Spiralock threading for barrels

29 October 2003, 09:33

triggerguard1

quote:
Originally posted by DemoSam:
The barrel had a reverse taper of about .006" on the diameter so the tool deflection would be .003". It seemed excessive for just tool deflection but who knows whats going on. This barrel came from a MT based smith. It scattered shots quite readily.

You would be surprised as to how much tool deflection can occur with the threading process. It is probably the single most effected cutting action out there for producing tool deflection.
You can set your indicators up and dial your lathe in to the knat's hair(othwise known as .0001"), take a cut, take all your dials and indicators back to the original position, take another cut, and under most circumstances, you could easily take as much as .005" or more per side off of your material. You could also repeat this procedure two three or four times, removing material almost everytime.

Some machining operations produce very little deflection, and consequently can be extremely accurate, and easy to accomplish. Threading is not one of them. Even running $200,000.00 CNC lathes, you'll get deflection just as I mentioned, but normaly not quite that bad, due to the extreme repeatability of the equipment as well as the preciseness of the inserts and speeds and feeds.

29 October 2003, 10:23

irv

Trigger guard; I sure that nothing you have read said thast the drift was a function of
flight time. What it did say was that it was a function of the delay time ( the amount the bullet was slowed). If you take time to read my post ( or better Vaughns book) the bullet
alignes itself so that the "wind" is straight on (zero angle of attact). Now the drag has a component down wind. This is what causes drift,and the wind does not "blow against the side of the bullet"
Vaughns book is the first that explains this.

29 October 2003, 10:29

wallyw

quote:
Originally posted by irv:
Trigger guard; I sure that nothing you have read said thast the drift was a function of
flight time. What it did say was that it was a function of the delay time ( the amount the bullet was slowed). If you take time to read my post ( or better Vaughns book) the bullet
alignes itself so that the "wind" is straight on (zero angle of attact). Now the drag has a component down wind. This is what causes drift,and the wind does not "blow against the side of the bullet"
Vaughns book is the first that explains this.

And hopefully it will be the last book to claim that a bullet in flight behaves like a sailboat with weather helm [Wink]

Wally

29 October 2003, 10:36

wallyw

quote:
Originally posted by triggerguard1:
[QUOTE]Originally posted by DemoSam:
[qb] It is probably the single most effected cutting action out there for producing tool deflection.
You can set your indicators up and dial your lathe in to the knat's hair(othwise known as .0001"), take a cut, take all your dials and indicators back to the original position, take another cut, and under most circumstances, you could easily take as much as .005" or more per side off of your material. You could also repeat this procedure two three or four times, removing material almost everytime.

Excellent point Matt. I've learned to chuck barrel as close as possible to 4jaw and take multiple cleanup cuts before advancing compound. You are right on about removing 0.010. too much due to deflection.

Wally

29 October 2003, 11:36

triggerguard1

quote:
Originally posted by wallyw:

And hopefully it will be the last book to claim that a bullet in flight behaves like a sailboat with weather helm [Wink]

Wally[/QB][/QUOTE]

LOL [Big Grin]

I was afraid that's what he was implying.

Well guys, that's it, I'm heading out tomorrow to shoot some 55 grain pills in high wind that seems to be rolling in quite well this afternoon.
Hopefully I'll run across an unsuspecting coyote, aim between his eyes and send one though one ear and out the other. [Wink]

I will bring back all the unverifiable data that I won't be able to obtain as quickly as I can't. Stay tuned for more developments. [Big Grin]

29 October 2003, 17:23

<G.Malmborg>

Can you immagine how confusing it must be for a bullet to encounter a whirl wind? It would be like a dog chasing it's tail. Just kidding... or, not.
[Big Grin]

Malm

30 October 2003, 03:59

DemoSam

I use a six jaw chuck and can't taper a thread that bad. Yes it takes alot of force but the tennon is short. I'll bet its over 2,000 lbs to create that much deflection the way I set up. The threads looked exceptional as if he made a finish pass. I cant imagine a setup as loose as you describe could create a good thread. Maybe the steady rest technique will cause more deflection or he got it out of alignment. How are you folks threading a tennon?

30 October 2003, 04:45

triggerguard1

quote:
Originally posted by DemoSam:
I use a six jaw chuck and can't taper a thread that bad. Yes it takes alot of force but the tennon is short. I'll bet its over 2,000 lbs to create that much deflection the way I set up. The threads looked exceptional as if he made a finish pass. I cant imagine a setup as loose as you describe could create a good thread. Maybe the steady rest technique will cause more deflection or he got it out of alignment. How are you folks threading a tennon?

Well, the surface finish will look pretty much the same from the first pass to the last pass, if you use a good quality insert and the proper speeds, but I assure you there is a significant amount of deflection in threading regardless of your setup. It's just the nature of the process.
The same thing could be said about form cutting. This method of machining, whether it be on a mill, or lathe, will produce a substantial amount of tool pressure, but still not as much as threading, on the average.

The steady rest debate is one that will unfortunately never be completely solved by the gunsmithing community.

The basic principal in machining is this:
Never let the workpiece extend from the chuck jaws over 5 times in diameter. In other words, if the workpiece is 1" in diameter, the barstock should not exceed over 5" from the chuck jaws. I prefer to stick with 4 times the diameter in most cases or less, less being preferable.
When you use a steady rest, you have to ask yourself, what am I doing this for?? I'm extending the workpiece out away from the chuck jaws many times more than I should, so to compensate for this, I use a steady rest to stabilize the barstock that shouldn't be sticking out that far in the first place.

Other than the steady rest method of chambering, the use of the headstock setup with a spider is gaining more and more popularity, but even that method can actually be a little redundent.

We've tested the system of chambering barrels without the spider, and simply dialed in the bore with a gage pin. The results would probably shock most died-in-wool gunsmiths. I honestly on paper couldn't tell the difference between the barrel that was dialed in on the rear with a spider and one that wasn't. They both shot under 1/2 MOA with run-of-mill factory ammo(core-lockt,power point,etc.)

The barrel needs to be steadied on the back end, but it doesn't necessarily need to be dialed in persay.