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rustranch
09-23-2003, 07:30 AM
I'm looking to put my surplus laptop to a good use. I've been wanting to build something to play with CNC for a long long time. I've tried to install Linux so I could use EMC on but jut to many issues to resolve so I've left it 98. Then I found this forum.
So would you chose stepper or servo?
Printer port or serial port
Master5 or ???
Controllers
Breakout box?
What set of plans would you chose?
I want something around 12", 12", 3" maybe as my first machine. Not much extra room in the garage. Strange my wife thinks she need to park her car in out of the weather. I keep telling her that I need some project space. It just doesn't work.
Oh man but then I get to dreaming 5 axis, 6 axis,????

ToyMaker
09-23-2003, 08:43 AM
rustranch:
A CNC machine, like a computer, is a tool - not an end in itself. So, like buying software, you should have a job in mind and then pick the tool best suited to it. You wouldn't buy Micro$oft Office to do (just) your check book. Nor should you buy a multiaxis machining center to (just) cut ribs for your model planes.
In my case my first hobby is mobile robots. I build circuit boards for my 'bots, so my second hobby is a small (6x6) CNC machine to cut pc boards. I may go to a larger stronger machine to cut mechanical parts for my 'bots.
If you are trying to learn about CNC then your first three steps should be 1: read, 2: read, 3: read.
And then having learned what kinds of solutions are available you should read some more to find out what fits your requirements and restraints (space & budget).

robotic regards,

Tom
= = = = =
"The U. S. Navy. It's not just an adventure, it's a job."
- - the gang at Saturday Night Live

chuckknigh
09-23-2003, 08:13 PM
In a small machine, like the one you're describing, the footprint of the machine will basically be double its capacity. Or at least that's my experience.

If you want a machine to work 12x12", expect it to take up 24x24" or thereabouts.

My 18x24" machine is 4' long and just about 30" wide. My 4x6" X-Y vise is just about a foot square in footprint.

*Structure* takes up space. Keep that in mind...because a CNC machine has to be reasonably stiff, and stiffness requires structure.

-- Chuck Knight

NeoMoses
09-23-2003, 09:10 PM
I chose servos for my first system because they were not that much more expensive than steppers. However, you can sometimes find very good deals on steppers which may tip the scales.

I also chose to use Gecko G320s and a breakout box, and a power supply that I snagged off of ebay. All in all it wasn't the least expensive way to do things, but everything worked well and I had very little problems setting it up. That was very nice for a newbie. :)

Perhaps you may want to take a look at crankorgan's plans. He has some very small, very inexpensive machines that might be good to start off with if you just want to learn about (and play with :D) CNCs.

You also might want to take a look at a Speedway or homier milling machine. They are pretty small and could fit on your average desk, and are relatively stiff compared to most small routers. They might also offer a decent platform for a beginner's first CNC conversion.

Hope this helps, but let us know exactly what you have in mind to do with the machine, and we can help you more.

chuckknigh
09-23-2003, 10:45 PM
You know, a conversion of an X-Y vise like mine might be a perfect introductory CNC project. The conversion is simple and straightforward, and the basic structure is already built.

I bought a cheap X-Y vise at one of those travelling tool sales (Cummins Tools) for $20. It's cast iron and of dubious quality, but it's got dovetail ways and adjustable gibs. Overall, not a bad little unit. Suspend a spindle (router or Dremel tool) above it, and you'd have a fully functional, if a bit small, platform on which to learn and play.

By replacing the lead screws, and cobbling together a motor mount, it is slowly becoming a nice little platform for CNC. Its capacity is only approximately 4x6", but once finished it would allow you to play with CNC in general, make small projects, and even new parts for a larger machine, if you decided to build another one.

My modifications, including a few failed starts, have cost me in the neighborhood of $5. Cost doesn't become a factor, when a whole machine can be put together for less than the price of a dinner at McDonalds, or a few cups of coffee at Starbuck's.

My steppers are taken from HP Laser printers that I get for scrap pricing -- the last one cost me a whopping 40 cents.

Now, realistically, I could have done the whole project in a weekend. But it's not done yet... You know how things can get. My next step will be attaching the motors to the framework -- I have some short offcuts of 2" square pipe, which I'll use as a mounting bracket, and I'm going to use the same high-pressure hose coupling system I used on my other machine. Should work just fine!

-- Chuck Knight

chuckknigh
09-23-2003, 11:41 PM
Sorry about not answering the rest of your questions. I'll answer them, inline, and try to keep it short. I can be somewhat long-winded, otherwise.



So would you chose stepper or servo?

I chose steppers, but that's because I can get them from tech surplus for extremely low prices. The electronics to control either type of motor are of comparable cost, and the accuracy of the systems is also comparable, if implemented right.

Due to the different torque characteristics of steppers and servos, steppers are often connected directly to the lead screws (simple) and drive the machines directly. Servos are often connected by a toothed belt drive, so that they can turn at a higher RPM, where their torque is better. This is an added layer of complexity, especially for the first time builder, but it's not a deal-breaker.



Printer port or serial port

Printer port, AKA parallel port. You'll see why, below.



Master5 or ???

TurboCNC for your first attempts, and EMC after that. TurboCNC is a shareware CNC controller program (free distribution is fully functional, with a $20 registration cost) which reads G code and outputs step and direction controls, by way of the parallel port. You can play with it for free, and buying it is cheap enough.

By the way, most software interfaces by way of the parallel port.

EMC is a pro-level package, and can control just about anything, with any number of axes, indexed in almost any unit known to man, through any device known to a LINUX system. And, you get source code, so you can modify it to fit your needs. It's FAR more complex than most of us need, and will cause you more problems at this stage, than it's worth. Don't get me wrong...it's good! It is, by some standards, the most powerful package out there!

It's kind of like asking if you should get a McLaren for your first car...when just starting out, you'd end up wrapping it around a tree!



Controllers

TurboCNC is the controller. The controller is the thing that reads the g-code file, and turns it into instructions for your machine.

I'm going to make an assumption, and assume you meant the board that drives the motors. This is known as the driver.

Gecko Drives makes some particularly good driver boards, and its owner, Marriss, is on the CAD_CAM_EDM_DRO list on ***********.com. A very good list, but it focusses more on metalworking and industrial CNC applications, whereas this forum focusses on home workshop CNC.

Now, I've heard good things about other drivers, too, but I've heard *nothing* but praise for Gecko Drives. That says a lot!



Breakout box?

This is essentially an insulating layer between your PC parallel port, and the driver boards. It usually entails optical isolation of the 2 sides of the circuit.

Geckos have optical isolation built into the boards, so this is a non issue.

If you want a separate breakout board, check out the offering from Bob Campbell, http://www.campbelldesigns.com if I remember correctly.



What set of plans would you chose?
I want something around 12", 12", 3" maybe as my first machine. Not much extra room in the garage. Strange my wife thinks she need to park her car in out of the weather. I keep telling her that I need some project space. It just doesn't work.

I wouldn't buy plans. I designed and built my first router, on my own. It was HEAVILY inspired by the designs at http://www.crankorgan.com, though. I'm one of those people he talks about, who can "look at the picture and figure out how to build it."

My second design, the modified X-Y vise, is just an obvious conversion, in my mind. Email me if you want a few details on how to do it -- it's simple!



Oh man but then I get to dreaming 5 axis, 6 axis,????
Do a google search for "stewart platform cnc" and see what comes up. Fun stuff!

Seriously, start with 3-axis, or maybe even 2-axis. (A computer controlled X-Y table mounted on a drill press or small mill, with the vertical movement controlled by hand. You put in a pause in the G-Code, and it just stops and waits for you to raise or lower the cutter.)

You don't have to *start* with the best possible machine -- consider it a learning process, and a further incentive to buy more and more tools as you progress! :-) We'll get that car out of your workshop, eventually!

-- Chuck Knight

P.S. Guess I was long winded, anyway! Sorry...

turmite
09-24-2003, 10:11 AM
I found some full/half step drivers on ebay for $39 buy now. They look really good but there is no plan in the future for the guy to make them microstep.

turmite