how to machine the pocket radius in a top break revolver.

kega48 · Sep 12, 2015

Since I don't know how to modify a post here I'm starting a new one.
My question is how was the inside radius of a top break revolver's hinge point machined. On my Webley upper frame the diameter of the, for lack of a better term, hub is .5743 as measured with my Starrett mike.
On the lower there are flanges on either side of that area where the pivot screw is inserted and which holds the upper and lower together.
So they are in the way of getting a Woodruff or similar cutter of that diameter in there.
If anyone has an old Iver Johnson or H&R top break you'll see what I mean.
Obviously they did machine that area out but how and with what.
Even today, Uberti makes a Schofield reproduction which has the same situation as it is also a top break.
I'm wondering if anything is out there on how S&W machined that area.

wesg · Sep 12, 2015

Maybe you can make some sense out of this:

https://books.google.com/books?id=R...etal shaper cutting breechblock lever&f=false

I also 'think' I've seen a diagram somewhere of an operation like this being done with a chain mortiser. No idea where, or even IF, I saw or dreamed it. I've found nothing on the web, or looking through some of the old books I have.

kega48 · Sep 12, 2015

Thanks. I'll have to study that. I know it sounds crazy but I wonder if a mini chainsaw type cutter could be made and used.
Think I'll have to study that idea also.
That has to be close to the way that cut is made. How else could you do it.
Let me tell, I've wracked my brain over this for at least a year. On and off that is.

Paolo_MD · Sep 13, 2015

kega48 said:
...
If anyone has an old Iver Johnson or H&R top break you'll see what I mean.
...

If you were to post a couple of pictures, probably, more members would know what you mean and could help you better.

Paolo

stephen thomas · Sep 13, 2015

Maybe you can make some sense out of this:

https://books.google.com/books?id=Rt...0lever&f=false

Brilliant!
Thanks for posing that, I can see some apps.
I wonder if the cutter teeth were unidirectional & the arm lifted on the "backstroke" (back rev) like a clapper to clear the chips and make it more efficient, or if it was just a sort of whittling operation with straight spur teeth.

smt

wesg · Sep 13, 2015

It describes a cam and fork arrangement that moves the fixture to provide relief, so I'm assuming the teeth are raked as the drawing shows. But I'm completely unable to picture in my mind what the geometry of the mechanism looks like.

My first thought was the cutter oscillates like an ice cream scoop. But I now think it rotates about the center of the cutter and the part is moved in time to relieve the teeth on the back stroke.

For a one off, the cutter could be used as a file and hand operated. It would be concentric to a shaft running in a bearing, but with a yoke arrangement to clear the sides resembling the cheeks of a crankshaft.

Seems fairly simple, but the devil is always in the details. The one thing I know I'd do from the start would be to stagger the teeth in a variable pitch to avoid chatter. I'd, personally, probably rough it out with EDM before heat treat, and shave the ugly bits out afterwards. At least while there's still one next door that I can use. Might save a couple hours of pulling on a handle, and regrinding the cutter after it dulls from inadvertantly rubbing it on the back stroke.

iwananew10K · Sep 13, 2015

i have no idea, but could this not be closely approximated with a single tooth cutter and an eccentric process???

GGaskill · Sep 13, 2015

I'm thinking you need to step away from convention and think in terms of rotating the work piece against a stationary cutter. Most of the material could be roughed out conventionally but the finished surface made as mentioned above.

Heavey Metal · Sep 13, 2015

Cutter is mounted on a crank shaft with the center of the teeth and center of the main bearings in line.

Fixture is on a slide and is relieved on the back stroke by the same cam that turns the crank.

kega48 · Sep 17, 2015

thanks for the replies guys. I was thinking of milling out most of the metal by holding the lower in a vise at the angle I need to go straight across 2 points. Then rigging up something to remove that little bit of metal that fills the inside radius.
I did rig up a piece of stock on a rotary table mounted vertically. Then using an end mill to cut the inside radius by rotating the rotary table. Didn't quite work out the way I had hoped. Maybe I need to experiment some more.
I'm thinking of sort of a pendulum motion. Only the pendulum, the end mill, remains stationary and the lower moves through an arc to cut the radius.
Just a thought.
Or making a series of cutters mounted on an axle that goes through the holes in the flanges. And basically scraping off a small amount of metal at a time.
Or one cutter that can be extended in increments to scrape the metal away one tiny amount at a time.
The amount of metal that would remain after milling across isn't all that much. Sounds time consuming but I've never been able to find out how that inside radius is done.
Also how do you post a picture here?
However,for those of you who aren't quite sure about the area I'm talking about, google up images of a Webley and you'll see the area where the upper is attached to the lower and pivots at that point.
Then wonder how they machined that inside radius.

catalytic · Sep 26, 2015

I replied on another forum, but will copy it here as well since nobody has come up with this yet as far as I can tell, and it seems to be a much easier solution than those offered:

OK, so suppose you want a truly perfect radius on the body to receive the upper 'leg'. To do this on the vertical mill, I would put in an endmill with a diameter the same as the thickness of the upper's leg. Now, put your horizontal/vertical rotary table in the _vertical_ position and attach your body flat against it ** so that the pivot hole in the center of the legs on the body is in the very center of the rotary table and the butt of the handle is sticking down next to the mill's table. You can now mill the perfect radius into the body by turning the body on the rotary table.

wesg · Sep 26, 2015

That would work too, assuming you have sufficient clearance to cut the entire thing. Probably would on this application. Maybe not on others.

But, it would leave the bottom of the groove not flat, or cylindrical actually. Not that it would really matter in terms of function, but wouldn't match the original, most likely. The inside faces also appear to be a fitted surface, so you'd probably be better off using an undersize endmill and offsetting it to get the dimension correct and the walls parallel. And if the groove is narrow that could be a challenge.

Same problem of fit would make milling it across and scraping out just the bottom more difficult.

Thinking a bit, seems this could be done in production with a CNC lathe with a C axis, but you'd have to mount the workpiece on the turret and the cutter in the spindle. Otherwise, it would be cutting backwards for the first half.

4575wcf · Dec 3, 2022

The only way I can think of to hold the machined radius is to use an arbored single point cutter working through a slightly undersized hinge screw hole which could be indexed out each pass. Same principle as a Criterion Bridgeport boring head, only much smaller. Then ream the hole to finish size, tap, couter bore, you are all done. Line boring for pins on heavy equipment is done the same way in a much larger workpiece.

trevj · Dec 3, 2022

4575wcf said:
The only way I can think of to hold the machined radius is to use an arbored single point cutter working through a slightly undersized hinge screw hole which could be indexed out each pass. Same principle as a Criterion Bridgeport boring head, only much smaller. Then ream the hole to finish size, tap, couter bore, you are all done. Line boring for pins on heavy equipment is done the same way in a much larger workpiece.

A post from 2015!

Either the problem has been long since solved, or the guy moved on to more practical things!

wesg · Dec 3, 2022

Kinda funny, I'm struggling to make sense of my own posts ;-)

trevj · Dec 4, 2022

The new Forum software seems to have a talent for suggesting eons old posts as "Similar Threads". Been happening a lot of late, esp in the For Sale section.

But yeah, I have had a few "Like" notifications pop up for stuff I wrote years and years ago, and it kinda baffles me why guys are digging that deep in to the past, or if they even know that the stuff they are looking at may be a decade or more out of date info.

awander · Dec 4, 2022

What is "out of date" about it? I'd like to know how it was done as well.

trevj · Dec 4, 2022

awander said:
What is "out of date" about it? I'd like to know how it was done as well.

Wasn't referring to this post, was referring to guys popping in, asking if items were still available from posts dragged up from decade-plus back in time, as if it were likely.
Or guys looking for sources of parts or materials, from posts similarly as old. Which was at least one of my outdated "likes" that I referred to.

It's all well and good that this site is pretty well optimized into the various search algorithms, but the end results sometimes are pretty funny to see!

Cheers!

Winterfalke · Dec 4, 2022

awander said:
What is "out of date" about it? I'd like to know how it was done as well.

It was the original die sinking process, you make a "cherry" that is shaped to match the pocket with file-like teeth on it. The cherry oscillated in a motion that drags the teeth in a cutting motion, then lifts up and advances forward again, similar to a shaper. The machine I saw just had an eccentric, the art was in making the cherry shaped so it cut just the right shape pocket with that motion.

john.k · Dec 4, 2022

Or...how was the socket for the block machined in a Martini Henry action?......The reciever forging was finished almost exactly to size,as can be seen from the unmachined surfaces inside , however the socket was definitely finished with a small rotary cutter...the only way it could be done was to install the cutter on an arbor through the pivot holes.

how to machine the pocket radius in a top break revolver.

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