Microscope objective thread

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Microscope objective thread

This topic has 20 replies, 10 voices, and was last updated 12 January 2010 at 15:19 by Nigel McBurney 1.

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2 January 2010 at 13:46 #46916
John Haine
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@johnhaine32865
I winder if anyone can help with a query on an unknown thread please?

I have a cheap microscope (from Aldi!) with a video eyepiece option which connects to a PC. I want to cannibalise it to mount the optics on a different base with a small XY table for measurement purposes using the “Centrecam” software. The microscope objectives have a fine thread which is 14.86mm OD, with a pitch I estimate to be about equivalent to 35 tpi. Sorry for the mix of units but apparently it’s common with microscopes to use inch threads with metric diameters! There is a standard thread called “RMS” for Royal Microscopical Society which is 36 tpi and made in different diameters so I wouldn’t be surprised if this thread is also 36 tpi. Also apparently some lenses are made with 15mm diameter but these are usually 42 tpi!

So my question – has anyone else come up against a microscope lens thread of about this size and could they confirm the exact dimensions?

TIA, John.
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2 January 2010 at 13:46 #15452
John Haine
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@johnhaine32865
2 January 2010 at 15:56 #46924
mgj
Participant
@mgj
Do you have a thread gauge? Tell you straight away , and whether its 55 or 60 deg form.
2 January 2010 at 19:04 #46928
Circlip
Participant
@circlip
And if it’s metric, it won’t be TPI

Regards Ian.
2 January 2010 at 19:16 #46929
KWIL
Participant
@kwil
RMS thread is whitworth form, ie 55 degrees.
2 January 2010 at 19:18 #46930
KWIL
Participant
@kwil
Circlip,

Not always true, look at the thread on a metric Clarkson milling cutter, yes its pitch is English tpi!!
2 January 2010 at 20:47 #46939
Circlip
Participant
@circlip
Yep, 20 TPI constant pitch throughout the range, And now give me the second example Kwil??

Regards Ian
2 January 2010 at 23:16 #46946
chris stephens
Participant
@chrisstephens63393
Hi Circlip,

I would suggest you Goggle “microscope threads” or just click on;

http://www.sizes.com/tools/microscope.htm

Sounds like Metric and TPI to me.

chriStephens
4 January 2010 at 21:33 #47019
John Haine
Participant
@johnhaine32865
Thanks for the responses.

As well as Clarkson cutters, microscope threads are characterised by metric diameter and TPI pitch – as in the link Chris provides. E.g. Japanese JIS and German DIN standards are 20.1 mm x 36 TPI.

I guess if I had a thread gauge I wouldn’t be asking…(if it had this pitch on it…)

Thread is certainly 55 degrees.

Chris, thanks I’d seen that website which got me to where I was when I posed the question….I think either I’ll take a punt on 15mm x 36 TPI, or just use some araldite!

Of course, once I’ve set up the microscope I could easily measure the pitch……there’s a hole in my bucket too.
5 January 2010 at 02:24 #47030
chris stephens
Participant
@chrisstephens63393
Hi John,

What, no thread gauge and Sandown just gone? Dear me, perhaps you should have gone shopping instead of introducing yourself.

Nice to have met you and good luck with your threading, which you will have to machine till it fits, no matter what size it actually is.

chriStephens

PS if 3BA (34.7TPI) thread is close, it will be the 36TPI option, if 5BA (43.05TPI) is close it will be 42 if that helps identify. Very short, fine threads are always a pain to identify, without very specialist equipment, which you are trying to build. Rather a “Catch 22” situation, methinks.
5 January 2010 at 21:19 #47064
Billy Mills
Participant
@billymills
Hi John and Gang.

Hold an etched rule against the thread then imprint the thread and rule marks onto a lump of plastecene/ staysoft/clay/whathaveyou then count the threads against the scale using the microscope. Any distortion in the media is common to the rule and thread marks so won’t matter.

OK it’s late but Happy New Year anyway.

Alan.
6 January 2010 at 09:10 #47075
John Haine
Participant
@johnhaine32865
Thanks Alan, a clever suggestion! I have tried counting the threads against a rule under a x10 glass, unfortunately the screwed section is very short, only 6 or so threads, so one can’t get a good average.

Happy new year to you also.

John.
6 January 2010 at 12:41 #47081
mgj
Participant
@mgj
Well the other way of course is a pencil mark and a dial gauge. Measure the travel, count the turns.
6 January 2010 at 13:04 #47084
Les Jones 1
Participant
@lesjones1
Hi Meyrick & John,

Meyrick I assume that you mean to put the two threaded parts together and set up a dial gauge to measure how much one part moves with respect to the other for a number of turns rotation.

Les.
6 January 2010 at 14:51 #47091
mgj
Participant
@mgj
Yes – or there may be some solid surface and one can use a set of calipers to measure the change in dimension. Or one can put a ruler up (tape it on etc just to give a reference) – any darned hting as a reference will do – edge of a screw or whatever.

I mean its not as if it has to be that accurate – if we get a figure of 31.9TPI after all the calculations, its a fair stab that its actually 32 TPI? Or metricate to suit. People don’t often make metric threads with a pitch outside whole fractions. (.5, .25 etc)

I though we were in danger of getting a bit bogged down in technicalities, when all we want to do is measure a pitch which shouldn’t exactly strain the grey cells.

Edited By meyrick griffith-jones on 06/01/2010 14:53:37
6 January 2010 at 15:12 #47092
Circlip
Participant
@circlip
The trouble is, you are trying to find a “Standard” for something you are only assuming to be made to a standard. Sadly, the far easterners have been applying their own standards to home manufactured goods for a number of years, it may well be to a western size, but dont bank on it. 14.86 dia.? hardly a “Standard” metric one, close to 14.9 which would be more in line with 15mm on a metric pitch thread, but why not 0.585 or 73/125″ dia.

If you’re sure about the 55deg. angle, the fact that you’re only cutting 6 pitches leaves a lot of alowance to make the threads fit. The afore mentioned 20TPI for the Clarkson auto lock cutters meant that when I cut some adaptor spigots to screw into the largest metric OR imperial Aouto lock collets I have, to enable the use of the three flute “Throw away” SKF cutters, although cut on a fully Metric machine, 1.25mm pitch fits in 20tpi.

Regards Ian
6 January 2010 at 16:18 #47097
Martin W
Participant
@martinw
John

Dropped you a message re a microscope, offer still there if useful and when weather relents.

Or how about turning a mount that is a snug fit to the objective lens thread that you have and then secure with grub/set screws. Alternatively, as you have the imaging system, you could make a new tube with a standard RMS thread and purchase a cheap second hand standard RMS threaded objective lens from ebay. That way you can select the magnification factor to suit and if you wanted to change it at a later date it would be simple. One can get good quality lenses for about £5 – £10 as single items, makes such as Lomo, Watson, Vickers, GS etc are always available. Should you go that way then steer clear of Infinite Focus lens these are speciality items.

Cheers

Martin

Edited By Martin W on 06/01/2010 16:33:24
6 January 2010 at 19:13 #47103
Peter Tucker
Participant
@petertucker86088
John, I have examined the thread of an objective from my German made microscope, and found it to be 36 TPI OD 20.17mm. Viewing with the sterio micrope shows a Whitworth type thread form.

I do know one Japanese made objective will fit my microscope.

Good luck

Peter.
7 January 2010 at 21:31 #47147
John Haine
Participant
@johnhaine32865
Thanks again to all, and especially to Meyrick for his very practical suggestion which I just carried out. Mind you it wasn’t easy, but it looks like the thread is about 0.6 mm pitch. Given that its diameter is just under 15mm and .6 mm is 42.222 TPI, looks like this is an example of that last microscope “standard” I referred to in my initial post. The fit of the lens in the turret is disgustingly sloppy anyway, so I don’t think it’s too critical, as Ian says. Turning the thread will be a good test for my lathe CNC conversion.

John.
7 January 2010 at 21:50 #47151
mgj
Participant
@mgj
Cut it mandraulically John – more of a challenge than letting the machine munch away while you slurp coffee with confidence!!

Actually there is a slightly serious note. If the thread is a bit erratic, doing it manually means you can find the standard as you proceed. ie bodge it a bit to fit fairly well. CNC machines don’t think that hard?
12 January 2010 at 15:19 #47303
Nigel McBurney 1
Participant
@nigelmcburney1
HI objective thread is 36 TPI Whit form, dias were given in decimal imperial But its 40 years since I worked as an instrument maker and I cannot remember the exact dias,Most instrument making was make to a good fit rather than precise dimensions,but the objective threads were always made to gauge as they had to be interchangeable.
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