Previous Drilling of Chamber

[Riesel]

OK, I have what may be a very simple question. When predrilling a chamber, how much smaller than
what (?) measurement on the reamer or case do you use. After predrilling, how exactly does the reamer work if no bore for the pilot to follow? If you predrill, do you abandon the floating reamer and chuck up in the tailstock after removing the drill bit. I'm working on a 6 Creedmoor for this project.
All threading and bolt nose relief work have all been done and barrel is through headstock dialed and rechecked from the get go using range rod on four jaw chuck and 4 way spider on outboard.

Thanks in advance,
Robert

 

[Cloudrepair]

OK, I have what may be a very simple question. When predrilling a chamber, how much smaller than
what (?) measurement on the reamer or case do you use. After predrilling, how exactly does the reamer work if no bore for the pilot to follow? If you predrill, do you abandon the floating reamer and chuck up in the tailstock after removing the drill bit. I'm working on a 6 Creedmoor for this project.
All threading and bolt nose relief work have all been done and barrel is through headstock dialed and rechecked from the get go using range rod on four jaw chuck and 4 way spider on outboard.

Thanks in advance,
Robert

However your set up or dialed in if your going to predrill I would drill it small enough to bore it .005-.010 per side under shoulder diameter before reaming because your drill will follow the bore of the barrel.
so it will not be true to the dialed in points without boring it to the final pre ream diameter.
I usually aim for .014 under shoulder diameter

 

[ridgeway]

I leave .010 after BORING with a boring bar and .010+ short on lenght. Use the twist drill for roughing. Twist drills won't make a round precise hole.

 

[Riesel]

Thanks, if I'm following you correctly, by having the predrilled hole .014 under shoulder size allows the reamer pilot to enter the bore and now begins
to actually cut the chamber with the reamer pilot leading the way. That sound about right?

 

[Cloudrepair]

Thanks, if I'm following you correctly, by having the predrilled hole .014 under shoulder size allows the reamer pilot to enter the bore and now begins
to actually cut the chamber with the reamer pilot leading the way. That sound about right?

Not really
The reamer will follow the trued bored hole.
I leave the removable pilot off most of the time if you dial in the throat and a inch or two ahead of it it wouldn't matter if you left the pilot on it will help guide the last half inch or so.
Of coarse this is just my experience

 

[Cloudrepair]

If you dial in the muzzle and throat the way i do then the pilot may try to influence the reamer off track when it engages the barrels bore before it gets to the throat area dialed in.
Or when it passes it maybe just a couple tenths or so but maybe enough to cause trouble

 

[Someoldguy]

Not really
The reamer will follow the trued bored hole.
I leave the removable pilot off most of the time if you dial in the throat and a inch or two ahead of it it wouldn't matter if you left the pilot on it will help guide the last half inch or so.
Of coarse this is just my experience

I have wondered about the same thing as the OP. So . . . . . if I follow what you are saying, an un-piloted reamer would render the same results with the system you use? I thought the entire premise behind piloted reamers with changeable bushings was to try and keep the throat/chamber as concentrically aligned with the bore as possible, along with floating reamer holders, provided a reasonable amount of care has been taken to mount the barrel concentrically within the lathe.

No need for the reamer pilot/bushing? Isn't this the primary reason blamed for factory rifle throats/necks which are found non-concentric? This doesn't make sense to me. I apologize if I mis-understand. Could you please elaborate?

 

[Someoldguy]

If you dial in the muzzle and throat the way i do then the pilot may try to influence the reamer off track when it engages the barrels bore before it gets to the throat area dialed in.
Or when it passes it maybe just a couple tenths or so but maybe enough to cause trouble

And I apologize once again if I mis-understand, but if the chamber area has been drilled and counterbored oversize so that the pilot is not in contact with the bore any longer, how can the pilot and/or pilot bushing possibly affect the path of the reamer? And would the bore not have to be curved significantly for the area between the neck and throat to be out a couple of tenths?

I'm not trying to start an argument, but this confounds me . . . . .

 

[TRA]

Thanks, if I'm following you correctly, by having the predrilled hole .014 under shoulder size allows the reamer pilot to enter the bore and now begins
to actually cut the chamber with the reamer pilot leading the way. That sound about right?

What they are saying is "their" chambering methods are a 3 step process.

1. Use a drill bit to enlarge the barrel chamber area.

2. Bore the rough drilled chamber with a boring bar at the identical taper, that the reamer is ground , leaving .010 on the od and the depth.

3. Finish ream the chamber with the finishing reamer.

FWIW, nothing follows anything unless the semi finished chamber is the same shape as the reamer. Twist drills will not follow a smaller bore. That drill will go wherever it wants. You will drill a accurate hole in a piece of solid far sooner than enlarging a existing smaller hole.

 

[Someoldguy]

FWIW, nothing follows anything unless the semi finished chamber is the same shape as the reamer. Twist drills will not follow a smaller bore. That drill will go wherever it wants. You will drill a accurate hole in a piece of solid far sooner than enlarging a existing smaller hole.

I suspect many opposing views will soon ensue. Perhaps the key is, follow or not to what extent?

I DO know that if a twist drill is dull or incorrectly sharpened, then an oversized hole is certain to follow.

 

[TRA]

I suspect many opposing views will soon ensue. Perhaps the key is, follow or not to what extent?

I DO know that if a twist drill is dull or incorrectly sharpened, then an oversized hole is certain to follow.

I have small drills, solid carbide and the last thing you do to one is, open up a predrilled hole in steel.Carbide coated Twist drills cost between 275.00 and 500.00 each. Enlarging a hole with a drill damages the outer edge of the flute and the drill wanders anywhere it wants to. Then your carbide drill is junk, as you have chipped or burnt the lip edges.

It really makes no sense to drill a ragged off axis hole and then bore with a boring bar. Enlarging a bore with a twist drill is totally against all good machining practices.

 

[Someoldguy]

I have small drills, solid carbide and the last thing you do to one is, open up a predrilled hole in steel.Carbide coated Twist drills cost between 275.00 and 500.00 each. Enlarging a hole with a drill damages the outer edge of the flute and the drill wanders anywhere it wants to. Then your carbide drill is junk, as you have chipped or burnt the lip edges.

It really makes no sense to drill a ragged off axis hole and then bore with a boring bar. Enlarging a bore with a twist drill is totally against all good machining practices.

Solid carbide, or carbide coated?

I do not recall any solid carbide small diameter twist drills costing between $250 and $500. 10% of that amount seems high . . . . .

I have never seen or used carbide coated twist drills, but it would seem a coated twist drill would be cheaper, not 10x more. (?)

And you are contending that all gunsmiths who pre-drill and then counterbore barrels are not following good machining practices?

That's odd. Such practices seem to be working quite nicely for quite a number.

 

[TRA]

Solid carbide, or carbide coated?

Solid and coated --solid meaning ground from solid round JFYI, a 3/8 drill can run 275.00 on up for a` quality drill. You obviously have not bought any hi quality tool.ing lately.

And you are contending that all gunsmiths who pre-drill and then counterbore barrels are not following good machining practices?

That's odd. Such practices seem to be working quite nicely for quite a number.

What about all the others?
Take it any way you want. Why dial,dial,dial,dial,dial to get a perfect setup then shove a drill and push the bore all over and then have to try to clean it up with a less than stable boring setup. then pray the reamer runs true.

You that proclaim that your drill, bore, then float a reamer in is the holy grail, there are a few well known chamber men who have talked in the past as to the gyrations it takes to get a 300 HH , 300Wea. or a 338l chamber in straight. The above methods only works on the little short cases such as the dashers and the ppc's.

 

[Riesel]

I want to thank all for your comments and input, but I believe the "Call of the Sirens" has passed and I've got cold feet. Seems to me I would be looking for trouble and I don't really need any more of that. I'll just keep my ship on a steady course.
Again, Thanks,
R

 

[Cloudrepair]

I have wondered about the same thing as the OP. So . . . . . if I follow what you are saying, an un-piloted reamer would render the same results with the system you use? I thought the entire premise behind piloted reamers with changeable bushings was to try and keep the throat/chamber as concentrically aligned with the bore as possible, along with floating reamer holders, provided a reasonable amount of care has been taken to mount the barrel concentrically within the lathe.

No need for the reamer pilot/bushing? Isn't this the primary reason blamed for factory rifle throats/necks which are found non-concentric? This doesn't make sense to me. I apologize if I mis-understand. Could you please elaborate?

Maybe I can explain it like this, drilling a .125 hole through 5" of stainless on a mill that needs to be on axis of the spindle of the mill. And you don't want to use a carbide drill that you need for a production run. So instead you use a hss #38 drill .1015 and drill a 1.000 deephole then you follow with a 7/64 .1094 endmill 1.000 inch deep then you drill it with a jober lengthy #32 .116 2.000" deep then with a extended length
.125 drill the rest of the way through now you have a hole that stayed on axis of the spindle better than if you used just a spot drill and a extended length drill.
Same principle on a lathe only the spindle is holding the part so thing have to be changed the bored hole is doing the same thing for the hss reamer as the endmill in the above refrence.
If you are using a carbide reamer or drills methods change.

What I am saying may be hard on the hss drills but that is why most machinist know how to sharpen them correctly. There are always compromises

 

[Cloudrepair]

I forgot to say when a deep hole is drilled the drill will wander that is the reason for pilot drilling methods
The pilot on a reamer will follow the bore that has wandered through the barrel.
These are the methods machinists use to place holes where they want them
Good machining practises I guess are subject to someones views.
And expectation Of accuracy.

 

[kendog]

...
What about all the others?
Take it any way you want. Why dial,dial,dial,dial,dial to get a perfect setup then shove a drill and push the bore all over and then have to try to clean it up with a less than stable boring setup. then pray the reamer runs true......

Reminds me of my ironworking days! We had a saying, "measure it with a micrometer, mark it with a keel (lumber crayon) , and cut it with an axe".
Me thinks most of this pre drilling stuff is extra work with a dose of witchcraft added.

 

[swd]

I want to thank all for your comments and input, but I believe the "Call of the Sirens" has passed and I've got cold feet. Seems to me I would be looking for trouble and I don't really need any more of that. I'll just keep my ship on a steady course.
Again, Thanks,
R

The previous responses have seemingly GREATLY complicated this very simple step. Running a drill in and taking the hole to .015"ish under the shoulder size is really easy and doesn't take hardly any time. It's not remotely hard or rocket science, works very well and doesn't take much if any more time than it does to read the complete thread.

Use a drill .020"-.040" smaller than the shoulder.
Run it in .010"-.030" shy of the shoulder depth.
True the hole with a boring bar to .010"-.015 under the shoulder diameter. Take a few zero passes.
Chamber your barrel. I still use a bushing.
Done.

I do it on everything larger than a Hornet chamber. The larger the chamber the more time it saves and helps keep the wear and tear off your reamers.

 

[ridgeway]

There is absolutely no need to run carbide twist drills for gunsmith work, lol. On a side note, carbide twist drills can be resharpened over and over again...If anyone is throwing away chipped carbide twist drills and endmills, send them my way. I'll pay postage, lol.

Like stated numerous times...Use the twist drill to rough and finish bore to make the hole round. The reamer will do the rest.

 

[TRA]

There is absolutely no need to run carbide twist drills for gunsmith work, lol. On a side note, carbide twist drills can be resharpened over and over again...If anyone is throwing away chipped carbide twist drills and endmills, send them my way. I'll pay postage, lol.

Like stated numerous times...Use the twist drill to rough and finish bore to make the hole round. The reamer will do the rest.

The comment was in response to someone questioning my statement that enlarging an existing hole with a twist drill was a bad machining practice.

Try to keep up guys, no one ever said anyone needed to use a carbide drill on a gun barrel. The fact is a drill will not follow an existing hole or bore, as has been stated here many times and it destroys the drill in the process, . That Info is available from just about any drill manufacturer. It's fact, not just my opinion.