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Rifles, Reloading, Optics, Equipment
Gunsmithing
Threading a barrel without taking barrel off?
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<blockquote data-quote="Blackhawk" data-source="post: 1783203" data-attributes="member: 105459"><p>As a retired tool and die maker with plenty of experience(over 45 years) running all types and sizes of engine lathes I will add my two cents worth. I would not attempt to thread a barrel which would be brass shimmed in a four jaw chuck unless I separated the barrel from it's action and here is my reasoning.Assuming that you had a lathe with a long enough tail and head once the barrel has been chucked up and indicated to dead zero(Trued Up) consider this, behind the tail the barrel and it's action will be turning at lets say 350-425 RPM. While on the other end you would have a barrel which usually has a tapered contoured OD. Now even though held in place by the chuck jaws as well as a steady rest you will have a certain amount of vibration emanating from the end attached to the action. All this is happening while you are trying to first turn the muzzle end of the barrel to lets say .625" Diameter for a 5/8" X 24 TPI. Once that has been done you must change tool bits as well as the compounds angle to 29 1/2 degrees. After that you must set the lathe to thread the correct number of threads and take a skim cut in order to verify that in this case cutting 24 threads per inch. Stop and after clearing your tool bit check your pitch by using a Thread pitch Gage. After that you will continue to thread the barrel by lets say .005" increments until you start seeing metal beginning to curl off your tool bit. Now you must apply a cutting lubricate to the barrel while chasing down your threads in lets say .002" increments to a given depth that you have trigged out before hand. All the time the barrel is still spinning with the barrel's action still attached and is flexing ever so slightly. This flexing or oscillation is transmitted the entire length of the barrel all the way to the muzzle. Yes it is negated by the steady rest to the point that you may not notice it,however if you were to place an indicator on the end of the barrel just ahead of the barrel nut and turn the barrel by hand you will see the indicators finger move from high to low, hence run out. Compound this by the lathes internal wear and opening up of it's tolerances and you may have the perfect recipe for disaster.</p><p>Mind you while you are cutting threads your attention is only on that particular operation and you really do not want to think about anything else much less vibration or barrel flex. It is so easy to have a lathe jump or skip a portion of a thread while cutting them why would you want to take a chance on cutting into a thread with a partial deforming of its crown? I for one would want as many potential problems taken out of the equation before hand, and once properly set up keep my head into the threading of the barrel only.</p><p>To that end I would separate the barrel from it's action before chucking up and indicating said barrel prior to turning and threading.</p><p>There are just to many things that that you must take in to account before you even start the threading of the barrel,and I myself will stack the odds of success in my favor. So for my money I would strip everything off the barrel that I could ( including the trigger assembly) in order to prevent even the smallest amount of barrel run out or barrel movement in any way.</p><p> Why take the chance on messing up an expensive barrel? I would treat it as if it were a brand new barrel and follow a prescribed method of achieving success. Just my thoughts !</p></blockquote><p></p>
[QUOTE="Blackhawk, post: 1783203, member: 105459"] As a retired tool and die maker with plenty of experience(over 45 years) running all types and sizes of engine lathes I will add my two cents worth. I would not attempt to thread a barrel which would be brass shimmed in a four jaw chuck unless I separated the barrel from it's action and here is my reasoning.Assuming that you had a lathe with a long enough tail and head once the barrel has been chucked up and indicated to dead zero(Trued Up) consider this, behind the tail the barrel and it's action will be turning at lets say 350-425 RPM. While on the other end you would have a barrel which usually has a tapered contoured OD. Now even though held in place by the chuck jaws as well as a steady rest you will have a certain amount of vibration emanating from the end attached to the action. All this is happening while you are trying to first turn the muzzle end of the barrel to lets say .625" Diameter for a 5/8" X 24 TPI. Once that has been done you must change tool bits as well as the compounds angle to 29 1/2 degrees. After that you must set the lathe to thread the correct number of threads and take a skim cut in order to verify that in this case cutting 24 threads per inch. Stop and after clearing your tool bit check your pitch by using a Thread pitch Gage. After that you will continue to thread the barrel by lets say .005" increments until you start seeing metal beginning to curl off your tool bit. Now you must apply a cutting lubricate to the barrel while chasing down your threads in lets say .002" increments to a given depth that you have trigged out before hand. All the time the barrel is still spinning with the barrel's action still attached and is flexing ever so slightly. This flexing or oscillation is transmitted the entire length of the barrel all the way to the muzzle. Yes it is negated by the steady rest to the point that you may not notice it,however if you were to place an indicator on the end of the barrel just ahead of the barrel nut and turn the barrel by hand you will see the indicators finger move from high to low, hence run out. Compound this by the lathes internal wear and opening up of it's tolerances and you may have the perfect recipe for disaster. Mind you while you are cutting threads your attention is only on that particular operation and you really do not want to think about anything else much less vibration or barrel flex. It is so easy to have a lathe jump or skip a portion of a thread while cutting them why would you want to take a chance on cutting into a thread with a partial deforming of its crown? I for one would want as many potential problems taken out of the equation before hand, and once properly set up keep my head into the threading of the barrel only. To that end I would separate the barrel from it's action before chucking up and indicating said barrel prior to turning and threading. There are just to many things that that you must take in to account before you even start the threading of the barrel,and I myself will stack the odds of success in my favor. So for my money I would strip everything off the barrel that I could ( including the trigger assembly) in order to prevent even the smallest amount of barrel run out or barrel movement in any way. Why take the chance on messing up an expensive barrel? I would treat it as if it were a brand new barrel and follow a prescribed method of achieving success. Just my thoughts ! [/QUOTE]
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Threading a barrel without taking barrel off?
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