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Thread: Johnford ST40 Lathe Turret Alignment

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    Default Johnford ST40 Lathe Turret Alignment

    Hi,

    We have a Johnford ST40 CNC Lathe, and all the tools are .06 - .09 below center.

    I beleive the turret got twisted a little from repeated crashes.

    I pulled the cover off the turret and it looks like there are 2 sets of screws and dowels.

    Does anybody have experience tryin to realign one of these turrets?

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    Default Re: Johnford ST40 Lathe Turret Alignment

    Remove the turret . replace the dowells pins ,if bolts got damaged replace it. check the center height of the turret it should be within 10 microns.

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    Default Re: Johnford ST40 Lathe Turret Alignment

    Does the turret have to come off?

    It doesn't look like it.

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    Default Re: Johnford ST40 Lathe Turret Alignment

    also, whats the best way to align within 10 microns?

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    Default Re: Johnford ST40 Lathe Turret Alignment

    Quote Originally Posted by pa4445 View Post
    Hi,

    We have a Johnford ST40 CNC Lathe, and all the tools are .06 - .09 below center.

    I beleive the turret got twisted a little from repeated crashes.

    I pulled the cover off the turret and it looks like there are 2 sets of screws and dowels.

    Does anybody have experience tryin to realign one of these turrets?
    Components of a CNC lathe are designed to move. You can't have a case of irresistible force and an immovable object. Accordingly, you will frequently have the Turret Disk, onto which the tools are mounted, the Turret Body that hold the Turret Disk, and the Headstock of the machine, all move during a crash. Correspondingly, its good practice to check the alignment of all these components after a prang.

    You should have a schematic drawing of the various assemblies in the Parts Manual of the machine. From this you will see how the components of the machine are attached.

    1. To align the Turret disk, remove the dowels as suggested by kiran, crack loose the bolts but keep them firmly nipped up. The dowels are usually tapered and are drilled and tapped to allow for extraction. Use a lever type dial indicator on a flat surface of the Turret Disk that is supposed to be parallel to the X axis travel. This is generally a surface where a turning tool locates in the Turret Disk. The bolts being firmly nipped and the dowels removed will allow the Turret Disk to be carefully moved using a block of wood, to protect against damage, and a dead weight hammer. Use the X axis travel and the dial indicator to check the alignment. Once correct, tighten the bolts that were previously loosened, re-ream the tapered holes to correct any deformation that may have occurred as a result of the crash, and install new dowels.

    2. The alignment of the Turret Body can be checked by applying a dial indicator to a surface of the Turret Disk that should be parallel to the Z axis traverse. In most cases there will be opposing jacking bolts provided to move the Turret Body into correct alignment. As with aligning the Turret Disk, start by loosening the hold down bolts of the Turret Body but keep them firmly nipped up. Using the jacking bolts provided, move the turret body into correct alignment as shown by the dial indicator when the turret is traversed in the Z axis. The alignment of the Turret body can also be checked by applying the dial indicator to the face of the Turret Disk and traversing the Turret Body in the X axis.

    3. The Headstock alignment is confirmed by taking a cut on a test shaft and measuring it for parallelism. This test should be done over a length no less that 300mm and the shaft should not be supported with a tail stock. For this purpose, I use a piece of aluminum with a minimum diameter of 75mm. The tool needs to be one having a minimal tool nose radius. I prefer to use a sharp pointed "V" tool or screw cutting tool with practically no tool rose radius. The idea is to avoid any deflection of the workpiece by it being pushed away by the cutting forces.

    i. Prepare the shaft by undercutting the centre, leaving a length of about 16mm at each end of the shaft so measure.
    ii. Create a program to take a very light cut, using a fine feed, at the journal furthest from the chuck. Allow the tool to feed past the journal into the undercut area, then rapid to just short of the journal near the chuck where a cut is made on that journal.
    iii. Have the program clear the tool of the workpiece and stop the machine.
    iv. Measure the two diameters to determine any tapper and hence, misalignment of the headstock.

    4. The Headstock is generally provided with opposing jacking bolts, similar to those described for the Turret Body. Loosen, but keep nipped, all the Headstock hold down bolts.

    5. Apply a dial indicator to the end of the shaft furthest from the chuck and use it to shown movement made using the jacking bolts. The movement shown on the indicator will NOT relate directly to the amount of taper in the Test Cut, as the Headstock will be rotating about a point roughly at its centre, and not at the journal closest to the chuck. However, after a few test cuts and measurements, you will soon get an idea of how much improvement occurs with a corresponding movement at the dial indicator.

    6. With regards to Taper Dowels for the Turret Body and Headstock, there are as many machines with such pins, as there are without. The schematic drawing in the Parts Manual will tell the true story.

    Regards,

    Bill
    Last edited by angelw; 05-25-12 at 04:50 PM.

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    Default Re: Johnford ST40 Lathe Turret Alignment

    Quote Originally Posted by angelw View Post
    6. With regards to Taper Dowels for the Turret Body and Headstock, there are as many machines with such pins, as there are without. The schematic drawing in the Parts Manual will tell the true story.

    Regards,

    Bill
    Thanks for the detailed post Bill.

    The schematic drawing doesn't show any detail in this area.

    I just need to be able to give our maintenance men some guidance to get the tools back on center.

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    Default Re: Johnford ST40 Lathe Turret Alignment

    Just wanted to update this thread.

    The alignment pins for this turret were #7 taper pins. The ones we pulled out were visibly bent.

    We installed new ones, tightened everything up, and the turret indicated within .001".

    Thanks for all the replys.

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