Bridgeport Feed Controller |
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This guide is for rebuilding a stock Bridgeport milling machine x-axis feed
controller to use a readily available inexpensive
DC motor controller from
Minarik. This retrofit will cost about $100 in off the shelf parts. The wiring is fairly easy to do using crimp connectors and some soldering. I soldered the wire extensions but you can use crimp sleeves instead. The electrical components were mounted to a aluminum panel cut to the same size as the original enclosure cover. The panel will also sink heat from the controller into the heavy stock cast aluminum enclosure.
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| Here is a picture of the
Bridgeport feed motor, gearbox, control lever and switch assembly. The
control box enclosure can be seen in the background mounted to the side of
the machine. The retrofit controller fits inside the stock enclosure. The
original fuse and on/off stitch are still used. I recommend using a 8A fuse,
but I was able to run it with a 5A fuse. However I was able to blow a 5A
fuse when I quickly changed rapid feed directions at the end of table travel
where the gibs feel the tightest. If you have a very free moving table, you
can use a 5A fuse, otherwise use a 8A fuse if your gibs are tight. But you
can use up to 10A with the controller if needed, but it is always good to
give yourself some extra safety. It is much easier to replace a fuse than
the controller.
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| This is an exploded drawing of the
feed assembly. Refer to this if you have to take your gearbox apart. The
biggest problem with these are oil leaks. The oil can leak into the switch
assembly and even into the motor if it is not sealed properly. If you ever
take it apart, pay extra attention to the seals and gaskets. A heavier
weight gear lube can also be used to help prevent leaks. A good automotive
gear lube works good and is thicker than regular way lube oil.
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| This is the original wiring
schematic from Bridgeport. The stock wiring harness is still used in the
retrofit except some wires are connected differently. I designed the new wiring schematic (below) to make the change over as easy as possible. The only change needed in the switch assembly is that the momentary rapid travel switch needs to be changed to a double throw switch. I ended up using a toggle switch rather than a button so that it will free up my hands while the table is moving. The Minarik controller comes with its own potentiometer that will replace the stock Bridgeport unit. The new potentiometer mounts right up into the original location and the stock knob fits the shaft perfectly.
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Here is the new wiring diagram I created. I used only the original wires in
the stock control cable between the controller and switch assembly. Some
wire connections on the switch assembly differ from the existing wiring, so
be sure to check all the wire colors with this drawing.
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| This is the new panel cover I made
from aluminum sheet with the components attached to it. I made as many
connections as I could on the workbench to make it easier to install.
The relays plug into the sockets which will make them easy to replace if needed. Both relays are the same. The relays must be rated for 90-120DC since they run on the field current for the motor. What is nice about this controller is the adjustable acceleration/deceleration curves. This will help protect the controller, motor, gears, lead screw from sudden start/stops. I set the limiter so that it had a 3 second ramp up for a smooth start up.
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Here is what the control assembly looks like after all the connections have
been made. I removed the enclosure and switch assembly from the machine and
cleaned them real good. This made it easy to work on and allowed me to make
all the connections on the workbench. Notice how I used two longer screws to
hold the panel to the heavy enclosure, this made it much easier to work on
since it held the panel close to the enclosure while wire connections were
made.
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| While you are rebuilding the
controller it is a good idea to clean the motor. My motor was very dirty
inside from use. There was a lot of black sludge around the brush area. The
brushes still had some life in them so I just cleaned everything with motor
cleaner, but it would be better to get new ones. I polished the commutator
with fine sand paper on the lathe. Be careful not to over do it or the
brushes may bounce if the the surface is not true. You could indicate it in
and turn it down with a diamond bit or very sharp carbide tool.
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Parts List |
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| Motor Drive Controller MM2300C Series 115VAC input, 0-90VDC output
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Minarik Part Number
$80.00 |
Surplus Center
$59.95 |
| Relay Module Square Base General Purpose Relay, Number of Pins 11, Contact Form 3PDT, Contact Current Rating Resistive 10 Amps, Contact Current Rating Inductive 10 Amps, Coil Voltage Rating 110 VDC, Coil Current Rating 51 Milliamps, HP Rating @ 240VAC 1/2 HP, HP Rating @ 120VAC 1/3 HP
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Omron Model Number MJN3C-DC110 |
Grainger Part Number 5ZH82 $11.60 |
| Relay Socket Relay Socket, Number of Pins 11, Mounting DIN/Screw, Length 3.00 Inches, Depth 1.03 Inches, Width 1.70 Inches, Current Rating 15 Amps, Electrical Ratings 300 Volts, Socket Square, Terminals Screw |
Dayton Model Number 5X853-M |
Grainger Part Number 5X853 $8.70 |