Set up a toolholder for the Prototrak mill

When you need to replace a broken bit, or you want to load a special one for a CNC job, here is how to do it.

  • Step 0: bit is broken

    Report the broken bit to a maintenance card, mentor, or metropolis-staff@

  • Place the toolholder in a vise

    Make sure to grab it by the flats

  • Blow off chips

  • Loosen the collet nut

    Use the collet nut spanner (in the endmills drawer in each mill cabinet)

    Turn the collet nut counterclockwise, viewed from the bit end

    If it’s tight, be careful not to mash your fingers when it lets go

    Using a deadblow mallet on the spanner is ok if you need to

    It may get stuck once more, after an initial loosening, just give it another twist with the spanner

  • Clean the taper

    Clean the inside of the taper with air and a rag.

    You don’t want any chips or excess coolant in there

  • Clean the collet and collet nut

    Clean the collet and collet nut with air and a rag

    You don’t want any chips or excess lubricant in there

  • Reinstall the collet and new bit

    If you took the collet out of the collet nut, snap it back in by tilting it and pressing in

    Insert the bit into the collet

    Screw the assembly back onto the toolholder

    Adjust the bit stickout

    Finger-tighten the collet nut

  • How much stickout?

    As a starting point, there should be 0 to 1 times the cutter diameter of shank exposed between the collet and the end of the flutes

    You can use a little more stickout for special cases, but always at least two shank diameters in the collet

  • Tighten

    Use the collet nut spanner to tighten the collet nut

    The torque spec for ER32 collets is 100 ft-lb. So pretty much as tight as you can get it with the spanner


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