Chamber Pre-Boring Thoughts

[jackieschmidt]

@jackieschmidt where do you source those bits?

the drill is just a twist drill ground 30 degrees

I ground the boring bar from a larger one. It is solid High Speed Steel.

 

[jackieschmidt]

* Dial it in the "Gordy way"
* thread tenon

Here are the extra steps
* see where the high spot on the muzzle end is, mark "top" on the chuck
* see how far off your action is from that top mark....
* do some math and recut the shoulder/breech end.

Takes 10 minutes "extra" if I'm also petting my dog.

Jackie, I know you're a BR guy so probably dealing with short(er) barrels. I'm doing stuff that's 10-15 inches longer, 30-32 inches. Everyone likes nice even land engagement, the "gordy" method gets you there.

If you have a 32 inch barrel that's 100 thou out from end to end, it makes sense to take a couple extra minutes and get the chamber aligned to the bore, vs the barrel aligned to the stock.

Thanks.

 

[jackieschmidt]

I will thow this out for people to ponder. I ran a wire edm for 25 years in a mold shop. Half my time was spent straightening out reamed holes. There is nothing guaranteed about a reamer following a hole. It can be like playing Russian roulet with a 6 fluted boring bar, which flute will cut this time? One dull edge will push the load to the opposite flute.

I have always said that reaming is about the worst way to produce a round truly straight hole.

That is one reason I keep as much of the reamer out of the equation as possible.

Basically, I am using the reamer just to establish the final shape and finish of the chamber.

By the way. I turn all of my chambering reamers by hand. It is really not that tedious because of The minimum amount of metal the reamer actually removes.

 

[Judd]

the drill is just a twist drill ground 30 degrees

I ground the boring bar from a larger one. It is solid High Speed Steel.

Your old timers and your grinders, I suspected that was going to be your answer…a quick check and I couldn’t find them anywhere. Thanks dude.

 

[DaveTooley]

Glad I'm on vacation and typing this on my phone. I'll just add a true roughed hole makes for a concentric chamber. The word concentric isn't used often but that is the single most important part of this.. Many ways to get there.

 

[therifler]

Your old timers and your grinders, I suspected that was going to be your answer…a quick check and I couldn’t find them anywhere. Thanks dude.

not many of us old timers left . grinding your own tools have been lost owing to the new tool advancments .

 

[Judd]

not many of us old timers left . grinding your own tools have been lost owing to to the new tool advancments .

You’re exactly right. I wouldn’t know where to begin past turning on the grinder . I also don’t claim to be a machinist.

 

[therifler]

You’re exactly right. I wouldn’t know where to begin past turning on the grinder . I also don’t claim to be a machinist.

i've been doing it for umm let me get a calculator, oh 54 years all manual . when the grinding wheels went bad we went down to creek and found a smooth flat rock and used that.

 

[Jonnyofalltrades]

My first question is, has anyone ever used a solid carbide endmill to rough bore the chamber? My thoughts were it wouldn't walk like a drill and it should cut a clean concentric hole for the reamer to follow. You could use for instance, a 7/16" endmill to rough bore a 308 chamber and that would leave roughly .008 per side under finished shoulder diameter. This would alleviate having to drill then bore the hole true and bore out the drill tip angle.

I though that's what would happen too. It didn't.
The endmill walked around in the hole and it ended up being about .025" oversized.
The lathe was a Colchester in good condition.

 

[DaveTooley]

i've been doing it for umm let me get a calculator, oh 54 years all manual . when the grinding wheels went bad we went down to creek and found a smooth flat rock and used that.

You are old

 

[DShortt]

Love the flat rock in the creek comment! That's hilarious!

i've been doing it for umm let me get a calculator, oh 54 years all manual . when the grinding wheels went bad we went down to creek and found a smooth flat rock and used that.

 

[DaveTooley]

I though that's what would happen too. It didn't.
The endmill walked around in the hole and it ended up being about .025" oversized.
The lathe was a Colchester in good condition.

Endmills have to be held rigid. I have some form tools for crowning barrels. W/O a pilot they dance around. I use them in the Haas held rigidly. No bushing required.

 

[Will Henry]

I have a lot of cutters which look a lot like the ones Jackie shows. Sometimes, that's just how things get done.
I have use an end mill (2 flute) as a boring bar. A 3/8 milling cutter, held in a boring tool holder, works great for things like cutting the counterbore on a Remington barrel. I don't think it would be an option as a chamber rougher though.
A properly ground drill, set straight and fed right, doesn't wander. It will follow the pilot hole (the bore in this case) absolutely. It will also drill surprisingly well in solid stock, but that's another story.
I started gunsmithing in the mid-seventies. Common practice in those days was to true the center cut in the breech and muzzle end of the barrel (generally, with a piloted center reamer) then set the barrel up between centers and drive it with a lathe dog. The tenon and threads were cut with this set up and a truing cut was made on the barrel shank. Once the barrels were threaded (I usually did a half dozen or so in a batch), the faceplate was removed and the three jaw chuck reinstalled. The barrel was held at the muzzle end and the shank was run in the steady rest. The chamber was roughed with a twist drill, to within about .050 or so of the shoulder. If the cartridge was a long one, the chamber was drilled just deep enough that the pilot still reached. The chamber was finish reamed (in the case of the long chamber, it was reamed, drilled some more, then finished) and the chambering job was done. In many cases, the job was done this way because the headstock spindles weren't big enough to work through the headstock. Mostly though, it was expedient. Many barrel makers used the same system but didn't bother setting up between centers. They just held the barrel in the chuck, threaded while supporting on the tailstock center, then chambered in the steady rest. This method is still used by many and, as long as the barrel is reasonably straight, good results are attained.
In an attempt to improve my set up, I decided to set up in the four jaw chuck and use a tiny boring bar to cut the center in the barrel; so I could be more certain it would run true between centers. I could dial the barrel in dead nuts and bore the center. It only took a couple barrels before it dawned on me; if I was already all dialed in why not go ahead and thread and chamber in the chuck? So I did. About then, I read that Ferris Pindell was roughing his chambers with a boring bar, so I tried that for PPC's and BR's. For hunting cartridges I just went with the drill and ream. I stayed with the 4 jaw set-up, unless there was some reason to use the steady (barrel too short, integral sight base etc.) Over the years I have refined my techniques to the extent that I can, kept some and abandoned others. A barrel I did last night was set up as Jackie described, pre-bored and chambered (a 6mm Dasher). One I'll be doing today, (a featherweight 6.5x55) will be done similarly, but will be roughed with the drill and finish reamed. My indicator won't reach the throat 55mm in, so I indicate as deep as I can and let the cutters do their best from there. I always indicate the drilled hole, and if it does run out, I'll bore for a half inch or so to give the reamer a straight start. That has always worked out OK.
A 30/40 Krag barrel I'll be doing for a Model 95 Winchester will get set up in the steady and done that way. Make the method fit the job. WH

 

[therifler]

You are old

yeah dave i've been around . 68 born with a micrometer as a pacifier .uncle was a machinist ,my cousins,my brother my nephew ,my niece . yeah we been brought up machinist and the other half are Doctors .

 

[DaveTooley]

yeah dave i've been around . 68 born with a micrometer as a pacifier .uncle was a machinist ,my cousins,my brother my nephew ,my niece . yeah we been brought up machinist and the other half are Doctors .

Hell I'm 73. Did a couple of years in the service before getting a degree in Industrial technology. I started smithing with nothing but HSS. Hell I couldn't afford carbide even if I knew what it was.

 

[Carl S]

A drill bit alone won't guarantee you a straight concentric hole.a boring bar is a better bet, especially when you take those light cuts prior to reaming.the less material the reamer has to cut the better it is.reamers are for reaming not drilling.keep things simple.trying to reinvent the wheel isn't always the best way..do what works for you.

 

[therifler]

Hell I'm 73. Did a couple of years in the service before getting a degree in Industrial technology. I started smithing with nothing but HSS. Hell I couldn't afford carbide even if I knew what it was.

well then you probably brased a couple carbide ones together in the day .

 

[therifler]

i guess to answer the question about end mills . boring bars are best for the chambering. when i make my muzzle brakes i use end mills they may wander .004 to .005 tho. but finish machining takes that out .

 

[Will Henry]

For quite a few years, I worked in a shop which specialized in hydraulics, but we would build anything. Anyway, one task was the production of hydraulic cylinder rods with a hole up the center (for tempasonic position sensors). One batch of rods we had to make were 54 inches long, with a 9/16 hole 52 inches deep. I drill these with a common twist drill, silver soldered to an extension. The length of the drill and extension was 29 inches. I drilled a 1/2 inch pilot hole, two inches deep; then bored it to about .550". I then drilled to about 28 inches with my drill and extension. I could drill about a half inch before pulling out to clear the chip. I drilled from both ends and met in the middle. Usually alignment appeared to be within .010" or less. In fact, there was often no misalignment at all. So a twist drill can do remarkably well, providing it gets a good start, is properly ground, and is pushed just a little bit.
Like I said, drill the hole and check it. If it indicates concentric, it is concentric; doesn't matter if you cut it with a spoon. If it is not concentric, then take a cut with the boring bar. WH

 

[DShortt]

For quite a few years, I worked in a shop which specialized in hydraulics, but we would build anything. Anyway, one task was the production of hydraulic cylinder rods with a hole up the center (for tempasonic position sensors). One batch of rods we had to make were 54 inches long, with a 9/16 hole 52 inches deep. I drill these with a common twist drill, silver soldered to an extension. The length of the drill and extension was 29 inches. I drilled a 1/2 inch pilot hole, two inches deep; then bored it to about .550". I then drilled to about 28 inches with my drill and extension. I could drill about a half inch before pulling out to clear the chip. I drilled from both ends and met in the middle. Usually alignment appeared to be within .010" or less. In fact, there was often no misalignment at all. So a twist drill can do remarkably well, providing it gets a good start, is properly ground, and is pushed just a little bit.
Like I said, drill the hole and check it. If it indicates concentric, it is concentric; doesn't matter if you cut it with a spoon. If it is not concentric, then take a cut with the boring bar. WH

Had a moment of clarity a while back and bought some sharpening gauges. That'll open your eyes if you sharpen bits by hand for roughing work. And not in a flattering way.