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  1. #1

    I think I have figured out my ATC tool jam problem on the 720.

    If the air pressure drops below 95 psi the ATC sometimes fails to load the tool holder, because the drawbar does not fully release. The drawbar air cylinder can only fully press the drawbar down at 97 or more psi. This of course is problematic because the 720 pressure should only be 80 psi according to the manual. This explains why sometimes the ATC moves seem to stop harder than I would expect, the previous owners had the 720 set at 100 psi.

    So this leads to the chicken and 2 eggs question? Is it a weak air cylinder, or a jamming drawbar, or both?

    I have heard of the spring washer breaking and jamming the stack, with this in mind I would like to remove the drawbar with the spindle on the machine.

    If any one has experience pulling the drawbar, I would really appreciate any tricks or traps I might run into. :-)

    I guessing there is some preload when reassembled?

    Thanks, Bryan

    Click image for larger version. 

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  2. #2

    I disassembled the drawbar and found many broken washers and some bite marks on the drawbar itself (See picture). The bite marks are only about .001 - .002 deep.

    Click image for larger version. 

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    I have some new washers on order, and have polished out the bite marks on the drawbar. I am going to coat the washers with Never Seez, see link http://www.neverseezproducts.com/regulargrade.htm This looks like good stuff to keep the washers happy, please let me know if I should be using something different?

    When complete, I am hopping the air cylinder can push the drawbar down at 80 pounds.

    Thanks, Bryan

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