View Full Version : Converting a mill to CNC

Kerry Pinkerton
02-01-2004, 03:23 PM
Carey, you mentioned you had converted your BP to CNC in a different topic. Can you elablorate on what is required and approximate cost. I've been thinking about CNC since I making lots of similar items and it would be best if all my ajusters, mounting plates etc were EXACTLY the same. I try to follow my prints but I'm not sure how interchangable things actually are.

Or better yet, I'll trade you an ewheel if you convert my BP... :lol:

Richard K
02-01-2004, 03:40 PM

Look at www.ajaxcnc.com

They have the conversions. I know a guy, one of our members who uses their wares.

Tom Lipton
02-01-2004, 06:41 PM
Hi Kerry,

I would not bother with a bridgeport conversion. The hassle factor plus the semi-automatic nature of the conversion lacks what the powerful features of CNC machinery.

Keep your bridgeport for second operation work and buy a mid to late 1980's small CNC machining center. Good Matsuura MC-500 and 510 can be had at auction and from machinery dealers for less than 10k. These machines have the features that really make CNC powerful. Tool changers, spindle speed, and flood coolant.

A good CNC will make your part making operation move in a parallel fashion instead of series. That is you can be working on another part or the second operation while the CNC chews out another part UNATTENDED. Its pretty cool to sit and eat your lunch while the machine is pounding away making you parts or $$.

The bridgeport conversions are good for a couple of things. They can produce geometry that is impossible manually. They also take up less space in a small shop.

I don't know what the current cost of a three axis conversion is but if you factor in your labor even at a very pathetic rate the cost ratio benefit is just not there. Also switching back to do a quick little part manually is less than optimal.

The older CNC machines are not as fast as the new ones but for our usages they don't have to have the latest and greatest controls and speed. The Matsuura I mentioned can cut with feedrates faster than the bridgeport conversion would rapid traverse. If your cutting steel or stainless its a mute point. You can only push cutting tools so hard regardless of the machine.

I can't tell you how many times I have had the mill running a part, the lathe turning something else and me welding the two pieces together. One guy, three operations simultaneously.

All I can say is if your even remotely serious think about a full blown automatic machine.


02-01-2004, 07:36 PM
I would guess that the cnc utility use would depend a lot on what you need out of it.

I hear Liptons comments loud and clear. A bridgeport mill is simply not rigid enough to hold tolerance at production cnc feed rates (or so I am told). that said, a slower version could still be more consistent than my attempts.

One of these days. . . . .

Here is another company that has been making controls for quite a while.


02-01-2004, 07:59 PM
Hi Kerry,

about ten years ago I worked as a machinist. At one of the small shops I worked at we had an early Bridgeport brand NC machine. It was essentially a modified manual bridgeport with a large NC head on it around, and in front of the quill. There were several nice things about it, and many more bad. One, the mess it made was unbelievable! Since there were virtually no guards, the coolant and chip spray was incredible.

Otherwise it took output from our CAM programs, you could easily do offsets at the machine, and it had much faster travel than a standard bridgeport power feed.

I think in an NC machine the control set or interface is the main thing. If you don't have something pretty common, and in a decent language (M code? g code?) then you're going to have a hard time figuring it out. If you have a Fanuc control, or something similar, you will be very happy! ;)

This is coming from someone out of the industry for five plus years, so it's just my $.02...

Good luck,


02-01-2004, 08:39 PM
Kerry: Converting a bridgeport to CNC involves several aspects. You mount stepper or servo motors to each axis. Generally using timing belts. I have mounted stepper motors on each axis without altering the machine in any way. My motor mounts use only existing bolt holes. It is best to replace the leadscrews with ballscrews to eliminate backlash. Actually the best way is to buy a CNC Bridgeport with burned out controller. Those can often be found a lot cheaper than manual Bridgeports. They will already have ballscrews and motors. Just put some step/direction drives on and it is ready to go. Servo motors are faster but a bit more complicated to set up and tune. But they can get away from you if you lose a encoder signal. Steppers are a lot simpler. All of the early Bridgeport Boss CNC machines had stepper motors.
You need drives for each motor. Most of the conversions use step/direction drives and the most affordable software is step direction from the parallel port of a PC. You need a power supply for the motor drive unless provided in the drive.
You need controller software to take your cad/cam generated g-code and convert it to step/direction pulses that the drives need to power the motors.
Then you need cad/cam software to draw the part and convert it to g-code.
I have spent hours doing research on the internet and quite a few bucks on ebay to convert my mill and my Hardinge lathe to CNC and learn how to make parts. I had a bunch of roll forming rollers to make and did the conversion of the lathe to do the job. I spent a lot of time clearing hundreds of pounds of chips. I did the lathe conversion in a day or two.
There is a learning curve to deal with,but you are a sharp guy so that should not be a large concern. I have to say that is amazing to watch. The rollers that I did had to match and all of them had fillets and a lot of them had curves that had to match with a .040" gap for the stock. That was a couple of years ago. My client got his patent while I was at the FormFest at George King's shop in 2002.
He had gotten bids to convert his existing roll form machine at 1.4 million bucks. I wish that I had seen a bit of that.
If you are serious about doing a conversion, I would be happy to help you. I bough everything on ebay or contacts from ebay purchases. It was a lot of fun to do.

Kerry Pinkerton
02-01-2004, 08:40 PM
I have a friend with an Excell CNC. This is an older machine with Nixie tube displays. The display will come on and then go out like whatever passes for the CPU is dying..

He wants 4K for it as it is. Don't really know anything about it but I SUSPECT the displays and cpu could be replaced by an obsolete PC with monitor (I have several).