Setting the pull stud height on a BT40 Bridgeport VMC 760
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  1. #1
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    Default Setting the pull stud height on a BT40 Bridgeport VMC 760

    Hello,

    I have a Bridgeport VMC 760 that has BT40 spindle.

    A lot of my tools get stuck in the spindle, and require a light tap with a mallet to get them out. The tool holders are new, and I've inspected the spindle bore taper, it is clean. I have proper air pressure.

    what I notice is that one of the older tool holders that came with the machine has a longer pull stud and it comes out of the spindle without issue.
    It's the only one that does, while any others that came with the machine and any new ones I purchased do get stuck.

    I've got the manual and I've read it in and out, and there is nothing to tell me what height I should have the pull stud at.

    Of course I did measure the one tool that works, but I'd like to do it the proper way and not just guess at it!

  2. #2
    Join Date
    Dec 2014
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    I would be concerned with the retention force of the longer pull stud. You need to have the retention force checked, it should be a minimum of 1600 pounds. The tool should knock out of the spindle .036" which is adjustable with the bolt on the end of the unclamp cylinder. The housing that the cylinder bolts to should raise up .020" when unclamped. This is set by a collar on the spindle shaft. What this does is take the load off of the spindle bearings when the unclamp cylinder strikes the drawbar. There should be a .020" gap on this collar and that is what you see when the unclamp button is pressed.

    There should also be a .020" gap between the bolt on the end of the unclamp cylinder and the drawbar without a tool in the spindle when clamped. Otherwise the drawbar will weld itself to the bolt on the unclamp cylinder.

    The gap between the spindle and the BT40 tool should be .078" according to the drawing. It should knock out of the spindle .036" when the unclamp button is hit. You can check this by setting up a .001" plunge indicator and mag base on the table and position it under a tool, then hit the unclamp button. Be sure to hold on to the tool, lol. You should be able to get a good reading this way. (clamp/unclamp and repeat)

    When adjusting the bolt on the end of the cylinder for the knockout, I have seen left handed threads, but not sure what you will have. There is a lock nut on the bolt. Call if you have questions, always willing to help a PM member. The link below shows the drawing for adjusting the knockout. Daryl

    Knockout Adjustment Drawings

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