How to remove Reichert microtome chuck?

[billbillt]

HELLO,

IF I REMEMBER CORRECTLY THIS A TYPE OF SELF RESETTING FUSE ON YOUR CIRCUIT BOARD..

[tgss]

Hi billbillt
I'm assuming it's a metal oxide varistor, but just because it looks like one and it's where you would expect to find one. I guess that's a sort of self resetting fuse, in that it goes to a low resistance if the voltage spikes above a certain level and absorbs the energy from the spike and so saves the remaining circuitry. If the energy absorbed doesn't exceed its rating it's good to go again. But if too much energy is absorbed it can be destroyed, or even catch fire. In any event it's my understanding that eventually, after too many hits, it does begin to degrade and can fail either open or short circuit. As you're probably aware they are used in surge suppressing power bars etc.

If that sounds incorrect please let me know.

Cheers
Tom

[billbillt]

HELLO,
HERE IS A REFERENCE ITEM WHERE I GOT MY INFO.. I HAD TO REPLACE ONE A FEWS YEARS AGO IS HOW I BECAME FAMILIAR WITH THEM..

https://www.ebay.com/itm/Self-Resetting ... 12SYl7LseA

THE BEST,
BILLT

[tgss]

hi again billbillt

Thank you for the information and the link regarding resettable fuses. I was not familiar with these devices and they look to be very useful. They also look identical to metal oxide varistors!

You've inspired me to check these devices out, and from what I've read, despite their similar appearance to MOVs, they are fundamentally different. The resettable fuse is a current sensitive device, its resistance increasing significantly if the current exceeds a certain value, therefore reducing the current flow to the load to a very low value. The MOV is a voltage sensitive device, decreasing its resistance when the voltage exceeds a certain value, and so shunting the current away from the load. So when using a resettable fuse it is put in line with the supply, like a regular fuse, but when using an MOV it is placed across the supply - or across the load depending on how you look at it.

In the case of the device in the microtome it is across the 120 volt supply, between the hot lead and neutral, so I'm assuming that in this case it is a varistor.

Thanks again
Tom

[PrecisionInstruments]

Now for the question. I have added a close-up of the front of the machine below. There are two light expansion springs and two pairs of round pins that are not being used for anything. Since one end of each spring is fixed the other ends must go to something that moves. The springs are very light so whatever they were connected to cannot be very heavy. Also there is very little space between this face of the machine and the inside of the cover. I'm wondering if there should be a shutter, or curtain, that blocks the slot in the front panel, as the ram moves up and down, to minimize the amount of wax or other debris that gets through the slot into the mechanism. If anyone can shed light on this it would be very helpful.

Thanks again for your interest.
Tom

The vertical movement is running on linear bearings. These bearing are cylinder bearings in a brass cage. The brass hooks at the ends of the springs fit through the slots and under the bearing cage. This then prevents the bearing cage from workings it’s way down the linear bearing which will in time cause the bearing cage to hit the lower limits of the linear bearing race, causing a knock sensation when the advance system moves through its lowest point (up, down & knock, up down & knock).
Move the system up to the top, feed the brass hooks through the slot in those front stainless plates, and then move the hooks up until you feel them fit around the bottom of the bearing cage.
It maybe possible that when they are located correctly, a knock is still present when rolling through the lowest point. If this is the case, place a steel block on top of the microtome base under the hooks (that are is correct position), using and rotate the hand wheel to Bentley lower the system to force the hooks onto the steel block and they’ll shift up (only move them a little then check, more if needed)

Sorry, don’t have much time to get on here to often. I was trained up on these instruments during my apprenticeship, and service/maintain them still 15years later. I haven’t come across a better system, and all customers complained when Leica moved away from the brass barrel system.
Great find, glad you got her up and running.