My son, who is in graduate school, uses a high quality but no longer
made microscope for his home studies. Recently, one of the small brass
pinions broke in the focusing unit and he asked me if I could repair it.
I was able to disassemble to access the pinion which is on a rod.
Unfortunately, since the scope is no longer made, the exact part is no
longer available, but I have determined that a 64p 16T 0.4 modulus would
fit it almost exactly except that the bore is too small (it is 3mm and I
need it to be 4mm... actually a bit wider at #21 drill bit sized).
Unfortunately, web searching cannot locate a pinion of the proper bore
size (all are either 2 or 3mm bore), so I am thinking of getting one of
the 3mm ones and drilling it out to #21 sized. The problem is that this
needs to be very precise and if off by even a little will cause binding
and other problems in the focus mechanism. So I pose the question: How
would I go about drilling this out from 3 mm to #21 accurately using
ONLY hand drill, vice, etc as I have no access to lathes, presses, etc?
Hopefully, you scolded him, told him to take better care of his toys,
and sent him straight to bed without supper!!
Is the rod "in play" (wrt being alterable in the solution)?
Could you, for example, replace the rod with a piece of 3mm drill
rod? Or, a length of 4mm that is stepped to 3mm at one end?
[without a photo, its kinda hard to imagine what other options might
be available -- that you might not be imagining]
Have you identified the (likely) cause of the original failure? I.e., does
it make sense to replace it EXACTLY as built (possibly perpetuating the
same failure mechanism) vs. tweaking the implementation a bit?
Define "a little"? EVERYTHING manmade has tolerances!
I suspect if you posted a doleful plea in rec.crafts.metalworking you'd
be able to find someone who'd drill it out for you if you mailed it to
them -- along with a postage paid reply envelope (I suspect you can do it
with a regular letter envelope though may wish to purchase a padded
envelope just to guard against the envelope tearing and the gear
falling out! The good samaritan can even reuse the original envelope
if you're helpful and include a label with your preprinted address).
[I repaired a control panel for a disabled gentleman's camper in NY in
this way; just cost him postage to mail it *to* me (a couple of bucks).
I had the parts on hand and could afford the return postage :> ]
Probably expensive, and unavailable for the part you need, but if you
put "Microscope repair" into the search engine of your choice, you'll
see quite a few hits. If you contact some of them, providing the
manufacturer, model number, and broken part, they would probably let you
know if they could mail the part to you and how much they would charge.
Since you were able to disassemble the mechanism and isolate the
broken part, obtaining it and reassembling the microscope would probably
not disappoint your son.
Another idea is to contact a few of the larger university science
departments and medical schools nearest to you and ask if they have any
scopes of the same make and model that they have scavenged for parts.
You may just get lucky.
Good luck. Hard to believe that the maker of a high quality microscope
either no longer supports their own stuff, or wasn't bought out by
someone who acquired the spare/repair parts from the original
manufacturer. In my student days (1960s and early 70s) there were 3
good scopes, American Optical, Bauch & Lomb, and Nikon. I sold my scope
before graduating med school and no longer am aware of that market.
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