? chucking up a barrel ?

Goodness...what an interesting thread. Amazing what you can find here!

I just can't help but say that the posts in this thread concerning alignment and the evils therein are excellent but are founded on assumption. Said differently, the initial reference point is the assumption that "straight" is better.

Surely, straight is the easiest way to go..imagine having to cut a chamber that is crooked just enough to make it shoot.
 
JerrySharrett said:
Fitch,
1 Yes.

2 Look at the reamer body. Drill a hole that is about 0.020-0.030" smaller in diameter than the cartridge is at the shoulder and stop the drill about 1/8" or so before where the cartridge shoulder will end. Then take a couple of light boring cuts about 0.005"/side and about 3/4" or so deep. What you will find is that the reamer bushing will enage the bore about 1/2"-3/4" before the reamer body starts cutting.

That is why it is best to have a straight hole not a tapered one, IMO. An experienced machinist like Jackie will have his compound set precise enough that in that situation it will not bias the chamber orentation. But if, say a novice, gets the angle wrong or cuts too much he may overbore the chamber.

If you are in doubt of what I am trying to explain, start the process by drilling more shallow, then and boring more shallow than I suggested above. Then insert the reamer and think about what is enagaing and where. I think you will end up in the general area I explained above on just about any bottle-neck cartridge.
Click to expand...

if the reamer follows the reamer bushing, how does pre-boring help? I understand that it minimizes wear on the reamer, but if the reamer is following the bushing, how does boring make a 'straighter' hole?
 
About a week ago I was dialing in a barrel when it decided to go weird. I use copper wire inside my jaw grooves so I can hold the piece with a pivot point. When I adjust the cathead the barrel pivots on the wires and I expect the needles to move a certain amount. I loosen and retighten both ends when I get perfect to make sure I did not induce deflection. Actually, it does cause a tiny bit of deflection so I know I need to relax it and start over, sometimes more than once if I place too much torque on one jaw to get it to align. I trust nothing. When I retightened this particular barrel, the dial moved in one direction then back the other, WTF? After a few minutes of concern because I was deflecting the barrel I noticed I had missed one of the copper wires and that jaw was flat against the barrel.

Preboring ensures the reamer will follow the pre bore diameter up until the pilot starts in the lands. After that the pilot will bend if it is not aligned straight and the chamber may go oversized if the barrel alignment is out too much. I dial it in then cut the major diameter up to almost full tenon length, recheck the indicators and then use that tenon major diameter to check on, then prebore, then recheck the indicators. After chambering I check and after threading I check again. Luckily I haven't had any readings past the test equipment's repeatabillity.
 
simple...no bushing and let the reamer follow the pre bore...
you have to indicate the bbl at the throat before the prebore....

mike in co
AMMASHOOTA said:
if the reamer follows the reamer bushing, how does pre-boring help? I understand that it minimizes wear on the reamer, but if the reamer is following the bushing, how does boring make a 'straighter' hole?
Click to expand...
 
mike in co said:
simple...no bushing and let the reamer follow the pre bore...
you have to indicate the bbl at the throat before the prebore....

mike in co
Click to expand...

i understand that -- except the post i quoted had the bushing on the reamer. i see that the idea is to not permit the chamber to go oversize.
 
AMMASHOOTA said:
if the reamer follows the reamer bushing, how does pre-boring help? I understand that it minimizes wear on the reamer, but if the reamer is following the bushing, how does boring make a 'straighter' hole?
Click to expand...

Several factors to consider. No barrel bore is perfectly straight so there must be several compromises made.

First compromise is where, how close and what with do you align the barrel in the lathe?

By where I mean what point(s) do we pick for alignment.

By how close, I mean how close do we need to indicate (0.010", 0.001", 0.0001" ??).

And by what with I mean do we use some kind of alignment rods and what design and how are they to be applied, or do we use a dial indicator that allows for direct reading on the alignment surfaces. I propose that any of the rod designs are indirect alignment tool since the measurement of the rods must take place outside the barrel.

Now, consider that if the reamer, which is probably HSS, will flex slightly there must be two points to stabilize it while reaming. If the front of the reamer is guided by a close fitting bushing and if a second point is along the reamer body then the reamer is very limited and should create a true chamber. That second point, IMO, should be a prebored guide hole that runs true with the area of the chamber where the bullet enters the barrel bore. That true bored hole can be a cylindrical hole or a conical hole the taper of the chamber body.

The next compromise must be made by the reamer itself in that if a portion of the curve is immediately ahead of the freebore/leade the reamer must flex slightly to make a true merge of the chamber to the bore. Remember, we are not talking about much curve. probably a maximum deviation of, say 0.010" from end to end.

Now, if all that 0.010" deviation is at the point where the bullet enters the barrel, (i.e. a 0.010" offset) the barrel certainly would not shoot very well. But we have eliminated any curvature in the immediate chamber area by preboring to guide the reamer body and using a tight bushing and that is the best we can hope for.
 
i'm different than both.
no need to expect the reamer to flex or bend,
you cannot control the flex/bend so why plan or depend on it ?
i use the prebore to guide the reamer and no bushing.

mike in co
 
mike in co said:
i'm different than both.
no need to expect the reamer to flex or bend,
you cannot control the flex/bend so why plan or depend on it ?
i use the prebore to guide the reamer and no bushing.

mike in co
Click to expand...

what happens when the reamer moves completely forward of the pre-bored area if there no longer is a bushing to guide it?
 
Not sure I follow you here, but the reamer is going to follow the pre-bored hole and continue past that still being guided by the hole previously bored, because the reamer will never totally leave the pre-bored hole. As long as your set-up is dialed in correctly it's not going to wander. If your not dialed in right with no bushing I could see the chamber getting out of round.

If you're not going to pre-bore, you should just cut the whole chamber with the finish reamer by letting the bushing guide the whole way.

Every chamber I have cut after initial dial in with a range rod and 2 indicators to .0002 or less have only been off .0005" or less at the throat. Then I tweak the set-up with the dial indicator (no range rod) at the throat to dead nuts. Then pre-drill, then go in with boring bar to make the hole concentric.

After I'm done with the chamber, I indicate check my work at the throat, neck and base of chamber. This will tell you if your set-up was good.
 
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Reducing bushing size

I've remembered Butch's comments about reducing bushing size and letting the bored and reamed hole guide the reamer.

My potential concerns have been about what effect bore curvature just ahead of the throat will have on the body portion of the chamber. Without a lot of experience to guide me, it seems to make sense to remove or reduce the size of the bushing once the bushing works it's way past the initial point of indication, the throat----but I don't know.

One of my reamers is an older model with the leading edge of the bushing positioned about 3/4" ahead of the later Kiff reamers.

I've tried to compensate for the bushing being so much forward of the throat by checking the runout ahead of and behind the throat----have been lucky and not found any significant difference but have thought I should consider cutting off a bit at the chamber end of the barrel---if---there were significant differences in runout ahead of and behind where I wanted to locate the throat. Luckily, I've never had to do this.

I've been very lucky in that my barrels have allowed me to locate the throats in the middle of a straight section that is a minimum of three bushings long------don't know just how to handle a barrel that throws me a curve in this section.

The method of holding the reamer by hand while pushing it into a prebored hole just plain works----all chambers have appeared to be cut to reamer size.

Any opinions on the effect of bore curvature just ahead of the throat ?

A. Weldy
 
"................Any opinions on the effect of bore curvature just ahead of the throat ?

Don't have an opinion but I have an example. PJ Hart placed well at the Super Shoot (once upon a time) with a barrel (bore) that was very very "curved". So curved that when you looked through it you saw an oval at the other end.

That said, I suppose I do have a minor opinion but it ain't worth writing about. Especially since I didn't catch anything in my "straight is better" net - except that tin can and rusty hubcap from Al.
 
If you indicate the throat and prebore to that indication, your bullet is seeing straight at that point. It really doesn't matter if the bore wanders after that and you couldn't do anything about it anyway. I don't care what method you use to indicate, you still can't straighten the bore out.
Butch
 
My thoughts exactly Butch. If you was to indicate dead nuts ahead of the throat a few inches or whatever, then how in the world would the bullet be seeing straight at the point in which it starts??? Unless of course the bore is perfectly straight, which none are.

IMHO, you start the bullet as straight as you can, then after that the barrel bore will do what it is going to do. Do your best at cutting a concentric chamber from that point back and that's about all you can do.
 
I am not intending to "stir the pot" here. Just want to offer some thoughts on a little experiment I did.

For giggles and grins I did a little experimenting with the rod method on a barrel with curved bore last night and this morning. One of the things that has bothered about the long or short rod method supported by bushing at the throat is that the rod is usually "grabbed" in a chuck, collet or something in the tail stock. That means that any movement of the rod from there to the throat creates strain in the rod. I wondered what that would do to the TIR that was being read on an indicator at the rear of the barrel. I set up that barrel and roughed it in on Deltronics pin at the butt of the barrel. The muzzle is allowed to rotate on a centered pin in the spindle. I "grabbed" the 6 inch rod in a Albrecht chuck in the tail stock and advanced the rod to coincide with where the bushing would be when the chamber was complete. A weight was hung on the rod 1 inch from the end of the barrel and the rod was indicated about 1/8 inch from the back of the barrel. I indicated until I had .0004 TIR-not good enough for chambering-but good for doing this experiment. I then rested a small ball point in the tail stock and rested against the center hole in the back of the rod. I put a retainer on the rod with elastic bands to pull the rod tight against the ball. The indicator then read .0002 TIR.

This tells me that if one wants to use the rod method, "grabbing" the rod in the tail stock and the associated strain that is induced in the rod will effect the readings one gets.

Will be doing some barrels for myself with three different methods to see if I can sort out effects and results. On a side note I won five Hall of fame Points with a Scrap barrel that was extremely crooked in the bore. I chambered it with a core reamer, a resize reamer and a finish reamer letting each one float with bald Eagle floating reamer holder. Chamber came out correct size with even throat. Gun shot great. Could not push the loads as chamber was not dead perpendicular to the axis of action because the reamer had followed the hole.


Jim
 
Jim

Thanks for the reply. It's always great to read your comments.
It will be interesting to read about your chambering results.

Hal
 
Jim Borden said:
This tells me that if one wants to use the rod method, "grabbing" the rod in the tail stock and the associated strain that is induced in the rod will effect the readings one gets.

Will be doing some barrels for myself with three different methods to see if I can sort out effects and results. On a side note I won five Hall of fame Points with a Scrap barrel that was extremely crooked in the bore. I chambered it with a core reamer, a resize reamer and a finish reamer letting each one float with bald Eagle floating reamer holder. Chamber came out correct size with even throat. Gun shot great. Could not push the loads as chamber was not dead perpendicular to the axis of action because the reamer had followed the hole.


Jim
Click to expand...

Jim, does this mean you and Joan are letting the eagles and squirrels rest for a while?

I'm not following you on your "chamber not being dead perpendicular to the axis of the action" (coaxial, parallel??). Can you please elaborate?
 
Jim,
Since we are stirring the pot...The rod that you used for your test, is not the one that Gordy uses. It is 13" long, and I believe that the instruction is to hold it with the tips of the tailstock chuck. Being an engineer (which I surely am not) I am sure that you are aware of the effect that doubling the length of a cantilever has. (For the rest of us, the deflection for a given end load is quadrupled.)

Also, related to Jerrys' question, what do you think about turning the shoulder and tenon after the chamber is cut, so that they may be perpendicular, and parallel to its CL ?
 
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You make me think too much Jim....but I like that. What about capturing the end of the Grizzly rod in the tailstock chuck jaws via small piece of.... lets say copper wire around the rod, like so many do when chucking up the barrel in the headstock, to allow that pivot motion when dialing in from the outboard side of the headstock?
 
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