doublegunshop.com - home Forums General Discussion DoubleGun BBS @ doublegunshop.com REPLACING A HINGE PIN

Another good article spotted this month. In the latest Shooting Times, Reid Coffield tells how to replace a worn hinge pin using the tapered pins and reamers available from suppliers like Brownells. Has anyone here done this?
Thank you,

Jim,
Over the years as a machinist and toolmaker, I replaced many pins in things other than guns.

My experience suggests that I would press out the existing pin and decide if simply replacing it with one of the same original diameter (sans the wear) would do the job or if I needed to install a larger one.

If an original sized pin would do the job, I'd turn a pin a few thou oversize, harden it, then polish to size, press it in and dress to the reciever as needed. A curved reciever may need an extension of a slipfit diameter to get the pin aligned to press it in, then that would cut off after pressing in.

If a larger one is needed I'd take a standard reamer of a larger size, spin grind it down to the diameter I wanted, spin a pilot section on it (this is necessary for recievers like the LC Smith and others with contouring around the pin hole, but if the surface of the reciever is normal (square) to the pin, a pilot isn't needed), sharpen the reamer and ream the hole, make the pin as above.

One thing to consider: the high speed steel reamers aren't going to like cutting casehardened steel recievers. I don't have a solution for that other than annealing the whole reciever or somehow annealing the area around and in the hole.

Chuck, I"m not a machinist so excuse the question if it doesn't make sense.
I thought the idea behind case hardening is to only harden the top few .001's inches of the receiver to protect it against wear, the inside should still be softer. Would a reamer really have that much difficulty cutting through those few .001's inches?

The case chips when the tool bites in.

Chuck, I meant to ask, How do you check for hardness in your replacement pins? Just with a file? Rockwell tester?

Rob,
For clarity for all readers, a reamer only cuts on the end. The o.d. is ground like a pin, with chip gullets and there is some relief to control the margins that contact the o.d.. However, only the end cuts as it advances into the part. The end has each flute with a relieved cutting edge.

Casehardened steel has a fairly thin very hard surface followed by a larger gradient of hardness back to the base metal hardness. Still, as the reamer comes into this thin layer, it has to cut it. This layer is hard enough to dull the reamer even though it's thin.

CZ,
As I said, I've not put a new pin in a gun, just mechanical devices and tools. But, I have hardened a good bit of things. I've used Rockwell testers as well has files and punches. For a hingepin, it would seem that there's no such thing as too hard. But rather than use a martinsitic steel (thru hardening), I'd think about a casehardenable steel to facilitate later recasing of the frame.

Chuck, I think your skills are well beyond adequate for changing a hinge pin.
I believe the replacement pin should closely match the original pin in material in order to keep the sacrificial piece the same. The hook, the pin, or both. Just my view.
Some years ago, one of this boards members said he made his pins with full and complete contact to the hook. A true craftsman, and not easily done, as the hook can be oblong, and not parallel to the pin because of wear/peening.

Some time back OWD was looking at an off face Webley action with integral pin. I wonder how he made out on it. Last I read he was having it magnafluxed.

Just a couple pages back Ken Hurst remarked that recutting engraving through a cased surface is difficult, and results in a less satisfying result. Burrs, chipping, and dull tools.

I think the number of zero's a person works at to be a real gift.

Thanks CZ. I agree with you on the material being of similar properties in that the pin should be of low carbon and casehardenable. It should also be of nicely machining alloy. As you likely know, 1020 or the like is a large grained steel that machines with a poor finish. I would pic any of the many leaded mild steels for this job as I think they are a great match and intended just for these type of applictions. The small amount of lead makes the steel very nicely machineable and has little impact on other properties, sans weldability.

According to info given in "L C Smith, Plans and Specifications" for the FW both the hinge pin & it's dowel were made of 1020 steel. The hinge pin had a taper of ¼" per foot.
For the R hinge pin simply called for "Soft steel" with a taper of .018" per Inch. It's dowel was made of "Tool steel".
I would "Presume"; The hinge was driven in tight, hole drilled & reamed through knuckle & pinned. All ends would have been finished to contour, engraved (dependant upon grade) & casehardened installed in frame.
Perhaps the slight difference in taper was from different time frames & both types were made with both tapers, don't know.
Perhaps early ones were untapered, don't know, never took one out.

Chuck, as a machinist of 35 years, I am inagreement regarding your preceedure.

I would only add that I might position the receiver on a verticle mill (bridgeport)and after getting everything indicated in,use a carbide boreing bar to get through the case hardened surface,at least on one side, and perhaps all the way through the receiver.

Also, I would think that a hardened dowel pin would maks a dandy hinge pin.

The radius on the barrels (the hook?) would need re cutting, based on measurements taken befor the job started.

I don't think this job is all that difficult, but it would probably take most of a day, so it wouldn't be cheap.

Miller,
That taper is a bit of a surprise. That'd mean the lug would have a six to seven thou contour to follow the taper across it?

They must have had their reasons for using a taper in this application, it's just not obvious to me what they were.