Re: [CAD_CAM_EDM_DRO] seeking CNC conversion advice

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>
>I just ordered a Rong Fu 45 and am dying to convert it to CNC.
>Basically, I know how to spell CNC, but that's about it. I'd like to
>buy parts that are known to work either on eBay or from a surplus
>house, put them together, and start using the mill!
>

I'm not familiar with that particular mill, but the basics are the same
for any machine.

If it's got a screw-drive already, you can just connect the screw to a
motor (couplings are easy) and run it that way. A stepper motor will
turn a specified number of steps per revolution (mine are 200 steps per
revolution, so 1.8 degrees per step) and will move only 1 step per pulse
from the computer.

There is at least 1 company selling parts and upgrades for Asian
mills...can't remember the URL off the top of my head, but it's
something like littlemachineshop.com I think he had some CNC conversion
kits available, at one time. A list member is also designing some bolt
on conversions for the Asian mills, but I don't think his kits are
available, yet.

>I'd like to use servo motors. What size, voltage, drivers, etc? Is it
>feasible to drive the screws directly without belts and pulleys?
>

Is it possible? Yes, of course. However, I've been told that because
of the torque characteristics of a servo, that it's best to run them
with a belt drive.

>After the mill is CNCed can it still be used manually? Is converting
>

It depends on how you do it -- the answer is a solid, maybe.

>to ball screws a must? Is the same size motor suitable for driving a
>rotary table? Can a servo-driven rotary table be accurately
>positioned for jobs such as cutting gears?
>

Ball screws are not necessary, but offer many advantages. They offer
very little backlash (also attainable in other systems, like ACME
thread) with much less friction than other systems. Lower friction
means you'll need a smaller motor.

It comes at a price, though -- they're VERY expensive, compared to the
other options.

A rotary table is something that can be added later -- get something
working in 3 dimensions, first, before adding even more to it. A rotary
table usually uses a motor of significantly smaller capacity than the
main axes, simply because it's moving comparatively little mass.

As for servos and accuracy -- they're more accurate than steppers, when
implemented correctly. In practical terms, there is often a series of
compromises which makes them *roughly* comparable.

My best advice to you is to just build something, and get it working.
It's human nature...you'll always see something you should have done
differently, or something you forgot, etc. Then you'll want to build
version *2* of your mill.

There is a forum for homebuilt woodworking routers at:
http://www.cnczone.com/forumdisplay.php?s=&forumid=48

Take a look around. These are VERY low end, homebuilt routers, for the
most part -- you can see the construction, and how everything interacts.
It's the best way to "understand" CNC short of actually building your
own mill.

-- Chuck Knight