This page describes the process of replacing and aligning microtome blades in the adhesive machining fixture, for later use in the micromachining process.
1. Remove the Old Blade from the Fixture
- Locate the blade clamp fixture in its box to the right of the office mill. Also locate 5/32" and 3/16" hex keys, the box of new microtome blades, and tweezers.
- Loosen and remove the four screws on the outer face of the blade clamp.
- Remove the clamping plate, and remove the blade using a pair of tweezers.
2. Clean Clamping Surfaces
Residues from the soap-based lubricant typically remain on the clamping surfaces, affecting blade straightness, and will need to be cleaned.
- Using a microtome blade, gently scrape off residues from the clamping surfaces of the fixture - both on the removed clamp plate and on the fixed clamping plate.
- Holding the blade at a shallow angle will allow easy scraping without catching on the aluminum plates.
- The blade used can in most cases be the blade just removed from the fixture.
- If scraping is insufficient, both surfaces can be carefully scraped with a 1000 grit honing stone.
- Make sure to use an oil on the stone to prevent clogging.
- Take care to preserve flatness of the faces.
- Clean both surfaces with acetone and a Kimwipe, and dispose of the old blade in a sharps container.
3. Install the New Blade
- Remove a new microtome blade from the case. Being very careful not to touch the edge, gently place it on the fixed clamp half so that the dowel pins capture the notches in the blade.
- Gently replace the clamp plate, again taking care not to touch the edge of the blade.
- Re-insert the four clamp screws, and gently snug them up to the clamp.
- Beginning with the center two screw, firmly torque down the clamp screws. Be extra careful not to slip and strike the blade with the wrench or your hand.
4. Align the New Blade
- With the 5/32" hex key, loosen the five screws around the perimeter of the clamp. They shouldn't be so loose as to come free, but should be loose enough to allow the clamp to rotate.
- Using a small hex key, loosen the brass stop nut on the fine adjustment screw.
- Loosen the adjustment screw a few turns to intentionally bias the blade to be higher at the front edge. If the blade clamp does not rotate, loose the five perimeter screws until they do.
- Place the vise pallet into the machine, and clamp the laser alignment sensor into the vise. Make sure to clamp the sensor horizontal and with the wooden brackets firmly against the outside edge of the vise jaws. Coordinate locations given for alignment assume this to be the case.
- Wipe the spindle nose clean.
- Slide the blade clamp onto the spindle nose, until the top mates with the alignment collar installed on the spindle nose.
- Rotate the blade clamp until the dowel pin mates with the tab on the alignment collar. Tighten the split collar clamp using the 5/32" hex key. Firmly tightening with the short side is sufficient (see photo).
- Turn on the laser alignment sensor; the button is located on the back, just below the USB plugs.
- The laser emitter at the left is set up to generate a converging beam; the beam goes through a focus point, and expands to illuminate a photodiode at right. A microcontroller reads this signal and displays it on the analog gauge. High readings are when the sensor is fully illuminated.
- With the blade installed in the clamp and the sensor aligned to the vise, the blade is in the beam focus at approximately X-5.0500 in machine coordinates. Moving the blade farther to the left decreases sensitivity. Initial alignment is typically easiest at approximately X-6.0000 to X-6.5000. Sensitivity at any point can be checked by jogging the blade in Z by 0.0001" and checking the sensor response. Placing the blade at the focus results in sensitivity up to 5 ticks per 0.0001".
- Using the sensor to measure blade deflection, use the fine adjust screw to align the blade to within 0.001" deviation between the end points, and within 0.001" straightness along the length.
- The blade pivot is located approximately 0.375" from the back edge of the blade. Jogging the z-axis to set a convenient reference point on the dial is best done at this y-coordinate, as the front edge can then be aligned to the same value.
- If the blade straightness is insufficient, the clamping surfaces may need to be cleaned and trued more thoroughly (see the section on cleaning).