I Feel The Same Way , Wish Someone Could Post A Basic Bill Of Materials For A Generic Set Up
I am converting a Lagun mill (Bridgeport clone) to CNC and have been searching CNCzone for information on what motors, drivers, power supply, breakout board etc to use. To tell you the truth all the info out here has left me somewhat overwhelmed and a bit frustrated. Especially all the talk about steppers vs servos, that really leaves me scratching my bald head.
Is there a kind sole, or two, willing to give a fellow CNCer the benefit of their experience gained by converting such a mill? A comprehensive shopping list of parts used for a BP clone mill conversion would be absolutely fantastic! Heck, just learning what motors to use would be a great start.
To put it another way, I am looking for someone to say, "if I were to convert another mill I would..."
Thanks in advance for any advice you care to offer.
I Feel The Same Way , Wish Someone Could Post A Basic Bill Of Materials For A Generic Set Up
If I were to convert on the cheep I would do something allong the plans avaliable from http://www.homecnc.info/
I purchased his plans for converting a round pole mill so it would not be right just to post his bill of materials. But they could be used as is just scaled up (length of screws, size of belts ect.. and not sure if you would come up with another way to do the Z. Since my mill was a geared head I had to put my Z actuator on the side of the mill body. But works) but would have to scale up for a real bridgeport sized machine. I have a BP s1 r2v3 now so glad I I'm not faceing a conversion of a large mill but I do like my converted round pole for small quick stuff.
I would check out camtronics http://s120220635.onlinehome.us/ for power supply info. And I'd probably go with his 1100oz servo motors if I were to fit a real BP mill. Those are the servos I used on my 4x8 router mill and they would be plenty strong to move around a BP mill I think..
Hopefully that is enough of a list..
Also.. For the record I'd do servo's and all 3 of my machines are servo based. I could never get around the possiable "loosing" a step and not knowing it because your feed was to fast or what ever. Becides my step dad owned a machine shop for years. And always comments about his first cnc being stepper based and how it would lie to you after a while if you weren't carefull. Since I'm not carefull I need my machine to tell the trouth or give up trying.
If this is your only milling machine(*see inflammatory note #1 at bottom), and it's not intended to be an industrial, 24/7 machine, AND you want to keep cost to the bare minimum, my suggestion would be to come to grips with about a $2000.00 USD price tag assuming you can do all of the fabrication and machining yourself. Further tradeoffs, and successful scrounging may get the cost down in the $1000.00 range.
I agree with wcarrothers on the servo / stepper argument.
I'm not going inundate you with details, but some important ones are:
geckodrives are on sale until the end of august from geckodrive cheaper than you can get used ones on ebay. Lowest prices I've ever seen , but maybe I'm not that observant. This is probably the most expensive component for a servo retrofit.
g320 drives $87, g340 $114. for three axes it's about $81 more for the g340's.
If you can afford it, get the 340's (I bought the 320's cause I'm tight).
Also, 38 volt ametek motors "almost encoder ready" are currently less than 3 for $100 from central surplus. Other vendors and ebayers also have this motor. It's probably acceptable for a starting point on your mill, and I'd guess that once the supply dries up, you'll at least break even selling them on ebay if you decide on more powerful motors later.
I would put "more powerful motors later" in perspective by asking you what your first lathe was? how long did it take until you wanted/needed a bigger one? Could you get along today with that 6 inch atlas lathe with change gears?
If you want to do this on the cheap, I'll try to help as much as i can. I've done homemade stepper and small servo with commercial driver. Homemade software (way back) and turbocnc. I'm no expert, but I pride myself on saving $!!
inflammatory note #1:
I think that if a person has only one milling machine, then it is foolish to install ballscrews. A mill with ball screws can not safely and reasonably be used manually with handwheels.
The Lagun will end up being my only mill, once I sell the round column mill that it's replacing.
If I don't get ball screw I will have to live with about .022 backlash on X and .011 on Y. That seems like a lot to me but I have no experience with this so I don't really know. The Rockford ball screw conversion kit is $1,000. That's a lot so if I could cut good circles without ball screws that would be great. After servos are installed is it not possible to run the screws manually? More confusion on what to do??
The folks at homeshopcnc.com have the .631 OD screws that would cost way less then half but the feel they are to small for my full size mill. Any thoughts on this?
The Gecko 340s and 38 volt ametek motors sound good but, oh how to wire them? And what about a power supply and breakout board? And the other stuff I don't know about yet?? Remember I'm a rookie at this and if I purchase parts here and there, I will need lots of help getting it all running. You are offering however and I will be taking you up on lots of tech support. I would like to look at the ametek motors. Where can do I find them?
As for the overall cost, that is a concern, but not the main one. I want to end up with a decent conversion here but I am all for saving money too. $1,000 to $2,000 is expected but if I can spend less I am all of it of course. My expectations of this mill are not super high so maybe I should start with the motors and stuff and install the ball screws later if I can't live with the backlash. Does that make sense?
The backlash will have you pulling out your eyebrow hairs if you have no hair left on your head.
I converted a BP with ballscrews and some pretty large steppers through a 1.5:1 reduction for X and Y and I have been nothing but satisfied. Hell - I still have all of my hair and eyebrows.
My conversion thread is here somewhere, but it's not very well updated.
My stepper conversion costs me about $2500 including the cost of the screws. I went with Hiwin rolled screws and they are really worth the effort - the backlash is less than .0004" each which is very easy to accomodate. The price of the ground screws just couldn't be justified for what I do with the machine.
Once you do the conversion and get confortable with it, you will have no need for manual operation.
Consistency is a good thing....unless you're consistently an idiot.
I know how you feel. When I came to CNCzone I could not figure it out either.
Here's how to start a new thread:
1. In the navigation bar found at near the top of each page, Click on the Forums tab located on the left side of the screen.
2. When the screen reloads, scroll down and click the link to the forum you're interested in starting a tread on.
3. When that screen loads, scroll down to the top of the forum and look for the New Thread button, agian on the left of the screen. That will take you to the screen for starting a new thread.
Hope that clears it up.
Thank you for your kind consideration of my receding hair line and eyebrows which, by the way, are still intact.
To further assist in maintaining what's left, would you care to offer some particulars about your conversion?
What breakout board?
What motor drivers?
What size stepper motors?
What power supply?
Specifically on the ball screw/ acme (original lead screw) choice:
The low-dollar, conservative approach (IMHO) would be to stick with the original lead screws initially, since you can always go to ball screws later.
The main advantage of this approach is obviously financial, since you can be making chips under cnc while you're deciding on whether to upgrade to ball screws. If or when you do decide that you want to go ball screw, you have an operational CNC to help fabricate the parts (bracketry etc.) for your ball screw conversion.
It also removes (or postpones) one level of difficulty, or source of frustration from your conversion.
disadvantages of this approach are that the original leadscrews will have many times more backlash than the ballscrews would, acme screws are going to require more power than ballscrews, much in the same way plain bearings require more power than ball bearings. (this is the screw systems' efficiency)
Neither acme nor ballscrews are likely to have zero-back lash
How is backlash dealt with by the cnc? Every software package I've heard of uses backlash compensation. This applies to commercial units as well. Even brand new full size cnc machines have backlash (usually in the .00001's or .0001's range) that is compensated for by the controller.
With proper backlash compensation, your circles will not have .022" "steps" at the noon,3,6, and 9:00 positions on your logan, using the original lead screws. Your actual results will depend on lot's of other factors of the machines condition also, which ball screws can't always fix.
I don't think any of the sherline, taig, size machines use ball screws, can they make "good" circles? How?
I can also understand the opinion of installing ball screws from the get-go, I guess it's sort of a preference type thing. There are also certain milling applications (intricate profiling, engraving etc.) that would incur a severe speed penalty on cycle time with a large backlash machine, since the backlash compensation has to actually move the screw (in your case .022") every time an axis changes direction. Rapid positioning rates are very important for some jobs, less important for others. Your logan might rapid significantly faster with ball screws than with acme, all other things being equal.
Again, just my two cent's worth.
The 38 volt ametek motors are at surpluscenter dot com item # 10-2351
$32.50 us dollars. These are almost encoder ready. I guy had a set of three on ebay a while back with encoders installed. It seems they didn't sell, I think he was wanting 150 or so for the set. I made a short shaft extension , and a small aluminum adapter plate to mount the encoder on mine. Also, the 5/8 PTO end is smooth, no keyways or flats, so you'd have to make a flat, or a keyway or use a tapered bushing type pulley or sprocket. I'm pretty sure these motors have been discussed on other posts. The G340 or g320 should be able to drive these. They're probably on the smaller end of the scale for servos applicable to a bridgeport sized mill.
On the geckodrive servo drivers (amplifiers):
These drives require an oscilloscope to be tuned (according to gecko's user manual). I for one consider this at least a considerable drawback, since I don't have an oscilloscope. What I am hoping is that I will be able to use a freeware PC based scope for the set-up. Otherwise I'll have to borrow or buy a scope (not cheap!).
lptscope.exe works from the printerport, requires a small circuit to be built.
I didn't bookmark where I downloaded it from. There are quite a few soundcard based scopes also. This is something to think about when you're considering your motor/driver choices.
There is the "semi-commercial" (my term) UHU driver that does NOT require a scope for set-up. It can also be had in versions that will drive HUGE servo motors. It's not so easy to find assembled and tested, and is in the $100 to $150 range(each axis). You can search for it in cnczone. Its also available in kit form. Not quite a mature product IMHO, but It has lots of good features.
I hope I'm not making this worse for you, as you can see, the servo option is definitely a bigger PITA to get going than the steppers. I don't think any stepper drivers require an oscilloscope for set-up.