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Thread: Brass pipe mandrels

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  1. #1
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    Brass pipe mandrels

    My first barrel fitting project is to fit an A1 type barrel to a Springfield 1911A1 slide and frame (Mil Spec model). I wanted a steel (not stainless) barrel and decent quality, so I chose to use a Kart barrel for the project. The Kart barrels have National Match dimensions, with a reduced barrel diameter beginning 0.375" back from the muzzle and extending back to the chamber. I wanted a uniform diameter barrel though, not NM spec. So I needed to take about 0.005" off the diameter at the muzzle end, to make the whole length uniform. This would leave me with a barrel that was only 0.003" under spec at the muzzle, and only 0.001" under spec for the remainder of the length (A1 spec).

    Not having a barrel mandrel, I needed to make one. I used a 1/4" schedule 40 brass nipple, cutting off the threaded ends to get them out of the way. Also, not having a 4 jaw chuck, only a 3 jaw scroll, I turned the mandrel to fit the chamber end of the barrel and left the mandrel in place in the chuck. I added a 10-32 brass screw to act as a dog against the side of the barrel hood.

    The muzzle end was supported by a live center at the tail stock. I took off 0.0005" at a pass, until it was 0.0005 over finish dimension. A stone and 2 grades of fine sandpaper then finished it. The barrel is now a uniform 0.575" along it's length. If there is any step left in the transition between the two original diameters, it is invisible, and imperceptible to the touch.

    This was all done on a mini lathe. These small lathes have some serious limitations, but as long as you work within those limits, you can do some serious work.

    My next mandrel will be for the barrel bushing and will use 3/8" brass pipe.

    Brass pipe is readily available in many sizes, and being pipe, not solid, it is lower cost than solid rod and easier to cut to length.

    -

  2. #2
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    Since you have chosen to eliminate the slight flare at the muzzle (which is there for good reason), you will not have to be very careful about barrel springing when fitting the barrel to the gun.
    Hawkmoon
    On a good day, can hit the broad side of a barn ... from the inside

  3. #3
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    You will also not be able to achieve a next-to-zero play-fit between the barrel and barrel bushing when the gun is in battery by modifying an NM barrel to Government Model specs. But that seems to be your goal.

    But it does sound like a fun project.

    Q: What is your reference for dimensions?
    When you can measure what you are speaking about, and express it in numbers, you know something about it; but when you cannot measure it, when you cannot express it in numbers, your knowledge is of a meagre and unsatisfactory kind. [Lord Kelvin]
    Last edited by niemi24s; 19th September 2017 at 13:24.


  4. #4
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    If I did that, I would want a Briley Ball Bushing with the appropriate I.D. ring.

  5. #5
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    But I've a hunch Megafiddle is making a "rattles when you shake it" mid-spec Government Model - using a Kart barrel, no less!!!!

    I wonder if the fitting pads between the upper radial locking lugs will be filed off to obtain the appropriate amount of vertical play at the aft end of the barrel? Stay tuned, folks.
    When you can measure what you are speaking about, and express it in numbers, you know something about it; but when you cannot measure it, when you cannot express it in numbers, your knowledge is of a meagre and unsatisfactory kind. [Lord Kelvin]

  6. #6
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    Thinking about the concept of using brass pipe as a mandrel for machining a precision piece. This doesn't strike me as a great idea. The standards for wall thickness of "pipe" are simply not tight enough for machining work, nor is there a standard for roundness.
    Hawkmoon
    On a good day, can hit the broad side of a barn ... from the inside

  7. #7
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    All those concerns were eliminated by the method described in paragraph 2 of Post #1.
    When you can measure what you are speaking about, and express it in numbers, you know something about it; but when you cannot measure it, when you cannot express it in numbers, your knowledge is of a meagre and unsatisfactory kind. [Lord Kelvin]

  8. #8
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    I still prefer to use rod.

    It is harder to deform it when tightening the chuck and can then be used repeatedly.
    Last edited by brickeyee; 20th September 2017 at 11:59.


  9. #9
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    Quote Originally Posted by Hawkmoon View Post
    Since you have chosen to eliminate the slight flare at the muzzle (which is there for good reason), you will not have to be very careful about barrel springing when fitting the barrel to the gun.
    That's true. I will be fitting the bushing as it normally would be for an A1 barrel, relieving the lower front and upper rear of the bearing surfaces inside the bushing.

    I have an idea for a tool to add this relief. This would be a rod with two long strips of silicon carbide sandpaper, one covering the upper surface of the rod, and one covering the lower surface. The strips would cover most, but not all, of the rods circumference. This would leave the sides of the internal bushing surface untouched. The overall diameter of the rod with sandpaper will equal the barrel diameter.

    -

  10. #10
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    Quote Originally Posted by niemi24s View Post
    You will also not be able to achieve a next-to-zero play-fit between the barrel and barrel bushing when the gun is in battery by modifying an NM barrel to Government Model specs. But that seems to be your goal.

    But it does sound like a fun project.

    Q: What is your reference for dimensions?
    I am using the A1 specs in the Kuhnhausen manual and the blueprints from the technical section of this forum. And Government Model specs is my goal here.

    So far, the only things out of A1 spec are the barrel diameter (0.003" under minimum at the muzzle, 0.001" under minimum for the remainder), and the bushing inside diameter which will also be a couple thousandths under minimum for a close fit.

    The A1 specs for the individual parts guarantee 0.001" clearance between barrel and bushing. Although my individual dimensions are off spec, my relative dimensions between the parts can still be maintained.

    -

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