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Bridgeport Feed Controller

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.



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.



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.



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.



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.



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.



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.



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.



Parts List

Motor Drive Controller

MM2300C Series

115VAC input, 0-90VDC output


Minarik Part Number



Surplus Center

Item# 11-2269


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



Omron Model Number



Grainger Part Number



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


Grainger Part Number





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