How to check headstock for looseness?

Discussion in 'Gunsmithing Forum' started by unioncreek, Dec 23, 2012.

  1. unioncreek

    unioncreek New Member

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    We have two lathes at work a newer South Bend has a six foot bed. We have another older South Bend with a four foot bed. I would like to be able to crown and chamber my own barrel. I would prefer to use the newer South Bend, but I work for the federal government. Most people wouldn't mind me working on a firearm, bit there's some that might. The older lathe is off site and the manager of that facility wouldn't mind me leaving a barrel in the lathe. I'm a rookie at this and have not been doing very precise work, but would like to. How can I check the headstock on the lathe to see if its precise enough for gun work?
     
  2. stoneam2006

    stoneam2006 New Member

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    From what Ik about them from the schooling I have as long as you indicate the part in it should be accurate to whatever you indicated to....machinehead knows more as he is a very good machinist maybe try a pm to him is a regular to the diy forum.
     

  3. stoneam2006

    stoneam2006 New Member

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    I have talked to machine head as he is a close friend and he said chuck up a piece of bar stock horizontaly and put indicator on headstock and pull back ind forth and look for movement on dial that will tell you slop
     
  4. unioncreek

    unioncreek New Member

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    Hi,

    Thanks for the info. Did he say how much movement?

    Bob
     
  5. stoneam2006

    stoneam2006 New Member

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    Any movement shows wear how much is what you will find out. Just remember the farther out from the headstock you machine the more the movement will show. And the less rigid the part will be don't be afraid to pm machinehead he will be more than happy to help you loves to promote diy gun builders
     
  6. MachineHead

    MachineHead New Member

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    A good headstock bearing would have less than .002" runout. What type of barrel are you trying to re-crown. Tapered or straight.If straight I would chuck the barrel up with only a couple inches sticking out and indicate close to the chuck to within .001" and the same at the far end. If that tolerance can't be achieved then the lathe might not be worthy of gun smithing. The better the part can be indicated the better the product function. If it is a tapered barrel and you have to have more sticking out you will want to use a steady rest and indicate the far end of the barrel the same. 80% of the time using a lathe is setup the other 20% is actually running the part. Good luck
     
  7. unioncreek

    unioncreek New Member

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    Machinehead,

    Thanks for the info. I have a Remington barrel that was rethreaded and short chambered for a Turkish Mauser. I'm almost finished with chamber, I'll finish that this weekend. I have a second Turk that I will be rebarreling to 7mm-08. Te newer South Bend we have has not been used very much soot should be within specs. The older lathe ill have to check.

    Bobg
     
  8. MachineHead

    MachineHead New Member

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    Sounds like you should be okay. Just remember indication of the barrel is critical.
     
  9. unioncreek

    unioncreek New Member

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    I have one indicator right now, but think we have another at work. I knows I could get by with one, but two would make it easier. I've watched a few Youtube videos that have helped a lot, just need to get some hands on.

    Bobg
     
  10. MachineHead

    MachineHead New Member

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    I have been a machinist for 5 years with a degree in machine tool technology and haven't even begun to scratch the surface but you have to start somewhere so get your hand dirty and don't let that hunk of metal (lathe)scare you off. Lol
     
  11. greydog

    greydog Member

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    If the older lathe has plain (babbit) bearings, there will be a certain amount of deflection always whn the lathe is at rest. When the lathe is turning, the oil film acts as the bearing and runout should be negligible. If the lathe has roller bearings, the amount of runout is related to the precision of the bearings and the preload on the beaings. Tapered rollers should be adjusted so there is a certain amount of preload (often this is established by the use of a Bellville washer under the adjustment nuts). Roller bearings are ajusted so there is just no play with very little loading.
    Chucking a bar and pushing on it to check deflection is a viable technique with a couple of caveats. First, be sure and mount the base on the headstock and not on the bed or carriage. You want to check the bearings; not the rigidity of the machine. It is often a good idea to apply the pressure vertically to check for bearing slop since the spindle will naturally rest at the bottom of the bearing. You can even just indicate on the chuck or face plate.
    On a typical toolroom lathe, it is relatively easy to deflect the chuck a certain amount because you can actually flex the headstock.
    On my own 13x40 lathe, I can see about .0003" (three ten thousandths) of deflection if I lift up as hard as I can on the chuck. I can curl a hundred pounds (not too many times, mind you!) so I would guess I 'm lifting about that hard on the chuck. If I pry on the bottom of the chuck with a bar, I can, of course move it a bit more but not a lot. If the bearings were loose, the deflection would be greater and would be accompanied by a clunk as the spindle was bumped up and down.
    As I said, plain bearings are a bit deceptive. A plain bearing must have some clearance (usually a minimum of .00075 " radially) to allow for lubrication and the establishment of a dynamic oil film around the shaft.
    If you clamp a cylindrical piece in the chuck and dial it in to within .001 or less TIR (total indicator runout), dialing it at the other end is valid only if the cylindrical portion is co-axial with the bore and the chuck jaws are perfectly aligned with the bore of the machine. If you are to dial both ends to run true, you have to provide a means for the end being held in the chuck to swivel. If the barrel is cylindrical, this can be accomplished by using a piece of 1/8 inch brass rod or wire between the chuch and barrel. If the barrel is tapered, it will swivel just fine.
    At the outboard end of the spindle you must have a means of centering the barrel. A spider with four screws to adjust the barrel to center works well. The installation of four screws in the outboard end of the spindle itself also works well.
    You can also crown by setting the barrel up in the steady rest. If the lathe lacks a sufficiently large bore to allow the barrel to go through the headstock, this is the only way you can crown it. You can use an adjustable spider on the barrel to center it up in the steady (the breech end is held in and driven by the chuck) or you can install a cat's head on the barrel. This is a sleeve over the barrel which is then turned with the barrel supported on the tailstock center so that the cat's head is concentric to the bore. The steady rest is then set up to so the cat's head runs on the steady bearings. Some run the stready directly on the barrel but there is likely to be some runout if it is done this way.
    With more experience, you will learn different set-ups and methods to minimize error. You will also find that, with experience, instruction which seemed like gibberish will suddenly make sense. Good luck! GD
     
  12. unioncreek

    unioncreek New Member

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    grey dog,

    Thanks for all the info. I'll have to check at least the older lathe and see how much movement is in the headstock. That's the only lathe I dare to use and leave something in it and not have to worry about it.

    Wish I could find a lathe in my area that would be enough to get by with and not have to worry.

    Bobg