Dirt Cheap Automatic Tailstock Feed for Your Metal Lathe

[Susquatch]

So now your spider is aligning the part so both end diameters are clocked perfectly concentric to spindle axis. But you cant control a distorted bore path like you were saying. Why should a deep re-drill or reamer now follow a straight path? Why wouldn't it be heavily influenced by existing bore and largely follow along any deviation? How do you quantify deviation & bore diameter before & after the re-dressing operation?

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Your drawing is incorrect at both ends.

Although this is a gross exaggeration of what things really look like, hopefully it will help you see the situation better.

The axis of the bore at the work end is what matters. It must be aligned with the axis of the spindle. In the drawing, even the face of the barrel at the right side is not square to the axis of the inside bore. It must be faced off square as the first step of any subsequent work. All indicating and alignment is done at the right side where the work will be done. The left side is only positioned (not centered) such that the right side is both centered AND aligned.

Why wouldn't it be heavily influenced by existing bore and largely follow along any deviation?

You are of course correct, it is HEAVILY influenced. But not TOTALLY influenced. In the pursuit of perfection, HEAVILY is not sufficient. To help achieve perfection, we do everything we can to make sure we are as close to perfect as possible.

There is no need to quantify deviation & bore diameter before & after the re-dressing operation. The end results and performance of the finished work is what matters.

 

[Susquatch]

So now your spider is aligning the part so both end diameters are clocked perfectly concentric to spindle axis. But you cant control a distorted bore path like you were saying. Why should a deep re-drill or reamer now follow a straight path? Why wouldn't it be heavily influenced by existing bore and largely follow along any deviation? How do you quantify deviation & bore diameter before & after the re-dressing operation?

View attachment 15492

Reading your post again, I think perhaps it would help if I added a few other points and explanations.

Your drawing assumes that the OD of the barrel is curved. It is actually straight. The OD is typically cut or ground from the original stock AFTER the bore is drilled by mounting it on centers at the drill entry and exit holes. We are concerned here with the ID, not the OD. The ID is the drilled hole. The drilled hole is what follows an arc inside the barrel. It is the axis of the drilled hole that is important.

To give you an idea of scale, high quality barrels usually have to be offset by 50 to 250 thou at the back of the headstock to achieve concentricity at the front. Their length is usually 26 inches or so. These are high quality premium custom barrels made with the finest materials and drilling technology available. I reject barrels that are over a quarter of an inch. A typical factory barrel will be out by 3/8 of an inch and often more. A typical factory install pays no attention to this internal arc. The factory simply centers the work at both ends (essentially the same as your drawing) and has at it. The result is a chamber and receiver fitting that is "cock eyed" and "misaligned" from the axis of the bore. This results in unbalanced forces and less than ideal performance in use. Competitive performance requires precision machining.

 

[PeterT]

Your drawing assumes that the OD of the barrel is curved. It is actually straight. The OD is typically cut or ground from the original stock AFTER the bore is drilled by mounting it on centers at the drill entry and exit holes. We are concerned here with the ID, not the OD. The ID is the drilled hole. The drilled hole is what follows an arc inside the barrel. It is the axis of the drilled hole that is important.

'Drawing' is being kind haha. It was just a quick, crude cartoon sketch in Excel so kind of limited to show detail. No, there was no assumption or implication on my part that the OD was this way or that. I'm just focusing on the bore path and how it becomes corrected be re-drilling re-reaming. My sketch (greatly exaggerated) would represent just one problem scenario where the factory setup was perfect, but the bore drilling operation took on some deviated trajectory deeper into the bore and just forget about the OD for now.

If you use the spider to dial in the bore ends relative to spindle axis (blue arrows) to within 0.00000001" the bigger challenge (to my simple mind) is what is happening to the bore at its maximum deviation... whatever that value is (0.001? 0.002" I'm not sure myself). I 'think' what you are hoping for is something like this, again greatly exaggerated cartoon. Where the bore is straight & slight enlarged ID is a necessary byproduct.

But mostly I was wondering how the trajectory deviation was quantified midway down a long-ish bore. How would one know its 0.001 or 0.002 off using my purely BS hypothetical example

 

[historicalarms]

Just some thoughts that might help a neophyte barrel chamberer that is reading this thread.
Actually, commercial barrel makers do have huge "staightening" iron-worker presses, that are used to straighten barrels fresh out of the boring/drilling process and the barrel straightening operators are the highest paid employees in the plant. Then they are stress relieved.
I get what you are saying about canted chamberings that do not line perfectly with the bore could be a concern for an F--class shooter but the reality for 99.9% of shooters, the miss-alignment that a 3" long chamber reamer will have on a bore that is out a few thou from "absolutely straight" will be pretty much completely impossible to detect without some very expensive "comparative" measuring devises. Many more "bad chambering jobs" are done because the operator forced the reamer to work faster by not removing and cleaning of scarf as often as required.

To take this further, actually a bent barrel will shoot just as accurate & to "point of aim" repeatedly just as good as a "measured perfectly straight bored barrel. You just cant spin a bent bore barrel onto an action that has been scope sighted in with a straight bore barrel and expect it to shoot to the same point of impact....it will change but that is what "adjustable sights" have been used for for a couple hundred years.
The barrel harmonics & heat dispersion from a barrel that doesn't have a "correct" bore in it will effect the accuracy much more than the bent bore itself. If a bore has a slight radius of a curve to it, after outside contouring the blank, will have different steel thicknesses that heat up more quicker than other spots and I think that is why F-class used barrels require some extra diligence in straightening & chambering.

 

[historicalarms]

'Drawing' is being kind haha. It was just a quick, crude cartoon sketch in Excel so kind of limited to show detail. No, there was no assumption or implication on my part that the OD was this way or that. I'm just focusing on the bore path and how it becomes corrected be re-drilling re-reaming. My sketch (greatly exaggerated) would represent just one problem scenario where the factory setup was perfect, but the bore drilling operation took on some deviated trajectory deeper into the bore and just forget about the OD for now.

If you use the spider to dial in the bore ends relative to spindle axis (blue arrows) to within 0.00000001" the bigger challenge (to my simple mind) is what is happening to the bore at its maximum deviation... whatever that value is (0.001? 0.002" I'm not sure myself). I 'think' what you are hoping for is something like this, again greatly exaggerated cartoon. Where the bore is straight & slight enlarged ID is a necessary byproduct.

But mostly I was wondering how the trajectory deviation was quantified midway down a long-ish bore. How would one know its 0.001 or 0.002 off using my purely BS hypothetical example

"trajectory" is never set by the barrel condition or straightness but bullet direction is. Trajectory is only a condition of velocity + gravity + distance. Bullet direction is a condition set by the barrel but ends at the bore muzzle, after that the "trajectory conditions" & ammo design take over. The barrels job starts and ends within itself.

 

[PeterT]

Sorry I said 'bore path' initially & then said 'trajectory' secondly which was misleading. Nothing to do with bullet in flight, I just mean the resultant geometry of connecting circular cross sections of the bore down the tube if one accurately could map it. Like a straight bore would be a line. A bowed bore would be a 2D curve. A wandering drill would be some kind of 3D spline path etc.

 

[Susquatch]

I'm just focusing on the bore path and how it becomes corrected be re-drilling re-reaming.

Nope. Nobody is correcting the existing path. Merely locating it and precisely following it with subsequent machining operations so that everything stays in perfect concentricity with the existing bore.

A bowed bore would be a 2D curve. A wandering drill would be some kind of 3D spline path etc.

Yup. But the machinist cannot change such things. They are what they are. We do the best we can with what we have. After that, the barrel either performs and is kept or it doesn't perform and gets discarded or turned into chunks of good steel used for other purposes.

 

[Susquatch]

Just some thoughts that might help a neophyte barrel chamberer that is reading this thread.

Right off the top, it's important to understand that my world is benchrest, not F-Class, or the other 99.99%. That probably explains a lot right there for all those who know the difference.

It's also important to understand that my first post was only to point out that barrels are not really straight. I didn't intend that this get carried off into a debate about methods or for that matter what the neophyte knows or doesn't know. In the process, I got asked some questions which I answered as appropriate.

Your knowledge of the subject matter tells me that you understand the debates as well as anyone. I'd prefer not to get dragged down those rabbit holes. I think you will agree that there are better places to do that than here on a metal workers forum.

In my experience, many of the points of view that you raise are valid ones. In fact, if you read the entire thread, you will find that I already said many of the things you did. For the ones that we don't agree on, I'd prefer to just agree to disagree and skip the debate.

I believe that the majority of benchrest competitors chamber the way I do it. But there are also those that don't. I did not develop my methods. I merely evaluated what the best of the best and all do, looked at their results in competition, and then decided that what works for them should work for me too. And it certainly does.

I will say that it has always struck me as odd that other competitive disciplines have different favoured approaches. But I don't think that's a bad thing. I think it's wonderful!

 

[historicalarms]

Sorry that I pi$$ed in your porridge...it wasn't my intention at all and if your read my post again you will easily see the reference to "neophytes"....if your preferred set-up does wonders for your group size then by all means continue.

 

[Susquatch]

Sorry that I pi$$ed in your porridge...it wasn't my intention at all and if your read my post again you will easily see the reference to "neophytes"....if your preferred set-up does wonders for your group size then by all means continue.

No worries. And of course I saw the reference to neophytes. I even quoted that.

But it did feel a bit unwarranted given the reason for posting. FWIW, I agree that competition tends to set unreasonably high standards for neophytes and the average Joe with factory equipment. On the other hand, I have owned a few factory jobs that performed way above average and built quite a few regular field class fly killers for average Joe's or at least let them try one of mine at the range. You couldn't wipe the smile off their face with a bulldozer!

And yes, Ive seen a hundred fellows who were thrilled with something I wouldn't keep in a wet corner of the barn. But there is an old saying - "Success is getting what you want, happiness is liking what you get." I do love happy people. So ya, I appreciate your point of view.

 

[historicalarms]

Ha ha ha ya I'm all better now too....not usually as touchy as that but maybe those damn Phizer shots hives may have finally influenced my usual "respectful demeaner".

After I pushed "send" it struck me that probably only one other topic in the history of man has garnered more discourse than guns since the Chinese invented gun powder in, I think the 14th century and that would be flight....I'm sure a couple homo-sapiens at the first ever gathering saw a bird flying and one of them said "UG" and the other replied UG-N-UG and the conflict was on as to how to do that better....been the same with guns.

 

[Susquatch]

Ha ha ha ya I'm all better now too....not usually as touchy as that but maybe those damn Phizer shots hives may have finally influenced my usual "respectful demeaner".

After I pushed "send" it struck me that probably only one other topic in the history of man has garnered more discourse than guns since the Chinese invented gun powder in, I think the 14th century and that would be flight....I'm sure a couple homo-sapiens at the first ever gathering saw a bird flying and one of them said "UG" and the other replied UG-N-UG and the conflict was on as to how to do that better....been the same with guns.

So true.