vickers focusing block

[Mr.Stone]

Hello Every one, been a while since i been around, have had a crazy couple of months with lots of bad luck

Anyhow, ive been making a new stacking setup and basically completed it this weekend, was really excited to test the new setup as it would be more stable and precise, but when most of the parts were on the focusing block, the fine focus did not work
It worked before, but for some reason its not working anymore.
The block came of a vickers microscope, there is what seems to be a model nr on the block: m170865, but when i google this there are no results.
The fine focus gear/worm gear(im not sure what gear this is, but its the fine focus knob you turn, when you turn it,it moves outwards and after quite a couple of turns it locks up, though this seems part of the design) seems to run through the middle of a bigger gear, i did not open this yet as the screws holding it are really tight , so i will apply some q20 to loosen them up.

Here is a picture of the block:



Im worried that the worm gear or what ever it it that is on the inside there might be stripped. If anyone can maybe help with some info on this tipe of gear or which specific microscope it came from, or advice on how to try and fix this, it would be great!

Thank you

[Pau]

I don't kow this focus block, but be aware that in not all the focus blocks the micrometer moves all the travel. With someones (Olympus BH and CH, Zeiss Standard for exemple and most modern ones) both macro and micrometer do travel all the lengh but with someones like Zeiss Universal despite being coaxial the micrometer moves through a very limited range (few millimeters). For typical microscope work this doesn't seem very important but for macro focus stacking it will be inadequate.

[ChrisR]

I have an old Vickers, different model, which does exactly that: "it moves outwards and after quite a couple of turns it locks up".

I think I remember reading that there's a tilting bar arrangement for the fine focus.
Good perhaps for a vertical adjustment in a horizontal setup, but not ideal for focus stacking.

[Mr.Stone]

Thank you for the replys
It seems strange to me, it was one of the first things i checked on the block it travelled for as far as i turned it. Im no pro when it comes too stacking but i do understand the basics, so i know what im looking for. I did however not notice the "lock" it has back then. When i took it apart last night there is a pin inside that stops the fine focus from turning once it reaches a certain point. This can be annoying, but only if you forget to "reset" this with every stack. I did not take the whole thing apart but i will do this tonight.

Last year i got hold of about 40 microscopes and a lot of spares, in all this only two blocks came out as practical for stacking, this one and then a leitz. But the leitz would require some butchering to be done in order for it to work, and the vickers moves in smaller increments. Of the other microscopes that there are, wild and zeiss, the back / neck of these where the focusing mechanism is located is rounded, and it would be hard mounting them on a horizontal setup. Other microscopes move the neck and not the stage. And another thing on these scopes, when you turn the fine focus the course focus moves along with it, and this makes it harder to make accurate adjustments.

@ChrisR: When you say :"I think I remember reading that there's a tilting bar arrangement for the fine focus."
Do you mean, it would only work at a given angle? Like when its on the microscope the way its meant to be - vertical, then it would work?

[ChrisR]

Tilting bar - in the sense of a lever doing the micro-lifting, and hence having a limited range. Do hope yours turns out to be what you need. I know I've got things wrong enough times - "it didn't do that when I looked at it before "....

[enricosavazzi]

In addition to the comments posted above, I would do some testing with the focusing rack in its original vertical orientation (or with a rubber band pulling the object stage toward the originally downward direction). I have no idea if this is the case with your focusing rack, but some focusing racks are designed to require the pull of gravity in one specific direction.

[Mr.Stone]

@ChrisR, Enrico: Ah, well the fine focus does not move i tried as many different positions as i possibly could, including the original position it was in to no avail And taking the block apart did not want to work either, out of 4 sets of different kinds of screwdrivers not 1 fit the screws that are located behind the knob. The screwdrivers that were thin enough to fit inside the slot were to narrow and the ones that were broad enough did not fit the slot. If i had hair id be pulling it out Here i added two pictures:

This image shows the course focus shaft, inside of that brass shaft(from what i can see) there is another shaft that turns when the fine focus is adjusted.

This image shows what i think causes some tension on the plate one would connect the stage too(in my case the bellows and camera).It rolls up as the course focus is turned.
Now what Enrico stated made me think, is this silver thing some sort of spring that provides the needed tension in order for the fine focus to work? Could this "spring" have become to weak? The course focus works regardless of the position of the block as i sed in my 1st post, this leads me to believe that the problem is indeed inside of the shaft where the fine focus is located.
Any ideas?

[enricosavazzi]

..
This image shows what i think causes some tension on the plate one would connect the stage too(in my case the bellows and camera).It rolls up as the course focus is turned.
Now what Enrico stated made me think, is this silver thing some sort of spring that provides the needed tension in order for the fine focus to work? Could this "spring" have become to weak? The course focus works regardless of the position of the block as i sed in my 1st post, this leads me to believe that the problem is indeed inside of the shaft where the fine focus is located.
Any ideas?

This is very likely a counterbalance spring that tends to pull the stage upwards, counteracting gravity. In this way, with the focusing rack mounted in its intended vertical orientation, turning the coarse focus knob in opposite directions requires roughly the same turning force. Without the spring, moving the stage upwards would require a higher force.

With the stage mounted horizontally, the spring would optimally need to be weaker. In some spring-loaded focusers, changing the orientation from vertical to horizontal causes the stage to slowly creep in the (originally) upward direction by itself instead of standing still. If your stage does not creep and the coarse focus knob does not require a markedly different turning force in opposite direction, at least for the moment you don't need to touch the spring.

[enricosavazzi]

This image shows the course focus shaft, inside of that brass shaft(from what i can see) there is another shaft that turns when the fine focus is adjusted
(...)

The (overexposed and very shiny) linear rack near the top center, seen head-on in the picture, engages with the helical gear at its immediate right. Turning the coarse focusing knob should turn this gear. If so, this is the easy part.

I don't quite understand from the picture what the worm screw in the foreground does. Does it engage another helical gear hidden behind the worm screw, mounted on the same axle as the gear visible at the top? Does the worm gear turn when you turn the coarse focus knob?

It seems that the worm screw also slides sideways along the thick horizontal (in the picture) brass axle. This sliding movement may be what turning the fine focus knob is supposed to accomplish. If this is correct, then the fine focus knob cannot cause the stage to travel the whole length of the coarse focus travel, but only a small part of it.

[Mr.Stone]

Thank you for the detailed reply Enrico. Now to answer some of the questions you have...

If your stage does not creep and the coarse focus knob does not require a markedly different turning force in opposite direction, at least for the moment you don't need to touch the spring.

There is no creep that i noticed, i had the bellows and camera hooked up on this and things were quite stable. And when the course focus is turned in either direction the force needed to turn it remains the same.

Does it engage another helical gear hidden behind the worm screw, mounted on the same axle as the gear visible at the top? Does the worm gear turn when you turn the coarse focus knob?

You are correct here, there is another gear hidden behind the thread of the brass shaft that is connected to the gear that is visible in the top of the picture. When the course focus is turned, this worm screw turns and moves the stage.

It seems that the worm screw also slides sideways along the thick horizontal (in the picture) brass axle. This sliding movement may be what turning the fine focus knob is supposed to accomplish. If this is correct, then the fine focus knob cannot cause the stage to travel the whole length of the coarse focus travel, but only a small part of it.

You could be right here, but at the moment the worm screw does not slide sideways. That could be the problem then.The gear at the back of the thread that can be seen is quite broad, if the fine focus had to be based on how much this moves sideways it would be very limited. This could however be what the "lock" is for, after quite a couple of turns in one direction the fine focus locks up and then the course focus is engaged. Thinking about it like that, then it would be fine for stacking. But i have to get it to work again before i can be sure...

[ChrisR]

then it would be fine for stacking

Only if your subject is less than a couple of mm (or whatever the travel is). My old Vickers is about 2mm, and a bit of a pain for 5x and lower. It's possible, but you have to be very careful when you "back up" the knobs. If you get an overlap inthe stack I believe you have to remove those frames, for Zerene Stacker - at least that's what I did.

[Mr.Stone]

@ChrisR, I dont know the travel of this one, but if its anything like your vickers then its likely to not be ideal for stacking. So i decided its best to rather try another block. I got a Leitz orthoplan block that would work. I checked it lats night and made real sure the fine focus travels all the way from the one point to the other in any position I just have to find a way to mount this to the setup i made, and i have to find a way to mount the bellows to this. But i have some orthoplan stages that would help here. And then i could maybe use the vickers block for vertical adjustment.

Any suggestions on what i can use to cut aluminium neatly?

[ChrisR]

to cut aluminium neatly?

Perhaps surprisingly, sharp Tungsten Carbide tipped woodworking tools work remarkaby well, and it doesn't wear the tools quickly.
I don't possess much/any machinery, but have used a chop saw, table saw, radial arm saw and a router.
I don't know the Orthoplan. On an Olympus the "head" is fixed via a dovetail disc held on by 3 screws. Fitted to a drilled, flat body cap it makes an adapter for tubes or bellows to sit on the microscope.

[enricosavazzi]

Any suggestions on what i can use to cut aluminium neatly?

For manual cutting without machines, I normally cut with an ordinary metal saw taking care of leaving an extra "layer" of metal 1-2 mm thick on the piece I am making, then file it down by hand checking the dimensions repeatedly. I do all cutting and grinding dry, but use cutting paste when drilling aluminium.

I use a coarse steel file with large straight-edged and very sharp teeth (each tooth about 2 mm high and spaced from the next tooth 3-4 mmm) to quickly remove metal. This file produces a very smooth, almost polished surface, but removes a lot of material quickly, and therefore cannot be used for precision pieces. Then I switch to ordinary files as the piece approaches its desired dimensions. A slight deburring/chamfering with the same files removes any burs and dulls any sharp edges.

For more machine-driven work, I often use a metal cutting abrasive disk mounted on an arbor in the chuck of a drill press. I fix the piece in a drill vice with the part to cut/grind away uppermost and projecting above the jaws of the vice. I lower the disk to the desired height, lock it at the right height and grind the piece by sliding it horizontally into the edge of the rotating disk (I do not grind by lowering the disk to the piece). I apply only a very slight pressure of the piece against the disk, move the piece very slowly, and use no lubricant/coolant.

Once the first cutting/grinding is finished, I keep moving and rotating the piece, held in the vice, around underneath the disk to plane away any unevenness of the surface. This takes time and patience, and I continue until there is practically no more contact between disk and piece. If necessary, I lower the disk by a small fraction of a mm and repeat the procedure if the piece needs some more grinding.

The above method is not officially recommended because it puts a moderate sideways load on the axle of the drill and therefore causes some unintended wear of its bearings, but I have been using the same small drill for twenty years and it is still going.

A metal milling machine of course would be better, but I don't have one and cannot justify its purchase.

[Mr.Stone]

Thanx Chris, ill give this a try on some of the scrap blocks i have lying around.
Ive wanted to try this setup that you are talking about, i might be mistaken, but didn’t Rik do this? I saw a post around here somewhere about that.
For the orthoplan im going to try and match it so that it could fit where the vickers block was mounted, like the first picture in the post.
While looking at other members setups i saw one that has a revolving nose piece where the objectives fit in, i then looked around and found quite a couple of nosepieces that have rms thread, these just simply screw in where your objective would, and then you can fit between 3 and 6 objectives at once which makes testing easier. but once im done with the whole thing ill post some pictures.
In the meantime ill build the new setup and wait for my flash to get sent back from Germany, think i got to wait two more weeks