Silver steel or stainless?

[BazyleParticipant @bazyle]

Another vote for the drill and tapped brass rod with a long grub screw to provide the thread. That way when it is broken you only have to replace the screw in 5 minutes. You could drill and tap the body and put a little line of spare screws in there.

Good idea abouthe sleeve by MG.

[Chris R 1Participant @chrisr1]

Not sure where you mean a sleeve.

There's no space between the surface which has a circular depression in it, and the inside of the end which has the 1.25 sticker on it. Maybe 1mm – enough for a washer is about all. Maybe there was a washer or washer pair once, but there isn't much thread…

On looking closer

Tell you what, I've had an idea – why don't I drill and tap and cut off an HT screw and…..

By the way if you think that threaded bit looks bent, you're right, it is.

[Michael GilliganParticipant @michaelgilligan61133]

Posted by Chris R 1 on 25/01/2019 10:44:42:

Not sure where you mean a sleeve.

[ … ]

By the way if you think that threaded bit looks bent, you're right, it is.

.

A thin tube fixed onto the actuating rod and a sliding fit on the stub on the cube … it only needs to bridge the gap.

Your pictures demonstrate my point nicely.

MichaelG.

.

Edited By Michael Gilligan on 25/01/2019 11:08:34

[VicParticipant @vic]

As Simon said earlier, a Hex Socket Set Screw would do the job, plenty of suppliers on the auction site but I tend to use Kay’s or sometimes Boltbase.

[SillyOldDufferModerator @sillyoldduffer]

Looking at the photo, I'd try fitting a brass bush to the hole in the case (ringed in red below). The rod would be a loose sliding fit through the bush. The thread probably breaks because the operator moves the rod sideways whilst turning the knob. Fitting a bush would minimise any sideways forces reaching the screw-end of the rod.

Best solution is of all to give the microscope to me. I promise to look after it! Don't give it to Michael – I have it on good authority he beats his microscopes to make them work harder and he keeps them in a leaky chicken coop next to a sillage tank full of nuclear waste…

Dave

[Michael GilliganParticipant @michaelgilligan61133]

Posted by SillyOldDuffer on 25/01/2019 11:14:01:

The thread probably breaks because the operator moves the rod sideways whilst turning the knob.

.

Nearly right, Dave …

But the rod works by moving in/out [left/right in the picture] not rotating.

In the jargon: It's a slidey thing, not a twiddley thing. 

MichaelG.

Edited By Michael Gilligan on 25/01/2019 11:30:06

[GordonHParticipant @gordonh]

Making a bush for the 6 mm rod would help reduce the bending moment. I wouldn’t bother though, I would turn down a larger rod to a sliding fit in the hole then drill and tap the end 3 mm. A 3 mm high tensile grub screw or bolt loctited in would be better than a turned thread.
Gordon

[Chris R 1Participant @chrisr1]

It might break because the operator does it by grope while he peers elsewhere.

Errm, the m3 ole in the cube holder isn't concentric with the ole in the red circle. (The cube holder runs along a dovetail track – which needs some light grease, where can I get something suitable? Not silicone – it wanders everywhere,)

And there isn't a stub on the cube.

 

My wife would love you to pop in and pick up the microscope. I'm told it weighs 105kg. I don't think I'm that strong, but it was a bit of a grunt to get it upstairs (while she wasn't looking).

 

If you're interested in a commercial med application: Probably boring until the result at 1min 40 on.

Auramine-Staining using Primo Star iLED – ZEISS Microscopy

Lots of things fluoresce if you hit them with UV, You don't always need a stain.

This chap uses it, without stains. Look for the pics with the funny colours:

https://photos.app.goo.gl/MV9IynUtBdaKkVj53

 

Edited By Chris R 1 on 25/01/2019 12:04:02

[ShadowParticipant @shadow]

I have repaired a number of these sliders with handles and they usually are plated brass. When t huh e rod is pulled out it is fairly long and is subject to being hit which along with the small thread size tends to break at the prism end. I believe they were designed as a precison instrument sometimes not taking into account the real world.other manufactures have the filter cube wall threaded and the rod will break off leaving the threaded end stuck in the filter usually set with thread locker.

[Michael GilliganParticipant @michaelgilligan61133]

Posted by GordonH on 25/01/2019 11:36:07:
Making a bush for the 6 mm rod would help reduce the bending moment. I wouldn't bother though, I would turn down a larger rod to a sliding fit in the hole

.

The clearance hole is in the casting … How sure are you that it's coaxial with the pushrod ?

MichaelG.

[Michael GilliganParticipant @michaelgilligan61133]

Posted by Chris R 1 on 25/01/2019 11:51:00:

And there isn't a stub on the cube.

.

Apologies … Appearances are deceptive

MichaelG.

[GordonHParticipant @gordonh]

Quote from Michael Gilligan:-
The clearance hole is in the casting … How sure are you that it’s coaxial with the pushrod ?

From the picture and the lack of information to the contrary, I assumed that the desiner had done a competent job and lined them up

Never done a quote before, I hope that my text isn’t added to the quoted text

Edited to attribute quotation

Gordon

Edited By GordonH on 25/01/2019 12:21:40

[Chris R 1Participant @chrisr1]

Unfortunately there's no space for a flange, inside the casting.

Edited By Chris R 1 on 25/01/2019 12:21:19

[Chris R 1Participant @chrisr1]

Ole is 8.1mm ish

When the rod is screwed in, hard up to its shoulder, it doesn't run true with its position in the hole, as you slide the cube.

Rod is steel, btw.

Edited By Chris R 1 on 25/01/2019 12:25:38

[Chris R 1Participant @chrisr1]

I see why it looked like there was stub – it was a reflection. Here it is unscrewed a bit.

Trying a bigger pic..

[Simon Williams 3Participant @simonwilliams3]

As I understand this it's an alignment problem rather than the rod being weak. If so, maybe the solution isn't to make the thread stronger, but to make the rod a bit bendy. I'd try drilling/tapping my favourite grubscrew into the end of a bit of nylon and see if that lasted better.

Rgds to all

Simon

[Chris R 1Participant @chrisr1]

The rod doesn't touch the casting, so alignment isn't hurting. A flexible rod would do, though.

[SillyOldDufferModerator @sillyoldduffer]

As Nikon aren't noted for bad design, perhaps this is an assembly defect?

Could it be that the rod breaks because it isn't being screwed firmly flat against the prism? Perhaps the thread is too long and bottoms out preventing full insertion? Or the rod's shoulders are rounded such that the end can't sit flat? Or a washer is missing?

If the rod isn't screwed hard in, any bending stress will concentrate on the thin part which is further weakened by having a thread cut into it. In a tight assembly of the same parts I think the bending stress would be taken by the thick rod instead. Perhaps it's essential the rod is torqued in hard so as to pull the whole assembly firmly together with no tendency to rock?

I wonder if the design is analogous to the way rivets work. The strength of a riveted joint depends more on the friction between the two plates as pulled together by tight rivets than it does on the side shear strength of the rivets alone. Red hot rivets make especially strong joints because of the enormous force generated as the metal shrinks during cooling.

Dave

Edited By SillyOldDuffer on 25/01/2019 14:54:18

[Michael GilliganParticipant @michaelgilligan61133]

Posted by Chris R 1 on 25/01/2019 12:39:09:

I see why it looked like there was stub – it was a reflection. Here it is unscrewed a bit.

Trying a bigger pic..

.

Thanks, Chris … That makes it clear

Simon Williams makes an excellent point … definitely worth a try.

A quick&dirty 'proof of concept' would be to fit a 3mm screw into a short length of nylon tube.

MichaelG.

[Michael GilliganParticipant @michaelgilligan61133]

Posted by Michael Gilligan on 25/01/2019 16:35:56:

Simon Williams makes an excellent point … definitely worth a try.

A quick&dirty 'proof of concept' would be to fit a 3mm screw into a short length of nylon tube.

.

Note: I do realise that the rod does not contact the hole in the casting … but a lightweight, flexible, rod would better accommodate the accidental side-loads generated by handling.

MichaelG.

[Howard LewisParticipant @howardlewis46836]

The casing would provide for an outrigger bearing, IF it was concentric with the rod.

How about making up a short slave screwed rod, to fit inside the casing and bored to act as a bearing for a counterbore, so that the hole in the casing can be made concentric with the rod? With a suitable bush, with an external flange, either screwed or "glued" into place, the rod would be supported so that it is subjected to minimal bending stresses.

I know that this sounds like making a big production of it, but once done, the chances of breaking the new rod would be reduced.

Howard.

[Chris R 1Participant @chrisr1]

I don't think there's a manufacturing defect, it works the way it's designed to.

There may be a washer – or perhaps one flat oand one spring washer – missing, but there's precious little thread to put them on as you can see from the close-up.

IF the shiny part into which the rod is screwed happens to be parallel to the outside of the box (there's no reason why it should be, with any precision) then I guess I could recentre the hole in the box, drill and tap it maybe 10mm and make a bush, for each rod (there's one each side).

But if that shiny surface is angled then the rod wouldn't stay in the centre of any hole, so things would bend inside when the rod is pulled/pushed. Can't have that.

My foot of 303 has arrived so I'll go that way for now. A slight annoyance is that the rod is not quite straight. Perhaps silver steel would have been ground, I don't know?

One significant contributor to the trauma is the nature of the dried up grease on the cubes' track, which makes them jerky. A dot of WD40 has helped but it'll evaporate.

Microscope greases ("Nye&quot tend to be very specific and expensive.

This isn't critical but what type of grease would be light, clean, and long-lasting?

Ta.

[Douglas JohnstonParticipant @douglasjohnston98463]

Let me be the fourth person to advocate the grub screw idea, must be the easiest and best method.

Doug

[Michael GilliganParticipant @michaelgilligan61133]

Posted by Chris R 1 on 26/01/2019 13:59:17:

[ … ]

Microscope greases ("Nye" tend to be very specific and expensive.

This isn't critical but what type of grease would be light, clean, and long-lasting?

.

PlusGas Formula A 'dismantling fluid' [mostly kerosene] seems to thin greases very well.

… much better than WD40, in my opinion.

White Lithium Grease, by 'Weldtite' [they couldn't have a less appropriate name] is good enough for me

… it's available cheaply from 'Chain Reaction Cycles'.

https://www.chainreactioncycles.com/s?q=weldtite+tf2+lithium+grease&cat=product

MichaelG.

.

P.S.

I am disappointed to see that you didn't use the lightweight, non-rigid rod

… Sometimes it's just better to re-think the 'engineering'

Edited By Michael Gilligan on 26/01/2019 16:24:46

[duncan webster 1Participant @duncanwebster1]

Posted by Chris R 1 on 26/01/2019 13:59:17:

…. My foot of 303 has arrived so I'll go that way for now. A slight annoyance is that the rod is not quite straight. Perhaps silver steel would have been ground, I don't know?….

Ta.

Roll it along a flat surface with a bright light behind to find where the bend is, then nip it in a vice with the bend at the edge and treat it to some light abuse with a soft faced hammer. You can get it pretty good if you're patient. Did the same with my motorbike front forks once, although we used a flypress and vee blocks

[Author]

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