A Leeuwenhoek microscope project

[S KParticipant @sk20060]

Yes, it's similar to a bell crank in function. Haha, haven't used the term "bell crank" since I was a kid making control-line model airplanes.

The effective focal length of the lens is 4.5mm. But because the lens is 3mm thick, the back focal length is only 3mm (about 4.5mm – 3mm/2). So a flexure-supported table should be about 3mm away from the base. I had imagined using 3 or 4 of the flexures I printed (or something like them – it was just a generic test structure) to support a stage at its edges. But it would have to be scaled down a lot further still, which looked to be a big problem – the arms were already only two extrusions wide. Maybe photo-etching could make parts small enough.

Anyway, the hinge it will be.

Referring to the hinge area of the printed part, I wonder how thin I have to make brass before it will bend appropriately over a few degrees? Or is it going to fatigue quickly and just break? I suppose I should test that before going much further.

 

Edited By S K on 18/05/2023 13:10:24

[John HaineParticipant @johnhaine32865]

Good practice for machining suspension springs from solid? Matthys recommends phosphor bronze IIRC.

[SillyOldDufferModerator @sillyoldduffer]

A traditional spring can be made from a length of Brass strip, which is usually annealed soft when new.

Gently hammering the strip down to about ⅓rd thickness should work-harden it into a reasonable spring. Not like a proper steel spring, but good enough for this application.

Now I want to make one, and I'm already far too busy!

Dave

[S KParticipant @sk20060]

Bronze … for when brass just isn't expensive enough! 😄

I'll order some. 🙂

[david bennett 8Participant @davidbennett8]

S K, it may be too far from the original concept, but have you considered a mechanism for moving the lens for focusing, rather than moving the specimen?

dave8

 

Edited By david bennett 8 on 18/05/2023 23:51:45

[S KParticipant @sk20060]

Not really. I wanted to maintain at least some resemblance to the original, and a steady flat face is a virtual necessity due to the shallow eye relief. He got that part right.

I ordered a sheet of bronze this morning, and it came this afternoon. McMaster is amazing.

It's cold-worked 510 bronze, and it definitely has a lively, springy feel compared to the dead feeling of brass.

[david bennett 8Participant @davidbennett8]

Yes, I can understand that. I was thinking of your lens set in a threaded bush through the main plate (threaded ), which need not mar the flatness too much.

dave8

[david bennett 8Participant @davidbennett8]

Yes, I can understand that. I was thinking of your lens set in a threaded bush through the main plate (threaded ), which need not mar the flatness too much.

dave8

[david bennett 8Participant @davidbennett8]

double post

Edited By david bennett 8 on 19/05/2023 02:01:43

[S KParticipant @sk20060]

Oh, yes, I've thought about interchangeable lenses! The lenses are so small that they could easily be mounted in threaded receivers, to be screwed into the main body. It would be easy since I already have the materials and small taps and dies that would be needed.

But that might be gilding the lily? I am happy with it so far. Maybe for the Mk. II version. 🙂

 

Edited By S K on 19/05/2023 02:33:45

[S KParticipant @sk20060]

A little more progress: I've completed the stage, which takes the place of the plastic version seen above. It's made from 510 bronze, with a brass ball on which the micrometer pushes. I gingerly tested the flexibility of the hinge, and it will move, but I may have to thin it a little more – not sure yet.

I've decided to fit the "slides" (10mm glass windows) into little 3-D printed holders, which then drop into the 12mm hole. In the event that I get the lens-to-slide distance badly wrong, I can reprint the holders to adjust the slide's position.

Still left to do is create a few mm thick shim with a very slight angle to set the distance between the body of the microscope and the stage, and drill the microscope's body to accept the stage. However, I'll soon need to mount the lens, at least temporarily, along with a slide, in order to judge how thick the shim needs to be, and perhaps what kind of angle to set. Then I'll be nearly done.

 

 

Edited By S K on 20/05/2023 21:03:08

[S KParticipant @sk20060]

I'm calling this one finished. It's a Leeuwenhoek homage microscope rather than a replica.

The lens is a 3mm diameter coated achromatic doublet with a 4.5mm effective focal length and a numerical aperture of 0.3. This gives it about a 55-56x magnification, which is on the low end of Leeuwenhoek's surviving microscopes.

Mine deviated quite a bit from his approach, though I tried to keep it recognizable as following in his footsteps. Some differences beyond the lens:

• The body of his microscopes were two thin metal plates sandwiching the lens, and then riveted together. Mine is a solid piece of brass into which the lens is held in a reamed hole.
• His "handle" was a screw that adjusted the vertical position of the subject. Mine is the micrometer head, which adjusts the focus.
• His had a crude means of adjusting the subject's horizontal position, whereas mine has none.
• His used a needle-like point to hold the subject, whereas mine uses a stage with a 12mm hole, into which glass "slides" can be placed.

It's sharp, with quite little distortion or chromatic aberration except at the far edges. The contrast is seems lower than I expected, but that's probably because I haven't figured out how to properly illuminate the subject yet. The field of view is decent, and is wide enough that you can "look around" the image a little.

I looked at a slide of a tiny smear of my own blood. At about 55x, you can clearly see the red blood cells, but they are only pale tiny roundish dots. You can imagine that they have a particular shape, but it's not clear.

If I could go back in time and give this to Leeuwenhoek, what would he think? Certainly the achromatic lens would have amazed him. But otherwise, his microscopes revealed as much or more than mine could given their generally higher power.

It was a fun little project. I already have a lot of ideas for a Mark II version. 🙂

[John HaineParticipant @johnhaine32865]

Looks very nice! How did you machine the circular neck in the bronze please? Maybe useful technique for making suspension springs.

[DiogenesIIParticipant @diogenesii]

Nice, mental 'note-to-self' filed away… ..thanks for posting..

[S KParticipant @sk20060]

I used a 1/4" center-cutting ball-end mill to cut the neck, just running it ball-end-down horizontally across the metal.

I think it wound up being 0.004" at its thinnest. I'd try for thinner next time, as it was still a little on the stiff side, but fine for this purpose.

To make a pendulum hinge, it would have to be considerably thinner still: 0.001" max, and likely less. Accurate work holding and precise tramming, to something like 0.0001" or better across the material would be needed for sure, lest one end of the cut be thicker than the other. Also, you would have to reverse the material and cut both sides equally. A lot could go wrong.

This bronze is reasonably hard and has a good ring to it. While it's much livelier than brass, I'm not convinced it's well suited for a spring as flexible as would be needed for a pendulum. I may try to make something as thin as I can to see.

[John HaineParticipant @johnhaine32865]

IIRC the BeCu shim I have is 0.1mm thick = .004in? Did you use PB?

[S KParticipant @sk20060]

My memory was wrong: It is probably about 0.04", or about 1mm, maybe slightly less. That looks about right. Unfortunately, I can't measure it properly without taking it apart again.

So if I was off by a factor of 10, maybe 0.004" would make an OK hinge after all. I'll have to try making one with it to see.

What is "PB"?

Edited By S K on 29/05/2023 19:30:52

[John HaineParticipant @johnhaine32865]

Phosphor bronze

Yes, looking again at your photo about 1mm looks reasonable.  The technique looks worth trying though.

Edited By John Haine on 29/05/2023 21:28:36

[Michael GilliganParticipant @michaelgilligan61133]

John …

Given your starting-point [thickness of material] … might I suggest that you consider the approach that I suggested elsewhere:

30/03/2023 16:03:27

**LINK**

https://www.model-engineer.co.uk/forums/postings.asp?th=184730&p=14

… It has the great advantage of imparting a gradual change in thickness.

MichaelG.

[S KParticipant @sk20060]

Per Wikipedia: "Phosphor bronze is a member of the family of copper alloys. It is composed of copper that is alloyed with 0.5–11% of tin and 0.01–0.35% phosphorous…"

It was designated by the supplier as "cold worked 510 bronze" in an "H08 spring temper." Here's the composition:

Material Composition
Copper	94.8%
Iron	0-0.10%
Lead	0-0.05%
Phosphorus	0.20%
Tin	5-6%
Zinc	0-0.3%

So while it wasn't called "phosphor bronze" by the supplier (those sorts of names often don't mean very much), it looks to be in that family. It was more than twice the cost of brass or pure copper.

I did follow the machining step by some sanding with paper wrapped around a suitably-sized rod, but that was mostly to remove a tiny machining mark in the bottom of the hollow left by the very tip of the ball-end mill. I was worried that it would be a source of stress if not removed. As it gets thinner and thinner, I'd feel more worried about introducing non-uniform thickness through hand sanding.

[VersabossParticipant @versaboss]

SK, would it be possible to take a photo through your microscope? I would very much like to see what you see, iykwIm!

Regards,
Hans

[S KParticipant @sk20060]

Here's a picture of the "slides": glass in printed carriers that drop into the stage. One is designed with a longer lens to subject distance than the other.

And here's a picture of some micro-print. It's a pretty bad photo, really, as it was quite difficult to take. It's very hard to position the camera lens. It looks much better when viewed directly, but at least it's something.

[Michael GilliganParticipant @michaelgilligan61133]

Posted by S K on 02/06/2023 22:32:56:

[…]

And here's a picture of some micro-print.

.

Give us a clue, please … approximately what actual height is the number 0

Thanks

MichaelG.

[John HaineParticipant @johnhaine32865]

Posted by Michael Gilligan on 29/05/2023 21:27:36:

John …

Given your starting-point [thickness of material] … might I suggest that you consider the approach that I suggested elsewhere:

30/03/2023 16:03:27

**LINK**

https://www.model-engineer.co.uk/forums/postings.asp?th=184730&p=14

… It has the great advantage of imparting a gradual change in thickness.

MichaelG.

Thanks for this Michael, and apologies for this slow response. Presumably this method is mostly applicable to thin material, which would readily wrap round the former? It would be difficult with say 3mm PB strip, especially to unwrap it and do the other side to get a symmetrical "neck". Or do I misunderstand?

[Michael GilliganParticipant @michaelgilligan61133]

Yes indeed, John … I was presuming you would be starting with shim-stock

… as per conventional suspension springs

MichaelG.

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