tightneck:
You bring to the table a very good question that many folks have very strong differing opinions about.
Let me say my intent with the first post was dealing with the inconsistent bolt raceway diameter. All those who know anything about machining know "drills don't bore round holes". Holes are drilled undersized, then reamed still undersized then lapped to spec. If one measures the ID of a bolt race most differ in the front and rear. Sleaving, Oversized bolts, and Borden bumps all address concentric and co-axial bolt slop. Truing and lapping the bolt lugs also address bolt surface support and flexing at the point of highest pressure.
Most bolt raceway reamers are piloted and follow the existing bolt raceway. The logic would be good consistent lead good consistent follow with the cutter. Inconsistent lead inconsistent follow with the cutter. The pilot lead is about .750 and the cutter is taking out .005-.010. The tool should be precision ground to follow the path it's cutter makes.
Many actions are now cut with a wire EDM then reamed and lapped.
Getting back to the topic. There are multiple issues at hand.
I was addressing Bolt Raceway ID consistency. I believe you were addressing concentricity and co-axial alignment.
That brings up another topic aligning the threads with the bolt race.
You asked about methodology and tooling.
I am familiar with Greg Tannels methodology and tooling. I think he is right on as far as logic and his tooling may be as good as it gets for what one can do in a lathe. Most folks think a lathe cuts very precisely. A lathe and mill both cut more precisely than one can do by hand. But a lathe and mill are very crude metal cutters when compaired to a grinders and hand lapping.
As for Dave Manson and Dave Kiffs piloted thread cutters. Both work off bushings and a pilot rod that is about .500 ID. They are designed to take off about .010. The work off the logic aligning off the bolt bore,sound theory). The differences in Dave Mansons tooling and Dave Kiffs tooling are the bushings. Dave Mansons bushings,two) are tapered and Dave Kiffs bushings come in different sizes .0005 differences. I once bought Dave Kiffs tooling and an 9 different bushings. Midway's advertisement stated "sets of bushings",being plural it thought it ment sets of two bushings) but when I received the product there were only one of each size bushing sent. I called them and they said the tool was not intended to use two bushings simultaniously. I knew the tool would not remain rigid enough with only one bearing surface being supported and returned the product for a refund. I talked with Dave Kiff about the subject and he confirmed my thoughts.
Most folks have no idea how much an action flexes. Steel has a memory and cuts must be made in small steps to get accurate cuts. This is the reasoning behind single point tooling versus geometric thread cutters.
You asked me what I used. I made several cathead/spiders from steel tube precision ground both OD and ID. They have alluminum sleeves that are split 90 degrees apart. The cathead/spider screws push against the aluminum fingers. This idea was given to me by Mike Bryant,very good gunsmith). I mount the Jig in the lathe and align it in the chuck as good as I can. Then mount the action inside the jig. I align the action with a precision ground rod inserted in the bolt raceway. The action is aligned with two .0001 indicators at least 4 inches apart measuring off the centered rod. This will get the action aligned as good as it can be in a lathe. The the threads are corrected with a couple of light passes or the threads are completely removed and recut.
All gunsmiths that I know who true actions have a trued barrel stub. After they get the action aligned in the truing jig. they can remove the alignment rod,mandrel) and insert the trued barrel stub. Then take measurements of the stub. This will give them the TIR. I use mine pre truing and post truing to confirm my work is accurate
There have been books and many artcles written about BluePrinting Actions. The subject has been approaced from many angles. Some theory is sound and some is not. I will say I learn something new everyday. The better gunsmiths change and adapt as the materials, tooling and methods change.
Again back to the topic.
Consistent bolt raceway contact with the bolt. IE: same ID front and rear.
concentric and co-axial alignment measured down to the .0001
Good bolt fit.
These are all basic foundations for accuracy in a rifle. These in conjunction with a good fitting barrel, aligned chamber, high quality barrel bore, good crown, good stock action fit, good scope, bases and rings, good trigger all added up to a better shooting rifle.
In todays world the rifles have gotten so good that with hand held rifles shooter skill of reading the wind is the most important factor for long range shooting. We have not even talked about bullets, powder, brass, primers, trimming, seating, neck tension etc.
Gives us something to talk about again, eh?
Rustystud