Need Help For New Cnc Retrofit

[machworx]

I have a millport mill (similar to a BP series 2) that I have installed ground ballscrews & am getting ready to CNC it. I can buy a ready built kit from AJAX for about 4000$ but I think I would rather do it myself for the learning experience (and less $). Initial questions are:Steppers VS servos, I've been told that servos are more accurate (Servos have a built in encoder/resolver & steppers do not?) but steppers are simpler to setup & less $. I want this machine to run off of a PC type computer so can I use either steppers or servos? In addition to the PC what components do I need for each axis? If I want servos is there a company that makes servo drives for home builders? If I buy the servos off Ebay do I want brushed or brushless? AC or DC? High voltage or low voltage? Similar questions if I go with steppers? How do I know what size motors to buy, what holding torque vs running torque?

[Hood]

I went the DIY route and am glad I did, not only is it a lot cheaper it will also be cheaper in the long run. Reason for that is I put it all together myself so if anything goes wrong I should be able to fix it, another thing is when it comes time to upgrade I will be able to do that.
Now steppers V servos, I am not able to answer as I just have experience with steppers. I dont really know enough about it to argue for one or the other but I will say that I use steppers on my Bridgeport Series 1 CNC and have never had a problem. I use 916oz/in and a 2.5:1 reduction and there is more than enough power and I have never even been close to stalling them.
What you will need for a CNC control is a drive for each motor and a power supply to power them. It is also best to have an optically isolated breakout board to connect to the parallel port with.
You can get drives for servos and steppers from www.geckodrive.com and www.rutex.com does them for servos.
Breakout boards can be had from www.pmdx.com , www.campbelldesigns.com , www.cnc4pc.com etc
For the control software there are quite a few, I use Mach3 and I think its the best but thats just my opinion.

Hood

[Al_The_Man]

If I want servos is there a company that makes servo drives for home builders? If I buy the servos off Ebay do I want brushed or brushless? AC or DC?

Brushed DC are a little easier to mix and match as far as different motors and drives as you don't have to be concerned with commutation issues as you do with DC brushless or AC.
The drives already mentioned take step/dir control which you will need.
Al.

[NC Cams]

You might be able to DIY the mechanicals but what about the software???

I"d first look at the software that will support a DIY system and then use whatever componentry that they recommend. If you don't do this, you could end up buying something that is not integrateable.

If you're not confused now, keep looking, you will be.

Here are a few links you just might find helpful:

Great NC controller thread - NC vs PC’s
http://www.cnczone.com/forums/showth...852#post182852

Lathe retrofits (real good buy vs build info)
FINALLY started BIG_CNC_LATHE conversion
NC Controller difference
Interest in Lathe retrofit

Research (how to - most people don't know how)
CNC Information
specifically post #15

Electronics books (buy them if you don't know electronics)
http://www.forrestmims.com
or
http://www.amazon.com/gp/product/pro...lance&n=283155

The "holy grail" of electronics info for the DIY CNC neophyte:
http://www.amazon.com/gp/product/052...lance&n=283155

Web-based books on electronics:
www.ibiblio.org/obp/electricCircuits/

Why parallel ports may sometimes suck at doing CNC control::

See post #5 in the following thread:
http://www.cnczone.com/forums/showth...852#post181852

Linear scales;
http://www.cnczone.com/cg...3;t=003181;p=0

Ball screw basics:
Ball Screws 101

Ball screw treatise, the hard core stuff:
Ballscrew Basics

PID tuning (for servos)
PID explanations?

Daisychaining ATX power supplies:

http://www.cnczone.com/forums/showth...015#post142015
http://forums.bit-tech.net/showthread.php?t=108208

Linear P/S design/construction
http://www.campbelldesigns.com/files...ply-part-1.pdf

How to properly phase a transformer in linear p/s:
http://cnczone.com/forums/showthread.php?t=14821&page1

Servo amp P/S design
http://www.elecdesign.com/Articles/A...7635/7635.html

Servo motor , servo amp, powersupply sizing for CNC
http://www.rutex.com/pdf/Mystique2.pdf

Bearing literature:
http://www.bardenbearings.com/literatr.htm
http://www.timken.com/products/bearings/catalogs/
http://www.jp.nsk.com/app01/en/catal...gi?ec=bearings

Get the NSK E1102 catalog for starters

Press fits:
http://www.eng-tips.com/faqs.cfm?fid=1230

Motor torque info/defininition
http://www.merkle-korff.com/formulas.asp#con

What gage wire to use:
What gage wire?
http://www.cnczone.com/forums/showth...480#post136480

Servo vs Stepper (READ THIS!!!!!!!!!!!!!):
Steppers and Servos...

Simply stepper info:
http://www.parkermotion.com/catalog/catalogA/A12.pdf

Stepper reverse engineering:
http://www.doc.ic.ac.uk/~ih/doc/stepper/others/

Stepper sizing:
Sizing Criteria for Torque of Stepper motor

Small stepper P/S
http://www.campbelldesigns.com/files...ply-part-1.pdf

G code parts counter
Fanuc parts counter

Haas TNC explanation
http://www.haascnc.com/customer_serv...he/96-8700.pdf

Finally, probably a majority of the DIY stuff is stepper oriented. Conversely, a preominant majority of the commercial machine tools that are "factory built" consist of servo based systems.

THERE ARE LIMITATIONS/ADVANTAGES TO BOTH.

[ger21]

Why parallel ports may sometimes suck at doing CNC control::

See post #5 in the following thread:
http://www.cnczone.com/forums/showth...852#post181852

Why post this? Parallel port control may suck based on someone's speculation of how he **thinks** the software works? Sure, if you try to use too slow of a PC, or a PC with software running that interferes with the control software, you may have problems. But people are buying $299 Dells and even $199 PC's from Fry's, and they all run Mach3 fine right out of the box.

There are over 5000 registered users of mach3, who found that it didn't suck too bad, because they all payed $150 for it, even after they got to try it out for free for as long as they wanted.


Servos are not necessarily more accurate than steppers.

For stepper and brushed servo drives, see www.geckodrive.com and for brushed and brushless servo driveres, www.rutex.com

Whether steppers or servos, you want DC, with the exception of possibly brushless, which is the most expensive route also. Voltage depends on the drives you choose to go with.

[NC Cams]

I usually edit out my "personal comments" before I post a crib note response to someone. I appologize for not doing so on this one. I figured that sooner or later he'd be asking a lot of the "usual" questions so I provided answers en-bulke. Besides, the note in question says "may suck", not "will suck" - big difference.

We've all seen cases where guys run into "issues" with LPT driven systems. They use laptops with low voltage LPT's, they use laptops with power managment strategies that mess with real time machine control. Folks even use "lamp cord" instead of shielded wire - even when TOLD to use shielded cable. Some folks just have issues, period.

As well as Mach is supported, it is not always that easy to implement. Most problems are due to use shortcuts, user deficiencies and or other things that crop up. Fortunately, there is a support base of folks who've been there and done that and know what to do to fix most anything.

Whereas at one time I thought Mach was "just another" S/D system (my stuff is commercial and servo based) I'd have to say NOW that the Mach method is probably THE ticket for lots of guys looking for a reasonable cost DIY CNC system. Just follow their recommendations for hardware and you should do fine.

Servos are a bit more difficult to get your arms around. YES, Mach will drive servos BUT you still don't have real time F/B to the PC during operation. I know of NO "Mach like" system for servos based retrofits that fit on medium to larger machines with FULL F/B - there are table top mill servo systems but these can't usually be scaled up and I dunno if they do FULL F/B.

Yes, steppers are not usuall more accurate than servos. BUT we've seen where, in spite of HUGE efforts to try, steppers can't match the performance/finish that a servo generates. WE've seen this time and time again it comes to precision form grinding ala cam profiles and/or OD grinding of journals. From this, we've simply come to expect more when WE judge a CNC - your needs may not be so stringent and probably won't be.

Besides, in our case, steppers were found to leave 'steps' and they can't hold shape adequately due to the rapid motion changes needed to achieve a cam profile shape.

To test the ultimate efficacy of ANY system (servo or stepper), simply try to cut a perfectly round OD or ID circle REALLY FAST.

When think you've got the system right, do the test cut and make it perfect as it with with NO chatter, no flats at the direction change points, no diametral deviation at the max velocity points at 45 deg and then RETURN to X=0.0000 and Y=0.0000 coordinates at the end.

Do that with ANY system and you've REALLY got something running SWEET. We can just do it with our Eztrak to within 0.0003" but the cut takes nearly an hour to finish. The neighbor's Haas does under 0.0005" but takes 10 minutes.

I'm not belittling Mach or any other step/dircection system. You just have to realize that some aspects of CNC just are NOT that easy to do well or on the cheap.

[machworx]

I want to thank everyone for the assistance so far. There's a lot of info to digest which I am working on. But as usual good answers routinely bring up new questions which I will ask as they come up. Everone talks about this Mach program, can one of the NC programs that come with either Unigraphics or Pro-E Do the same thing? The part about stepper driven mills & the not truly round problem I experienced myself when I was running a "bandit mill" back in the 70's & would be my main reason for wanting a servo driven mill. But it seems that the servo driven option is more expensive & maybe a little more of a headache to set up. Any guesses on a typical ratio of ($ for servo driven)/($ for stepper driven) so I can deem if it's worth the extra $. I have gathered that S/D means step/direction but what about F/b or FULL F/B? Enough questions for now until I catch up. Thanks

[NC Cams]

I'll provide a oversimplified feed back (f/b) explanation.

A stepper moves based on pulses or steps sent out by the controller. THis is done in conjunction with a direction command - step - directin or S/D. Send a step, it moves, send another another move, do it fast enough, psuedo commutation occurs and you have "smooth" rotary motion. Smooth being relative in this instance - you're still stepping only real fast. Real fast steps can cause inductive heeby jeeby's that half stepping can mitigate.

The resolution for each step is a function of the motor design. Some motors have X steps per rev and some have Y steps per rev. THus, unless your controller is capable of partial step resolution, the smallest step your motor take is a function of it's design characteristics. You can research the steps per rev or deg/step for yourself.

So, the PC sends out steps and the motor moves those steps. Well, the steps were sent but did the motor move any of them, some of them or all of them???

That's were F/B comes in.

Add an encoder and feedback is sent back to the controller so you can close the control loop - move this many steps, yes sir, I moved them and here's proof.

The situation is that steppers are usually parallel port driven. They don't have enough f/b channels available to accept the encoder f/b from all the channels simultaneously. You can add more and more LPT ports but the data you put on the port ONLY is read when the port(s) are scanned by the PC. Since this may not occure every clock pulse of the PC, you don't have instantaneous f/b. (essentially true for this simple explanation).

So, you simply try to build a robust stepper system that behaves and moves when and how much you say to and not do so spasdically because you really don't have f/b to the PC.

Ok so along comes Rutex and Rogers machine. They build provisions for encoder f/b. BUT does it go ALL THE WAY back to the controller for instantaneous control? Essentially no.

They both do error verification remotely to a predetermined amount of step misses (recall this is oversimplified for conceptual, not full technical explanation of what's going on).

Thus, if you have an error window of 50 counts (250 sent but only 199 equivalent steps are reported as having been taken) the Rutex or Rogers machine thingies send out error pulses to stop program execution. Since the machine may have a resolution of 0.000002 per pulse, 100 millionths error is pretty paltry but what if you're stepping at 0.0001 resolution??? Is 0.005 error tolearable??? That's your call. This error window varies but we're only trying to explain the concept, not design a system.

The typical servo contoller has similar f/b but instead of the f/b going to some remote device for decision making, the encoder counts go back to the PC and the PC does the comparison process in real time mode. Due to more sophisticated control regimes that are available to a servo, you can now do more sophisticated feedback via PID loops and other stuff beyond the realm of this simple explanation. However, this control has to be interpreted by the PC.

In the system that I'm most famiar with, the pulses being returned are coming back pretty darn fast. Thus, you can actually move so fast during a prescribed move that the incoming datastream comes in too fast for PC to count. Or signal noise blurs the count. Or inertia can't be overcome and the stuff did't move like it should have. You can end up with error as well. So you have a choice, slow down the machine or widen the error window so you can run the SOB.

Both systems servo and stepper are taking pulses and turning them into motion. F/B is added for verification that the prescribed motion did occur. However, electrons get lost and stuff just happens. THings don't go as planned.

When you can cut a perfectly round circle, do it real real fast, have no steps, chatter or out of roundness and return to 0.0 origin each and every time, time after time, you've got a damn good control loop - whether stepper or servo based.

Why a circle?? You're creating a sin wave velocity loop which will tend to force a system into sympathetic resonance. You're also forcing two axis to keep perfectly syncronized motion while doing so in simultaneously opposite directions (as X is going faster, Y is going slower, by exact same amount - if it don't, the circle goes out of round).

Call it a test for the controller to rub its belly and pat it's head at the same time.

See how simple it is???

[fkaCarel]

Parallel port control may suck based on someone's speculation of how he **thinks** the software works?

In the other thread this was rejected as speculation. I asked why. No answer came. If there is only denial I can only assume I'm right, till proven wrong.I have read up over the years quite a few things about Intel processors. Just go figure out where large data and program processor-caches come in handy and where you can't use them.

I programmed a G-code interpreter with a 2-Mhz (yes, TWO) processor in 1986. Maximum real time speed: 40 Ipm. Linear and circular interpolation. It's just good for my ego to see that these results can't hardly be beaten by a processor that's 1000 times faster.

[NC Cams]

I think, if I interpret Carel's post properly, that he and I are on the same page in this regard: newer faster PC's aren't providing better or faster code processing with regard to today's CNC controls. Complexity in search of a need.

I'm amazed that Bridgeport did 4 axis machining with their VMC 1000's back in late 90's and only used a DOS box and BMDC3 for control. Some were 386 and some 486 but no Pentiums. In fact, you can't even use a Pentium faster than 133 to retrofit to the "legacy" systems.

What did they know about machine control that they incorporated into their DOS based DX32 system that isn't being or can't be done today???

Hmmm. Simultaneous motion with legacy, nearly free O/S's and PC's. Talk about value and a DIY dream. In some regards, the guys who did DOS programming had to be smarter.

Oh if there were only a legacy based DIY servo style retrofit kit that worked. Probably wouldn't sell - too much reliance on windoze anymore.

[Al_The_Man]

I'm amazed that Bridgeport did 4 axis machining with their VMC 1000's back in late 90's and only used a DOS box and BMDC3 for control. Some were 386 and some 486 but no Pentiums. In fact, you can't even use a Pentium faster than 133 to retrofit to the "legacy" systems.

But a distinction has to be made as to what was doing the processing, did the BMDC3 card have its own processor for motion control?
There is a distinct difference between a PC processor doing the actual motion calculation and a motion control card, which now have 32bit RISC processors dedicated to the motion trajectory.
Galil and others where doing it this way back in the 80's for 8 axis control.
I am still using some of their DOS capable Legacy cards for simple/low cost retrofit projects.
Al.

[NC Cams]

BMDC3 used 68CH30 Cpu and and 68882 coprocessor.

It also had D-A +/-10 drive for servo drive signal to amps and a host of other chips. It was a single slot ISA board that ran mill (2, 2.5 & 3 axis), VMC (3 or 4 axis), lathe (2 encoders and 2 hand wheels plus spindlle F/B); and/or surface grinder.

I'd be interested in knowing more about what kind of canned software you use with the Galil stuff to do legacy controls. Advise via P/M if you wish....