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Author:  Don Williams [ Mon Mar 26, 2007 1:30 am ]
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I'm going to build a small CNC. It will have a cutting area of roughly 32" x 48". I will be using linear rails for the LM, and 8020 and aluminum plate for the frame. I'm going through the mental debate on whether to start off with steppers, or jump right into servos and Gecko drives. Trying to understand about motors alone is like learning a foreign language.

So what do I look for in motors? How does amperage, torque, holding power etc. affect the operation when comparing step and servo motors? Like I said, it's all Greek to me.

And how does one choose ball screws, based on which motors??

I'm feeling hopelessly ignorant, perhaps some of you good folks can give me an education?

Thank you...

Don
Author:  Bob Garrish [ Mon Mar 26, 2007 12:17 pm ]
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An education, maybe not, but I can point you toward a good school: cnczone.com is a real resource.
Author:  Don Williams [ Mon Mar 26, 2007 12:20 pm ]
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Yeah, been there...but there's 1.5 million threads, and none of them seem to address the issues head on, like with a nice convenient list, or spreadsheet explaining "use x or y motors with a or b ballscrews, etc. That sure would take the headache out of it all...
Author:  John Watkins [ Mon Mar 26, 2007 10:30 pm ]
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Don, because we are friends I feel I can be frank without offending you. I hope that's the case.

Your questions are too vague, because you've done zero research. The less research you've done, the more explaning someone will have to do in order to help you.

I'd have given my left arm for those 1.5 million threads when I was trying to figure this stuff out. If searching through them is more hassle than you counted on for this project, then I'm not sure you're going to like what's ahead of you once you get the parts and start building it. It's nothing BUT problems and research and more problems and more research.

I would encourage you to post specific questions as they come up, but those would probably also be better served at CNCzone.com.

Good luck!
Author:  Don Williams [ Mon Mar 26, 2007 11:58 pm ]
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Ouch. Thanks Frank....
Author:  JJ Donohue [ Tue Mar 27, 2007 1:47 am ]
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Sounds like good advice. John is as honest as they come and I would certainly appreciate such frankness!

I know I researched guitar-building on 3 forums and read several books for a year before I ever ordered a set of wood! Then again, I'm probably not as smart as you guys and needed the extra time!
Author:  Pwoolson [ Tue Mar 27, 2007 2:26 am ]
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I agree with JJ that John is as straight of a shooter as they come. Very soon after John had built his first machine I started thinking about getting into buildign one of these machines. I was doing the same thing as Don is going through. I didn't want to do the work and wanted the information to somehow be teleported into my brain.
John only lives 70 miles from me and I find myself in his shop pretty frequently. I know first hand the trials and tribulations that go along with this kind of work.
My advice to you Don, is that if you are only at the stepper vs. servo point, you might want to pull back on the reins a bit. Spend a lot of time on the CNC forums and really learn what you need to learn before you start purchasing things.
I think if you just start building as you have/get information you are going to find yourself very frustrated in the long run.
Author:  Don Williams [ Tue Mar 27, 2007 3:55 am ]
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Straight shooter or not, he entirely missed the mark.

Thanks guys for coming to his defense so readily and easily.
I've been reading my head off on this stuff for a couple weeks, but there's a big difference between reading and understanding. I was merely looking for clarification on some things, and wishing to open some discourse here on the OLF. Perhaps that was a mistake, expecting a section on CNC to cater to basic questions on cnc. Heck, let's just send everyone who asks a newbie guitar question over the MIMF or somewhere else. What the @&%\8* is that kind of thinking?
Real nice.
I spent many years doing mechanical design and drafting, CAD and other stuff like that, but I never dealt with motor specs, or the engineering behind the parts I was to turn into a working part of a machine. This is entirely new for me. I could design a lot of things on paper that would work mechanically just fine with some basic clarification. Heck, if I can work on designs of jet fighter radar systems, I think I can handle the basic mechanical stuff of a small cnc with a little clarification on the electrical issues.

Thanks guys. Lots of help here trying to straighten me out.   
Author:  John Watkins [ Tue Mar 27, 2007 4:53 am ]
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Don, you didn't ask for clarification. You asked for a summary how-to. The answer to each of your questions is "it depends".

One could (any many have) write a book on such a broad question as "How does amperage, torque, holding power etc. affect the operation when comparing step and servo motors?".

What's the weight of your gantry? What's the pitch of your lead screw? What kind of moment is placed on the drive when the load is at it's highest center of gravity? What is the ratio of the distance from the drive to the load vs. the drive to LGs? What speed do you need? What's the budget? Etc? Etc? Etc?

I've posted numerous how-to's in this and other forums in the several years since you first expressed an interest to me in building a CNC machine, so forgive me if I don't spend too many hours repeating myself in order to add to my list of competitors (again).

Here's what I would do in your position;

a) search the MIMF for CNC and read the article I wrote about steppers vs. servos.

b) search cnczone.com for 'screw pitch' and look for articles related to speed vs. torque.

c) acquire appropriate ball screws based on the size and pitch that you need for what you want to do.

d) call the motor and drive vendors with as much info as you can surmize regarding your screw specs, loads, and desired speeds. let their engineers do the math and recommend products.

e) be pissed at me if you want to.
Author:  JJ Donohue [ Tue Mar 27, 2007 5:24 am ]
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Don...my input was obviously not what you wanted to hear. I meant no harm...you know me better.

But if it makes you feel better you can be pissed at me as well. For the record...I'm not pissed at you for essentially being accused of ganging up on you...or insulting your intelligence or whatever you feel I/we did to make you fly off the handle.

This topic is well above my pay grade anyway and I had no business commenting in the first place.
Author:  Don Williams [ Tue Mar 27, 2007 7:03 am ]
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[QUOTE=John Watkins] ...so forgive me if I don't spend too many hours repeating myself in order to add to my list of competitors (again).[/quote]

Well, that says it all doesn't it? Warm, open, and willing to share the knowledge in a spirit of comraderie.

Another place your assumption was wrong. I'm no competition, present or future. I want a cnc as a tool for building my guitars and other fun stuff. I'm not stupid enough to enter into a limited market that has enough players. This is all hobby for me...even the guitar building is to some degree now. This isn't my job, it's my fun. Or at least it's supposed to be.
Thanks. Tell me again, why do you want to participate on a forum like this? Oh yeah, I guess it because there's a buck to be made. Eh?

That's the last time I'll ask for your advice. Ever.
Never again. Thanks anyway...happy trails to you.


JJ, I wasn't pissed at you personally, and I am truly sorry I blasted at you. You were just trying to be encouraging I think. I was mainly pissed at being raked over the coals for trying to open up some exciting and adventurous dialogue for myself and others here who might be interested in getting started building a cnc. I guess it was a bad move on my part.

I guess I thought folks who were Newbies here in different ways would be treated differently than that. I mean really, these forums are for folks to ask questions, get directions, LEARN, and SHARE, and BUILD etc., not told they are idiots for not doing enough research before asking a question, and how difficult it was going to make other's jobs.

So I will no longer ask any questions here about cnc. And nobody else will get the benefit of the process I go through, and get to see the results, or celebrate in the achievement, or even know if I ever built the darn thing. I'm done. No more replies, no more dialogue on the subject.
Author:  John Watkins [ Tue Mar 27, 2007 7:13 am ]
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[QUOTE=Don Williams]Oh yeah, I guess it because there's a buck to be made. Eh?[/QUOTE]

Way over the line, Don.
Author:  LanceK [ Tue Mar 27, 2007 7:26 am ]
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Easy does it Were all friends here. I know nobody means any harm. Must be that spring fever
Author:  Pwoolson [ Tue Mar 27, 2007 8:34 am ]
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Geesh Don, your panties are certainly in a bunch today.
I’ve got to wonder what you thinking was when you posted all of this. You get on a guitar forum to ask a CNC question, knowing full well that there are only a handful, a very small handful at that, of guys that really know CNC. Then when two of the most knowledgeable CNC guys here tell you that you’ll have better luck on a CNC forum, you throw a fit.
You were never insulted, you were never called names, yet your “Oh yeah, I guess it because there's a buck to be made. Eh?” comment was completely out of line. It was just plain mean spirited. John was on this forum WAY before he was doing the CNC thing as a career.
I’m curious why it makes John a bad guy because he doesn’t want to put his work on hold, sit down at his computer, and type out a lengthy dissertation of the workings of CNC, when he has previously done that, simply because you are not willing to do the leg work to learn your new “hobby”. I would think the fun of a new hobby would be to really learn the ins and outs of it.

DW ”I was mainly pissed at being raked over the coals for trying to open up some exciting and adventurous dialogue for myself and others here who might be interested in getting started building a cnc.” Though it is very noble of you to be thinking of others, you certainly weren’t raked over the coals. You were simply told to do your research and then ask specific questions that could be answered.

DW ” not told they are idiots for not doing enough research before asking a question, and how difficult it was going to make other's jobs”. Give me a break! You were never called an idiot and NOBODY said anything about how difficult it was going to make their job. You were told to do the research so that you could ask specific questions. John stated very clearly that there was a lot to think about rather than just the broad question of “what do I look for in motors?” JW “What's the weight of your gantry? What's the pitch of your lead screw? What kind of moment is placed on the drive when the load is at it's highest center of gravity? What is the ratio of the distance from the drive to the load vs. the drive to LGs? What speed do you need? What's the budget? Etc? Etc? Etc? ” I think that’s pretty clear that there are many more questions that need to be thought about and researched before you can decide on something like, “what do I look for in motors?”. Compare it to a fellow that has never built before asking, “What kind of wood should I use on my guitar”. Questions would have to be asked, electric or acoustic?, size?, Playing style?, etc, etc.

DW ”So I will no longer ask any questions here about cnc. And nobody else will get the benefit of the process I go through, and get to see the results, or celebrate in the achievement, or even know if I ever built the darn thing. I'm done. No more replies, no more dialogue on the subject.”        &nb sp;    
DW “Well, that says it all doesn't it? Warm, open, and willing to share the knowledge in a spirit of camaraderie.”

Hello Pot? This is Kettle. You’re black!
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