Chamber run out issue

[Boyd Allen]

I am not sure why counter rotation works, but when the subject came up, some time ago, in a discussion on this same topic, with an experienced machinist/machine shop owner, he told me the following story.

He and his partners were involved in the production of close tolerance aircraft parts, hydraulic cylinders of some sort, that required accurate deep hole drilling. After struggling with producing the parts to the required tolerance, he decided to see how the competition was getting it done, and applied for and got a job in their shop. (as little industrial espionage, as it were)They were counter rotating. If I remember correctly, he said the machines that they used were big lathes that were fitted with a headstock on both ends.

I think that he attributed the problems that they had without counter rotating to the cumulative effects of gravity as the hole got deeper. Who knows? In any case, they adopted the procedure, and the problem was solved.

[Bob Kingsbury]

Counter rotation is a way of increasing cutting speed .Given the same or
small increases in feed rate, the chip is smaller. Smaller chips evacuate
much easier and allow a better finish.Should the chips hang up, the drill
can take a new course. Lots of things on the plus side.

[Big Al]

Think of all the problems and fun you could have with material removal with wire EDM trying to do the same job just to get a straighter hole? Think barrels cost plenty now?

I pretty well satisfied on what the barrel makers turn out now.

[alinwa]

Originally Posted by TRA

When you drive into a tunnel you do not worry where the exit is, as it does not matter, hitting the entrance straight does.

LO-frickin'-L!!!

Nicely said

al

[therifler]

i read quite a few posts on how to get a true chamber . now over the years i have heard stories of holding within a millionth runout which seems to me to i mpractical . but could someone please tell me what is tolerable when it comes to runout between bore and chamber ? lastly what makes a gun shoot half minute of angle at 600yds . with a chamber that has .003 total indicator runout ? T.R.

[Butch Lambert]

tr,
I don't think any of us can answer your question.
Butch

[jackie schmidt]

I have posted a procedure in the past on how toactually check your work, what criticle areas to indicate to verify that all of the criticle surfaces do indeed run reasonably true with one another.

You mentioned .003 runnout. That is extreme. But, if the Rifleshoots at a competitive level, then who knows.

In reality, while a lot of runnout might not affect accurcy, it does start to manefest it's self in other areas, such as difficult extraction........jackie

[Bob Kingsbury]

If you had a perfect chamber and put crooked ammo in it, would it shoot any better. At least with the crooked chamber the error is always in the same
direction--- Food for thought