Fellas, I was looking around on PT&G website and i came across a tool that i cant quite figure out. The tool is called a barrel centering bar. This bar is spring loaded and it claims that this bar will center the barrel to the lathe. This tool is under there new products section if you would like to take a look. How does this work and is it worth having? Please advise. thanks Lee
PT&G tool, Barrel centering bar??
- Thread starter skeetlee
- Start date
JerrySharrett
Senile Member
Doesn't look to me like anything that could be used to dial in a bore?? It implies that it fits and size up to 45 cal. I guess the pointed end goes in the bore??? Then the knurled end must have a center in it???? Then what??????
nhkuehl
New member
I'm only guessing.... it's for chambering between centers. The knurled end is spring loaded to maintain tailstock pressure, so is the groove for the steady rest and you indicate off the bar to center the bore allowing for any tailstock misalignment by adjusting the steady rest? Beats me! Does Dave Kiff weigh in on the forum? - nhk
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Woodhunter
New member
Pretty close.
I have one gathering dust somewhere in the shop.
Barrel through the spindle, the end you are working on (breech or muzzle) extending out the 4 jaw. Other end of the barrel in the cathead or spider. Place point of indicating bar in the center in the end of the barrel, the other end of the bar is secured by the tailstock center. Apply pressure with the tailstock hand wheel.
Place indicator point on the bar as close to the barrel as possible. Rotate the chuck and dial in as usual.
Dialing in to a bore pin (also known as a range rod or a gauge pin) is more accurate. Dialing in to the groves with a long stem tenths indicator is much more accurate.
With the indicating bar you are indicating to the center placed in the end of the barrel, not to the bore or grooves. And you have stacked tolerances due to the sliding fit in the indicating bar and the several machined surfaces of the bar. If your tailstock center is not dead nuts another tolerance rears its ugly head.
I would say this tool is OK for roughing in but not really necessary in barrel work. It is handy though for indicating a rough casting in the 4 jaw or a piece of stock with just a center punch hole marking the center of a hole to be drilled or bored. I used mine when I worked in a machine job shop but never for barrel work.
nhkuehl
New member
Naw, I missed it by a mile. - nhk
MilGunsmith
Member
It is also called a pump center. Used as described for indicating in work off a punch mark or a hole. Since it should not rotate in use, the tolerance stacking issue does not apply.
JerrySharrett
Senile Member
Great idea Skeet, to buy the range rods. Since you are new to all this and do not already have an opinion or bias. Report back and tell us what you think, but please do it in a new thread to keep confusion to a minimum.
Oh, if you order by phone and can get some technical person on, ask about the intended use of the "bore centering" tool.
dennisinaz
New member
Woodhunter, why do you think dialing into the "grooves" with a long stem indicator is "much more accurate" than dialing into the lands with a long stem indicator? Should there be any difference? Which is more important?
Woodhunter
New member
Outer diameter of the bullet rides on the grooves, this is where you want the barrel dialed in.
RE the lands, how do you know if each land is the same height? You are putting your trust into the hands of the rifling button grinder.
All that being said, I usually dial in on a tight fitting bore pin, or range rod, or gauge pin, whatever you call it. I am not worried about benchrest accuracy, a 3/8' to 1/2" group is just fine for my hunting rifles. Besides I am too old and have bad eys and do not shoot benchrest, I just like building rifles.
RE the lands, how do you know if each land is the same height? You are putting your trust into the hands of the rifling button grinder.
All that being said, I usually dial in on a tight fitting bore pin, or range rod, or gauge pin, whatever you call it. I am not worried about benchrest accuracy, a 3/8' to 1/2" group is just fine for my hunting rifles. Besides I am too old and have bad eys and do not shoot benchrest, I just like building rifles.
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Woodhunter
New member
Yea they will rotate, especially if you lube the dead center as you should, or you use a ball bearing center. But tolerence stacking does not need to have rotation.
Don't forget the wobble factor of the sliding fit.
Stack the tolerances: Fit of center in tailstock , tailstock spindle misalignment, accuracy of center in the end of the "pump center", accuracy of the bore and the plunger in the pump center, accuracy of the 60 degree center point on the pump center, accuracy of the center machined into the barrel. The center in the end of the barrel is referenced to where? If a pilot bushing style center drill was used, it is referenced to the bore, not the grooves and it may be out by 0.0002" or more to the lands alone, no telling where to the grooves. You can change the tailstock spindle alignment by how tight you secure the spindle lock. So for the best in dead nuts barrel alignment to the lathe center, do not have that tailstock in the picture!
Extremely accurate machining is plus or minus 0.0001" when grinding. You will be very lucky to hold 0.0002" with machining. So add the numbers.
Accuracy in barrel fitting may be discussed until all of us turn into dust, each guy has his proven method. I just use a simple bore pin and a tenths reading indicator for my hunting stuff. I am not a good enough shooter to use a true benchrest rifle, so I leave the benchrest rifle building to the guys with the correct skills and machinery.
For fun search for and read Butch Lambert's post "50 Millionths Man". I think it is over on the Practical Machinist site, but it may be here on the BR forum also.
dennisinaz
New member
I am still not following you. First, you are assuming that we are all using button barreled rifles. Most of mine are cut rifled barrels. In either case, the barrel is drilled, reamed and lapped before anything else is done to it. The bore at this point is as perfect as anything in the rifle is going to be. Cutting grooves in the barrel does NOT affect this bore. How do you know if the grooves are all cut the same depth?? It is very easy for a cutter to jump a cycle and skip a groove at some point. The bore has not changed. I think it is better to indicate off the original bore on a cut barreled rifle.
Now, on the button rifle. You say we are putting our trust in the button grinder??? Why is the groove any better than the land with this argument?? The same button, ground by the same guy, on the same tooling is swaging the groove is it not? Does the button move the original bore more or less than the lands??
I don't think you are making a very good argument for your method here. It is certainly possible that it is in fact better, but not for the reasons you put forth.
JerrySharrett
Senile Member
IMO, it is much more important, in the chambering alignment, to dial in off the lands. The lands are the result of the drilling and reaming process, not the grooves. The grooves are generated from the tool, button or cutter, that is guided off the original bore, which is the lands. The chamber reamer pilot guides off the lands, not the grooves.
All that being said, sometimes I cut a micro-bevel on the crown. This is a bevel that just cuts from the lands to the grooves, about 0.002" X 45 degrees. If I am cutting a micro-bevel, I indicate off the grooves off that end only.
Why a micro-bevel? It makes the crown much less subject to damage from the cleaning process, and if properly cut, it does not harm accuracy.
Generally though, if your lands and grooves are not concentric you have a crappy barrel anyhoo!!
All that being said, sometimes I cut a micro-bevel on the crown. This is a bevel that just cuts from the lands to the grooves, about 0.002" X 45 degrees. If I am cutting a micro-bevel, I indicate off the grooves off that end only.
Why a micro-bevel? It makes the crown much less subject to damage from the cleaning process, and if properly cut, it does not harm accuracy.
Generally though, if your lands and grooves are not concentric you have a crappy barrel anyhoo!!
dennisinaz
New member
This is exactly my logic. Glad someone else agrees with it.
Incidently, if you are using a Gordy rod, this is what you are bearing on, not the grooves. I won't get into the tolerance stacking argument.
MilGunsmith
Member
The way I was taught to use a pump center, by the old toolmakers, was to put the indicator as close to the point as possible. Do not let it rotate, and the only movement should be of the point in the punch mark of the work. It is like putting a right angle, pointed extention on the indicator. The same principle as the grizzly rod, except a point instead of a pilot.
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Spring loaded pointed center or pump center..
This tool was designed when barrel work was mostly done center to center. Brownells and MSC has sold this tool for 50 plus years. Works great for what it was designed for. This tool has been replaces by the piloted rods and deltronic pins.
I'll bet my friend Kevin (Military Gunsmith) even has one in his tool box.
Nat Lambeth
This tool was designed when barrel work was mostly done center to center. Brownells and MSC has sold this tool for 50 plus years. Works great for what it was designed for. This tool has been replaces by the piloted rods and deltronic pins.
I'll bet my friend Kevin (Military Gunsmith) even has one in his tool box.
Nat Lambeth
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MilGunsmith
Member
I have two in my box, one I made over 40 years ago and the other was my grandfathers.
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JerrySharrett
Senile Member
Thats OOOLD technology. Back in the days when we were still running our lathes off a water wheel and still watching TV by candle light (light bulbs had not been invented) we used a nail point on a Willow limb for that chore!!
F