Chamber run out issue

[AZLarry]

223rem chamber has run out of .0015" at the last half of the chamber. But the neck and lead areas look good with no run out.

Q: What caused the back half of the chamber to have run out and how can it be avoided?

Details:

a) Indicated barrel bore using long stem indicator. Looks good the length of case.

b) Drilled then straight bored chamber to .347" diameter for a depth of 1.3" (that is the longest carbide boring bar I had on hand)

c) 223rem chamber was cut with a removable pilot reamer held by a floating holder similar to the bald eagle type. Chamber looks good with no chatter or obvious cutting issues.

d) Used through the lathe headstock method with spider and 6 jaw chuck. 125 rpm spindle speed.

Thanks, Larry

[Rflshootr]

I peronally never liked the floating reamer holders. That may have been what caused your problem. Check the diameter of the chamber nearest the head of the case to see if it is oversized as compared to the reamer. That may give you a clue as to what is happening.

[David Sengelaub]

Larry

Did you measure for run out after you bored the hole? Even though you used a carbide boring bar it is a small diameter and the boring bar may have been pushing off. With a floating holder the reamer is only going to follow the hole.

[AZLarry]

The bored hole was running true.

What about technique on holding reamer and stopping the lathe while reamer is still in the bore????

Do you leave the reamer in the bore and back off on the pressure while stopping the lathe spindle?

Or just pull out the reamer while the lathe is turning?

Thanks for the reply's....

[jackie schmidt]

.0015 is a lot of runnout considering you did pre-bore the chamber.

The only thing I can think of is your reamer pilot encountered a spot up in there that did not run true with your initial indicated spot, influrencing things to where you ended up with the runnout.

I have had chambers run out as much as .0004 after everything is done, but that is no where near as much as what you are experiencing.

As a little tip, when this happens, (sometimes it does despite all of our best efforts), re-indicate the chamber exactly in the midle of the chamber, before you finish your tenon. That way, you are "splitting the difference" with the runnout, and the chamber will at least be as close to alignment in the action as possible.............jackie

[Bob Kingsbury]

The floating reamer holders I have are all a disappointment. I don't use them. They all seem to have problems. Its just better to allign the tail
stock. Once alligned, dowel pin it and recontour barrels elsewhere. It
doesn't take much to put a dead center back in the tailstock on a chip
blown out of the chamber , attention to detail can't be taken to far.

[AZLarry]

Just a thought. Because only the out board half of the chamber was out of round the spider screws might of "moved" causing the other end of the barrel is wobble???

I should of checked run out before the chamber was to finished depth. Also don't finish the barrel threads before the chamber. Lessons learned.....

[Bob Kingsbury]

That would make an egg shaped chamber

[Jim Borden]

It is not odd to me that the back end of the chamber runs out more than the neck. When measuring run-out from what is believed to be a properly bucked in bore at the throat-you are measuring angularity. That is what Jackie was referring to when he said the bushing must have followed part of the bore that did not align with center of lathe spindle. The farther back from that point you get, the more run-out you have.

It would be mighty difficult to have a consistent run-out from back to chamber to throat-unless the entire barrel was dialed in eccentric.

[HCP]

I haven't used a pilot since I can remember. I indicate throat, rough drill, angle bore then finish ream. If you have indicated the throat and forward of that (where the pilot rides rides) is out, as most of them are, all of the other work is a wasted effort. The reamer is going to follow the pilot to some degree even with single point bored hole. Bore scope the throat when you are done. We are reaming the throat @ about 1.5 degrees, any misalignment will stick out like a sore thumb. This is the business end of reaming for accuracy.
Regards...Herb Coates

[Bnhpr]

Originally Posted by HCP

I haven't used a pilot since I can remember. I indicate throat, rough drill, angle bore then finish ream. If you have indicated the throat and forward of that (where the pilot rides rides) is out, as most of them are, all of the other work is a wasted effort. The reamer is going to follow the pilot to some degree even with single point bored hole. Bore scope the throat when you are done. We are reaming the throat @ about 1.5 degrees, any misalignment will stick out like a sore thumb. This is the business end of reaming for accuracy.
Regards...Herb Coates

Interesting...

Thanks Herb

[Butch Lambert]

I agree with Herb.
Butch

[AZLarry]

Thanks for the input.

I agree about the reamer bushing alignment causing issues. Will try without the bushing.

[ultramagmed]

So you guys are not using a pilot at all if you pre-drill and taper bore prior to reaming?

[mike in co]

Originally Posted by ultramagmed

So you guys are not using a pilot at all if you pre-drill and taper bore prior to reaming?

true..

go do a search on this forum..jackie has posted his process.

mike in co