microscope refurbishment

I'm in the process of refurbishing a 1940s OMT toolmakers microscope. Its a lovely machine and deserves to be brought back to life. It has no significant damage but cosmetically has deteriorated a lot in some areas and I could do with some thoughts and guidance on a couple of things.

The micrometer heads have unsightly patches corrosion in the knurling. I could remove the rust with a soak in citric acid but I'm worried it might damage, discolour or lift the plating. To be honest I'm not actually sure what the plating is. Is it an unpolished chrome ? Perhaps there is a better/safer way to improve the appearance of the heads ?

The rotary table is very dark and discoloured and has some areas pitting but this isn't too deep. To clean it up it could be very lightly skimmed on a surface grinder. Its 300mm diameter. Alternatively I have seen some examples which have been scrapped. This looks impressive but I can imagine this would be quite challenging to do well, particularly as I'm not versed in the art. May be I could engine turn it instead ? The surface doesn't need to be super flat. Any thoughts on how to clean up this part ?

Gerry

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A mighty fine ‘scope !!

The plating is ‘Satin Chrome’ ... which unfortunately I have never found a satisfactory way to renovate.

Please let me know if you have any success

Meanwhile: With renewed interest I will have another look around.

MichaelG.

I wonder if it would be possible to use an artist's masking fluid to cover all but a tiny part of the knurl prior to running a test with your citric acid - so i it is going to cause problems they are very limited.

The rotary table might come better just with a metal polish?

In any event my instinct is that there;s nothing wrong with old stuff showing it's age and just preventing further deterioration is a triumph in itself..

pgk

Is it possible that much of the knurling defect is actually embeded dirt?.....try a wooden toothpick and a drop of WD40 and see if you can 'chase' the grooves in the knurling........I would gamble momney that it will look hugely better, even if not like new....

For the table I'm with pgk.......metal polish and some elbow grease. If it was mine I would use my short stiff steel brush on my angle grinder VERY LIGHTLY to burnish the surface, holding the angle grinder in both hands firmly....had brilliant results with that in the past!

Very nice! You might improve the satin-chromed knurling with a small wire brush or a glass-fibre brush, but, short of having it re-chromed (after removing the corrosion and making it beautiful), I think that's the best you'll do. I wouldn't want to change the surface appearance of the table by scraping or engine turning. Also, attacking it with a powered wire brush or surface-conditioning wheel (Scotchbrite, etc.) runs the risk of rounding-over crisp corners and edges. Perhaps that shows my lack of skill, however.

You can achieve a good visual approximation of surface grinding by the use of abrasive paper or film, supported on a surface plate. Keep the strokes short and strictly linear - use a guide of some sort. IIRC, Barry Jordan did that to model surface-ground surfaces on his wonderful miniature machine tools. Also, see Robin Renzetti's video:

**LINK**

If you're not familiar with Robin Renzetti's work, you can spend many useful, instructive and jaw-dropping hours on his YouTube and Instagram videos.

I have had the same problem of satin chrome knurls with rusty spots and have improved it by brushing with a brass bristle brush.

.... reminds me that the word "refurbish" and "restore", although often used interchangeably" have rather different meanings. Not totally sure what's intended here.

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Which in turn prompts me to quote this from Merriam-Webster:

Did You Know?

If you're wondering if "refurbish" implies the existence of an earlier "furbish," you are on the right track. "Furbish" was borrowed into English in the 14th century from Anglo-French furbiss-, a distant relative of an Old High German word meaning "to polish." In its earliest uses "furbish" also meant "to polish," but it developed an extended sense of "renovate" shortly before English speakers created "refurbish" with the same meaning in the 17th century. These days "refurbish" is the more common of the two words, although "furbish" does continue to be used.

MichaelG.

Just a quick one if I may. A number of the visible brass parts on the microscope, including the nameplate, are plated with a steely coloured material obviously to match the genuine steel parts. The plating is not too hard as its worn away in many places from just hand rubbing. Would I be correct in assuming the plating will be nickel ?

For those that are interested, Im still stripping the machine down, which is actually a pleasure. There are no chewed up screwheads, nothing overtightened or with mangled threads and a few surprises like this part:

I didn't expect to find this iris in the backlighting tube. The lighting unit already has a rheostat in its circuit so perhaps the purpose of the iris is to allow the colour of the light to be maintained even when you don't want much intensity. I don't know, I'm just guessing.

I've not yet attempted 'storing' of the rotary table or the micrometer heads. When I do I'll let you know what happens.

Gerry

Gerry

I'd guess that iris is to help collimating the beam for high power work.

pgk