A few years ago I (more accurately, my company) bought a nice, clean Interact with a Heidenhain 370 controller dating from around 1994. It worked pretty well until one day the X-Axis servo drive stopped working.
Finding a replacement for a Control Techniques MIDI Maestro proved a challenge. I wound up buying one from a 'dealer' of such things for £700 with a generous 7 day warranty. It worked OK for about six months, then the X and Z axis drives died
Although I use the machine a lot for prototyping - I just could not justify spending another £1400 on something with no guarantee of it working for long. I decided to bite the bullet and convert it to Mach3.
Previously I had converted my Lathe to Mach - and I love it - so there was only one choice really.
I have to thank the many people including Hood & JH Choppers who offered advice before I started.
With the heidenhain, I used a Panasonic Toughbook CF18 notebook to run the CAM software. These are ideal for workshop use as they are coolant and swarf proof and have a good touch-screen built in. These days you can pick them up for a little over £100. I decided to use it to control the mill and use a Smoothstepper to interface between USB and the breakout boards.
The Bridgeport had SEM DC Servo motors fitted as standard, operating at about 140v, 25A maximum. I therefore needed fairly high voltage servo drivers. I could limit the power and go for Gecko Drives (my preferred option) or buy Dugong Drives from CNCDrives.
I had a chat with the makers of the Gecko, who very kindly suggested that something bigger such as the Dugongs would be a more sensible option. I ordered 3 x Dugong drives, one of their HDBOB (Heavy Duty Breakout Boards) from CNCDrives and a Smoothstepper from Warp9.
The SEM servo motors use an optical encoder which is only really compatible with heidenhain controllers. There is a place on eBay who sells converters to allow these to talk to a modern digital drive - but they were way too expensive to be viable. Instead, I bought AMT103 capacitive encoders from Digikey. CNCDrives also sells them - but they are 2x the price of Digikey.
I also had a relay board, bought from eBay for something else (made in China and very inexpensive). It connects to the Parallel port and has 10, 15A relays on board. I've used these for enable lines, mains power, spindle, coolant, lube pump. It does the same job as a BOB / Relay board - but for a fraction the cost.
Converting the motors to use the AMT Encoders turned out to be easy. Once you have stripped out the old encoders from under a cover on the end of the motor, there is a shaft with a M12 thread sticking out. I just turned up an adaptor with a female M12 thread and an 8mm spiggot on the other end for each motor. Drilled a 13mm hole in the end cap and screwed the encoders to the outside of the end caps. Sorry, didn't take any photos - but once you take the end off the motor, the solution is more than obvious!
I stripped out most of the original wiring, labelling as many of the wires that connect to important things like the servo motors as possible.
I fitted the Smoothstepper, Relay Board, HDBOB and three Dugongs, wired them up over a couple of days and remarkably, when I first powered it up - all three axes moved and the spindle ran, first time!
Once all the bits had arrived, it only took a week to have the machine running - but that's where the fun really started!