CNC machine electrical parts break down help needed

[ydeardorff]

Hello to all.
I have used the search on this site, and found alot of info, just not what Im looking for yet, I guess, I could use some help in shopping.

I am stepping my way toward my first CNC machine build. However, I am bedazzled at the choices online. There are so many choices online, one get sensory overload like those search engine commercials.

My goal is to be working with wood, plastic, and fiberglass pieces. Although a project or two may involve metal, one can never tell the future.

I am not looking for the snail speed mill here. Some of these mills may be accurate but redicilously slow. And some of the parts Im working on are going to be big. So again I have no idea what to buy. Ideally Id like a two speed setup, where the mill gets up and moves quickly to its new location, but goes into accurate slower mode for the cutting.

Stepper motors, I see high speed, and low speed, high torque, and low torque ones. Im hoping to have a work area on my table of 48" by 60".
I deffo need help choosing these. I would imagine they should all be matching correct?

The driver units: I see 3, 4, 5 axis units, with varying specs. So no clue there, some state they will lower the voltage when the motor is not in use to save the motors? LOL

Seems to me if the motor aint moving, it would have no juice to it right? or is the juice holding it in place?

I am thinking that having the option of having that 4th axis, to rotate the tool right or left might come in handy, later. so again I have no idea on what good or not.

I would really like some help. I know very little about the details, I do know how to build, conceptualize, and fabricate things easily.

And I have an idea of what I want, I just need some help getting the details worked out. Im hoping for no more than a few hundred dumped out for the driver board, and motors. (hoping) LOL
So please fire away and help me find what I need. Or at least the tools, so I knwo what I need to be looking for.


Thanks

[ger21]

Do you have a machine built yet?

[ydeardorff]

No,
I have the plans, and just waiting until payday to buy the MDF to cut out the pieces.
I plan on lengthening the x - y axis from 14" x 10" to a much larger 48" by 60"
I may have to thicken the materials, or change to metal parts. But over all adjusting a couple of the parts in this machines plans will give me the lengths I need. And I (at present dont plan on adding anything to the Z axis, Ill leave it at 4" for now).

Im looking for any help I can get choosing the electrical parts. The best bang for the buck, as well as understanding what Im looking at when Im reading those ebay ads.

[Pplug]

I think your best bet is to look at what techno did with their 4896 models. All the axis are ball screws with servo motors. They are fast, accurate and expandable. Just mimic their design. If I didn't buy one I would have built one just like it.

[ydeardorff]

do you have a link?

are you saying use their motors and boards too? Or just copy the structural design?

Im guessing I need a for dummies book here or something. Ive seen these things in action, but never built one, nor used one. But Im ready to jump in and build one now.

[ger21]

Motor and electronic choice depends on a lot of factors. How much weight are you moving, how fast do you want to go?

Are you using screws. or rack and pinion. What is the pitch of the screws, any gearing?

Need more info.

[ydeardorff]

my plan was to use all thread jack screws, and barrel nuts. The frame work would be supported via a combination of polished round steel rods, brass bushing, and needle roller bearings.

So I dont have those variables yet.

[Crevice Reamer]

Hi yd. That's a very large scale-up. Yes! Need more info.

Maybe reading some of this will help:

http://www.cnczone.com/forums/showthread.php?t=78713.#3

CR.

[ger21]

What plans do you have?

[wildwestpat]

Hi

There are two main classes of axis drive. Closed loop servos and Open loop servos. The closed loop need positional encoders either built into the motor or as a linear glass scale bolted to the machine bed of that axis. Open loop use stepper motors and a simple electronics telling the motor how many steps to move but no method of checking that it has moved as instructed. Cost and drive power quickly separate the two types. Power of course is a factor in how much mass + friction you are trying to accelerate - i.e. how long to machine. To much power is not necessarily good particularly for steppers but can also cause problems for closed loop as what has been accelerated has to be slowed down on nearing the final destination. When cutting complex curves speed is of less importance as the cutting path has to be accurately followed.

Look at commercial designs such as:-
http://legacywoodworking.com/products.cfm?product=48
and of course the router mills built by other enthusiasts.

A lot of factors but start with looking at established designs as the rocket fuel to take you on your CNC journey.

Regards

Pat

[ydeardorff]

Originally Posted by Crevice Reamer Hi yd. That's a very large scale-up. Yes! Need more info. Maybe reading some of this will help: http://www.cnczone.com/forums/showthread.php?t=78713.#3 CR.

Thank you! Thats very good info, althought abit overwhelming to take all in all at the same time.

What do you think of the new Chinese 4 axis boards available on eBay? I have bought quite abit of chinese stuff in recent months, to my suprise, most of it is pretty decent.

heres a link:
http://cgi.ebay.com/NEW-4-Axis-TB656...item3a54e87fac

(just a note, Im not the seller, and I dont know the seller, just asking what ppl think of this board I found today browsing on ebay)

Also,
I have found nema 23 motors all over the place, like everyones trying to get rid of em, and nema 34's are almost not there...
not to mention the 3 to 1 ratio regarding price. The nema 23's are 3 for 80 bucks, and the 34's are 1 for the same price. LOL

Hmm I wonder which is better? Is there really that much difference? Other than size?

[ger21]

I haven't really seen anyone using those Chinese drives yet.

As for the steppers, Nema 23's typically have between 100oz-in to 450oz-in of torque. Nema 34's start at around 400 oz-in and go up to about 2000 oz-in.