sort of OT: widening a brass pinion for a microscope?

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? Thanks!
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On Friday, February 19, 2016 at 5:39:17 PM UTC-6, Bill Baxter wrote:

At minimum you need a drill press run at high speed. I bought a lightly used HF one for $25. Borrow or buy one...
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wrote:

There are drill press stands available. Ebay has plenty. Are there any general welding/fix it shops in your area? Maybe they're limited to rural areas.
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Bill Baxter wrote:

Take it to a jeweler
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On Friday, February 19, 2016 at 8:44:26 PM UTC-5, dadiOH wrote:

3 D printing at the library (Maker Zone) may solve your problem.
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+1 Good idea.
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On 2/19/2016 4:39 PM, Bill Baxter wrote:

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 :> ]
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Don Y wrote:

He wouldn't even have to go to RCM ... Bill , if you want to mail it to me I can do that for you . My reply-to email is good . You might want to send the shaft and old gear too .
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On 2/19/2016 6:39 PM, Bill Baxter wrote:

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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