Just attempted to drill a Swedish Mauser receiver for scope mounts, and found out how hard these are. I'm looking for recommendations other than "don't do it". I can get a carbide bit, but then I still have the problem of hardness when I go to tap the hole. I considered spot-annealing, but havn't done this before. I read about spot-annealing with a car battery and a carbon rod. Any recommendations?

I use the Wheeler bit's and taps that Midway sells, they go thru any reciever, easy.

Have you actually drilled into it? A lot of older receivers are diamond hard outside, and dead soft inside (by design). Things I have found to help keep the tip of the bit from wandering, if you're drilling without a guide:
1) have as short a length of bit outside the chuck as possible
2) use a smaller bit to drill a partial depth pilot hole
3) use a small carbide or diamond burr in a dremel tool to mark the surface, so that the point of the bit sits in it.

Use carbide taps; if they break, you can shatter them with a punch (I haven't had to do this). Work carefully when laying out holes -- just a slight off-axis hole can totally screw up the job.

Good luck.

Todd

Todd, I did try a smaller bit and it did break through, but I still can't seem to go any farther with a larger bit. Really puzzles me. I'm using new high speed steel bits. I've drilled a lot of different materials but this one stands out.
GSF1200, thanks for the tip. I'll take a look at those bits and taps. I'm sur that this isn't the only hard receiver I'll run into. Still wondering if anyone anneals these receivers, and what to watch out for. I don't want to anneal so much as to soften the lug bearing area, as that's the section of the receiver I'm having a problem with.

Start with a solid carbide spade drill to break through the hard surface. DO NOT DRILL ALL THE WAY THROUGH WITH IT! It will break.


[ 01-12-2003, 18:44: Message edited by: Bear Claw ]

[ 01-12-2003, 18:43: Message edited by: Bear Claw ]

I did run into a floorplate once (intalling a Meiers lever) that was so incredibly hard it was chewing up the cheap HSS bit. I got through that with a TiN coated bit -- maybe give that a try?

Good luck,
Todd

To spot anneal, try this. Cut a small cube of steel to approximately one half inch to a side, no larger. Make sure it sits in full contact with the area you want to anneal. Heat it to cherry red and place it on the spot you wish to drill and leave it until it's cold. This should do it without affecting the rest of the receiver.

Savageshooter,

Bearclaw is right on the mark. Use a carbide bit to just break the hard surface and then drill and tap with carbon stuff. If you try tapping with a hardened alloy tap and it snaps, you may play hell in resolving the problem.

Don't spin your drill too fast or you may work harden the piece and cause yourself some grief.

Good luck,

Malm

Car battery and What???

Thanks for the suggestions all. I'll try the carbide bit. I know the spade bit can't drill too deep, but I saw a three-fluted carbide bit that supposedly can be used all the way through. Anyone try one of these?
Malm, I read about the car battery thing in Roy Dunlap's "Gunsmithing". By the way, was turning the bit at 1380rpm. Is this too slow? Always heard when in doubt, go slow.

[ 01-13-2003, 02:55: Message edited by: savageshooter ]

You can also spot anneal with this old method.
(1) car battery

(2) 1/2 " diameter or so length of graphite
about pencil length.

(3) one end ground to a pencil
point.

(4) A "GOOD" insulator to go around the length
of graphite

(1 set) leads to go from pos & neg from battery
to rear end of insulated graphite pencil
you made.
Need I say: DO NOT WEAR RINGS OR A WATCH
WHILE DOING THIS? WEAR EYE PROTECTION!

Hold the graphite point on the spot to be
annealed. Watch for the color change.

You might try this little trick from some of the guys on the old Gunsmithing List to spot anneal. I use TiN coated #31 drills and haven't needed it yet, but will give it a try next time I run into something that hard. Take a 3/16" or so drill bit and chuck it backwards (with the flutes in the chuck) Spin at 1/3 or so more RPM than you would drill. Bear down hard, pressure and speed = friction = heat. These guys swore by the method, claiming good results on '03 Springfields, Savage 99's and other stuff you normally know is going to be a bi#ch to drill and tap. If it works as slick as the guys claimed, it would be pretty quick to just swap drill bits and bushings - wouldn't even have to move the jig. Anyone here ever tried this one?

I have a chunk of 1 inch diameter drill rod about 1 inch long that I've ground to just match the contour of a Mauser receiver ring. I heat it to red heat with an oxyactetylene torch and then lay it on the receiver. Allow it to cool completely. Repeat the procedure on the rear bridge. You can now readily drill the redeiver with std #31 drills and taps. Works every time!
I've also got a neat new EDM machine that I can use to burn out the broken taps you will produce using some of the other methods described above.-Rob

[ 01-13-2003, 09:04: Message edited by: Robgunbuilder ]