Y, and they wouldn’t cut a ribbon, until I changed angles. Why?

Think of it like the steering wheel in a car. What is the ONE correct height and angle? Doesn’t it depend upon the height of the person, the girth of the person, the make of the car, the angle of the seat, and what feels right (it works) for that person?

So the first thing to realize is that the marks on the side of the blade holder do not mean anything. They are simply reference marks. They do notindicate degrees of angles.

BEVEL ANGLE: Think of the shiny edge of the blade – the bevel. If you looked at it from the side of the blade, the bevel comes to a point, similar to a triangle. This is the bevel angle. If you are using a sturdier blade, the base of the triangle is wider across, so the bevel angle at the tip is a larger number, than if you were using a thinner blade, which is narrower across the base and thus has a smaller bevel angle. The thinner blade is less sturdy, so it can’t cut harder tissue, but probably gives you a nicer ribbon.

CLEARANCE ANGLE: The marks on the side of the blade holder are reference points for clearance angle. This is the angle between the front face of the block and the one side of the bevel triangle that is facing the block. Normally, this bevel angle should be between 3-8 degrees. The smaller the clearance angle, the sharper but less sturdy the blade is. Conversely, the larger the clearance angle, the sturdier the blade but less sharp it is. So the “correct” angle depends upon what type of tissue is being cut (need for sturdiness) and how thin the section needs to be (need for sharpness).

CHANGING ANGLES: Let’s say you were using a thicker, sturdier blade, with a wider bevel angle, and had set the clearance angle at 5 degrees. If you switched over to the thinner, sharper blade with the narrower bevel angle, but didn’t move anything else (didn’t move the angle), the new clearance angle would be wider, say 6 or 7 degrees, because of the thinner bevel.

This is what is happening when you change from one vendor’s blade to another. The bevel angle may not be exactly the same, so therefore the clearance angle is not the same as you were using. In addition, the height of the blade may not be exactly the same.

TO FIND THE BEST CLEARANCE ANGLE:

  1. Contact the manufacturers: Both the vendor who sold you the microtome and the vendor who wants to sell you their blades, want you to be able to microtome. Tell them the vendor microtome you have, and the vendor blade you are using. They should be able to tell you which mark on the blade holder usually works the best. You may have to adjust it a mark up or down, to get the blade to work right for you.
  2. Test out the microtome yourself: Start with a plain block of paraffin, or a block with non-dense tissue in it. Set the blade angle to the highest setting (e.g., 10). Try getting a ribbon. If that doesn’t work, lower it one mark. Try again. Keep doing this, until you are getting good, strong ribbons without bunching. Now try is with other blocks with various types and sizes of tissue, and at different thicknesses. Adjust the angle a little bit either direction, as needed.

You will soon have the best clearance angle for the way YOU cut YOUR tissue on YOUR microtome with YOUR blade!

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