Receiver Thread Headaches

[Ron J]

So I'm still working on my 1st Mauser (Turk). I believe the recvr threads have a helix problem. In the fastener business we call it a "drunk" thread. After cleaning inside, I decided I didn't like the rough thread flanks. I made a cast iron lap .980 -12 tpi 55 * that fit snug and started lapping the thds with 6 micron diamond. I put only 3 threads on the lap so it would not taper. (This is a common repair for a thread ring gage.) It had spotty contact at best. After lapping till it wore, I slotted the lap and spread the ID a hair and kept doing this until I cleaned up a good % of the flanks. Pitch dia is not a problem I'm threading the barrel. Then we made the mandrel for facing the lip off. The pilot gets tight/loose-tight/loose in the rails. The 2 torque shoulders are parallel w/ .001" but the inner is tapered forward in the center. Then we made a tool for lapping the inner torque shoulder. When tightened, it does not stop square to the rcvr face. It's .005" out on one side. I really don't think lapping existing thds will make them run out. Seems to me that unless I make the barrel threads small enough to allow the shoulders to meet evenly, the barrel will be pointing cock-eyed and I won't be able to achieve the "crush fit" deal. I don't like this, but am I worrying too much? Has anyone seen this?

[Doble Troble]

Wow.

 

Let me start by saying that all the tooling you made is beyond me, so I probably don't have anything useful to add.

 

What I think is important in-terms of putting a barrel on a receiver is (1) that the bore should be centered relative to the chamber (this has nothing to do with the receiver) and; (2) that the face of the bolt should be perpendicular (at exactly 90*) to the chamber and bore (here the receiver comes into play).

 

If the bolt itself is not perpendicular to the bore it seems that some improvement can be made at the bolt face. But the only way I can think of to make this cut is relative to the the receiver threads - the only tool I can imagine making to correct the bolt face must be secured by the receiver threads.

 

I would start by making sure that the face of the receiver is square with the receiver threads - it sounds like you've done that, so we're back to point 1.

 

Next, make sure that the threads of the barrel shank are true to the bore and chamber - how do you do this? I'm not sure. Set-up the barrel between centers and put a dial indicator on your saddle? Move it in thou by thou until it touches the peaks of the threads, move it along the shank to see if you have a taper? If this is a problem it may be difficult to correct, and a new barrel or if the shank still has enough meat, new threads are in order.

 

BTW the Turks I've worked on have been true (to the extent I'm able to tell) with the inner ring and bolt face, but there's probably a million of them out there and any time you make a million of anything chances are you'll encounter every possible problem.

[Ron J]

Well it seems you're on target with my problem. More so than this rifle will probably be! I did not get a barrel blank yet so chamber/threads will be done together & concentric/square. It seems to me that the rails are in line with the shoulders. The recvr thds are whats goofy and everything will work off them. I'm considering running a 1.00" - 12 TPI 60 * tap into the recvr if I can find a way to pilot it through the rails. That may open it up enough to clean up whatever exists. Tooling, heck we made the bolt face lapping tool and the spring loaded gizmo that puts pressure on the bolt face while lapping the lugs. All this for naught if I open up the threads again. Thanks for thinking about it.

[tinkerfive]

I'm considering running a 1.00" - 12 TPI 60 * tap into the recvr if I can find a way to pilot it through the rails.

 

I've been working on this idea.

 

I've taken a section (8") of old barrel and turned it down to the bolt diameter + enough to make it

snug in the bolt guides, this is the 'pilot guide'.

 

The "pilot" will be a 10" section of drill rod.

 

The "pilot" will be centered, squared and welded to a 12TPI tap.

 

The 'pilot guide' will be drilled out the same size ( diameter) as the "pilot"

 

The 'pilot guide' is then slid into the receiver in place of the bolt from the rear and butts up tight to

the bolt side of the "C" ring.

 

Then the pilot passes thru the "C" ring and into the guide.

 

It's very late now, hope that this is clear enough.

Tinker

[Ron J]

It's very clear. And it would work. I've been thinking along those lines all week. Although, I don't have a way to drill a 10" deep hole. The idea I came up with was to make a mandrel snug to the rails with a .500" I.D. at one end maybe 1/2" deep. If I buy a decent tap it should have been ground on centers. The smooth shoulder between the threads and the square should be concentric to the threads. That could be held in my 5C rotating collet deal at work and the lead threads ground on a surface grinder into a stub to fit the .500" hole. It may or may not not need to be welded. The tap would push the mandrel while tapping. If this works, there's no reason it could'nt be loaned out to other members who may be experiencing similar issues.

[Limpid Lizard]

You can make a slip fit mandrel for the receiver. This can then be used to align the receiver in the lathe in the following way. Take a piece of round stock with a hole in it large enough to take the receiver. It should be at least as long as the distance from the receiver ring to the bridge. Drill and tap it for 8 set screw evenly space around the perimeter. 4 go on the ring end, 4 on the brige end.

 

Mount the round stock with the receiver in it into a 4 jaw, with the screws accessible between the chuck jaws. Slide the mandrel into the receiver. Using two DTI's dial in the mandrel using the set screws. Single point the thread straight. Face the primary and secondary torque shoulders.

 

I had to do the above to square up a K.Kale. LL

[Ron J]

I followed you up until the part about using 2 DTI's. Are DTI's dial test indicators? How did you indicate the end of the mandrel that was in the jaws while the cylinder was in them?

[Limpid Lizard]

I followed you up until the part about using 2 DTI's. Are DTI's dial test indicators? How did you indicate the end of the mandrel that was in the jaws while the cylinder was in them?

You only indicate the end sticking out of the receiver ring. If you use two dial test indicators spaced a few inches apart on the mandrel, they should indicate the same when the receiver is lined up with the axis of your lathe.

[Ron J]

Gotcha. I have one more question. Assuming it's now too far off, would this set up handle boring out and single pointing to the thread size a large ring Mauser has?

[Limpid Lizard]

Gotcha. I have one more question. Assuming it's now too far off, would this set up handle boring out and single pointing to the thread size a large ring Mauser has?

Most likely, however this is pure conjecture on my part as I have not tried it. I would think if one was going to attempt something like this his best bet would be to see if it could be cut to accept Remington tenon spec barrels. You would be going to 60* threads. I'm not peppy enough tonight to get the books out, but since Rem falls between large and small I'm supposing it would work. For that matter, as long as you were cutting both threads, just clean up and cut 60*'s on both shank and receiver.