Circular Dovetail [Microscope fixings]

Most microscopes use a circular dovetail arrangement to attach viewing heads, photo adapters, etc.

Unfortunately there are several 'standards', some of which are similar but not identical ... and I have, so far, failed to find a definitive list

In the excitement of bargain-hunting, it is all-too-easy to buy a mystery item which doesn't quite fit.

It is comparatively simple to measure the [male] dovetails 'properly', but I am looking for a quick-check gauge [pocket sized] to carry to the micro-jumble events. My best idea is to modify a calliper, by fitting 4mm diameter rods to the jaws ... then start building my own list of 'effective diameters' from known components.

Very grateful for any better suggestions !!

MichaelG.

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P.S. ... the dovetails are typically in the order of 40mm diameter, with a 60deg slope, but there are many detail variations.

Edited By Michael Gilligan on 27/12/2014 09:50:28

How about making a set of moulds?

When I was into using/buying microscopes (and fixing staff damage) I used Brunel Microscopes and they are very helpful - may well be able to give you a list of ancient and modern variables.

pgk

Is it just the dia you are measuring, not the dovetail angle? How about a strip of metal with a notch at one end to locate on the edge of a female dovetail and the other end a series of steps at known lengths that fit your equipment as a go no-go test.

Hi Michael,

I understand I am not the only one with a microscope, I don't know how accurate your measurements need to be. Since a couple of rods and calipers are used for measuring straight dovetails, shouldn't it be possible to use ball-bearing balls of suitable diameter to measure the circular dovetails? You would need to bring calipers and ball-bearing balls with you though.

Thor

Thanks for the replies:

pgk: The moulds are a nice idea, and I may make some for the 'shop ... but the big problem is that I don't have specimens of all the possible variants [and also, I want one small gauge for use in the 'jumble' environment.]

Bazyle: strangely, the diameter is more relevant than the dovetail angle ... because the 'female' is typically a three point arrangement [one of which is the locking screw]. On the better instruments, the two 'fixed' points are adjustable [to allow fine centering] and often have spring-loaded ball ends.

Thor: perhaps I'm being thick today, but I can't see why balls would be better than rods for measuring the male dovetail. [?]

Thanks again

MichaelG.

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P.S. for those interested ... there's a relevant discussion here

Edited By Michael Gilligan on 27/12/2014 12:03:10

How about a firm joint calliper style device with ball rather than sharp tips. Should be possible to arrange a scale or multiposition locking device to either measure the opening in some suitable unit or set it for direct comparison with suitable sizes to mate with your equipment.

Way back in the late 1970's when I was young and hairy we had a device of similar ilk in the "what the heck is it, can't throw it away 'cos its on the asset list" box at the back of the optics lab. I used it a time or two for similar comparisons where sharp caliper arm points were unacceptable. Around two an' thruppence three farthin' back in 1950 something. Took me around 4 years to convince the powers that be to let me write it along with 20 odd similarly inexpensive, obscure and even more dusty items off instead of hauling them out every year for stores stocktaker inspection. Just one of the joys of Civil Service employment at an MoD research establishment.

Clive

Hi there, Michael,

A fellow microscopist I often encounter at club events simply carries a plastic Vernier caliper in his top pocket!

With every respect to earlier posters, I think they haven't appreciated that you definitely need the device (whatever you eventually adopt) to be capable of one-hand use.

Separate balls and/or rods wouldn't hack it in the fevered flea-market environment, where you actually need third and fourth hands (and elbows) to fend off rivals while you make your assessment!

Incidentally, I understand that with Ernst Leitz (of Wetzlar) microscopes, the dovetail calibre denotes the tube-length. However, I can't from memory quote which diameter goes with which tube-length.

Best regards,

Swarf, Mostly!

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Well spotted, Sir !! ... excellent analysis

The plastic VC may actually be the most appropriate solution.

MichaelG.

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P.S. ... What clubs are our fellow microscopists in?

Mine are: Manchester Microscopical Society, and the Postal Microscopical Society.

Clive,

Good to hear from a fellow 'Liberator' of unappreciated hardware.

MichaelG.

Sorry Michael,

I guess its me being thick, I thought you wanted to measure the inside dovetail. For the outside, rods should work well, I have just measured the major diameter and depth when making something that should fit.

Thor

Edited By Thor on 27/12/2014 15:59:39