Drilling receiver for Sights

[Nora]

I have tapped things before...why do you tap and clean so much here...because of the hardness of the steel?

For the most part it's to just get the cut chips out of the way. If aloud to build up the threads will start galling. As well as increase friction. Possibly also causing the tap to bind. This is the same practice used when drilling a deep hole. drill a little let up to clear the flutes of the metal, then drill some more.

my .02

Nora

[StarMetal]

I was taught when you're tapping a hole you run the tap a little clockwise, then turn it back counterclockwise..then repeat, then you clean it and go at it again. The flutes in the tap collect the chips, you have to clean before the flutes gather too much. I've never had any trouble tapping with this method. I disagree some with if the tap squeaks it's worn out. There are things that can cause a new sharp tap to squeak. Too many to list here.

I too always set the tap up with what I used to drill the holes first, example a drill press. I don't do anything but remove the drill bit and replace it with the tap to insure the tap will be straight.

The 92 Rossi I had in the early 80's had one of the hardest receivers I've seen except for the Jap rifles.

Joe

[HABCAN]

The last thing I am is a machinist, but I have drilled and tapped a lot of receivers for sights. Biggest problem was always establishing WHERE to drill, and preliminary fixing of the base in place, as mentioned by pdawg, has been my solution, although I used 5-minute epoxy vs. Crazy Glue. Once set properly you can then centerpunch through the base holes, knock off the base(s), and have at it.

[Char-Gar]

I have always used machinest clamps to hold the base on the receiver while I used it as a jig. Has worked for me nigh on 50 years.

[JIMinPHX]

As has been said, it is important to use a good quality drill bit (or 2). In my opinion, it it even more important to use a good quality tap. Taps come in many different geometries. The best tapping method depends on the type of tap that you get. If you get a standard 4-flute "hand tap" (the most common type) then the advice already given is correct. If you get something like a spiral point gun tap, then stopping & backing up to clear chips is actually a bad thing to do. If you are using screws with a common machine thread, then you can get taps with just about any geometry that you want. If you are using screws with one of the special threads that is commonly used for sights, then your selection of available taps is going to be very limited.

Regardless of what tap you use, one of the most important things (right along with good lubrication) is to be sure that the tap is lined up straight with the hole. I can not overstress how important this is. Starmetal's recommendation of using the drill press as a tap guide is a good way to ensure this. I would suggest one of two methods. The first is to simply grab the tap in the drill press chuck & then turn the chuck by hand for the first 1-1/2 or 2 turns to get things started straight & then change over to a tap handle to finish the job. The second method is to chuck a short piece of 1/4" round bar & with the drill chuck spinning, file the end to a point around 30 degrees. Then jam this point into the back of the tap handle to keep the tap straight. Many T type tap handles have a hole already there for that purpose. If not, then you can either eyeball it, or add the hole yourself.

[Willbird]

Another vote for the cobalt bits. WARNING: they're so sharp they go through soft metal like a hot knife through butter.

One thing about cobalt drills, they are not as hard as a good HSS twist drill. Cobalt is added to allow the tool to resist heat better. There are not many metals out there that cannot be drilled with a GOOD QUALITY HSS twist drill. I used to drill hundreds and hundreds of holes in A2, D2, M4, M42, 4140HT, S7, and H13 steels with a single good sharp HSS twist drill, then put it away, and the next guy would sharpen it and drill hundreds more.

Many T handle tap wrenches have a center in the back end of them, if you grab a twp the correct size, often a 1/4" or a 5/16" it has a nice ground male center on the back end, just chuck that tap on on the smooth part (not the threads) with the square end (with nit's nice ground male center on it)and you have your tapping center . They often hold taps between two female centers to grind them is why they have this male center on the back end.

Before I tapped the receiver if you have not done a lot of small drilled and tapped holes I would take a few practice runs on some odd steel (not hardened) you have laying around.

Older gunsmiths have told me they used a tap ONCE on Springfield receivers than threw it away , and this was even after they got around the case hardening in some way.

Bill

[Morrison Machine Shop]

You definitely need to use a drill jig, don't drill or tap without it and don't go all the way through. And use a carbide drill bit. Countersink or spot drill the locations first, you do not want the drill bit to walk.