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Lathe progress
- Thread starter skeetlee
- Start date
Boyd raises a valid point. A close look at a stress and strain analysis of the threaded joint shows that maximum deformation occurs at the front (rec face) and gets progressively less, to near zero at the rear (bolt face.) And, I DO look at it as a lever, just not the same as Boyd. IMO when the shoulder unloads it pivots to a new position by pivoting on the threads. The shoulder "picks up and moves over" to reset itself when the chamber collapses. The fulcrum occurs in the threaded joint. Similar effect though to Boyd's description, the achievable (and undesirable) offset is based on the length of this lever arm. The difference is that in my mental picture threading to the shoulder is better in one regard, worse in another. On the one hand, receiver deformation is maximized but on the other hand there's less play sideways when the joint loosens.
This is all my personal, speculative view based entirely on the work done by Vaughn.
al
This is all my personal, speculative view based entirely on the work done by Vaughn.
al
Boyd Allen
Active member
Al,
Taking your point about where the barrel pivots. What I am talking about is like inserting a pry bar too far under a heavy piece of machinery that you are trying to move. If you put in a little ways under, the machine is moved, too far and it would take more lift than you can generate. Perhaps if we bond a tube to the face of the action, and move the shoulder forward....at some point the lateral force at the front of the tube and at the threads is reduced to the point where the barrel is able to be immobilized , relative to the action, by the available friction.
Taking your point about where the barrel pivots. What I am talking about is like inserting a pry bar too far under a heavy piece of machinery that you are trying to move. If you put in a little ways under, the machine is moved, too far and it would take more lift than you can generate. Perhaps if we bond a tube to the face of the action, and move the shoulder forward....at some point the lateral force at the front of the tube and at the threads is reduced to the point where the barrel is able to be immobilized , relative to the action, by the available friction.
C
Chip Soles
Guest
I would imagine that this is why thread form accuracy, minimum clearance at the pitch dia., true perpindicularity between the axis and face of the mating parts, and proper torque all work together to prevent, or at least minimize any shift after the assy. is made. If the flank angles of both the internal and external threads, are in fact parallel to each other, with the proper clearances at the root and crest areas, the proper torgue should, in theory load all of the threads equally. If they are both cut with the same lead screw that has a standard lead, and uses the same gear train, all of the threads should have an equal axial spacing, whether it is .06250",
.06253", or however it comes out. Minimum clearance at the pitch dia., and a good lubricant, perhaps a mix of teflon grease and fine grain moly powder, to prevent galling from friction.
There will indeed be an axial stretching in the unsupported length of any unthreaded areas. The cutting of a groove, either internally or externally will reduce the cross sectional area of these short areas, and concentrate
the tensile load created by the proper torque. Once that preload is made, the mating parts should reach a state of equalibrium.
Threading as close to the shoulder, with a threading tool that is ground to allow only minimum amount of flank length, on the shoulder side should minimize the length to be preloaded. If a clearance groove is needed, a fillet should be made as large as possible to spread the stresses created. Any rake that is ground on the threading tools, should be ground perpindicular to the cutting edge. This will allow a tool to cut rather than push the metal from the form. Grinding the rake perpindicular to the axis will narrow the effective thread form, which if this narrowing is not equal on both parts, will create a situation that will create line contact along the helix of the thread which may create issues of radial shift, or even an issue with harmonics.
About thirty years ago, I had a 16" engine lathe from the flat belt era. It had a taper threaded spindle, on the order of pipe threads, but about a 6 tpi thread. Now you are using an inclined plane to push two parts into a tapered hole, while loading the shoulder joint. For this you need either a taper attachment, or a CNC controlled lathe/turning center. Another factor to be considered is the finish of the thread flanks. A smoother finish will allow more torque to be applied to the assy. due to the reduced friction.
Reducing the effects of the harmonics, is from what I have read, mainly a matter of testing different barrel length and contour combinations. The days of knocking over a soup can with the old Red Rider are long gone! A salute to progress, and change for a reason, after unbiased thought and planing, the consultation of your friends(no beer here!) ;-)
Regards,
Bob
.06253", or however it comes out. Minimum clearance at the pitch dia., and a good lubricant, perhaps a mix of teflon grease and fine grain moly powder, to prevent galling from friction.
There will indeed be an axial stretching in the unsupported length of any unthreaded areas. The cutting of a groove, either internally or externally will reduce the cross sectional area of these short areas, and concentrate
the tensile load created by the proper torque. Once that preload is made, the mating parts should reach a state of equalibrium.
Threading as close to the shoulder, with a threading tool that is ground to allow only minimum amount of flank length, on the shoulder side should minimize the length to be preloaded. If a clearance groove is needed, a fillet should be made as large as possible to spread the stresses created. Any rake that is ground on the threading tools, should be ground perpindicular to the cutting edge. This will allow a tool to cut rather than push the metal from the form. Grinding the rake perpindicular to the axis will narrow the effective thread form, which if this narrowing is not equal on both parts, will create a situation that will create line contact along the helix of the thread which may create issues of radial shift, or even an issue with harmonics.
About thirty years ago, I had a 16" engine lathe from the flat belt era. It had a taper threaded spindle, on the order of pipe threads, but about a 6 tpi thread. Now you are using an inclined plane to push two parts into a tapered hole, while loading the shoulder joint. For this you need either a taper attachment, or a CNC controlled lathe/turning center. Another factor to be considered is the finish of the thread flanks. A smoother finish will allow more torque to be applied to the assy. due to the reduced friction.
Reducing the effects of the harmonics, is from what I have read, mainly a matter of testing different barrel length and contour combinations. The days of knocking over a soup can with the old Red Rider are long gone! A salute to progress, and change for a reason, after unbiased thought and planing, the consultation of your friends(no beer here!) ;-)
Regards,
Bob
martin zuck
Member
Chip Soles,
When it comes to threading up tight to a shoulder(internal or external) whats wrong with using a dial indicator?
Martin
When it comes to threading up tight to a shoulder(internal or external) whats wrong with using a dial indicator?
Martin
A
allenn
Guest
Al, pm sent.
F
frwillia
Guest
Chip Soles,
When it comes to threading up tight to a shoulder(internal or external) whats wrong with using a dial indicator?
Martin
Nothing. When I cut the square threads on the Springfield -03 barrel right up to the shoulder I used the dial indicator to cut the power. Lathe coasted to within about a quarter turn. I finished the cut manually by pulling on the drive belt. I was using an HSS tool. Doing this with an insert tool is not recommended.
I set the dial indicator up so the needle starts moving exactly one revolution before I want to flip the switch. That way I get to see the needle moving and can be more accurate with my timing.
Fitch
martin zuck
Member
Frwillia,
My question was some what tongue in cheek. I use a method similar to yours!
Martin
My question was some what tongue in cheek. I use a method similar to yours!
Martin
F
frwillia
Guest
Frwillia,
My question was some what tongue in cheek. I use a method similar to yours!
Martin
No problem. I elaborated a bit so that Lee (or anybody else that hadn't done it) would understand what we were doing.
Fitch