Hoffman Mechatronics
Bridgeport Mill J1 Rebuild
to drive the Z from the rack and pinion of the hand crank. I did not want to lose the ability to
pivot the head on the mill, so I centered the drive system at the pivot shaft. While a 3:1 reduction
was not ideal for this installation, it did suffice until I was able to find a planetary gearhead for
this axis. Figure 62 below shows my installation. Note that I preserved the feed handle for the
initial installation, but once the gearhead is installed the feed handle will have to be removed.
Figure 62 – Z Axis Installation
12.7 Phase 5 – The Planetary Gearhead for Z Axis
After searching on the online auctions for some cost friendly gearheads, I stumbled upon a 60
series mount 20:1 gearhead that I knew I could alter to fit the NEMA 34 mount used by my
stepper motors. I bid on the item, and to my surprise, I won the gearhead for $15. This does not
happen often and you can expect to pay closer to $150 for used NEMA 34 or 60 series gearheads
online.
The first thing I did when the gearhead arrived was to turn the input shaft. I felt some resistance
and figured I would disassemble the gearhead. Planetary gearheads are not very complicated and
after about 15 minutes I had this unit completely disassembled and awaiting new bearings. I went
searching through vendors and online auctions, and after about 10 minutes a new set of bearings
was found for, yes, you guessed it $15. While I had the gearhead apart, I turned the output shaft
down to 0.5” from the original shaft diameter. This would allow me to keep my existing timing
gear setup intact. With the addition of this planetary gearhead I would be able to increase the
resolution of the Z Axis from 3:1 to 60:1.
The series 60 gearhead required me to make a few more modifications while I was waiting on
the bearings. The Z Axis brackets that I had made would not work for the series 60 footprint, so
a new set was designed and machined while the old setup was still in place. I also had to mill out
the holes on the NEMA 34 motor, but decided to wait on those until I was ready to install the
gearhead.
Figure 63 below shows my new installation with the planetary gearhead installed. I am much
happier with the resolution of the Z Axis.
BPJ1RBLD_002
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January 31, 201111