1981 Bridgeport Series 1 CNC

I picked up this 1981 Series 1 CNC for $500 today. Not sure if I should have, but I’m currently using a small grizzly mill that’s 3/4HP and have been wanting something bigger.

What I’m wanting to do is install a VFD so I can run it on 220 single phase and upgrade all the servos and controller so I can use fusion 360 to make some parts on it. Figured the old tapes are hard to make lol.

Anyone done something similar can guide me on where to start?

Does anyone sell a complete kit for this mill?

Dakotahm88 said:

I picked up this 1981 Series 1 CNC for $500 today. Not sure if I should have, but I’m currently using a small grizzly mill that’s 3/4HP and have been wanting something bigger.

What I’m wanting to do is install a VFD so I can run it on 220 single phase and upgrade all the servos and controller so I can use fusion 360 to make some parts on it. Figured the old tapes are hard to make lol.

Anyone done something similar can guide me on where to start?

Does anyone sell a complete kit for this mill?

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Don't pissoff the folks at centroid and they will sell you an all in one bare system. Anyways do you have steppers or SEM DC servos? if you don't have steppers then that is the best option. if not then something like machmotion very $$$$ but great service and they don't piss off like the folks from Ajax. About the VFD easy to install and run, but use VFD rated cable, derate the ampacity and Ground Ground Ground. YOu don't want to have servos start moving when you operate the VFD

Sorry was trying to attach photo, it’s got steppers I’m pretty sure, very large diameter with heat exchange fins on the outside.

Here’s my most important question. Is it better to spend $15-20k on this machine, or buy something in the 15-20k range.

This machine I bought because it’s hardly been used, the ways etc… are all immaculate. I was just thinking that it would make a great frame to upgrade. Seems like newer stuff these days isn’t as heavy duty or well built.

Not to be negative but you can buy a modern good condition vmc with tool changer and enclosure for way less than 20k and be miles ahead with no time invested.


Fixing up old cnc mills is for people looking for a project in itself. I have been down that road a long time ago. Sad thing is unless it is a very special type of machine retrofits are not worth it unless you enjoy the tinkering or you don't value your time. They are a hobby in themselves, which is all good if that is what you want, but the main attraction should not be that you are getting a good value.

I have a half dozen cnc machines in my shop and the only thing I would ever consider retrofitting is my CNC cylindrical grinder, and that is because they are incredibly expensive and this one is built in such a way that the ways don't wear during operation.

The other thing is the resale value of a self retrofitted machine is basically its scrap value. I just scraped one of my retrofit cnc lathes. I would never sell it even though it was functional. I don't want the liability of something I built hurting someone, nor do I want to be someones tech support for my less than professional control integration.

Some drives and a control and a pc and a monitor- plus good wires, for less than 2g you can have your mill doing milling things. It will not be speedo. It will be a 1980’s mill.
Would you buy one as a shop, no.. is it worth doing just to do and getting a mill out the other side? Yes.

Yeah if you get anywhere near $20k with that you are doing it very, very wrong. New drives should be under a grand, and a computer running mach or linuxcnc should be similar or less.

It won't ever be more than it is, but if you are a hobby guy and can get it making parts for $2500 all up, that may be good for you.

More than that would be a waste.

Do Yal know of any Servos that bolt up to this mill without having to make adapter brackets? Figured if I can just spend a few grand and get it somewhat cnc capable to do some basic stuff then I will do that while I watch for a haas mill in auctions to go cheap.

I was looking at centroid like the one guy suggested. Their kits start at 16k$ According to their site.

I found most the components I need, but there are so many choices of Mach 3 controller cards…. Any recommendations? I’d like something that will work with the factory Honeywell limit switches

Limit switches are just switches, on/off. Unless you are moving to prox switches, which still are on off but need power plus signal.
Stay with the steppers if you can. (I will be beaten for Saying that- but man are they easy, work, and have backbone to them compared to hobby level servos).
I would recommend a real controller over Mach, each their own.
Drives, annieham or gecko raptors for best bang/buck. Automation direct drives with built in power supply look tempting. Parker, abb, sew eurodrive, Siemens if you want to throw money around. I am not suggesting not going with seimens- but I will never buy or recommend anything they make ever again.
If your motors still have power supply you are golden. This is one place more is more, bigger is better- then double that.
Automation direct has all the wires you need, check sales section for end runs to save a good amount of money.
Controller is biggest decision: there are hundreds of them out there. Edding and planet are very capable, lesser service. Centroid or flascut have better service, cost more, less/equal capable. It is not hard. Tedious work, not hard work.

I have converted tape drive boss 5 bridgeport, it works fine with original steppers, a cheap breakout board and mach 3. If I had to do it again or redo it I'd use Centroid Acorn, which uses the same software as the Centroid allinoneDC that I used on my DC servo router converted from a fagor, or maybe Masso. No sense in putting over 3k into an old machine that's not a bed mill without a tool changer like this, but it does fine at what it is supposed to do. Stay with the steppers if they work or you'll be in for an extra $400/axis minimum. Check out Clearpath servos if you do.

Next question… someone put a Kwick switch 200 spindle in this mill….. anyone have a recommendation to a better replacement that’s easier to find stuff for.

So far I’ve spent about $3200.00
$2300 on the retrofit and control board(with 3 new servos with drives and a VFD)

And the rest I spent on PC components and a touchscreen monitor so I can put it’s own PC inside the old case and make it look original as possible. Not that it matters. Just wanted to!

I’ll post photos as I get parts in and start this project.

Meanwhile, any good auction sites I might have missed to find a light production capable mill? Most the stuff I make will fit in a 10 x 10 space, although it would be sweet if I could mill 18” sprockets and taper the teeth on my lathe when done.

Is there a reason not to put the Z axis servo on the knee ball screw rather than the spindle? I feel like it would be more rigid if the spindle didn’t have to move…

If nodding head quill is only way.
Why for the love of lazy move to servos when you have sizes steppers already attached? Unless your servos are oversized moving table, vice, parts- and cutting forces becomes a large target in tuning.
You really will not notice rigidity difference in 3/8 or smaller end mill with quill not fully extended.

memphisjed said:

If nodding head quill is only way.
Why for the love of lazy move to servos when you have sizes steppers already attached? Unless your servos are oversized moving table, vice, parts- and cutting forces becomes a large target in tuning.
You really will not notice rigidity difference in 3/8 or smaller end mill with quill not fully extended.

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Okay, that makes sense. Quill it is.

Anyone know what voltage the oiler pump and coolant solenoid is on these 81 model bridgeports? Trying to set up relays to run them.

Dakotahm88 said:

Is there a reason not to put the Z axis servo on the knee ball screw rather than the spindle? I feel like it would be more rigid if the spindle didn’t have to move…

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Speed
It will not be more rigid
Stick with the quik switch, it has a lower taper and in my experience chatters less than anything you will replace it with
Avoid reinventing the machine
make it run

The stock Bridgeport steppers had abnormally long shafts.
I was able to take the mounting flanges off the stock stepper motors and machine them to be adapters for the new servos. Had to bore the middle hole from 40 mm to 70mm on all three, face the round shoulder off, then used indexer to drill 4 new holes.

The stock steppers had 5/8” shaft 3.25” long. The new servos are 19mm(3/4) and 1.25” long. I bought step down adapters from 3/4” to 5/8” that will give me a total length of 3.5” and I’ll trim them to fit.

I filled up two 55 gallon plastic teach cans with old electrical components and circuit boards .

The series 1 CNC had two large cabinets, one for drives and tape reader and one for the electric input and transformers.

I took the former off and move the latter to the side where the other one was so my cables for servos would reach breakout board.

Got a touchscreen monitor and mounted it on ball ram arm so it works in the same fashion as stock (kind of.)

I mounted a 64gb ram 1TB SSD m.2 open chassis PC inside the cabinet, and hooked it up to Ethernet so I can use my surface pro to Remote Desktop and can actually draw files directly on that PC. Going to try Mach 4 on there. Set up a network folder to transfer from office desktop straight to it, my cnc plasma, and soon my VMC.

I’m waiting on some taper locks to come in as I broke one removing it incorrectly, and waiting on a metric broach. Then I’ll be finished and can fire it up. I’ll post photos after I paint it.