[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]

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.

[ydeardorff]

450 oz- in?
trtanslated in to in-lbs would be what,... 28 inch pounds of torque? Wow thats not very much. Kinda like stickin a geo metro motor in a locomotive and expecting it to move. LOL

[ger21]

Yep, 28in-lbs of torque. My router has 30" x 45" of travel, and does up to 190ipm with 250 oz-in motors.

[Crevice Reamer]

Read the basic info--especially the parts about stepper motors and power supplies.

What drive system are you going to use:Acme thread, ball screws, rack & pinion, what?

CR.

[ydeardorff]

more than likely acme thread.

[Crevice Reamer]

more than likely acme thread.

Okay. Now we need to arrive at a thread count & start. How fast do you want the rapids to be? How fine do you want the resolution to be? what is the hardest material you must regularly cut?

CR.

[ydeardorff]

Im not sure what a reasonable rapid would be. But say if Im replicating a part, on a large piece of 3/4" MDF, then I would expect it to jump to its next project, not act like it hasnt been oiled in ten years. I would expect an average rapid speed would be fine.

Typically Ill be making costume, and car parts with it, maybe even some fine work like circuit board etching.

Ill be typically cutting MDF, plywood, fiberglass, glass, foam, and plastics. Maybe occasionally soft metals like aluminum, copper, or brass.

I would like to resolution to be pretty darn good, to minimize finishing work to automotive parts, and other projects, like etching photos onto glass.

Does that help?

On a side note: I came across some 1/2 bolts, that at first looked normal, but when something caught my eye, I picked one up to find the head of the bolt, was actually a sealed bearing.
Are these common? Ive never seen one before. But my mind jumped directly to possible applications in a CNC mill.

YD

[Crevice Reamer]

Usually a milling machine is used for close tolerances in metal. 48 x 60 is a fairly large router. Larger = more expensive. Routers do not generally have the resolution and accuracy of a milling machine. Routers DEFINITELY don't have the stiff rigidity that is necessary for cutting metal quickly. You might just need at least two different machines to do what you want to do, and might have to make a lot of compromises to keep cost down.

In this link is a video of a 24 x 36 commercial router using 387 oz steppers and a G540. Watch the video and see if 250 IPM rapids are fast enough for you:

http://www.cnczone.com/forums/showthread.php?t=77409

CR.

[Al_The_Man]

On a side note: I came across some 1/2 bolts, that at first looked normal, but when something caught my eye, I picked one up to find the head of the bolt, was actually a sealed bearing.
Are these common? Ive never seen one before. But my mind jumped directly to possible applications in a CNC mill.

YD

That sounds like a cam follower. It is used in many and varied applications.
http://images.google.ca/images?q=cam...ed=0CCEQsAQwAw
Al.