Isoma centering microscope

[Bernard Laycock 1Participant @bernardlaycock1]

I have aquired an Isoma centering microscope (unfortunately without instructions). It is mounted on a 3MT arbor which fits directly into the headsock of my mill. In order to zero it, I usually drill a tiny centre in a piece of metal, zero the cross hairs by reference to the drilled centre and can then use this setup to locate a reference point on the workpiece to be machined. I have found this necessary because each time I mount the microscope, the registration is different.

This procedure is time consuming, but I can't think of any better way of ensuring correct registration, or figure out why the registration is different each time I mount the instrument.

Any helpful hints would be appreciated and/or a photcopy of istructions for this or a similar instrument would make my day.

Bernard

[Bernard Laycock 1Participant @bernardlaycock1]

[Raymond AndersonParticipant @raymondanderson34407]

Bernard,

You might have some dirt in the spindle socket or the arbor is not perfectly true or even the spindle is not running true. Have you checked the spindle for truth? and the arbor also? I would check these areas first.

Once you have checked the spindle and arbor [and they are good] then you should try to calibrate the scope, the usual method [although it can vary from make to make] is to blue a piece of metal and using a tiny drill or some other true running pointed object in the chuck just mark the blue with the point the remove the point and insert the scope and you should be exactly over your tiny mark. if no then you adjust the crosshairs/concentric rings until true, then turn the chuck around 180° and check again. Remember every little movment is magnified with the scope.

Raymond.

[Bernard Laycock 1Participant @bernardlaycock1]

Hi Raymond. Thanks very much for your reply and helpful suggestions.

I set about checking the spindle first and ideally would have liked to own a 3MT test bar, but find it difficult to justify the cost of this as my preferred maker is Arrand and hsi cost about £80. There are other and cheaper versions available, but I wouldn't dream of buying one as they publish no information about accuracy. I settled for the next best thing and mounted a ground bar (silver steel) in a collet in the spindle and was pleased to find no deviation from the vertical that I could measre over 4". Rotating the bar, there was no measurable wobble at the collet and 4" away I detected 0.001" TIR. I reckon I should be happy with that – would you agree?

Next I followed your suggestion with the scope mounted (after removing the 3MT arbor and cleaning the contact faces). Initially it was a bit out and I adjusted it to be spot on. Then I freed the taper and re-engaged it at 90deg and the cross hairs were off centre. I repeated this at 180deg and 270deg and at all these positions the scope was off centre ny as much as 0.012". Which is not good news. I found the place where it was correct and marked the spindle, removed the scope and re-inserted it in the same place, but very disappointingly, it was now out by about .006".

I think all this means that the scope is inaccurate, but I don't have any idea what I can do to correct it.

Best wishes

Bernard

[Keith LongParticipant @keithlong89920]

Hi Bernard

Why not try an e-mail to the follwing address:- info@isoma.ch – they might just be able to help.

Keith

[Clive HartlandParticipant @clivehartland94829]

There is the possibility that there is a loose component inside that moves erratically as you remove and reset its position.

Shake it gently and can you hear any rattle?

If its an old instrument this is a possibility.

The fact it will not recenter by rotation means to me an internal problem as you have eliminated all other possibilities.

I often come across prisms in optical instruments that have shifted and it can take lots of work to find it.

Another possibility is that the graticule itself is not stable due to pressure springs not seating properly, lubricants dry out and they stick.

If you are brave take it to pieces and see what you can find.

Clive

[Bernard Laycock 1Participant @bernardlaycock1]

Thanks to Keith and Clive for your very helpful comments. I followed your suggestion Clive and shook it gently and I can hear something loose in the eyepiece. I'll follow Keith's suggestion and contact Isoma by e-mail and see if they can help, although I have heard that they aren't very helpful in this department. Still, I'll give it a go, nothing ventured, nothing gained as my old Mum used to say.

Bernard

[Keith LongParticipant @keithlong89920]

Hi Bernard

If Isoma in Switzerland can't help the following url:- http://www.alouettetoolco.com – is for a/the US distributers for Isoma. They might be a bit more forthcoming.

Keith

[Bernard Laycock 1Participant @bernardlaycock1]

I thought that those of you who were helpful with my query might like to know the outcome. Contrary to my expectations, a response to my email to info@isoma.ch was virtually immediate and they proved most willing to help me solve the problem. When I sent them photos of my instrument they said it was probably one of the first they produced and was upwards of 50 years old. They offered to do a full service, repair and adjustment and I have accepted their offer. So, good result, thanks.

Bernard

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