Motors

[joq]

Hi there

I want to build a cnc machine, to work on metal and wood but i don't want to spend a lot of money(actualy the less possible).
I am thinking of using step motors from no-use appliances
I would like to get advise on:

- minimal recommend step motors torque ?
- In which household machines are common such motors?
- if I cannot get such motors from my domestic junkhard, what is your commercial recommendation (manufacture, model, etc).

For the main motor,
- what is your advise?
- Again, it's possible to get a motor from used aplliances- which?
Correct if i'm wrong but isn't this a simple ac or dc motor? As such I can do a speed controler(pwm) for it?

Thanks in advance

[chuckknigh]

The requirements of a machine for working metal, are significantly higher than the requirements for a machine to work wood. Let me just tell you this, up front...one for cutting metal of any appreciable thickness is going to be a LOT stiffer, and consequently heavier, which requires bigger motors, etc, etc, etc.

It might be more cost effective to build 2 machines...a "big" one for woodworking, and a small, very stiff machine for cutting small metal parts. It is possible to convert an existing machinist's cross slide vise, and have it function as a metalworking tool of reasonable precision.

Now, let me address your questions, one at a time.

- Minimal recommended step motors torque?

This is a tough one, because it's a function of how much force is needed to move the parts of your machine. A general guideline is that somewhere around 100 oz-in is sufficient to move a homebuilt router...more is better, to a point, and I've seen people mention successful designs with as small as 60 oz-in motors.

- In which household machines are common such motors?

This is easy. The common Hewlett Packard (HP) Laserjet series of printers use stepper motors. HP LaserJet models I, II, and III all used the same motor...a single 100 oz in stepper of very good quality.

Another possibility is the old IBM Selectric typewriters which often turn up in junk bins...they have several steppers, of various sizes inside.

For the main motor, - what is your advise? - Again, it's possible to get a motor from used aplliances- which?

Which are you calling the main motor? There are typically 4 motors on a router...one stepper motor for each axis X, Y, and Z...and a high powered motor attached to a cutter head, like the one inside a router.

Yes, the router uses a standard AC (usually) motor, but routers are reasonably inexpensive on the used market, and you might even have one in your workshop. Many of us just find/buy a trim router, or one of the Bosch or Porter Cable full sized routers...see what you have available, and try to figure out if it'll be usable.

-- Chuck Knight

[joq]

Thanks for your answer

The motors from the HP laserject are unipolar or bipolar? Just for you to know I will made the steppers board form the squematic on this page http://hans-w.com/modular_cnc.htm .

Originally posted by chuckknigh Which are you calling the main motor?

I was refering to the high powered motor attached to a cutter head. Its this motor the router? And what is a trim router?
Maybe this questions sound stupid but i'm a newbie in cnc and Inglish is not my language.

p.s.- Could you tell me/explain how a cnc cut things? it just make go down the drill and then it makes the drill moves in contact whit the material?

thanks again

[chuckknigh]

The high powered motor is generically referred to as the spindle. It's the cutting head. We often use routers, a woodworking tool, for the cutter head.

Other options exist, like a trim router (miniature router used for trimming plastic laminate countertops), and even a custom made high speed spindle. Another potential cutter head is a Dremel tool...a handheld, high speed cutting tool.

You can use almost anything for a cutter head. I saw one guy who used his drill press for a spindle...he converted an X-Y table to CNC, and just raised and lowered his drill press, manually.

Perhaps routers are called something different in your country, just as some Europeans call a vise (American) a mangle.

This is a router...this one is made by DeWalt.


Now, how CNC machines cut things. You understand that the computer makes each axis move according to its instructions, right? In and out, up and down, left and right. Well, with a correct cutting tool (endmills are common...the sides and end have cutting surfaces) you just drag it through the material, under computer control, and it follows the path you tell it to.

Have you ever used a router? Same thing, basically, but the movement is under computer control.

-- Chuck Knight

[joq]

thanks for your anwer
about my last question "how a cnc cut things?" I was refering how the machine itself cut things. To you understand the cnc machine doesn't have a mountain range(i think that is that the name) so how can it cut things?

Not wanting to be rude you didn't anwer the question that I have made about the tipe of stepper motor in the hp LaserJect

[balsaman]

They are unipolar

The cnc can cut in all 3 dimentions at the same time, so the routher moves up and down, right left, and forward and backward, making it posible to cut 3D shapes.

Eric