Hoffman Mechatronics
Bridgeport Mill J1 Rebuild
There is a change I am planning for my mill. After having used the mill for about a year now, I
intend to turn the X axis stepper motor inward. The will give me a little more room in front of
the mill. I would like to turn the Y axis inward as well, but may not have the clearance with my
new planetary gearheads to do this.
From a performance standpoint I am able to reliably drive my mill at 30ipm in both the X and Y
during rapid move operations. I have been playing with the drive parameters within Mach3 and
feel that by modifying the settings I could probably get the system to travel as fast as 50ipm
during rapid moves.
12.6 Phase 4 – The Z Axis
I have looked at a lot of commercial CNC mills based on the Bridgeport design and I have been
less than thrilled with their implementations of the Z Axis. Mine is not the most accurate, but
does preserve the original machine without destruction. Most models replace the quill stop
micrometer screw with a ballscrew and drive the Z Axis from a bracket attached to the quill stop
collar that bolts to the quill with a single bolt. While this provides the most accurate depth, I have
seen many mills that have had to have their quill replaced after this bolt eventually ripped out. I
have also seen installations where the motor drive system was attached to the microfeed
handwheel, but these are problematic from an installation standpoint. For my installation I chose
BPJ1RBLD_002
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January 31, 201111