new guy checking in

I've finally decided to join up. I've visited many times in the past.
A little background on me. I'm a retired carpenter/cabinetmaker. But I've always been fooling around with machinery since I was a kid.
After I retired I got a job as the gunsmith in a local gunshop. Repaired a lot of firearms. I enjoyed working on the old ones. Especially the old Iver Johnson and H&R revolvers.
I'm also a certified Glock Armorer.
I have a mill and an old 109 lathe. Yeah it's old but it does the job for the small jobs.
I've been building various firearms for several years resurrecting piles of junk into legal firearms.
One of my present projects is building a Webley revolver. I have all the parts but the lower.
So I plan on making one.
Here's my question that I have asked several machinists and tool and die makers. So far no one has the answer.
On a top break revolver there is the hinge area where the top strap pivots on the lower.
My question is: How is that inside radius machined? The radius has to be the same as the hinge point on the top strap. But I can't figure out how they machined the inside as if you try to use a larger cutter then the inside won't be the same diameter.
This has had me scratching my head for a long time.
Obviously it was done, but how and with what tooling.
So, anybody know how it is done?

Jeez , you should be able to look at the tool marks and tell that. What's it worth to ya to find out?

I know it's rotary cutter of some sort but how did they get inside to cut it without hitting the tabs.

Many of use have lots of ideas and tools, ..
but no great experience of firearms.

Perhaps a sketch and some photos might be helpful ?

Any nr of machinists here could do it, if they saw what the problem is (not necessarily me).
Many of them might use tools and methods that are not what was originally used, but if it works..

This (similar) has been discussed on PM in the past, not sure it was ever positively resolved, or maybe I missed it. I understand the problem and don't know the answer.

Have assumed it was probably hand work after milling close with oversize cutter from outside the pivot point. How much actual extra metal would need removed by had to make the contour match a (say) 1/4" radius vs milling it to start with a 3/4 or 1" radius (1/2 cutter plus shank dia) from outside. I think a Gack or similar shaper could do it, but also assume that was not the real answer in US factories 100 yrs ago.

You should read the rules and fix the title or this will get locked and those of us in the dark won't learn the answer.

smt, carpenter/millwork maker day job

I don't know who will lock the thread (I won't) but you will get better response to your question if you put something in the title that gives a clue to what you are looking for.

ok, I'll do that. thanks