over size chamber

J

JDR

Guest
I hope some one can help me on this. I chamber a 257 weatherby chamber I did not use the long weatherby free bore the reamer is built with a free bore of .100 . after dialing in the barrel and taking a lot of care this is not my first one. I chamber the blank it looks great and has a good head pace But the chamber is over size some in the web next to the belt musures 518 it should be 511 the front is 596 chamber seems to have very little run out what happened? or is she way the reamer was made? I shot it some seemed to shoot ok Thanks Jerry
 
What does the reamer measure?

CAREFULLY with a caliper....

If the reamer's right may I suggest a tight fitting barrel bushing and a hand held reamer pusher? My chambers have .0000 wiggle in the back.

al
 
JerrySharrett said:
Looks like another case of "floating holder at its worst".
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Jerry. It is obvious you don't like floating reamer holders. Do you see the problem being the holder or the operator? I use a Bald Eagle floating reamer holder, and don't see how one could ream an oversize chamber with it unless the operator did something seriously wrong.
 
From a machinist standpoint, if the reamer is the correct size, then something caused it to bind and cut larger than it should have. Without seeing your set-up, it would be difficult to say how this happenned.

It is really not that uncommon, especially on very long chambers. Many times, the culprit is that you reamer's pilot encounters a spot up in the barrel that is running out, and since the reamer will not bend, it simply cuts oversize. The hole will still be perfectly round and true, just oversized.

I have said many times that from a machinist outlook, a reamer is the worst way to establish a precision hole in anything. Too many things can go wrong. But, for chambers, it is a tried and true practice due to the varied sizes, ie, body, taper, neck, throat, etc.

Your chamber is pretty big, .007 over normal expansion, that much brass expansion is not a good thing, mainly when you re-size it and re-use it. But I see brass at the range all the time that was obviously shot in a chamber that is quite oversize, judging from the bulge at the web.

My advice, it might be ok as far as shooting goes, just shoot the brass one time.........jackie
 
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JackieStogsdill said:
Jerry. It is obvious you don't like floating reamer holders. Do you see the problem being the holder or the operator? I use a Bald Eagle floating reamer holder, and don't see how one could ream an oversize chamber with it unless the operator did something seriously wrong.
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I've seen too many situations where the floating reamer holder caused an oversized chamber to get into an argument about its usage, properly or improperly. If you have one and it works for you by all means use it.
 
jackie schmidt said:
.............My advice, it might be ok as far as shooting goes, just shoot the brass one time.........jackie
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I would think that while 0.007" oversize is certainly excessive, neck sizing would limit the stress on the brass and would be acceptable for subsequent firings. Indexing the brass might be required to produce best accuracy.

Obviously the only other solution would be to set the barrel back and re-chamber it.
 
Thanks for the reply I have not had a chance ot measure the reamer yet but I will do so soon I did not use a floating reamer holder the tail stock and the headstock are very true and I used the tailstock and linedead center to push the reamer about .030 at a time Jerry
 
JDR said:
Thanks for the reply I have not had a chance ot measure the reamer yet but I will do so soon I did not use a floating reamer holder the tail stock and the headstock are very true and I used the tailstock and linedead center to push the reamer about .030 at a time Jerry
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I'd be astonished to hear the reamer was 0.007" oversize. Not impossible, but very very unlikely.

A reamer wants to follow the bore unless you push it to go someplace else. That's both the good news and the bad news.

The good news is that if the bore segment where the chamber will be is straight, aligned with the spindle centerline, and the reamer is allowed to follow it with no side force (floating holder), the chamber will be as close to reamer size as a chamber gets because nothing is pushing it off to one side or the other. The goal with chambering is to make that happen. It's not very hard to do, unless of course, one pushes with the tailstock center which has exactly zero radial compliance and buckets of angular compliance - the exact combination that is best for making oversize chambers if everything isn't exactly perfect, which it never is.

With out a floating holder, it's very easy to push the reamer off to one side or the other. Pushing with the tail stock center requires both perfect alignment of the bore segment to be chambered with the spindle axis, and perfect and repeatable for every cut, alignment of the tailstock with the spindle axis. Good luck with that. It can happen, but if it does, it's almost certainly better luck than good judgement.

Another way oversize can happen: If the bore isn't streight, if it has a slight curve, or wanders about, say .007" in the length of the chamber, which it certainly could in a chamber as long as a .257 Weatherby, the reamer will try to follow it. Since the reamer has length and is trying to go something other than streight, it will cut an oversize hole as the reamer cuts a chord on the curve. This can happen with a floating pusher as well.

There are lots of other ways, but those are two obvious ones.

Since a floating holder was not used, my hypothesis is the tailstock pushed the reamer sideways 0.0035" relative to where the bore was going. That would certainly do it, and it's easy to do pushing with a tailstock.

Fitch
 
frwillia said:
With out a floating holder, it's very easy to push the reamer off to one side or the other. Pushing with the tail stock center requires both perfect alignment of the bore segment to be chambered with the spindle axis, and perfect and repeatable for every cut, alignment of the tailstock with the spindle axis. Good luck with that. It can happen, but if it does, it's almost certainly better luck than good judgement.


There are lots of other ways, but those are two obvious ones.

Since a floating holder was not used, my hypothesis is the tailstock pushed the reamer sideways 0.0035" relative to where the bore was going. That would certainly do it, and it's easy to do pushing with a tailstock.

Fitch
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Fitch, I think it would help to explain to this guy the difference between a "floating holder" and a "floating pusher" like you use.
 
JerrySharrett said:
Fitch, I think it would help to explain to this guy the difference between a "floating holder" and a "floating pusher" like you use.
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Ur right, thanks.

I use this floating pusher:

ReamerPusher-2RS.jpg


I got the idea for it from Mike Bryant's website.

The piece you see in the tailstock was made by turning a #3MT on a piece of rod from the junk box. It was reversed, placed in the headstock of my 9" SB (which has a #3MT), drilled to be about 0.040" bigger than a reamer shank deep enough that the reamer shank wouldn't bottom in it until it was in farther than the collar on the reamer will allow, truned to the shape shown, then faced dead true. The rim of the hole, the face, is the part of this piece that does the work. The important thing is that the plane of the rim is perfectly orthogonal to the axis of the pusher.

The collar with the handle on it was machined all in one setting except for one side. It was turned to it's current OD (just took a cut to clean the rust and scale off the OD), faced to create the side that the piece in the tail stock will push against, then drilled undersize and bored to be a light sliding fit on the reamer shank. That results in the one side being perfectly perpendicular to the bore. I parted it off, drilled and tapped it for a setscrew to tighten on the flat on the reamer shank, drilled and tapped it for the handle (short enough to spin with out hitting the carriage), made the handle, and it was done.

In use I hold it with the fingers of my left hand curled under the handle, my thumb on the set screw. Holding it that way I'm applying a torque couple to the reamer that resists it turning with out applying noticable side force. The tail stock piece slides over the reamer shank to push on the collar. The reamer is free to move radially within the ~.020" clearance of the hole in the pusher around the reamer shank, and is also able to move angularely if it has to to align with the bore.

In practice, I adjust the feed with the tail stock handwheel to maintain an even pressure (torque). When the cut is at the desired depth I let go of the handle, let the reamer spin, back off the tailstock, remove and clean the reamer, blow out the chamber, dip the reamer in cutting oil, and start the next cut. The reason for letting go of the handle is that I can pull the reamer straight back out of the chamber after sliding the tailstock out of the way. That eliminates the chance for a chip to get under a reamer lip and scrub the chamber wall.

The Bald Eagle reamer pusher (pictures are available on the WEB) is functionally similar to the one I use. I like the inherent geometric stability of the design I use, but the Bald Eagle will work just fine.

My buddy (an actual practicing gunsmith) has a Manson floating reamer holder. You can find pictures of them on the WEB, I don't happen to have a picture of it. The Manson holder has a MT shank to fit the tailstock. It has a flat surface on the piece in the tail stock that mates with a flat surface on the reamer holder that tightens on the reamer shank. The manson has two bolts in the pushing flat surface that fit loosely into slots in the pushed flat surface and thus act to transfer the reamer torque to the piece in the tailstock. It is designed so that the two flat surfaces can float radially, and maybe even a bit angularely, with respect to each other to accomodate things like the tail stock being a few thousandts high, etc. He chambers a lot of rifles in the course of a year and is happy with the Manson floating holder, but says he's had chatter in a couple of chambers and didn't realize it, which left him with some rework.



I liked the design I use for several reasons:
  1. It is inherently stable and tries to correct any misalignment.
  2. The reamer shaft is captured so it can't move very far which takes some of the thrill out of starting the reamer. (Also true of the Bald Eagle)
  3. The price was right. About 4 plesant hours in the shop and it was done. My SB has a taper turning attachment which I used to turn the #3MT.
  4. I can feel what's happening. If chatter were to start, I'd know it almost immediately. (Also true of the Bald Eagle).
  5. It lets me chamber with out spending days learning how to scrape my tailstock into perfect alignment with my spindle. This is a huge feature because just leaning on the headstock to get a better look can move it .0005 with respect to the tailstock. My tail stock axis is parallel to my spindle axis but 0.005" high. I'm not about to try to fix that, and if I did, the next time I moved the tail stock it would start to wear itself into being low!
  6. So far it's worked perfectly. I've not had any oversize chambers which I think is rather amazing considering the fact that I've only been doing this for a year or two and am far from a professional at it. It took me 4 hours to cut a .30-06 chamber.
There are others who can do 50 minutes of impromptu speech on why the way I do it won't work or isn't the best. And they make really good chambers doing it their way.

I'll let someone else explain how it's done with the perfectly aligned tailstock.

If I was going to chamber on a NC lathe, I'd doubtless use a reamer holder like Chad does, but I'm not, so I don't.

Fitch
 
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