Author Topic: Counter Boring ? How To (Read 988 times)

hylander · « **on:** September 14, 2005, 11:42:22 AM »

I want to counter bore a couple of Mosins and a Turk.
Have a couple of ?
Quote:
Originally Posted by Nordicthug
I ground negative rake cutting edges on a 3/8" HS twist drill and chucked it in a 3/8" drill motor to c-bore the second rifle. It self centered and followed fine with a bit of Butter Flavor Crisco to lube it. The Neg. rake cutting edge cut very smoothly and didn't bite.
Nordicthug

1: What is a negative rake cutting edge ?
2: Can I use an End Mill bit
3: What type Bit do the Smith's use in their Lathe.

I am going to be doing this with my table top Drill Press.
I have a Mauser barrel to practice on.

Shorty · « **Reply #1 on:** September 14, 2005, 02:18:48 PM »

hylander,
1. A twist drill has positive rake to shear and force the chips out along the flutes. Compare that to a masonry bit which has a neutral rake. Masonry crumbles so there are no chips to eject. A negative rake is even less than flat. It can't "grab" because it is plowing material ahead of its feed. This type of point is used for brass which is "grabby" yet crumbly. On a steel gun barrel, I would expect to get one heck of a burr pushed into the bore!
2. An endmill would "grab" like heck AND not self-center.
3. I'm no gunsmith, but I'd expect that they would use a boring bar, maybe a reamer (?)

A hand drill? A benchtop drillpress? Scary!

gunnut69 · « **Reply #2 on:** September 14, 2005, 06:02:50 PM »

A boring bar with the barrel set up between centers(use a turned spud in the bore) and then set up in a steady rest, drive it with a lathe dog. A spider may be needed to get the front of the barrel turning evenly around the center of the bore. I have seen it done with a homemade spade type piloted reamer or drill. Pilot has to be a little long to get past the damaged bore at the muzzle. That job was done by hand.. It seems to me that the important thing is that the rifling terminus be even..square to the borem, more so than the counterbore be perfectly centered..

oinkmaster · « **Reply #3 on:** September 15, 2005, 03:13:45 PM »

May be I missed something, how can something be countered bored and held between centers at the same time?

John Traveler1 · « **Reply #4 on:** September 15, 2005, 04:22:17 PM »

Gunut69 is correct. He is describing how the barrel is first SET UP between centers, and then the tailstock center REMOVED, with the barrel supported on a steady rest. The counterboring is then done using a boring bar or a special tool for the counterboring operation. This is to assure that the c.b. is done concentric to the bore axis to maintain the rifle's accuracy.

BTW, a piloted tool that looks much like a chambering reamer is used to make those DEEP c.b. that repair badly worn or damaged muzzle.

HTH
John

hylander · « **Reply #5 on:** September 16, 2005, 03:04:50 PM »

Well:
You all will no doubt Cringe :shock: , but I'm going to set my Barreled reciever up in my table top drill press and use a 3/8 cobalt standard bit to do the initial bore, then use an Center Cut End Mill bit to clean it up with a flat cut.
Wish me Luck :-D

John Traveler1 · « **Reply #6 on:** September 16, 2005, 08:51:02 PM »

I'm cringing already!

If you can find a properly PILOTED end mill cutter, you might get better results. Without that pilot (riding on the lands) I'd suspect your end mill will wander all over the place. What are you using to hold the barreled action? A bench vise with the benchtop drill press hanging over it?

Let us know how your c/b works out!

hylander · « **Reply #7 on:** September 17, 2005, 07:14:30 AM »

I'm using the Standard bit first, that should self center.
Then the End Mill bit just to finish the cut to make it flat.
I'm going to clamp the barrel to the Drill Press Plate.
Ya' I know sounds Oky, but hey I'm from the MidWest :-D
Sounds good inside my head :eek:
We'll see how it works outside my Head :shock:
Oh' Ya':
I do have a Junk Barrel to test on first :wink:

trotterlg · « **Reply #8 on:** September 18, 2005, 11:58:12 AM »

I found a reamer with a .303 shank, cut some edges on the back end of the reamer flutes and put the shank in the barrel for the guide, then chucked the end of the reamer in a drill motor and counter bored a 91-59. Larry

hylander · « **Reply #9 on:** September 18, 2005, 04:53:47 PM »

Well:
I finished the first part of my Counterbore's on my 43 Izzy & 39 Tula
Went about .5" deep with the Standard 3/8" Cobalt bit.
Stuck the barreled Receiver in the vise and Free Handed it with a
Hand Drill :eek:
They look pretty good if I do say so Myself

When the Mill bit gets here I will see if I can make them a touch smoother.

Oh' Ya':
I did a practice run on a junk Muaser barrel, Nice egg shape Muzzle was the result :roll:
However, I had cut it with a hack saw and the face of the muzzle was not flat so the bit walked to one side, The Mosins were unmolested crown's so the bit followed the bore :-D .
I have two More Mauser's I plan on doing.