Taking my Bridgeport Series I to CNC

[Klean-Power]

What a great bunch of Very knowledgeable people here!

I am shopping around to take my Bridgeport series 1 knee mill to CNC
I have looked into various retro fit kits.
I have a wife & 3 kids so $$ is limited.

My question is if anyone here has suggestions and experience on retro fitting their Bridgeport to a 4 axis for under $6,000.

[Karl_T]

I'd suggest you start by looking at software packages. Look at Mach 3 - low cost, Centroid/Ajaz - mid cost, Camsoft - hi cost. (I'm a camsoft guy) Mach3 may meet your needs, but you do get what you pay for.

Do You have servos or steppers on your X,Y,Z axis? What sort of device do you have for the fourth axis? A few series 1 machines had tool changers, does yours?

If you do the work yourself, you should easily stay in your budget.

Karl

[Klean-Power]

Thanks Karl_T

Well I was previously looking at
http://www.cncmasters.com/CNC%20Supr...ofit%20Kit.htm
They have a full kit with software and 4th axit for around 7 grand but I am hoping to do better price wise. I am getting Bobcad V20 , it should be here today.
I will check into Mach 3
from what I have read, servos are better than steppers but a bit more costly, is this correct?
I would like to put a tool changer on it but I dont know if this is possible.

Tony

[Karl_T]

I misundstood, I thought you had a machine that was already a CNC. It may be cheaper to just find a Series 1 with a dead BOSS control so you get all the ball screws servo/stepper motors limit switches etc. already on the machine.

If you're already committed to retro this machine, I'd shop Ebay and other used outlets for servos and ball screws. You'll also need limit switches, two or three per axis. I'd suggest a VFD to drive the spindle.

The kit you found looks fine. You'll spend more $ and less time. Seems like it allways a choice of time or $. I probably wouldn't go with that software.

Mach 3 is very popular software for what you're doing. Lots of help here and on the yahoo Mach NG.



Karl

[jdelaney44]

Tony, if you have the machine you should be able to do it for $6K. I really need to add up all my costs so we have at least one bench mark. I think I'm at $8K including the purchase of the machine.

Um...I'm almost done with mine. I have the whole thing posted here in my conversion blog. Not saying that I have the way to go, just a way to go.

Servos -v- steppers. The debate rages on. Steppers seem to be the defacto standard for the hobby group and a lot of commercial machines. But a lot of commericial machines are using servos or steppers with encoders. The realy key here is not the motor, it's the closed loop feedback. People put encoders on steppers too.

Steppers can be made to behave more precisely in the first place. Thus no need for an encoder to ensure position. A servo is just a pretty normal DC motor with a shaft encoder on it. So it has to have drive electronics to complete the feed back loop.

Couple of recent developments.

Rogers Machine has worked with Jim Cullins to come up with an interface board to act as a DRO AND communicate with Mach3. Rogers wrote some software that allows Mach to be tripped into e-stop when the servos get behind. This is an improvement since the only way for that to happen now that is kinda of the shelf is to have the servo driver trip an e-stop. Then you are at the mercy of the servo driver. I am using Gecko G320s. They fault at 128 steps out. A circuit has to be built to trip the software e-stop via some kind of communication with the PC. Many of the break out boards have a pin or two for this kinda stuff.

Depending on you ratios and encoders, 128 steps could be a lot of distance. On my machine it's .004. I can live with that but I'd like it to be .001. Then I get into a higher drive ratio. Then I need a two stage belt drive and the complexity goes up.

So an electronic solution is really attractive.

Gecko has something called the GRex. It is a little computer really. It takes USB from the PC and hooks up to the servo motors and the encoders. Mach4 will have support for it later this year. It should, if I'm reading the tea leaves, allow some real feedback that will allow the servo motor speed to adjust as steps begin to get off. It will eventually fault out but this should make the servos darned near unstallable. I believe Grex also supports steppers and Gecko has been working on the unstallable stepper for a while. They do this by putting and encoder on the stepper.

This is really interesting to me because then the stepper is essentially a servo.

Then there is the whole EMC camp. This is the Linux based controller. Jon Elson, Pico-Systems, has some hardware that allows EMC to behave in a proportional manner as I described. EMC has a great following. It is free. It is a little harder to install.

In my opinion if you don't close the loop to the computer you are running open loop, so why bother with the servo? I didn't figure this out until recently. I'm waiting for Mach4 to make a decision. The Grex is additional cost.

Having said that, my motors are tuned such that I have not had this kind of a problem. I crashed a tool once and that screwed the datums up, but I'm not sure anything can prevent that. So, I could just as well be running steppers right now.

The smart thing to do now might be to get steppers that at least have the encoder shaft on them. Then you can upgrade to a closed loop system if you feel you need it.

That's my relatively non-technical explanation of what's going on.

Best,
-jd

[Klean-Power]

Wow
What alot of good advice!
Thank you.
I do already have the machine, so I will need to retro fit it.
JD, you have some nice products.
form reading what is on this site, it looks like I will be tearing my machine apart and rebuilding it with and replacing some parts.
I have time, I wont have my cnc up and running until about August.
I should do it right the first time.
Thanks again for your advice

Tony

[jdelaney44]

Thanks very much!

Yeah, might be a good idea. I am going to have to tear down my 2J Head sooner than later. I think it's the clutch. Anyway, we'll see what evil lurks in there when I get to it.

I look at mxtras rig and drool over all the pretty blue paint. Very nice job he's doing there.

-jd

[NC Cams]

Please, somebody, post a link someplace so that JD's explanation above can be easily referred to.

It is a clear concise and non-technobabble sumary that should be required reading for any budding DIY CNC retrofitter.

I admittedly have a preference for servos. Why??? They do have feedback already designed/built into the system. It seems to me that addition of encoders et al to steppers is a way to try to do a back door conversoin of a stepper into a servo. Besides, my neigbor's HAAS has them and if it cost that much, it has to be better. 8-)

Steppers are a bit more economical and, if driven properly by well developed code/drivers, you should not have step loss problems. The thing to remember is that TIME becomes the factor.

Ultimately, can the stepper respond as fast as you plan to send the code??? If not, lost steps and unsatisfactory results will occur.

Remember: It is easy to get the electronics to respond at some gigamegahexahertz rate. Electro mechanical stuff is plagued with inductance, capacitance, slop, backlash and friction and F=MA issues that the computer, sadly, easily ignores...

These ultimately cause more problems than a "you should'a used a servo" or "darn overpiced servo didn't work any better than the stepper I just sold" moment....

Even with servos (well tuned and maintained) we still slow things down when we're trying for optimum accuracy.

[FPV_GTp]

hi guys

I'm in the same situation as TONY_HUGHES ,

not meaning to hijack this thread

nor did i want to ask the same question

and start another thread and consume site space

any help would be appreciated i would like to convert a mill to cnc to

cheers

[jdelaney44]

Here's the link to my thread.

JDs BP J-Head CNC Conversion Blog

I have been at this for like 2.5 years. Many interuptions and a lot of learning. Still this is not easy and it is not simple. But it can be done. I feel like I knew nothing about being a machinist when I started. I now feel like I know enough to hold my own around here.

There is NO easy guide. I think my thread is one of the most complete and detailed threads available. It is not perfect. Is is not a total newbie's guide either. But it is pretty detailed and very specific on many things.

Someday I want to make it better, but time is the problem. Doing the best I can.

Here are the basics steps if you don't know them:

You need a mill. I suggest getting a mill that is already CNC capable but that's not where this thread is going.

Next you are going to need the following major components:

Servo or Stepper motors
A computer
Controller software (Mach3 / TurboCNC / EMC...etc.)
Parallel port break out / interface (Sound Logic & others)
Motor Drivers (Gecko, Xylotex & many others)
OBTW - There is a great thread on this site about a DIY servo driver
A control / electrical cabinet
Unregulated DC power supply for the motors
VFD (Variable frequency drive to run the main motor on your single phase 220 dryer or stove circuit, in most cases)
Misc wire, relays, switches, and terminal blocks
Several pounds of nuts & bolts
Several pounds of alum. & steel.
CAD software
Maybe CAM software. A lot of stuff can be "hand" coded.

I would approach it like this:

1.) Get the X-Y drives built first
2.) Get them running under CNC control
3.) Make the Z drive using the two axis machine you have now
4.) Finish up the limit switches & other items that are needed but not bare minimums.

Does that help? Is that more of what you were looking for. It's hard to figure out where everyone is starting from.

-jd

[CNCfun&games]

Hi Guy's,
JD's thread is very informative and a must see! Also check out Roland Friestad's series of articles in Home Shop Machinist Magazine. They can also be viewed at his site www.cardinaleng.com.
I have been retrofitting both a Bridgeport 2 J and a Boss 4 and the Boss was much less costly because the 3 axis hardware is already installed and the only serious work is stripping the "old"
electronics and this is detailed very precisely in the HSM articles. You can do the whole retrofit
for under $1000. On the 2J The ground Ball Screw kit from Hiwin cost me that much. I paid $1500
for the Boss on EBay because their resale value seems to be less than the 2J. The BPretrofits are
great machines! Watching them run is awsome! Will Smith MV CA

[jdelaney44]

Thanks very, very much for all the kind remarks. Very much appreciated.

Roland does some great stuff. Something to aspire towards. Well, heck, there are so many really smart and capable guys & gals here and over on the Yahoo boards it's amazing. I'm just tryin'g to keep up most days.

Will:

Did you get that Series II Boss that was on e-Bay about a year ago in Arizona that went for $1500? Man, that was a steal. $1500 is a steal no matter where you got it at! Yeah, that's the way to go no doubt.

Yeah the 2J's seem expensive. I think their price is actually kept up by the import iron oddly enough.

-jd