Custom CNC X & Y axis >$300 w/ steppers?

[BANE]

Hello, I'm still looking to make a custom CNC mill that can milll aluminum.  I don't think the design on Instructables will be strong enough.  So i'm resorting to ether buying just the X & Y axis or have them made out of some other design.  I was wondering if anyone has any recommendation on were to buy or a realistic design. 

http://www.mcmaster.com/nav/enter.asp?pagenum=1071
I think i would like to get something likethis^ only less precise and cost less >$300.

Thanks, Bane
 

[Admin]

CNC that can do aluminum for under $300? No such thing.

http://www.sherline.com/
http://www.micromark.com/

Or just farm it out:
http://www.societyofrobots.com/robot_parts_list_manufacturing.shtml

[BANE]

yea I was trying to go cheap but i guess theres no way around it.

bane

[jibeling]

Look for used industrial supply companies. Up in here in Minnesota there are several that have used equipment from all the local manufacturers. You can get parts for pennies on the dollar in some cases. Also ebay is ok for linear slides but more expensive.

[benji]

make your own ,,x and y only isnt too hard,,
2 ac motors,, 2 inverters controlled by a micro,,,some software to interpret image files,,
maaan it would be awesome like that,, any other ideas for a design?

[izua]

don't go with ac motors, they are killer to control, plus you'll need position feedback. steppers are the way to go for cheap, they can be controlled open-loop (no feedback required, position is 95% guaranteed)

[benji]

when you talk CNC machines you need torque,, too much torque.. and buying a stepper with big torque can be pretty expensive
ac motors are the cheapest , thats why people invented the inverter,,
you really should have the guts for ac motors if you wanna keep things affordable

[izua]

i disagree. a nema23 stepper in specs puts around 11-12kg/cm. With adequate reduction for transmission, say 1:2 or 1:3, you'll have enough torque.
the problem with ac (and dc for that matter) motors, is that you have no way to know where your motor is. encoders are expensive, and the circuitry that will drive the inverter according to the encoder is even more expensive.

[benji]

a nema23 stepper in specs puts around 11-12kg/cm

do you call that a torque??? thats nothing for a Cnc,, the cnc should drag push an iron table attached to it a mold or any piece of iron

[izua]

I think we should be constructive here instead of just bashing Tell me what you consider torque and why.
I've seen 2.5 axis CNCs made with nema17 steppers that cut through aluminium in multiple Z passes. True, they were built with this in mind, but you don't need huge torques to mill metal. As long as the Z passes are fine enough, nothing can be bad. Having a lot of torque and using it mindlessly will tend to induce a lot of vibrations which will require more expensive error correction mechanisms.

I do not disagree, torque is needed, and dc/ac motors have it. But for cheap, I beleive steppers are the way to go.

[benji]

consider having a 60 kilos plastic injection mold made of iron
to make holes in this thing you need to use steel heads and there would be big loading (motor)
ac/dc motors would drag big current to maintain the motion desired,,while this ma cause problems with steppers
i cant imagine a stepper can lift a table made of iron and a big piece of iron is attached to it, lets say 150 kg
while this requires huge torques its very very costly with steppers,, even im not sure there are steppers with such torques

ac motors are known of their lets say CHeapness,,steppers are the most expensive
i dont consider the driver cost because its part of making the cnc,, i dont expect to buy an already made driver,i consider building it
i know its insanely hard but its not impossible, its a Cnc you are making

post some links to big torque steppers if you find, im interested

[izua]

nanotec.de has good ones. you can find decent ones (nema17, nema23) even on ebay. They'll work better overvoltaged and with current limiting. Another good source I've noticed to be used are old printers.

what i'm saying is, BANE goes cheap (like most of us poor hobbyists do ). And he'd probably want it quick.
I doubt that a decent AC controller with encoders can be built at home cheap. And just for milling aluminium, it will be more than ok, IMO. And to go for an encoder at home, 512 lines at least (to reach a stepper resolution), heck, that's overkill. But that's just what I think.

BANE, what exactly is your goal? Anything more specific than milling aluminium?

[Admin]

steppers are the way to go for cheap, they can be controlled open-loop (no feedback required, position is 95% guaranteed)

I disagree - steppers have finite steps that will result in vibration (rough edges on your milled out part), and poor resolution.

An even cheaper/better way to go would be a DC motor with encoders.