True Bore Alignment System

[BuffaloBill]

Direct dial at a pivot. And thats all Im going to say...

Otherwise too much interaction…….

 

[Larry Koch]

Cracks me up when I hear its only good to .0005". The speedo on my truck only reads every 10 mph too. I blew up the dial and measured the width of the marks. The black line is .00011" wide. So theres your tenth mark.

just use a hammer and a nail.

 

[xr650rRider]

Otherwise too much interaction…….

Indicating at 1 point doesn't mean the part is running true.

 

[FireMedic]

Jackie brings up a point that you never see talked about. Balance. There was an issue with a very good action got traced back to that problem. When you dial in a part, it’s not spinning. When you turn the lathe on, if the chuck or part is out of balance things will flex due to centfifical force and your part is no longer dialed in while spinning. Yes this is a real problem. One of the reasons that I have not gone cnc or bought this style of chuck. Theres other reasons but balance is the main one.

If the part is held securely in a 6 jaw and the bearings are good and adjusted correctly, then how relevant is this? What is flexing?

I use a tbas with a tmx 6 jaw. I can indicate the barrel in, drill, bore, then check the bored hole, and a .0001 indicator and it doesnt wiggle.

The chamber throats come looking square (provided the groove doesn’t have any ratchet) and the chamber is on size.

I chamber at lower rpm (typically 150-200 depending on the reamer). I don’t see balance becoming a factor at those speeds if you have a rigid machine with good bearings.

When I used an inboard/outboard spider, I typically would get some movement in the setup during the machining process. Some times it was just a couple tenths, sometimes it didn’t move at all. But the movement disappeared when I went to a tbas. I do still support the outboard end with a spider to keep that end of the barrel from whipping. it does provide some additional holding force in the system as well.

 

[xr650rRider]

I use a tbas with a tmx 6 jaw. I can indicate the barrel in, drill, bore, then check the bored hole, and a .0001 indicator and it doesnt wiggle.

No matter how you hold and it can have considerable runout. After you bore, then the bore will indicate true to the spindle, unless your spindle bearings are worn out. So your indicator not wiggling is saying, my bearings are good, nothing more.

 

[FireMedic]

No matter how you hold and it can have considerable runout. After you bore, then the bore will indicate true to the spindle, unless your spindle bearings are worn out. So your indicator not wiggling is saying, my bearings are good, nothing more.

Let’s think this through…

If the area you feel is important is dialed in to .0000. For me that’s the shoulder to about where the bushing will end up.

Then you bore out the bulk of the chamber….

Then you recheck the area you dialed in and the area you bored and they both still read .0000 then explain to me where the runout is?

Not calling you out, just wanting to learn something

 

[Alex Wheeler]

You cant check runout when your running 200 or 800 or whatever rpm. If we are trying to dial to less than .0001" then yes this matters. Put a .0001 indicator on a part and lift the chuck with your hand or a small pry bar. Theres plenty of flex going on. It doenst take much to flex a spindle a tenth. The issue I mentioned with the custom action was made on a much more rigid machine than we use to chamber. And it flexed enough to cause major issues.

 

[DaveTooley]

There is always work piece deflection when turning. Reaming not so much.

 

[FireMedic]

I believe borden uses a trubore when machining his actions

 

[Alex Wheeler]

He does use one for some ops. Or at least he did. I consider Jim a friend. We kind of see things the same way. I dont think he uses one to chamber barrels. Its not a bad tool. But its not for me.

 

[FireMedic]

He does use one for some ops. Or at least he did. I consider Jim a friend. We kind of see things the same way. I dont think he uses one to chamber barrels. It’s not a bad tool. But it’s not for me.

I’ve studied everybody that’s anybody’s methods of chambering.

Although some are more tight lipped than others! Cough, cough, lol

I have seen posts by Jim telling his methods. He uses an inboard/outboard spider setup without pivot pads.

Barrel is Indicated with a gauge pin in both ends. Then reamed with the finish reamer and good fitting bushing to just past the shoulder. Then drill just deep enough so the pilot will stay engaged. Then finish reaming.

It obviously works for him.

I’ve never been able to indicate a barrel in with an inboard/outboard spider setup (with no pivot pads) and not bend the barrel. A lot of record breaking barrels have been chambered that way though it seems

 

[sdean]

I’ve studied everybody that’s anybody’s methods of chambering.

Although some are more tight lipped than others! Cough, cough, lol

I have seen posts by Jim telling his methods. He uses an inboard/outboard spider setup without pivot pads.

Barrel is Indicated with a gauge pin in both ends. Then reamed with the finish reamer and good fitting bushing to just past the shoulder. Then drill just deep enough so the pilot will stay engaged. Then finish reaming.

It obviously works for him.

I’ve never been able to indicate a barrel in with an inboard/outboard spider setup (with no pivot pads) and not bend the barrel. A lot of record breaking barrels have been chambered that way though it seems

I can't get my head around the barrel bending thing. If you are indicating 2 points in the first 3 inches the barrel isn't bending there. Can it? Seems like it would bend between there and muzzle. How can you measure if you bent the barrel? I use a 3 jaw set-true with bent copper pennies and outboard spider.

 

[boltfluter]

I can't get my head around the barrel bending thing. If you are indicating 2 points in the first 3 inches the barrel isn't bending there. Can it? Seems like it would bend between there and muzzle. How can you measure if you bent the barrel? I use a 3 jaw set-true with bent copper pennies and outboard spider.

Kind of along the lines you are thinking. When I flute a barrel held on both ends, before my support fixturing is in place, I can very easily bow the barrel .005 with hand pressure. Imagine how easy a 4 jaw or spider could do it. I believe most people are referring to bending the barrel in the middle and not the first few inches. If I am wrong I am sure someone will correct me. Lol!
Paul

 

[sdean]

Kind of along the lines you are thinking. When I flute a barrel held on both ends, before my support fixturing is in place, I can very easily bow the barrel .005 with hand pressure. Imagine how easy a 4 jaw or spider could do it. I believe most people are referring to bending the barrel in the middle and not the first few inches. If I am wrong I am sure someone will correct me. Lol!
Paul

I understand bending in the middle. Just don't see how that affects the chambering operation. The barrel will go back original when you release it.

 

[boltfluter]

I understand bending in the middle. Just don't see how that affects the chambering operation. The barrel will go back original when you release it.

Generally speaking, it is never a good idea to machine any kind of metal with the metal in a stressed condition. As you stated, metal does have a memory, and will return to it's happy place. Most everything we do, accuracy wise, is to have a stress free rifle that shoots well. Bending a barrel during any type of machining is never a good idea. Who is to say where the bend starts and ends. At least in my opinion.
Paul

 

[FireMedic]

I can't get my head around the barrel bending thing. If you are indicating 2 points in the first 3 inches the barrel isn't bending there. Can it? Seems like it would bend between there and muzzle. How can you measure if you bent the barrel? I use a 3 jaw set-true with bent copper pennies and outboard spider.

If you loosen your outboard spider bolts and the point you indicated moves then you are flexing the barrel.

How much it matters I’m not sure

 

[Greg Y]

Properly used, the .0005 interapid will get you well under a .0001". I know this because I have dialed in a lot of crowns with them and checked them with true .0001 indicators. Thats how you learn how to use the long stem indicator

I have checked my long probe with my 50 millionths b&s and found similar results to Alex.

 

[Greg Y]

I can see the argument for balance working against any setup but on centers. If I true one end, the other is certainly not on center and therefore is not going to balance.

If I load a TBAS similarly it's going to have the same issues, arguably with more mass on the chuck end to dampen or possibly multiply that effect.....but either method has everything in the headstock acting as a jumprope.

Funny thing about all this fixturing talk is that I am pushing my reamer with a dead center which is the simplest possible form and the chambers keep coming out as close to perfect as we could ask for.

 

[V35]

I have chambered in a steady, four jaw with pads, three jaw set true with pads, and the TBAS. I cant find a difference in quality of the chamber between all of them. It has been many years since I used a steady, so that comparison may be off. My opinion is that whatever system you use, just make sure your methods are right, with no compromise, and you will have a good chamber.

 

[Alex Wheeler]

There's 3 problems with flexing a barrel to get it dialed. One is that some cartridges are long enough that the flex is in the chamber. Another is if you index barrels the flex will fool you as to where to point the barrel. But the most important one is that when your flexing the barrel its fighting the setup and when you start putting cutting pressure on it its far more likely to more during the process. The barrels should not be moving. So if your checking your work and finding you need to dial out a tenth or two after threading for example you have a problem. Most likely flex in the barrel is the issue as well as sacrificial metals like a copper ring in a 4 jaw. Thats a recipe for movement. Now I know someone will ask how much all this matters. I dont know and dont care. Im charging the customer to do the job to the best of my abilities, so thats what I try to do. For the hobby guy, this probably is not an area to fuss over too much.