Spot annealing

[ebb]

I drilled and tapped a Remington 521T 6-48 the other day and looked up on the net the drill size. Lincoln Machine has a chart listed that gave the drill size as a number 62 IIRC when all was said and done I had almost no threads. Further searching on the net revealed many other sources that listed 61 as the drill size. PLEASE check this out before you drill it too big like I did. EGW sent me another set of screws 6-48 and a set 7-40, for free and were great to deal with as none of this was their fault. My 521T now has a nice EGW picatinny rail held on with 7-40 screws.

 

[epc308]

I drilled and tapped a Remington 521T 6-48 the other day and looked up on the net the drill size. Lincoln Machine has a chart listed that gave the drill size as a number 62 IIRC when all was said and done I had almost no threads. Further searching on the net revealed many other sources that listed 61 as the drill size. PLEASE check this out before you drill it too big like I did. EGW sent me another set of screws 6-48 and a set 7-40, for free and were great to deal with as none of this was their fault. My 521T now has a nice EGW picatinny rail held on with 7-40 screws.[/QUO
A #31 is the correct size for a 6-48 screw. I wonder why the sources you checked had the wrong one listed. A #61 is much smaller than a #31, .039 vs .120, so you should have had plenty to work with. Drilled with one so small, the tap wouldn't have even started. You may have had a drill that was marked incorrectly. By the way, I have never heard of, or seen, a #7 screw. That's a new one on me.

 

[epc308]

Drilling them is no problem. Straight flute 2 groove carbide drill bit will punch cleanly through them all. Tapping is another story. Usually the hardness on the back side of the hole will get you. I use a Smith mini torch. Drill hole, polish a small area around hole to bright metal, heat hole till it turns blue, then polish the blue away with some sand cloth, or craytex. Heat, polish, rinse, repeat in a small area and stop when the blue creeps back on its own into the area you just polished. Then let it cool slowly. This usually gets the back side of the hole with no damage to the lug seats. Run tap backed up with a guide in the mill spindle. No achy breaky that way. Usually it is the ring that presents the biggest problem, once in a while I have come across a hard bridge also. Whatever you do, do not let it get quenched while you are doing this, as it will get harder than rat's teeth and no amount of annealing will undo it.

Kendog-
I spot annealed the Rock Island '03 today with complete success. It drilled and tapped easily. Oddly, the rear bridge seemed a little tougher than the front ring. I was pretty leery of this whole job, but instead, I learned something today. Figuring out how to hold the receiver in the mill vice was interesting, with all its lumps and protrusions, but I got around that too.
Thanks for the great advice.

 

[kendog]

Kendog-
I spot annealed the Rock Island '03 today with complete success. It drilled and tapped easily. Oddly, the rear bridge seemed a little tougher than the front ring. I was pretty leery of this whole job, but instead, I learned something today. Figuring out how to hold the receiver in the mill vice was interesting, with all its lumps and protrusions, but I got around that too.
Thanks for the great advice.

Glad it worked for you. It's a lot quicker and easier to do than it is to write it out! I hold the barreled action in the mill vise in a Forster jig, but you can nestle the flat bottom of the receiver on 1-2-3 blocks or something like that. Regular 6" parallels are too long. You could also fabricate a block to screw the receiver to, to hold it. I have one that fits 1903's and M98's. Remington's I hold in a shop made V-block fixture.

 

[epc308]

Glad it worked for you. It's a lot quicker and easier to do than it is to write it out! I hold the barreled action in the mill vise in a Forster jig, but you can nestle the flat bottom of the receiver on 1-2-3 blocks or something like that. Regular 6" parallels are too long. You could also fabricate a block to screw the receiver to, to hold it. I have one that fits 1903's and M98's. Remington's I hold in a shop made V-block fixture.

I set the receiver flats on two 1/2” lathe bit blanks. Milled a 3/8” piece of flat bar to bear against the left lug raceway. I cut it wide enough to stick out past the knobs on the right side and seat against the fixed jaw of the mill vice. A piece of random 1/4” aluminum took care of the protrusions on the left side. All tightened up it was square to the world. A piece of 1” round stock just slipped in the minor diameter of the threads to let me pick up center. I wasn’t going to make a fixture for just one, and this was a relatively quick solution that can be used again, should I ever get another one. Thanks again for the good advice. This tip alone was worth getting on the forum.

 

[SBS]

Another way to solve the problem of tapping case hardened receivers (top half of holes) is to use a #4 carbide center drill to start the hole and go deep enough so that the diameter of the cut just allows clearance for the tap. You can accomplish the same thing with a carbide chamfering tool after the hole is drilled -- just to remove the case around the hole. The tap then doesn't have to cut through the cased surface. Unless you make blind holes on the front ring, you'll still have to use a dremel to break thru the case on the underside and of course access is easier on the rear bridge hole(s). The slight chamfer around the hole also makes the tap start easier and once tapped, it is barely noticeable as the 1st thread always is pushed up a little.